ALBERT

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Zhu Weilin, Zhong Kai, Fu Xiaowei, Chen Chunfeng, Zhang Minqiang, Gao Shunli〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Back-arc basins and the related subduction systems have been extensively studied, however back-arc basins exhibiting episodic jumps of extension centers by the subduction of different ocean slabs are poorly known. The East China Sea Shelf Basin (ECSSB) comprises two eastward-younging subparallel depression zones, and its formation and evolution is accompanied by a complicated subduction history and regional tectonic events offer an excellent opportunity to decipher the various geological features of back-arc basins. Here, we review the tectonic and sedimentary features of the subbasins in the ECSSB and its adjacent regions and then reconstruct the evolution of the sedimentary paleogeography. The west depression zone (WDZ) of the ECSSB experienced rifting in the Late Cretaceous during the subduction of the Izanagi Plate at the eastern continental boundary. In the northern WDZ, the Changjiang Depression was mainly dominated by fluvial to lacustrine deposits. This depression experienced strong compression characterized by folds and erosion during the transition from a synrift to postrift setting at the end of the Paleocene. Then another compression event occurred that resulted in extensive folds and uplift accompanied by a large-scale alluvial fan in the eastern Changjiang Depression, coinciding with the subparallel subduction of the Izanagi-Pacific ridge in the early Eocene. However, the Lishui-Jiaojiang Sag characterized by diffuse extension rather than focused rifting in its late rifting period. This sag was mainly covered by paralic to marine deposits and experienced extensive erosion caused by tilted sequences from the late Eocene to Oligocene, which shared the same characteristics as basins around the Taiwan region. It is widely accepted that the formation and evolution of basins around Taiwan were controlled by the evolving of the South China Sea (SCS) and the related regional tectonics. Considering the eastward extent of SCS, it would seem that the southern ECSSB was part of the passive margin of SCS. Accordingly, the southern ECSSB might be significantly influenced by the SCS. The east depression zone (EDZ) commenced rifting in approximately the middle Eocene as inferred from the absence of the compressional event that occurred in the early Eocene and the existence of a thick layer reflection below the Pinghu Fm. (late Eocene) due to the subduction of the Pacific Plate. The depocenters of the ECSSB and the Okinawa Trough jumped eastward successively triggered by the three oceanic slabs of the Izanagi Plate at ~72 Ma, the Pacific Plate at ~50 Ma and the Philippine Sea Plate at ~15 Ma. Thus, a new model for the formation and evolution of the ECSSB is suggested in which a back-arc basin of episodic extension with jumping depocenters in respond to subduction of three oceanic slabs, meanwhile its differences between northern and southern part are caused by the dominant subduction and opening of SCS, respectively. The ECSSB and Okinawa Trough might formed mainly by rollback of the oceanic slab, possibly, due to slab stagnation and toroidal flow related to the subduction, however the effects of large-scale mantle flow cannot be exclusively identified in this research. In addition, further research in this region will give new insights into both the formation and evolution of the SCS and the continental breakup process.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Li Zongxing, Feng Qi, Li Zongjie, Yuan Ruifeng, Gui Juan, Lv Yuemin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The cold regions of western China are referred to as the “Asian Water Tower” and mainly include the Tibetan plateau and surrounding mountains. Its prominent hydrological feature is multiphase water transformation, which accelerates the water cycle and affects spatial and temporal patterns of water resources. Under the effect of lengthening ablation periods and increased annual precipitation, multiphase water transformation is accelerating. There are three main manifestations characterizing the transformation from solid to liquid water in the period since 1990: (i) the melting of glaciers has accelerated; (ii) the depth of permafrost active layers is increasing and their maximum freezing depth is decreasing; and (iii) a marked decrease in snowfall and increase in rainfall has been observed. The transformation from liquid to gaseous water was mainly concentrated on accelerating evapotranspiration. The transformation from gaseous to liquid water was observed as enhanced moisture recycling. The final hydrological effect of these transformations was observed in the change of the runoff components, increase in runoff, and lake expansion. A theory of multiphase water transformation is proposed, which is expected to contribute to the understanding of cold region hydrology in the future.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): V. Di Renzo, R.A. Corsaro, L. Miraglia, M. Pompilio, L. Civetta〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Mt. Etna, in Sicily (Italy), produces effusive and explosive eruptions from summit craters and flanks. Petrology of erupted products has proved fundamental to explore the relationship between magma dynamics within the plumbing system and eruptive styles. Data of Sr〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Nd isotopes are quite scarce if compared with the great number of chemical analyses carried out in products of last decades. We measure Sr〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Nd isotopes, major and trace elements in products emitted from 2001 to 2012, and consider also published analyses of the 1995–2001 eruptions, because carried out in the same laboratories of 2001–2012 ones. Furthermore, we take into account other published analyses extending back to the 14th century, even if performed by different facilities. Based on this dataset, magma dynamics operating at different timescales inside the volcano's plumbing system have been explored. Our analyses evidence that, from 2001–2012, three magma types are present in the volcano's plumbing system: (i) a deep and poorly evolved basaltic and K-trachybasaltic magma, enriched in radiogenic Sr and LILE, erupted during the 2001 and 2002–03 flank activity; (ii) a shallower more evolved K-trachybasaltic magma, less enriched in radiogenic Sr, feeding both summit and flank eruptions and (iii) an uncommon, and scarcely radiogenic hawaiitic magma, LILE poor, emitted exclusively from a small sector of the 2002–03 eruptive fissures. By considering a broader time scale, from 14th to 21st century, we conclude that: (i) different magmatic components are present in the deep volcano's plumbing system, at about 10–12 km b.s.l; (ii) a decoupling of geochemical and isotopic features in magmas stored at different depths is observed after the 1974 flank eruption up to date; (iii) mixing between different magmas is an efficient magmatic process to produce magma differentiation at Mt. Etna, regardless of the investigated temporal scale.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Cheng-Hong Chen, Chi-Yu Lee, Jian-Wei Lin, Mei-Fei Chu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The provenance of sediments in western Taiwan has been the subject of debate in recent years. Previous investigators, solely based on the U-Pb zircon geochronology for the detrital grains, all advocated the important roles, but with varying emphasis, of drainage systems in the South China Block. Influence of the Changjiang (Yangtze) River from the far-source Yangtze block versus nearby systems like Zhujiang, Minjiang and Jiulongjiang Rivers in the Cathaysia block has been the main issue. However, the fundamental question of whether the provenance is really the South China Block has never been evaluated. Here we report both the U-Pb zircon and Electron MicroProbe (EMP) monazite age data for seven sediment samples from two sides of the Taiwan Strait and synthesize the published data for all these rivers and sedimentary strata in western Taiwan to tackle this problem. The lack of, or insufficient, ~1.8 Ga monazites in the sediments of river mouths for all drainage systems in the South China Block makes them unlikely to be the source of Miocene sediments in western Taiwan where ~1.8 Ga monazite grains occupy 14.5–33.3% of the total age population. With reference to the tectonic evolution of the coastal southeast China-Taiwan region during Early Cretaceous to recent time, we propose a new explanation that invokes a now-concealed microcontinent along the Manila Trench. This microcontinent, probably related to a Paleoproterozoic orogen in Gondwana, eventually collided with the South China Block causing uplift of the easternmost structural element—the Pingtan-Dongshan Metamorphic Belt (PDMB) at ca. 130–120 Ma. It then drifted away sometime after 100 Ma and split into two parts with one becoming today's Palawan-Mindoro terrain of the Philippines. As indicated by the geophysical data near southern Taiwan, the remainder of this split microcontinent had subducted underneath the Philippine Sea plate along Manila Trench as a result of the opening of the South China Sea at ~33 Ma. Both the Peikang and Kuanyin basement highs in the offshore western Taiwan represent the unsubducted remnants of this microcontinent and also the major suppliers of Late Oligocene-Miocene sediments in western Taiwan. On the other hand, the Eocene-Early Oligocene strata of the Hsuehshan Range in central Taiwan show both zircon and monazite age patterns resembling the Eocene-Early Oligocene and recent sediments of the Zhujiang drainage system, indicating the southwestern origin of the protolith Taiwan. This scenario also matches the recent proposition that part of the Central Range belongs to the deep-level accretionary prism of a Miocene subduction system.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Eduardo Garzanti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Descriptive petrographic classifications of sand and sandstone proposed more than half a century ago are still in use, although they were formulated at a time when depositional and post-depositional sedimentary processes were poorly understood, and before the relationships between tectonics and sedimentation could be interpreted in modern plate-tectonic terms. As a consequence, too many scientific articles and technical reports are still encumbered with obsolete concepts, graphical tools, and ambiguous terminology that make sediment descriptions awkward and misleading. A renovation that treasures the legacy of the pioneers is required.〈/p〉 〈p〉The descriptive petrographic classification of sand and sandstone proposed in this paper is based on the quasi-universally used Gazzi-Dickinson point-counting method, and simply translates into words ternary compositions of quartz, feldspar, and lithic fragments without introducing any new names. The classic QFL plot is subdivided into 15 fields - labelled by adjectives introduced long ago by K.A.W. Crook and endorsed by W.R. Dickinson and more recently by G.J. Weltje - which reflect relative abundances of the three main framework components (provided they exceed 10%QFL). According to standard use, the less abundant component goes first, the more abundant last (e.g., litho-feldspatho-quartzose composition translates into Q 〉 F 〉 L 〉 10%QFL). For lithic-rich sand and sandstone, information on the prevailing rock fragment type can be added by an additional free adjective (e.g., metamorphiclastic, carbonaticlastic), as proposed long ago by R.V. Ingersoll. For lithic-poor feldspatho-quartzose and quartzose sand and sandstone, further formal subdivisions are proposed, thus reaching a total of 18 compositional fields overall. Modern sand known to be derived from different source rocks and found in major world's rivers, deserts, and deep-sea fans fits in the pigeonholes defined by the relative abundance of quartz, feldspar, and lithic fragments.〈/p〉 〈p〉The aim of this classification is to restore directness in sandstone petrology, and to avoid ambiguities generated in the past by making reference to badly defined archetypes, such as greywacke or arkose, thus confusing petrographic composition with subjective considerations about plate-tectonic setting, texture, hydraulic behaviour, mechanical durability, or chemical durability in the illusion that a classification could be genetic at the same time as descriptive.〈/p〉 〈p〉“You ask what is the use of classification, arrangement, systematization? I answer you: order and simplification are the first steps toward the mastery of a subject — the actual enemy is the unknown.” (〈em〉Thomas Mann, The Magic Mountain, Encyclopaedic〈/em〉)〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Lorenzo Marchetti, Sebastian Voigt, Spencer G. Lucas, Heitor Francischini, Paula Dentzien-Dias, Roberto Sacchi, Marco Mangiacotti, Stefano Scali, Andrea Gazzola, Ausonio Ronchi, Amanda Millhouse〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The tetrapod footprint record of Permian eolian environments has long been underestimated because of overall poor preservation and its apparent monospecifity. The best known and most abundant Cisuralian record of tetrapod footprints is from the Coconino and De Chelly formations of Arizona, which, however, thus far encompassed only the ichnogenera 〈em〉Chelichnus〈/em〉 and 〈em〉Dromopus〈/em〉. We revised the locomotion and taphonomy of these footprints and propose a new model, basing it on: 1) trackways changing direction, 2) trackways heading in different directions on the same surface, 3) trackways in situ, and 4) laboratory experiments with common wall lizards, 〈em〉Podarcis muralis〈/em〉. In all cases, the 〈em〉Chelichnus〈/em〉-like appearance of footprints is due to digit tip sliding on inclined depositional surfaces, masking the original footprint shape and orientation. Also, the trackway pattern and body position are largely influenced by the angle of inclination (dip) of the substrate being walked on. Based on an anatomy-consistent ichnotaxonomy, 〈em〉Chelichnus〈/em〉 and 〈em〉Laoporus〈/em〉 are here considered 〈em〉nomina dubia,〈/em〉 and the footprints from the Coconino and De Chelly formations are revised and assigned to: parareptiles/captorhinomorph eureptiles (〈em〉Erpetopus, Varanopus curvidactylus〈/em〉), bolosaurid parareptiles/ diapsid eureptiles (cf. 〈em〉Dromopus〈/em〉), varanopid synapsid (cf. 〈em〉Tambachichnium〈/em〉) and reptiliomorph amphibians (〈em〉Amphisauropus, Ichniotherium sphaerodactylum〈/em〉). The ichnoassociation is dominated by parareptile/captorhinomorph tracks, similarly to all the late Cisuralian marginal marine, floodplain, alluvial fan and ephemeral lacustrine tetrapod ichnoassociations of North America, Europe and North Africa. A review of all the available data including the new results suggests a facies-crossing transition between an early-Cisuralian amphibian- and synapsid-dominated ichnofauna (〈em〉Dromopus〈/em〉 track biochron) and a late Cisuralian parareptile/captorhinomorph-dominated ichnofauna (〈em〉Erpetopus〈/em〉 track biochron) at low latitudes of Pangea.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Santonu Kumar Sanyal, Jeremiah Shuster, Frank Reith〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Microorganisms are key-drivers of carbon-, nitrogen-, sulfur- and metal cycling on Earth. Through their metabolic activities they directly and indirectly link element cycles. This leads to the cycling of elements through the Earth’s ecosystems from/to the atmosphere to/from the lithosphere. Gold (Au) is a rare, redox-active, noble transition metal, which is neither essential as a nutrient nor, reputedly, mobile in the environment. Therefore, observations published in recent decades, which have shown that gold is highly mobile and subject to biogeochemical cycling largely driven by microbiota, have surprised many. Questions concerning the fundamental biogeochemical processes mediating gold cycling, the organisms involved and the benefits they may gain have puzzled researchers. In this review we integrate the cycling of the major biogenic elements carbon, nitrogen and sulfur with that of gold. We identify key-processes that drive gold cycling and evaluate how different chemical Au(I/III)-species affect microbiota that form biofilms on gold-bearing minerals and placer gold particles. Additionally, we assess how the cycling of the gold-associated metal(loid)s silver, copper, iron, manganese, mercury and arsenic is linked to that of gold. Microbially produced compounds resulting from carbon, nitrogen, sulfur, iron and manganese cycling (〈em〉e.g〈/em〉., organic acids, cyanides, (thio)sulfates, ammonium, iron sulfides/oxy-hydroxides and managanese oxides) can each play important roles for the mobilization of gold. Highly toxic, mobile Au(I/III)-complexes affect the phylogenetic and functional composition of microbial communities resident on gold particles. This leads to gold detoxification coupled to active and passive biomineralization, and ultimately the aggregation and (trans)formation of metallic gold particles. The complex interplay between gold, microbiota and physicochemical conditions modified by these organisms (〈em〉e.g〈/em〉., redox or pH) has throughout the Earth’s history led to the aggregation of gold particles (grains to nuggets), led to the formation of the largest known gold deposit (〈em〉i.e〈/em〉., Witwatersrand paleo-placer), and the largest gold reservoir in seawater. Today it opens up exciting biotechnological pathways for mineral exploration, processing and remediation.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Hanlie Hong, Thomas J. Algeo, Qian Fang, Lulu Zhao, Kaipeng Ji, Ke Yin, Chaowen Wang, Shi Cheng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Factors controlling variations in the clay mineralogy and geochemical composition of volcanic ash beds deposited in different types of depositional environments remain incompletely understood. The well-correlated, altered volcanic ash beds (tuffs or K-bentonites) of Permian-Triassic boundary (PTB) successions in South China provide an opportunity to better understand processes of alteration and diagenesis of volcanic materials in terrestrial, paralic, and marine sedimentary facies. The types of authigenic clay minerals produced vary among facies: mainly mixed-layer illite/smectite (I/S) clays in deep-marine, shallow-marine, and lacustrine facies, and kaolinite and mixed-layer I/S or kaolinite/smectite (K/S) clays in paludal and mixed marine-terrestrial facies. Furthermore, the stacking sequences of I/S clays in the ash beds are notably facies-dependent: mainly R3 with minor R1 in deep-marine facies, mainly R1 in shallow-marine facies, and mainly R3 in lacustrine and paludal facies. Ordering of I/S clays seems to have been controlled by porewater K〈sup〉+〈/sup〉 availability, solution pH, and energy levels of the depositional environment. High-pH conditions favored the formation of feldspar and inhibited the illitization of smectite, and loss of K〈sup〉+〈/sup〉 during early alteration of ash was related to environmental energy levels. However, the stacking sequences of I/S clays in terrestrial facies were dominantly controlled by burial conditions. The MgO and K〈sub〉2〈/sub〉O contents of altered volcanic ash were related to sediment clay-mineral composition and thus also facies-dependent. Marine-facies ash beds contain relatively more MgO (i.e., MgO/K〈sub〉2〈/sub〉O 〉 0.30; MgO/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 〉 0.056) than terrestrial-facies ash beds (MgO/K〈sub〉2〈/sub〉O 〈 0.30; MgO/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 〈 0.056). MgO was generally retained during alteration of ash beds, and its concentration was largely a function of parent magma type and depositional and diagenetic conditions. K〈sub〉2〈/sub〉O was almost completely leached out of volcanic glass, leading to formation of I/S clays by reaction with smectite.〈/p〉 〈p〉Rare earth elements (REE) generally exhibit little variation within a single section but strongly facies-dependent distributions across South China. The REE distributions of deep- and shallow-marine ash beds are similar, characterized by enrichment of light REEs, slight depletion of heavy REEs, and negative Eu anomalies. The REE distributions of terrestrial ash beds are notably different, with weak negative Eu anomalies in lacustrine facies and little to no Eu anomaly in paludal facies. REE distributions can be influenced by adsorption-desorption processes on clay minerals and by dissolution-precipitation reactions involving accessory minerals. Thus, the use of REE patterns of volcanic ashes as fingerprints of source-magma chemistry must take into consideration their sedimentary and diagenetic histories.〈/p〉 〈p〉Trace elements such as Nb, Cu, Zn, Co, Cr, Ta, Mo, V, La, Th, and U exhibit different concentration patterns between ash samples of different facies and even between samples from a single section. Devitrification of volcanic glass to clay minerals can lead to redistribution of TiO〈sub〉2〈/sub〉, which shows a close association with the clay fraction of altered ash beds, especially in terrestrial facies. TiO〈sub〉2〈/sub〉/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 ratios of felsic ashes reflect the effects of physical reworking and chemical alteration. It is proposed that TiO〈sub〉2〈/sub〉/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 values 〈0.055 are indicative of primary ash composition, 0.055–0.140 of moderate secondary overprints, and 〉 0.140 of strong secondary overprints. The use of Zr/TiO〈sub〉2〈/sub〉 vs Nb/Y diagrams for source rock discrimination must take into account such reworking and alteration processes. In terrestrial and shallow-marine facies in which ash-bed reworking is common, the ratios of immobile elements of the clay fraction can still indicate magma source within the range of sensitivity afforded by empirical discrimination diagrams.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 5 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Caineng Zou, Rukai Zhu, Zhong-Qiang Chen, James G. Ogg, Songtao Wu, Dazhong Dong, Zhen Qiu, Yuman Wang, Lan Wang, Senhu Lin, Jingwei Cui, Ling Su, Zhi Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Organic-matter-rich shales are the main target rocks for unconventional oil and gas exploration and development across the world. In China, shale-gas geological resources are estimated as approximately 110 × 10〈sup〉12〈/sup〉 m〈sup〉3〈/sup〉, with recoverable gas reserves of ca. 20 × 10〈sup〉12〈/sup〉 m〈sup〉3〈/sup〉. Recoverable shale-oil reserves are estimated as ca. 5 × 10〈sup〉9〈/sup〉 t. A total 35 important organic-matter-rich shale units have been recognized from Mesoproterozoic to Cenozoic strata across the entire China. These shales are categorized according to their origin under marine, marine–nonmarine transitional and lacustrine conditions. Shales of marine origin, with ca. 9 × 10〈sup〉12〈/sup〉 m〈sup〉3〈/sup〉 recoverable resources, dominate China's potential in terms of total volume of organic-carbon. Currently, the most favorable marine shales for oil and gas exploration are found in the Sichuan Basin within the lower Cambrian Qiongzhusi Formation and in the Wufeng-Longmaxi formations of uppermost Ordovician through lower Silurian. A fortuitous combination of of sea-level variations, of paleo-productivity, of tectonic activity causing development and migration of partially closed deep basin depocenters, and of sediment accumulation rates controlled the extensive deposition and distribution of organic-matter-rich shales in these Wufeng and Longmaxi formations. Organic-matter-rich shales in marine-nonmarine transitional facies associated with coal measures occur in North China within the Carboniferous and Permian, and in South China within the Permian. These Carboniferous-Permian organic-matter-rich shales are important source rocks for the gas fields in the Ordos and Sichuan Basins. Abundant organic-rich shales are also widely distributed within coal-bearing clastics and coal-measure shales of fluvial, lacustrine, and swamp facies in Upper Triassic to Middle Jurassic successions of many basins. Lacustrine organic-rich shales were deposited during the Permian through Neogene in various freshwater to saline lake settings. Lacustrine organic-matter-rich shales are the main oil source rocks in the Songliao, Bohai Bay, Ordos and Junggar basins. Lacustrine algae contributed to the rain of organic matter; and the preservation of organic matter and distribution of organic-rich shale was controlled by lake currents, water depth and oxygen-poor conditions, with enhanced preservation when buried by turbidity currents. Algal blooms were partly induced by trace nutrients from volcanic ash falls in all of these lacustrine basins. Seawater intrusion into the freshwater lake of the Songliao Basin promoted some episodes of black shales. Saline lacustrine basins, such as middle Permian Junggar Basin, contain organic-rich dolomite mudstone that mainly formed during hot climate conditions when the lakes had high salinity and stratified water columns that deprived the bottom waters of oxygen, thereby preserving massive amounts of organic matter. Laminated calcite-rich mudstone in the saline lacustrine settings formed in more brackish waters under stable warm conditions and weak biological activity. The modeling of the factors controlling the distribution of organic-matter-rich shales within China's basins is important for the exploration and development of unconventional oil and gas resources.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Zhaoliang Song, Congqiang Liu, Karin Müller, Xiaomin Yang, Yuntao Wu, Hailong Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The terrestrial biogeochemical silicon (Si) cycle may significantly influence the stabilization of soil organic carbon (SOC), and thus plays an important role in regulating the global carbon (C) balance and climate change. Processes involved in Si-enhanced SOC stability at a decadal or centennial scale include protection of SOC through amorphous Si and interactions of Si-iron and Si-aluminum. Strategic manipulation of the Si cycle in terrestrial ecosystems offers a new opportunity to enhance soil C sequestration. Rock powder amendment, establishment of Si-rich plant buffer strips and innovative management practices that return Si-rich biomass materials to soil can be implemented as strategies to enhance soil C sequestration through regulating the terrestrial Si cycle. However, quantifying (i) the contribution of different processes to the enhancement of soil dissolved Si and secondary Si minerals, (ii) the relative importance of different SOC stabilization mechanisms, and (iii) the potential and cost of different measures has not been attempted.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Stefano Patruno, William Helland-Hansen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Clinoforms are inclined and normally basinward-dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems. The study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir, seal and source rocks along shoreline to basin-floor profiles.〈/p〉 〈p〉Here, we review clinoform research and propose a more systematic description and classification of clinoforms. This is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions, together with the genesis, drivers and dynamics of their constituent sedimentary units.〈/p〉 〈p〉Four basic clinoform types are here distinguished in delta/shorelines, lacustrine and marine environments, on the basis of their overall spatial and temporal scale, morphology, outbuilding dynamic and geodynamic and depositional setting: (1, 2) delta-scale clinoforms, which in turns are sub-divided into shoreline and delta-scale subaqueous clinoforms; (3) shelf-edge clinoforms; and (4) continental-margin clinoforms. Delta-scale clinoform sets are tens of metres high and typically represent 1–10〈sup〉3〈/sup〉 kyr, with progradation rates ranging from 1,000–100,000 m/kyr for shorelines and “subaerial deltas” to 100–20,000 m/kyr for subaqueous deltas; shelf-edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0.1–20 Myr (usual progradation rates of 1–100 m/kyr) by successive cross-shelf transits of delta-scale clinoforms; continental-margin clinoform sets are thousands of metres high, hallmark key geodynamic/crustal boundaries (e.g., continent/ocean transition) and slowly prograde basinwards in ca. 5–100 Myr, with typical rates of 0.1–10 m/kyr.〈/p〉 〈p〉As a consequence of the very different progradation rates and of the difficulty of large-scale clinothems to backstep during transgressions, shorelines are the most dynamic clinoforms with regards to position, continental margins the least, and shelf-edges are intermediate. Shortly after a transgression, therefore, the four clinoform types may prograde synchronously along shoreline-to-abyssal plain transects, forming “compound clinoform” systems. During the subsequent regressive cycle, however, due to the dissimilarity in progradation rates, different clinoform types will normally merge progressively with each other, giving rise to “hybrid clinoforms” (e.g., shelf-edge deltas), and fewer depositional breaks-in-slope are distinguished along a single shoreline-to-abyssal plain transect. Overall, all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum, regulated by the cyclical backstepping of the smaller-scale system within natural progradational-retrogradational cycles of larger-scale clinothem outbuilding.〈/p〉 〈p〉All clinothem types may show either an accretionary/active or draping/passive style, depending on the proximity to the sediment source. Draping clinothems are nearly-always composed of condensed fine-grained sediments, while actively accreting clinothems can be composed of predominantly coarse-grained (i.e., reservoir-forming) or predominantly fine-grained (i.e., non-reservoir) lithotypes.〈/p〉 〈p〉A novel hierarchical classification scheme for both Recent and Ancient clinoforms is here proposed, consisting of 12 classes. The four basic clinoform types (delta-scale shoreline, delta-scale subaqueous, shelf-edge and continental-margin) are sub-divided into eight accretionary/active and draping/passive sub-types (8-division). Each accretionary sub-type is then sub-divided into a sandstone-prone and mudstone-prone variant (12-division), which can be at least tentatively predicted on the basis of the clinoform morphology, even in the absence of direct stratigraphic logs.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): M. Oliva, M. Žebre, M. Guglielmin, P.D. Hughes, A. Çiner, G. Vieira, X. Bodin, N. Andrés, R.R. Colucci, C. García-Hernández, C. Mora, J. Nofre, D. Palacios, A. Pérez-Alberti, A. Ribolini, J. Ruiz-Fernández, M.A. Sarıkaya, E. Serrano, P. Urdea, M. Valcárcel〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The relatively warm climate conditions prevailing today in the Mediterranean region limit cold geomorphological processes only to the highest mountain environments. However, climate variability during the Late Pleistocene and Holocene has led to significant spatio-temporal variations of the glacial and periglacial domain in these mountains, including permafrost conditions. Here, we examine the distribution and evolution of permafrost in the Mediterranean region considering five time periods: Last Glaciation, deglaciation, Holocene, Little Ice Age (LIA) and present-day. The distribution of inactive permafrost-derived features as well as sedimentary records indicates that the elevation limit of permafrost during the Last Glaciation was between 1000 m and even 2000 m lower than present. Permafrost was also widespread in non-glaciated slopes above the snowline forming rock glaciers and block streams, as well as meter-sized stone circles in relatively flat summit areas. As in most of the Northern Hemisphere, the onset of deglaciation in the Mediterranean region started around 19-20 ka. The ice-free terrain left by retreating glaciers was subject to paraglacial activity and intense periglacial processes under permafrost conditions. Many rock glaciers, protalus lobes and block streams formed in these recently deglaciated environments, though most of them became gradually inactive as temperatures kept rising, especially those at lower altitudes. Following the Younger Dryas glacial advance, the Early Holocene saw the last massive deglaciation in Mediterranean mountains accompanied by a progressive shift of permafrost conditions to higher elevations. It is unlikely that air temperatures recorded in Mediterranean mountains during the Holocene favoured the existence of widespread permafrost regimes, with the only exception of the highest massifs exceeding 2500-3000 m. LIA colder climate promoted a minor glacial advance and the spatial expansion of permafrost, with the development of new protalus lobes and rock glaciers in the highest massifs. Finally, post-LIA warming has led to glacial retreat/disappearance, enhanced paraglacial activity, shift of periglacial processes to higher elevations, degradation of alpine permafrost along with geoecological changes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Johannes Schoenherr, Lars Reuning, Maximilian Hallenberger, Volker Lüders, Laurent Lemmens, Bianca C. Biehl, Anna Lewin, Maike Leupold, Katharina Wimmers, Christian J. Strohmenger〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Dedolomitization converts a dolomite into a calcite, and conventionally is interpreted to form in an eogenetic or telogenetic diagenetic environment where meteoric water dissolves evaporites to supply excess calcium. Hydrologic connectivity between a dolostone and the surface water may then lead to a dedolomitized interval, often times being a diagnostic indicator for an erosional unconformity, subaerial exposure, and/or karst. In contrast to the classic models, we present a case study for pervasive burial dedolomitization, unrelated to meteoric fluids. Dedolomitization of the Zechstein-2-Carbonate (Ca2) gas reservoir in NW Germany is strongly altering reservoir quality on a regional scale. The Ca2 shows a textbook correlation between reservoir quality and mineralogy. Petrographic analyses show that approximately 80% of all observed calcite reveal a dedolomite microtexture, causing a reduction of average matrix porosity by 5 to 10% compared to the dolomite. Dedolomite follows initial layering and abundantly forms massive concretions, which are surrounded by compaction-related curvature of the depositional layering in the dolomite host rock. Such an early burial timing is supported by a slight burial-related shift of ~3‰ δ〈sup〉18〈/sup〉O and ~1‰ δ〈sup〉13〈/sup〉C towards lighter values in the dedolomites compared to dolomite. An exceptionally large amount of calcium-rich fluids must have been mobilized to account for 〉50% of the Ca2 rock volume to be dedolomitized. However, core fabrics related to meteoric diagenesis, such as karst fabrics or typical fresh water stable isotope signatures have been observed neither in the Ca2 nor in over- and underlying anhydrite beds. Instead, excess calcium likely comes from gypsum-to-anhydrite conversion and pressure solution within over- and underlying anhydrites. An influx of strontium-rich waters from the anhydrite beds is indicated by up to 5 times higher strontium contents measured in dedolomite fabrics compared to their dolomite host rock. Homogenization temperatures between 51 and 56 °C measured in some early fluid inclusions in dedolomite textures further exclude a pristine meteoric water input and suggest fluid entrapment in a burial depth range of 900 to 1400 m. Comparing these results with literature data furthermore indicates that mesogenetic dedolomite is either volumetrically underestimated in other carbonate-evaporite settings or formed under unique diagenetic conditions across the Southern Permian Basin during Zechstein times.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 22 March 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Genming Luo, Huan Yang, Thomas J. Algeo, Christian Hallmann, Shucheng Xie〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Lipids can survive long geological intervals within sediments and provide a unique tool that allows the reconstruction of past organismic diversity and environmental conditions. The lipids discussed in this review include all substances produced by organisms that are insoluble in water but extractable by organic solvents. Lipid 〈em〉biomarkers〈/em〉 refer to both functionalized biolipids as well as their hydrocarbon derivatives in geological materials that contain diverse information about biotic sources and environmental conditions. In spite of diagenetic and catagenetic alteration, lipid biomarkers commonly preserve the hydrocarbon structure of their biotic counterparts and have been found in rocks up to 1.6 billion years in age. These features have promoted the use of lipid biomarkers in many fields, including petroleum geology, paleoclimatology, oceanography, meteorology, geobiology and environmental science. Here, we (i) review the use of lipid biomarker records for the reconstruction of environmental conditions in deep time, including climatic conditions (temperature), sedimentary environments (redox, salinity and chemical composition) as well as catastrophic terrestrial events (soil erosion and wildfire), and (ii) generate new insights into environmental perturbations during the Permian-Triassic transition based on investigation of lipid biomarkers. We further propose that the ratio of dibenzothiophene to phenanthrene (DBT/P) in marine carbonates may be a robust proxy for seawater sulfate concentrations in deep time. Our compiled DBT/P records show substantial variations in seawater sulfate levels through Earth history that are consistent with the results of other proxies. We discuss the future outlook for application of lipid biomarker records to deep-time environmental research.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): Qing Zhu, Michael J. Castellano, Guishan Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Interactions among soil water processes and the nitrogen (N) cycle govern biological productivity and environmental outcomes in the earth's critical zone. Soil water influences the N cycle in two distinct but interactive modes. First, the spatio-temporal variation of soil water content (SWC) controls redox coupling among oxidized and reduced compounds, and thus N mineralization, nitrification, and denitrification. Secondly, subsurface flow controls the movement of water and dissolved N. These two processes interact such that subsurface flow dynamics control the occurrence of relatively static, isolated soil solution environments that span a range of reduced to oxidized conditions. However, the soil water-N cycle is usually treated as a black box. Models focused on N cycling simplify soil water parameters, while models focused on soil water processes simplify N cycling parameters. In addition, effective ways to deal with upscaling are lacking. New techniques will allow comprehensive coupling of the soil water-N cycle across time and space: 1) using hydrogeophysical tools to detect soil water processes and then linked to electrochemical N sensors to reveal the soil N cycle, (2) upscaling small-scale observations and simulations by constructing functions between soil water-N cycle and ancillary soil, topography and vegetation variables in the hydropedological functional units, and (3) integrating soil hydrology models with N cycling models to minimize the over-simplification of N biogeochemistry and soil hydrology mechanisms in these models. These suggestions will enhance our understanding of interactions among soil water dynamics and the N cycle, thus improving modeling of N losses as important sources of greenhouse gas emissions and water pollution.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 19 October 2017〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Yanxin Wang, Kunfu Pi, Scott Fendorf, Yamin Deng, Xianjun Xie〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Geogenic enrichment of arsenic (As) in groundwater has been a topic of worldwide concern over the past several decades due to the severe health threat to an estimated over one hundred million people. Despite the genetic diversity and the spatial variability of As concentrations, the most common geogenic As-enriched groundwater occurs in flat, low-lying river floodplains and fluvial-lacustrine plains. Within river systems draining the Himalaya, tectonic movement, sedimentological processes and palaeoclimatic optima after the Last Glacial Maximum have created favorable conditions for the formation of high-As aquifer systems mainly within the Late Pleistocene-Holocene deposits. The co-deposition of As-bearing Fe oxides and reactive organic matter within sediments of deltas/floodplains or fluvial-lacustrine plains forms the premise for As release under reducing geochemical environments. However, depending on the reactivity of organic matter and As-bearing Fe oxides, as well as the availability of aqueous sulfate, geochemical mechanisms controlling As enrichment in the groundwater differ between the coastal floodplains of South and Southeast Asia and the fluvial-lacustrine plains of North and Central China. The indigenous geomicrobes thriving to adapt to specific aquifer environments may mediate Fe-S-As biogeochemical cycling responsible for As speciation transformation, dissolution/desorption, and hence mobilization. Hydrologic processes regulated by the local and regional groundwater flow regimes control As transport as well as its spatial distribution. Special attention must be paid to anthropogenic perturbation from intensive groundwater pumping and land use changes that affect the aquifer hydrological conditions and the biogeochemical processes, thus altering groundwater As levels. To decipher the patterns of As variation within the aquifers, an integrated approach characterizing the major sedimentological, hydrobiogeochemical and anthropogenic processes influencing As release and transport needs to be applied to ensure sustainable water supply for domestic and agricultural needs.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): D. Amblas, J.A. Dowdeswell〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Predicting the source areas for Antarctic Bottom Water (AABW) requires knowledge of how cold, dense water masses form and move from the Antarctic shelves to the continental slope. Here we use a review of nearly 50 years of direct hydrographic observations to infer the main broad-scale influences on the distribution of dense shelf-water (DSW) overflows that cascade down the continental slope around Antarctica. The dynamics and distribution of large ice shelves, coastal polynyas and the physiography of the Antarctic continental shelves are each considered. The catalogue we present increases the number of DSW observations to 27, adds 20 additional stations where this process is likely to have occurred, and identifies 41 areas where DSW appears to be absent. Our pan-Antarctic, multi-decadal review enhances the understanding of the formation and export of DSW and highlights the variability and complexity of ice-ocean systems on high-latitude continental margins. The study also provides a context for understanding recent episodes of Antarctic ice-shelf instability, and how the relationship between DSW and AABW may evolve with climatic and oceanographic changes.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 3 October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Ashleigh Murszewski, Tara R. Edwards, Alexander R. Cruden, Brian Armstrong, Giovanni Boschian, Andy I.R. Herries〈/p〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Changjia Li, Richard Grayson, Joseph Holden, Pengfei Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Peatlands cover approximately 2.84% of global land area while storing one third to one half of the world's soil carbon. While peat erosion is a natural process it has been enhanced by human mismanagement in many places worldwide. Enhanced peat erosion is a serious ecological and environmental problem that can have severe on-site and off-site impacts. A 2007 monograph by Evans and Warburton synthesized our understanding of peatland erosion at the time and here we provide an update covering: i) peat erosion processes across different scales; ii) techniques used to measure peat erosion; iii) factors affecting peat erosion; and iv) meta-analyses of reported peat erosion rates. We found that over the last decade there has been significant progress in studying the causes and effects of peat erosion and some progress in modelling peat erosion. However, there has been little progress in developing our understanding of the erosion processes. Despite the application of new peat surveying techniques there has been a lack of their use to specifically understand spatial and temporal peat erosion dynamics or processes in a range of peatland environments. Improved process understanding and more data on rates of erosion at different scales are urgently needed in order to improve model development and enable better predictions of future peat erosion under climate change and land management practices. We identify where further research is required on basic peat erosion processes, application of new and integrated measurement of different variables and the impact of drivers or mitigation techniques that may affect peat erosion.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): J. Craig, N. Hakhoo, G.M. Bhat, M. Hafiz, M.R. Khan, R. Misra, S.K. Pandita, B.K. Raina, J. Thurow, B. Thusu, W. Ahmed, S. Khullar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Himalayan orogeny has shaped the sedimentary basins of the region, where continuous deformation formed both ‘conventional’ and ‘unconventional’ petroleum systems at multiple stratigraphic levels ranging in the age from Precambrian to Neogene. Himalaya is considered to be prospective for hydrocarbon exploration because of its suitable tectono-sedimentary environment, oil/gas shows, and the presence of commercial oil and gas discoveries in broadly similar structural settings in the eastern and western regions. Although detailed surface geological mapping, the acquisition of geological data and the drilling of wells has considerably improved the understanding of the geological and structural setting and the hydrocarbon potential of the NW Himalaya, commercial discoveries have remained largely elusive.〈/p〉 〈p〉In the NW Himalaya the Precambrian-Cambrian sequences that are of primary interest include the Salt Range Formation (Potwar Basin), and also some sequences in the Lesser-and-Sub-Himalaya, such as the Proterozoic Sirban Limestone Formation; in the Kashmir and Bhadarwah-Chamba basins further to the northeast, and in the Garhwal Group and the Krol belt in the southeast.〈/p〉 〈p〉The Palaeozoic sedimentary rocks exposed within the Lesser Himalaya and the Tethyan Himalaya (represented by the Kashmir, Zanskar-Spiti, Kinnaur-Uttarakhand and Kumaon basins) have been subjected to low grade metamorphism, and presently have no significant hydrocarbon generation potential. The Cambrian Khewra and the Permian Tobra formations form hydrocarbon bearing reservoirs in the East Potwar. The Palaeozoic stratigraphy of the Zanskar Tethyan Himalaya in northern India is rather similar to that of the Peshawar Basin in Pakistan. The thick argillaceous successions are the best potential hydrocarbon source rock horizons within the Palaeozoic.〈/p〉 〈p〉The Mesozoic and Early Eocene successions of the Tethyan Himalaya were deposited in the shallow southern margin of the Tethys Ocean. In the western Himalaya, the Tethyan Himalayan succession is exposed in Kashmir, Zanskar, Chamba and Spiti basins. The Mesozoic successions include thick sequences of organic material rich argillaceous sediments. The Triassic and Jurassic strata are generally poorly developed or absent in the eastern Potwar Basin, while they get thicker towards the west Potwar and Kohat basins. The sandstones of Jurassic age are proven reservoirs, and potential source rocks are present. The Mesozoic succession of the Kashmir Basin is represented by the formations of the Triassic age. Some of the shales contain organic matter (OM) and could represent viable hydrocarbon source rocks, while some of the limestones, dolomites and sandstones have sufficient reservoir characteristics. The OM content of the argillaceous sediments within the Mesozoic-Tertiary succession of the Zanskar-Spiti Basin (Ladakh Himalaya) is appropriate for hydrocarbon generation.〈/p〉 〈p〉The Cenozoic foreland basin of the Himalayan orogen was deformed by a southward migrating thrust system during the Late Miocene-Quaternary. The Sub-Himalaya Zone contains a sequence of Cenozoic sedimentary rocks divided into the Subathu and Dharamsala (=Murree) formations, and Siwalik Group. Hydrocarbon source rocks are present in the Subathu and Dharamsala formations; while the Lower Siwalik, Kasauli and Dagshai formations contain potential sandstone reservoirs. The Eocene Subathu Formation is a key exploration target in the NW Himalaya with both potential hydrocarbon source and reservoir rocks sealed by a thick clay sequence. The coeval shales within the Patala and Nammal formations are considered to be the main source rocks in the Potwar Basin, whereas, the fractured carbonates of Palaeocene and Early Eocene age are the main reservoirs. The Miocene Murree Formation is the youngest oil-producing horizon in the Potwar Basin. Palaeocene Hangu Sandstone and Lockhart Limestone are the main reservoirs in the Kohat Basin. The stratigraphy of Kohat-Potwar Basin extends into Margalla, Kalachitta and Samana Ranges. In these ranges the Jurassic-Eocene strata is exposed, so sub-thrust sheets could have hydrocarbon potential.〈/p〉 〈p〉In the NW Himalaya, the surface gas seeps are characterised by a high nitrogen content, and are either thermogenic or biogenic in origin, while the gases encountered in the wells are typically methane rich (dry) with low nitrogen concentrations, indicating thermogenic origin. There appears to be a strong linear correlation between the relative concentration of methane and nitrogen in the Himalayan fore-deep gas shows. There are numerous references to biogenic gas seeps in the Plio-Pleistocene sediments and lignite fields in the Kashmir Valley, and also in the shallow Plio-Pleistocene sediments in the Peshawar Basin.〈/p〉 〈p〉The evolution and establishment of the key petroleum system elements, the generation, expulsion, migration and accumulation (entrapment) of hydrocarbons at multiple stratigraphic levels in NW Himalaya has been controlled by the regional tectonic events. These events are associated with the source rock burial and maturation history, coupled with hydrocarbon generation, ‘peak oil’ and subsequent migration occurring concomitantly with the peak activity along the major regional thrusts. The complex and variable structural geometries have allowed a variety of traps beneath sections where source rocks have adequate burial depth, and where traps have not been breached. In NW Himalaya, the key to understand the direct relationship between tectonics and the evolution of petroleum systems are the accurate estimates for the timing of the related tectonics and that of the hydrocarbon generation, accumulation and critical moment. Here, the exploration has been hampered by the structural complexity, difficult terrain, drilling complications and poor seismic data quality. Timing of the trap formation 〈em〉vs.〈/em〉 hydrocarbon charge, trap integrity, seal presence and capacity, and reservoir quality are the key geological risks that have to be addressed.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Yongqiang Zhou, Thomas A. Davidson, Xiaolong Yao, Yunlin Zhang, Erik Jeppesen, Javier Garcia de Souza, Huawu Wu, Kun Shi, Boqiang Qin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Harmful algal blooms have become increasingly frequent due to the dual pressure of excessive nutrient loading and climate change in recent years. Algal-derived dissolved organic matter (DOM) is a potentially large component of the labile organic matter pool, and also climate warming may affect the DOM pool, although the results on the latter so far are equivocal. The question of how eutrophication and climate warming may drive the accumulation of autochthonous DOM is much debated. Here, we analysed published data on DOM world-wide and field data that we collected from 97 lakes and major rivers in China (〉 4500 samples) as well as results from the longest running shallow-lake mesocosm climate experiment in the world at a research facility in Denmark. Our results indicated that dissolved organic carbon (DOC) concentrations decreased with increasing temperature and enrichment of δ〈sup〉13〈/sup〉C-DOM. A negative relationship was found between latitude and %protein-like fluorescence, which increased significantly with increasing elevation and enrichment of δ〈sup〉13〈/sup〉C-DOM. Specific ultraviolet absorbance at 254 nm (SUVA) decreased with increasing elevation and enrichment of δ〈sup〉13〈/sup〉C-DOM. Fluorescence intensity of autochthonous microbial humic-like substances increased notably with eutrophication but decreased weakly with warming. DOC, biodegradable DOC, chlorophyll-〈em〉a〈/em〉, δ〈sup〉13〈/sup〉C-DOC and autochthonous substances identified using DOM fluorescence and high resolution mass spectrometry from the mesocosm experiment were notably elevated at the high nutrient levels, while the effect of temperature was insignificant. We conclude that while eutrophication promotes DOM, warming potentially suppresses the accumulation of autochthonous DOM in inland waters.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0012825218302174-ga1.jpg" width="342" alt="Unlabelled Image" title="Unlabelled Image"〉〈figcaption〉〈p〉Principal component analysis of optical characteristics of the CDOM samples collected in the mesocosm experiment. Relationships between the microbial humic-like C3 and stable isotope δ〈sup〉2〈/sup〉H, and between C3 and δ〈sup〉13〈/sup〉C-DOC.〈/p〉〈/figcaption〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): Yuejun Wang, Xin Qian, Peter A. Cawood, Huichuan Liu, Qinglai Feng, Guochun Zhao, Yanhua Zhang, Huiying He, Peizhen Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Phanerozoic record of Southeast Asia preserves the history of opening and subsequent consumption of the Paleotethyan Ocean and the assembly of continental fragments into Asia as part of the broader-scale reconstruction of Pangea. However, uncertainty remains as to which of the many suture zones in Southeast Asia represents the relict of the main ocean, when final ocean closure occurred, and the assembly history of the Eastern Cimmerian and Southeast Asia continental fragments. Our overview of the geological features of the suture zones, the bounding continental fragments and their magmatic, metamorphic and sedimentary records resolves many of these key issues. The sedimentary, biogeographical, structural, lithological, geochemical and geochronological data from the Changning-Menglian, Inthanon and Bentong-Raub suture zones argue for their linkage with the Longmu Co-Shuanghu suture zone in Central Tibet, and together constitute the main East Paleotethyan Ocean relict. The eastward subduction of the ocean resulted in the development of a series of magmatic arc-back-arc basin and continental fragments in Southeast Asia, including, from west to east, the Lincang-Sukhothai-East Malaya arc, the Jinghong-Nan-Sa Kaeo back-arc basin, the Simao/west Indochina fragment, the Luang Prabang-Loei back-arc basin, the south Indochina fragment, the Wusu and Truong Son back-arc basins, the north Indochina fragment, the Jinshajiang-Ailaoshan-Song Ma branch/back-arc basin and the South China Block. Assembly of these fragments resulted in Indosinian high temperature and high pressure metamorphism and related tectonothermal event. Available data indicate a switch from subduction of the main East Paleotethyan Ocean to the collision of the Sibumasu with Simao/Indochina blocks at ~ 237 Ma, with subsequent 〈em〉syn〈/em〉- and post-collisional events at ~ 237–230 Ma and ~ 230–200 Ma, respectively, along the Changning-Menglian, Inthanon and Bentong-Raub suture zones. The timing of initial-, 〈em〉syn〈/em〉- and post-collision events along the Jinshajiang-Ailaoshan-Song Ma suture zone with its record of back-arc basin closure is at ~ 247 Ma, ~ 247–237 Ma and ~ 237–200 Ma, generally ~ 10 Ma older than that along the Changning-Menglian, Inthanon and Bentong-Raub suture zones. Our synthesis of all available data enables establishment of a comprehensive geodynamic model for the East Paleotethyan evolution. This model links the spatial-temporal pattern across Southeast Asia into a series of tectonic events including ocean/back-arc basin opening, subduction/closure, subsequent assemblage and orogenic collapse, along with associated igneous, metamorphic and sedimentary activities.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Xing-Kui Li, Jun Chen, Ru-Cheng Wang, Cai Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The western segment of the South Qiangtang terrane (W-SQT) is an ideal place to investigate the Late Mesozoic crustal architecture, tectonomagmatic evolution and regional mineralization of this terrane, where the emplacement of voluminous Late Mesozoic granitoids provides favorable conditions to form some world-class porphyry Cu-Au mineral deposits, as well as a series of Fe, Pb-Zn, and W mineral deposits or occurrences. Here we synthesize the spatial distribution, geological, geochronological, geochemical, and isotopic data of the Late Mesozoic granitoids and associated mineral deposits or occurrences in W-SQT. These data suggest that the granitoid magmatism in W-SQT lasted from ca. 170 Ma to ca. 110 Ma, with two magmatic flare-ups at ca. 170–150 Ma and ca. 130–110 Ma. In particular, the granitoids formed between ca. 170 Ma and ca. 120 Ma are generally younger from north to south, indicating a southward migration of magmatism during this period. The compositions of the granitoids vary considerably across W-SQT, becoming more reduced and evolved from the ancient coastal area (i.e., the area close to the Bangong–Nujiang Suture Zone) to the continental interior area. Moreover, the zircon ε〈sub〉Hf〈/sub〉(t) values of the granitoids also gradually decrease from the ancient coastal area to the interior area, indicating the ancient crustal components in the source of the granitoids increase continentward. We therefore concluded that an ancient crustal basement with Archean to Paleoproterozoic ages must exist beneath the interior of the South Qiangtang terrane, i.e., the South Qiangtang terrane has been an older microcontinent. Based on this conclusion, a comprehensive model involving the flat subduction, break-off, rollback, and complete detachment of the Bangong–Nujiang oceanic slab was proposed for the Late Mesozoic tectonomagmatic and metallogenic evolution of W-SQT. In particular, the thickening of W-SQT crust during Late Jurassic and the occurrence of magmatic gap (ca. 140–130 Ma) were interpreted to be associated with the flat subduction of Bangong–Nujiang oceanic slab. The development of regional extension recorded by Early Cretaceous (127–122 Ma) mafic dikes and bimodal volcanic rocks, and the southward migration of granitoid magmatism were attributed to the break-off and rollback of Bangong–Nujiang oceanic slab. Our study also shows that the Early Cretaceous mantle-derived (juvenile crust-derived), highly-oxidized and less-evolved granitoids are most favourable for the generation of significant porphyry Cu-Au deposits, while the Middle-Late Jurassic mature crust-derived, relatively-reduced and highly-evolved granitoids are highly prospective for Pb-Zn and W mineralisations. In addition, the granitoids generated by a mixture of mantle-derived and mature crust-derived components have high potential for skarn Fe (〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Cu) deposits. For the W-SQT magmatic belt as a whole, Cu-Au-prospective granitoids, Fe (〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Cu)-prospective granitoids, and Pb-Zn-W-prospective granitoids exist in the south, the middle and the north, respectively.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): Baochun Huang, Yonggang Yan, John D.A. Piper, Donghai Zhang, Zhiyu Yi, Shan Yu, Tinghong Zhou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Although the axial and dominant geocentric character of the Earth's magnetic field means that paleolongitude is indeterminate, paleomagnetism is otherwise the only truly quantitative method available to the Earth scientist for constraining paleogeography and reconstructing the kinematic evolution of continental blocks. During the past half-century numerous paleomagnetic results have provided substantial quantitative constraints on the origin and tectonic evolution of the major tectonic divisions now comprising Eastern Asian. In this paper we first assess the available Early Paleozoic to Early Cretaceous paleomagnetic results from the South China, North China, and Tarim blocks using internationally-recognized reliability criteria. We then construct a running mean through a 20 Ma window by weighting the poles according to their Q-factors and fit a spherical spline with smoothing factor of 300 to derive apparent polar wander (APW) paths for these three major blocks during this Early Paleozoic to Late Mesozoic time interval. Together with Late Paleozoic to Early Mesozoic paleomagnetic poles from the Qaidam, Qiangtang, Lhasa, Sibumasu, Indochina, and some other smaller blocks/terranes of East Asia, we produce a series of paleogeographic reconstructions for these major blocks and lesser terranes of East Asia between mid-Ordovician and late Jurassic times (~460–160 Ma) which, although based primarily upon paleomagnetic evidence, aim to embrace the geological constraints. Finally, we discuss the current evidence for closure times of the Paleo-Asian, Mianlue, and East Paleo-Tethyan oceans which incorporate fundamental issues concerning the formation of the East Asian continental collage and collision with the northern main body of the Pangean supercontinent. We use the collective evidence to argue that these major paleo-oceans had closed by the Late Triassic, and that the East Asian sector of the supercontinent had united to become an integral part of Pangea by that time (~220 Ma).〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 184〈/p〉 〈p〉Author(s): G. Shanmugam〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉By their impressive paper title “Ichnological analysis of contourites: Past, present and future”, Rodríguez-Tovar and Hernández-Molina (2018) have implied that the paper is about a comprehensive review of the topic in space (i.e., global) and time (i.e., past, present, and future). But in reality, the paper has covered only three case studies in Europe. In the real world, bioturbation and burrows are not unique to contourites; they are equally abundant in turbidites, hyperpycnites, tempestites, and even in deformed seismites. Therefore, the immediate challenge is in distinguishing contourite facies from other facies (e.g. hyperpycnites with intense bioturbation). Disappointingly, the review has neglected to address this fundamental issue. Without resolving the basic issue of distinguishing contourites, any ichnological analysis of “contourites” is purely academic and has no relevance in advancing contourite research.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Remus Prăvălie〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Forests are among the most important terrestrial ecological systems in terms of the multitude of ecosystem functions and services they provide. These biotic systems are vital not only for ensuring the wellbeing of human society and for preserving global biodiversity, but also for regulating the climate system, decarbonizing the atmosphere via carbon sequestration (in biomass or underlying soil carbon pools) and evaporative cooling processes that mitigate climate warming. However, forest ecosystems are currently being subjected to a wide range of natural and anthropic disturbances that pose a real threat not only to forest health and the various benefits forests provide for human society, but also to the overall functioning of the global system. This paper is a review that aims to analyse, in a brief and holistic manner, the main perturbations Earth forest ecosystems are currently facing, both the obvious (e.g. deforestation) and discrete/silent ones (e.g. defaunation) that have generally not yet been tackled strictly as ecological forest issues in the international scientific literature. At the same time, the paper aims to highlight the possible effects generated by forest perturbations in the global warming process, through carbon fluxes and biogeophysical feedbacks between these terrestrial systems and the atmosphere. Upon analysis of a vast scientific bibliography, it was found there currently are 12 major forest disturbances that can be grouped into three categories based on the prevalence of triggering causes, i.e. climatic (phenological shifts, range shifts, die-off events, insect infestations), anthropic (deforestation, fragmentation, air pollution) and mixed (defaunation, fires, composition shifts, net primary productivity shifts, biogeochemical shifts) perturbations. These ecological issues, which occur frequently, intensely and on large spatial scales, are able to significantly disrupt forest productivity and therefore strongly erode the forests’capacity to stabilize the climate system. All identified disturbances can amplify global warming in various ways, including by means of many positive feedback mechanisms in the case of climatic perturbations. Finally, this review paper proposes five major anthropogenic strategies to fight this multidimensional forest crisis – mitigate, adapt, repair, protect and research actions, which, if implemented rapidly, efficiently and on a large scale via international policies, can successfully stabilize these terrestrial ecosystems and, implicitly, the climate system in the 21st century.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 27 June 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Eric Desjardins, Marco Van De Wiel, Yannick Rousseau〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper brings a philosophical perspective on computer simulations in the field of geomorphology. The first part of our analysis presents a general framework within which to interpret and evaluate the adequacy of simulations models pursuing three broad epistemic goals (modes): prediction, explanation, and exploration. It also explains the diverse relationships existing between the phenomenon of equifinality and each one of these modes. The second part of the paper applies this framework to a case in fluvial geomorphology. This application enables further specification of the three modelling modes and shows how they can work together in the inquiry of natural phenomena. Finally, our analysis looks briefly at the path-dependent nature of model building, which highlights the importance of historical contingencies in model development and further support the pragmatic stance endorsed in the framework.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Marissa J. Betts, John R. Paterson, Sarah M. Jacquet, Anita S. Andrew, Philip A. Hall, James B. Jago, Elizabeth A. Jagodzinski, Wolfgang V. Preiss, James L. Crowley, Tom Brougham, Ciaran P. Mathewson, Diego C. García-Bellido, Timothy P. Topper, Christian B. Skovsted, Glenn A. Brock〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The most successful chronostratigraphic correlation methods enlist multiple proxies such as biostratigraphy and chemostratigraphy to constrain the timing of globally important bio- and geo-events. Here we present the first regional, high-resolution shelly fossil biostratigraphy integrated with δ〈sup〉13〈/sup〉C chemostratigraphy (and corresponding δ〈sup〉18〈/sup〉O data) from the traditional lower Cambrian (Terreneuvian and provisional Cambrian Series 2) of South Australia. The global ZHUCE, SHICE, positive excursions II and III and the CARE are captured in lower Cambrian successions from the Arrowie and Stansbury basins. The South Australian shelly fossil biostratigraphy has a consistent relationship with the δ〈sup〉13〈/sup〉C results, bolstering interpretation, identification and correlation of the excursions. Positive excursion II straddles the boundary between the 〈em〉Kulparina rostrata〈/em〉 and 〈em〉Micrina etheridgei〈/em〉 zones, and the CARE straddles the boundary between the 〈em〉M. etheridgei〈/em〉 and 〈em〉Dailyatia odyssei〈/em〉 zones, peaking in the lower parts of the latter zone. New CA-TIMS zircon dates from the upper Hawker Group and Billy Creek Formation provide geochronologic calibration points for the upper 〈em〉D. odyssei〈/em〉 Zone and corresponding chemostratigraphic curve, embedding the lower Cambrian successions from South Australia into a global chronostratigraphic context. This multi-proxy investigation demonstrates the power of integrated methods for developing regional biostratigraphic schemes and facilitating robust global correlation of lower Cambrian successions from South Australia (part of East Gondwana) with coeval terranes on other Cambrian palaeocontinents, including South and North China, Siberia, Laurentia, Avalonia and West Gondwana.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Antonioli F., L. Ferranti, P. Stocchi, G. Deiana, V. Lo Presti, S. Furlani, C. Marino, P. Orru, G. Scicchitano, E. Trainito, M. Anzidei, M. Bonamini, P. Sansò, G. Mastronuzzi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉We report detailed morphometric observations on several MIS 5.5 and a few older (MIS 11, 21, 25) fossil tidal notches shaped along carbonate coasts at 80 sites in the central Mediterranean Sea and at an additional six sites in the eastern and western Mediterranean. At each site, we performed precise measurements of the fossil tidal notch (FTN) width and depth, and of the elevation of its base relative to the base of the present tidal notch (PTN). The age of the fossil notches is obtained by correlation with biologic material associated with the notches at or very close to the site. This material was previously dated either through radiometric analysis or by its fossiliferous content.〈/p〉 〈p〉The width (i.e. the difference in elevation between base and top) of the notches ranges from 1.20 to 0.38 m, with a mean of 0.74 m. Although the FTN is always a few centimetres wider than the PTN, probably because of the lack of the biological reef coupled with a small erosional enlargement in the FTN, the broadly comparable width suggests that tide amplitude has not changed since MIS 5.5 times. This result can be extended to the MIS 11 features because of a comparable notch width, but not to the MIS 21 and 25 epochs. Although observational control of these older notches is limited, we regard this result as suggesting that changes in tide amplitude broadly occurred at the Early-Middle Pleistocene transition.〈/p〉 〈p〉The investigated MIS 5.5 notches are located in tectonically stable coasts, compared to other sectors of the central Mediterranean Sea where they are uplifted or subsided to ~100 m and over. In these stable areas, the elevation of the base of the MIS 5.5 notch ranges from 2.09 to 12.48 m, with a mean of 5.7 m. Such variability, although limited, indicates that small land movements, deriving from slow crustal processes, may have occurred in stable areas. We defined a number of sectors characterized by different geologic histories, where a careful evaluation of local vertical land motion allowed the selection of the best representative elevation of the MIS 5.5 peak highstand for each sector. This elevation has been compared against glacial isostatic adjustment (GIA) predictions drawn from a suite of ice-sheet models (ICE-G5, ICE-G6 and ANICE-SELEN) that are used in combination with the same solid Earth model and mantle viscosity parameters. Results indicate that the GIA signal is not the main cause of the observed highstand variability and that other mechanisms are needed. The GIA simulations show that, even within the Mediterranean Basin, the maximum highstand is reached at different times according to the geographical location. Our work shows that, besides GIA, even in areas considered tectonically stable, additional vertical tectonic movements may occur with a magnitude that is significantly larger than the GIA.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Rosario Esposito, Kimberly Badescu, Matthew Steele-MacInnis, Claudia Cannatelli, Benedetto De Vivo, Annamaria Lima, Robert J. Bodnar, Craig E. Manning〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉One of the main goals of studying melt inclusions (MI) is to constrain the pre-eruptive physical and chemical processes that have occurred in a magma reservoir at the micro-scale. Recently, several studies that focused on magmatic differentiation of volcanic systems produced detailed interpretations based on data from MI trapped at different times and locations in the plumbing system. Ideally, MI data should be collected and tested following the melt inclusion assemblage (MIA) protocol that consists of studying and analyzing groups of MI that were trapped at the same time, and, thus, at the same chemical and physical conditions. However, the rarity of MIA in juvenile volcanic phenocrysts precludes this methodology in many cases, leading to uncertainty concerning the validity of the MI as recorders of pre-eruptive conditions.〈/p〉 〈p〉In this study, we focused on MI from the Campi Flegrei (CF) and the Island of Procida (IP) volcanic systems in southern Italy, including data from this study and data from the literature. The database included MI hosted in sanidine, clinopyroxene, plagioclase, biotite and olivine, and, thus, represents melts trapped at various stages in the overall differentiation process. We developed a protocol to select the most reliable MI from a dataset associated with a single magmatic system. As a first step we compare MI data with bulk rock data for the same magmatic system. This comparison reveals that most MI show major element compositions that fall within or close to the range for bulk rocks – these MI are considered to be “normal”. Some MI show anomalous compositions and are not representative of the melt in equilibrium with the phenocryst host and were excluded from the data set. In the second step we selected only bubble-free MI from the previously identified “normal” MI to interpret the volatile evolution. In the third step we compare compositions of the “normal” bubble-free MI to compositions predicted by rhyolite-MELTS simulations, assuming a variety of initial conditions.〈/p〉 〈p〉Comparison of data obtained from basaltic-trachybasaltic MI with rhyolite-MELTS predictions indicates that one group of MI records the geochemical evolution of a volatile-saturated magma differentiating by polybaric fractional crystallization from ≥200 MPa (≥7.5 km) to 30 MPa (~1 km). Another group of MI records recharge of the magma chamber by a primitive basaltic magma that mixes with the preexisting primitive trachybasaltic magma before eruption. Extensive isobaric crystallization of the trachybasaltic magmas at ~7.5 km beneath CF may have generated trachytic-phonolitic magmas, such as those associated with the Neapolitan Yellow Tuff (NYT) that is characterized by a relatively high H〈sub〉2〈/sub〉O content. These volatile-saturated trachytic-phonolitic magmas likely trigger high-magnitude eruptions during their ascent to the surface.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Xiaoyu Guo, Rui Gao, Junmeng Zhao, Xiao Xu, Zhanwu Lu, Simon L. Klemperer, Hongbing Liu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Tibetan Plateau's enigmatic collapse, which was indicated based on extensional faulting in the interior of the plateau and large eastward-directed strike-slip faults, has inspired intensive geologic inquiry and debate. Interaction of the subducting Indian plate with the overlying Asian lithosphere is one factor that may be affecting the plateau. A more detailed image of the subducting Indian plate can help constrain its role, but regional high-resolution seismic data have not been widely available at a relevant scale. Here we present an integrated interpretation based on two types of seismic datasets: (1) two N-S oriented deep seismic-reflection profiles that cross the Yarlung-Zangbo suture, and (2) two 〈em〉E〈/em〉-W receiver function profiles that cross the Xainza-Dingjye and Nyima-Tingri rifts, respectively. These images reveal different crustal-scale structures in the dominant collision zone between the western and central regions, as well as distinctly offset Moho discontinuities across the N-S trending rift grabens in southern Tibet. These crustal variations, combined with previous tomographic studies in Tibet, outline an easterly tilt of the subducting Indian slab, along which crust-mantle decoupling occurred. Together with the spatio-temporal distribution of synchronous potassium-rich volcanics exposed within the grabens in southern Tibet, this offset Moho structure beneath the grabens lends support to the hypothesis that eastward steepening of the subducting Indian slab was accompanied by slab tearing beneath each north-south striking rift. This overall crustal geometric variation suggests a stepwise flattening of the torn Indian slab from west to the east, a process that brought easterly migration of gravitational instability to the overriding Tibetan crust that drove collapse of the Tibetan Plateau once gravitational instability reached a critical level to the east.〈/p〉〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Stefani Daryanto, Bojie Fu, Lixin Wang, Pierre-André Jacinthe, Wenwu Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The maintenance of soil health in agro-ecosystems is essential for sustaining agricultural productivity. Through its positive impacts on various soil physical and biological processes, cover cropping can be an important component of sustainable agricultural production systems. However, the practice of cover cropping can be complex, and possible trade-offs between the benefits and side effects of cover crops have not been examined. To evaluate these benefits and potential trade-offs, we quantitatively synthesized different ecosystem services provided by cover crops (e.g., erosion control, water quality regulation, soil moisture retention, accumulation of soil organic matter and microbial biomass, greenhouse gas (GHG) emission, weed and pest control, as well as yield of the subsequent cash crop) using data from previous publications. We used a simple indicator (δ), defined as the ratio of an observed variable (i.e., ecosystem service) under cover crop and under fallow condition, to evaluate the impacts of cover crops on a given ecosystem service. Our results showed that cover crops provided beneficial ecosystem services in most cases, except for an increase in GHG emission (δ〈sub〉〈em〉CO2〈/em〉〈/sub〉 = 1.46 ± 0.47 and δ〈sub〉〈em〉N2 O〈/em〉〈/sub〉 = 1.49 ± 1.22; 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mover accent="true"〉〈mi〉x〈/mi〉〈mo stretchy="true"〉¯〈/mo〉〈/mover〉〈/math〉 ± SD) and in pest (nematode) incidence (δ〈sub〉〈em〉nematode abundance〈/em〉〈/sub〉 = 1.29 ± 1.61). It is also important to highlight that, in some cases, tillage could offset the extent of ecosystem service benefits provided by cover crops. Based on this synthesis, we argue that cover crops should be incorporated into modern agricultural practices because of the many environmental benefits they offer, particularly the maintenance of soil and ecosystem health. More importantly, there was generally an increase in cash crop yield with cover cropping (δ〈sub〉〈em〉yield〈/em〉〈/sub〉 = 1.15 ± 0.75), likely due to improvement in various soil processes. Despite its benefits, the complexity of cover crop management should not be overlooked, and site-specific factors such as climate, soil type, cover crop species and tillage practices must be considered in order to optimize the benefits of cover cropping. In addition to crop yield, detailed economic analyses are needed to calculate the direct (e.g., reduction in the amount of chemical fertilizer) and indirect monetary benefits (e.g., the improvement of soil quality) of cover crops. Such a comprehensive analysis could serve as incentive for producers to integrate cover crops into their management practices.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Willie Wei-Hock Soon, Ronan Connolly, Michael Connolly, Peter O'Neill, Jingyun Zheng, Quansheng Ge, Zhixin Hao, Hong Yan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Most estimates of Chinese regional Surface Air Temperatures since the late-19th century have identified two relatively warm periods – 1920s–40s and 1990s–present. However, there is considerable debate over how the two periods compare to each other. Some argue the current warm period is much warmer than the earlier warm period. Others argue the earlier warm period was comparable to the present. In this collaborative paper, including authors from both camps, the reasons for this ongoing debate are discussed. Several different estimates of Chinese temperature trends, both new and previously published, are considered. A study of the effects of urbanization bias on Chinese temperature trends was carried out using the new updated version of the Global Historical Climatology Network (GHCN) – version 4 (currently in beta production). It is shown that there are relatively few rural stations with long records, but urbanization bias artificially makes the early warm period seem colder and the recent warm period seem warmer. However, current homogenization approaches (which attempt to reduce non-climatic biases) also tend to have similar effects, making it unclear whether reducing or increasing the relative warmth of each period is most appropriate. A sample of 17 Chinese temperature proxy series (12 regional and 5 national) is compared and contrasted specifically for the period since the 19th century. Most proxy series imply a warm early-20th century period and a warm recent period, but the relative warmth of these two periods differs between proxies. Also, with some proxies, one or other of the warm periods is absent.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Nester M. Korolev, Aleksey E. Melnik, Xian-Hua Li, Sergey G. Skublov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the past decade the oxygen isotope composition in rock-forming minerals of mantle eclogites (δ〈sup〉18〈/sup〉O = 2–12‰) has been actively discussed as a most reliable proxy of their origin and evolution. In the present study, the possibility of using the oxygen isotope composition as a proxy for the origin of mantle eclogites is carefully tested, and conclusions regarding its application limits are drawn. Contributions of all processes leading to variations in the isotope composition from protolith (oceanic crust) formation to ascent of eclogites in kimberlite to the surface are discussed, including hydrothermal alteration by sea water; fractionation of oxygen isotopes upon metamorphism, dehydration and the removal of volatile components in subduction zone; metasomatism in subduction zone; partial melting; mantle metasomatism; and variation in the oxygen isotope composition upon the exhumation of mantle xenoliths by kimberlitic magma. The total contribution of all processes (excluding mantle metasomatism) typically does not exceed a deviation of ±3.5‰ from the initial δ〈sup〉18〈/sup〉O value established in a protolith. Variations of δ〈sup〉18〈/sup〉O in mantle eclogites (2–12‰; and 〈3% out of all samples display δ〈sup〉18〈/sup〉O over 8‰), which have inferred basaltic and cumulate (gabbroic) protoliths, do not fully match those in the oceanic crust (0–15‰). This limited overlap could be attributed primarily to the small initial volume of protoliths with δ〈sup〉18〈/sup〉O 〉 8‰, which subducts into the mantle (up to 5%), and the preferential erosion and partial melting of the uppermost layers of the oceanic crust. The statistical data show that eclogite garnet mainly preserves more ancient oxygen isotope signatures (including the initial δ〈sup〉18〈/sup〉O of protolith) than clinopyroxene. Garnets with δ〈sup〉18〈/sup〉O of 〈4.5‰ typical of the cumulate portion of oceanic crust, occur mainly in mantle eclogites from the Kaapvaal Craton (22.3% of finds, a total of 157 samples). For all other cratons, the percentage of garnet with δ〈sup〉18〈/sup〉O 〈 4.5‰ is not 〉1.5% (a total of 451 samples). Oxygen isotope composition in a considerable portion of mantle eclogites that originated from the oceanic gabbro based on their chemical composition (δ〈sup〉18〈/sup〉O 〈 6‰) was re-equilibrated, and they acquired “basalt” isotopic signatures (δ〈sup〉18〈/sup〉O 〉 6‰).〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): Yigui Han, Guochun Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Tianshan and Junggar orogenic collage occupies the southwestern part of the Central Asian Orogenic Belt and was assembled by collision/accretion of several continental blocks and island arcs during late Paleozoic-early Mesozoic time, following the consumption of the Junggar and South Tianshan oceanic basins in the western segment of the Paleo-Asian Ocean. Considerable and continuing controversy has surrounded when, where, and how this orogenic collage was eventually amalgamated, which plays a crucial role in understanding the formation of the Central Asian Orogenic Belt. This review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains.〈/p〉 〈p〉A comprehensive data compilation indicates that the formation of ophiolites along major sutures in the Tianshan and Junggar region lasted to the early Carboniferous for the Kalamaili suture zone, to the mid-Carboniferous for the West Junggar region and the North Tianshan suture zone, and to the late Carboniferous for the South Tianshan suture zone. Ca. 325–310 Ma (ultra-)high pressure metamorphism along the western part of the South Tianshan suture occurred nearly synchronously with the collision between the Tarim Craton and the Central Tianshan-Yili Block. The oceanic closure and collision events were sequentially followed by widespread and intensive A-type granitic and bimodal magmatism, which commenced in the mid-Carboniferous along the Kalamaili belt and in the latest Carboniferous to earliest Permian in other regions. Contemporaneously, large-scale strike-slip shearing took place along major faults subparallel to main sutures, with a dominant dextral sense and deformation time since the Carboniferous-Permian transition. Available data and geological evidence support an eastward propagating, scissor-like closure of the western segment of the Paleo-Asian Ocean along the South Tianshan and North Tianshan suture zones over a period from the mid- to end Carboniferous, with the South Tianshan belt representing the final suturing site. In the early Permian, the Tarim mantle plume likely merely affected the southwestern part of the assembled Tarim and Tianshan region, as indicated by regional discrepancy in type and geochemistry of early Permian A-type granitoids. The amalgamation of the Tianshan and Junggar orogenic collage was associated with the tectonic bending of the Kazakhstan orocline, leaving a piece of trapped oceanic crust in its middle part, beneath the present Junggar Basin.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 184〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Laurent Jolivet, Armel Menant, Camille Clerc, Pietro Sternai, Nicolas Bellahsen, Sylvie Leroy, Raphaël Pik, Martin Stab, Claudio Faccenna, Christian Gorini〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present here a number of geological observations in extensional contexts, either continental rifts or back-arcs, that show different situations of potential coupling between asthenospheric flow and crustal deformation. Several of these examples show a deformation distributed over hectometre to kilometre thick shear zones, accommodated by shallow dipping shear zones with a constant asymmetry over large distances. This is the case of the Mediterranean back-arc basins, such as the Aegean Sea, the northern Tyrrhenian Sea, the Alboran domain or the Gulf of Lion passive margin. Similar types of observation can be made on some of the South Atlantic volcanic passive margins and the Afar region, which were formed above a mantle plume. In all these examples the lithosphere is hot and the lithospheric mantle thin or possibly absent. We discuss these contexts and the main controlling parameters for this asymmetrical distributed deformation that implies a simple shear component at the scale of the lithosphere. These parameters include an original heterogeneity of the crust and lithosphere (tectonic heritage), lateral density gradients and contribution of the underlying asthenospheric flow through basal drag or basal push. We discuss the relations between the observed asymmetry and the direction and sense of the mantle flow underneath. The chosen examples suggest that two main mechanisms can explain the observed asymmetry: (1) shearing parallel to the Moho in the necking zone during rifting and (2) viscous coupling of asthenospheric flow and crustal deformation in back-arc basins and above plumes. Slipping along pre-existing heterogeneities seems a second-order phenomenon at lithospheric or crustal scale.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Johann Hohenegger〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Growth of multichambered foraminifera can be studied by investigation of chamber volumes. This approach is applicable to the vast majority of living and fossil species. Cell growth is represented by the test volume, whereby chamber volumes exhibit the increase in cell volume by growth stages. Two models fit foraminiferal growth, the unlimited linear and the limited sigmoidal function. The growth stage, in which reproduction begins, is represented in sigmoidal growth by the point of inflection; this stage cannot be determined in the unlimited linear growth model. The timing of chamber building is apparently correlated with cell growth, thus the “chamber building rate” remains constant in linearly growing cells whereas it decreases and ultimately approximates zero in limited growth. Longevity can be estimated for living individuals with sigmoidal growth by the inverse of the chamber building function at the inflection point of the cell growth function. Calculating the mean chamber building function for a species inhabiting a distinct geographical region, its inverse can be used in this region to estimate the individual lifetime based on the final growth state (= chamber number). Deviations of observed chamber volumes from theoretical values determined by the chamber building function can be irregular or oscillating. Periods of oscillating functions in larger foraminifera may point to tidal, lunar and seasonal cycles. Based on the determination of seasonal oscillations in the test by stable isotopes, lifetime ≥1 year can also be estimated for fossil species. The development in foraminifera is expressed in a huge variability of test forms with different wall textures depending on functional and constructional aspects. The historical-phylogenetic approach enables a differentiation into three groups, the Tubothalamea, Globothalamea and the Nodosariids. Within the Tubothalamea and Globothalamea, several subgroups feature symbiont-bearing foraminifera with large tests designed to optimize the surface/volume ratio allowing the symbiotic microalgae to occupy an optimal position near the test surface.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 4 October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Octavian Catuneanu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Stratal stacking patterns provide the basis for the definition of all units and surfaces of sequence stratigraphy. The same types of stacking patterns may be observed at different scales, in relation to stratigraphic cycles of different magnitudes. At each scale of observation, stacking patterns define systems tracts, and changes in stacking pattern mark the position of sequence stratigraphic surfaces. The construction of a framework of systems tracts and bounding surfaces fulfills the practical purpose of sequence stratigraphy. Beyond this framework, model-dependent choices with respect to the selection of the ‘sequence boundary’ may be made as a function of the mappability of the various types of sequence stratigraphic surface within the studied section.〈/p〉 〈p〉Sequence stratigraphic frameworks are basin-specific in terms of timing and scales of the component units and bounding surfaces, reflecting the interplay of global and local controls on accommodation and sedimentation. A stratigraphic sequence corresponds to a cycle of change in stratal stacking patterns, defined by the recurrence of the same type of sequence stratigraphic surface in the rock record. Sequences, as well as component systems tracts and depositional systems, can be observed at all stratigraphic scales. Sequences of any scale may include unconformities of equal and/or lower hierarchical ranks, whose identification depends on the resolution of the data available. The relative ranking of sequences of different scales is defined by their stratigraphic relationships, as lower rank sequences are nested within higher rank systems tracts. Despite this nested architecture, the stratigraphic framework is not truly fractal because sequences of different scales may differ in terms of underlying controls and internal composition of systems tracts. A scale-independent approach to methodology and nomenclature is key to the standard application of sequence stratigraphy across the entire range of geological settings, stratigraphic scales, and types of data available.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): Roberto F. Weinberg, Raul Becchio, Pablo Farias, Nestor Suzaño, Alfonso Sola〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Two Early Paleozoic orogenic cycles in the Gondwana margin of NW Argentina were driven by subduction, and interrupted by collision of continental ribbons of Laurentian affinity. Subduction started at the passive margin of Gondwana, possibly in response to the end of amalgamation of the supercontinent. The passive margin was underlain by a hyper-extended continent-ocean transition, and low-angle subduction gave rise to a wide and hot fore-arc region during the Pampean orogenic cycle. The arrival of the first continent ribbon ended the Pampean cycle, steepened the subduction, further heating the fore-arc and restarting arc magmatism, after a magmatic lull, 250–300 km trenchwards, initiating the Famatinian orogenic cycle. This cycle started with a 30 Ma-long period of extension and marine sedimentation, followed by the arrival of the second continent ribbon and inversion the back-arc, initiating a ~20 Ma-long shortening event culminating with the shutting down of the arc. This event gave rise to a 300 km-wide, low-topography, hot orogeny. Thus, the many peculiarities of the two Paleozoic orogens of NW Argentina result from a subduction history that efficiently transferred heat to a 300–400 km-wide belt of turbidite-dominated sediments, that was first part of the Pampean fore-arc and then part of the Famatinian retroarc, developed at the extended continental margin of Gondwana. The two orogenies with continued high heat flux lasted ~110 Ma, giving rise to two calc-alkaline arcs separated by a 300 km belt of high-T – low-P migmatites and peraluminous granites formed by anatexis of sediments deposited on the passive margin as well as those deposited in the wide Pampean fore-arc. These turbidite-dominated sequences were metamorphosed and melted to form a continental crystalline basement and accreted to the cratonic margin, adding 500 km of crystalline rocks to the margin of Gondwana, at the same time that a similar process was happening in eastern Australia along the same continental margin. Interestingly this wide accretionary orogen has now become the region where the Andean system developed a wide orogeny above flat-slab subduction.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Jin Lai, Guiwen Wang, Song Wang, Juntao Cao, Mei Li, Xiaojiao Pang, Zhenglong Zhou, Xuqiang Fan, Quanqi Dai, Liu Yang, Zhibo He, Ziqiang Qin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The tight sandstones are characterized by low porosity, low permeability, complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced. Understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones. Diagenetic facies, which is the comprehensive description of the diagenesis and diagenetic minerals, determines the formation and distribution of sweet spot. By correlating the diagenetic facies to well log responses, the subsurface distribution of porosity and permeability can be predicted. However, the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task. This paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones, and establishes a model for prediction of diagenetic facies via well logs, as assessed from peer reviewed papers in the literature as well as from the authors' personal experiences. This review begins with reviewing the impacts of compaction, cementation, dissolution and various types of diagenetic minerals on reservoir quality evolution. The definition and classification schemes of diagenetic facies are then discussed, and the reservoir quality as well as diagenetic evolution sequence of various diagenetic facies is summarized. The same diagenetic facies commonly display similar compositional and textural attributes, matrix and cement, as well as porosity systems. The well log responses (GR, AC, DEN, CNL, and RT) of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections. By translating the diagenetic facies to conventional well logs, a predictable model, which can be used for subsurface reservoir quality prediction, is established. Then the theory of ECS logs is reviewed, and the application of ECS logs in diagenetic facies evaluation is discussed. At last, the quantitative characterization for various type and degree of diagenesis is reviewed, and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss, cementational porosity loss and dissolution porosity content via well logs. Correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones. This review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): Jun-Hong Zhao, Qi-Wei Li, Hang Liu, Wei Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The South China Craton consists of the Yangtze and Cathaysia blocks that were welded together along the Jiangnan Fold Belt in the Neoproterozoic. The Neoproterozoic magmatism in the western and northern margins of the Yangtze Block is characterized by voluminous volcano-sedimentary strata, numerous felsic intrusions and many mafic-ultramafic plutons which provide a good opportunity to examine the geodynamics and tectonic evolution of the South China Craton during the assembly and breakup of Rodinia. Based on the geochronological and geochemical data, our study shows that the Neoproterozoic igneous rocks in the western and northern margins of the Yangtze Block were formed in subduction- and rift-related tectonic settings, respectively.〈/p〉 〈p〉In the western margin of the Yangtze Block, the Neoproterozoic mafic and ultramafic rocks show arc-affinity trace elemental compositions that are indicative of mantle sources enriched by slab fluids. High-δ〈sup〉18〈/sup〉O mafic rocks (850–780 Ma) were derived from mantle wedges that were modified by sediment melts, whereas low-δ〈sup〉18〈/sup〉O mafic rocks (750–740 Ma) were formed by partial melting of mantle sources further enriched by altered oceanic crust melts. The widespread calc-alkaline I-type granitoids in this region, generated between 870 and 750 Ma, show negative to positive whole rock εNd (−4.9 to +4.8) and variable zircon εHf values (−1.9 to +10.6), similar to those of the contemporary mafic-ultramafic rocks, suggesting that they were produced by melting of the juvenile crust. The 780–750 Ma adakitic granitoids are characterized by high Sr/Y (19–318) and low Y (1.78–17.9 ppm) and have relatively constant εNd (−2.1 to +2.9) and εHf (+4.3 to +7.1) and mantle-like δ〈sup〉18〈/sup〉O values (3.40‰ to 6.86‰), suggesting that they were partial melts of a subducted oceanic slab. These three types of igneous rocks demonstrate that the Neoproterozoic magmatism in the western margin of the Yangtze Block was controlled by a continuous subduction system.〈/p〉 〈p〉However, Neoproterozoic magmatism in the South Qinling Belt at the northern margin of the Yangtze Block generated both arc- and rift-related igneous rocks. The arc-like mafic-ultramafic rocks are thought to have been derived from a subduction-modified lithospheric mantle source, whereas the MORB-affinity mafic rocks were probably sourced from an asthenosphere mantle. Associated Neoproterozoic granitoids were produced by melting of the juvenile mafic crust, except minor felsic rocks derived from the ancient basement. Widespread 800–700 Ma volcano-sedimentary sequences and 650 Ma mafic dike swarms suggest an extensional environment. Neoproterozoic magmatic zircons from felsic volcanic rocks and HP/UHP metamorphic rocks preserve low-δ〈sup〉18〈/sup〉O values that were inherited from their protolith which underwent high temperature hydrothermal interaction in a rift setting. On the basis of these observations, the Neoproterozoic magmatism in the South Qinling Belt is proposed to have been controlled by a subduction-transform edge propagator (STEP) in relation to the continuous subduction system at the western margin of the Yangtze Block.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): Sanzhong Li, Shujuan Zhao, Xin Liu, Huahua Cao, Shan Yu, Xiyao Li, Ian Somerville, Shengyao Yu, Yanhui Suo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉As a complex paleo-ocean located between the Tarim-North China and the Sibumasu/Baoshan blocks, the Proto-Tethys Ocean was opened from the rifting of the Supercontinent Rodinia and mainly closed at the end of the Early Paleozoic. The known studies suggest that there were many continents and/or micro-continents in the Proto-Tethys Ocean. During closure of the Proto-Tethys Ocean and assembly of these continents/micro-continents, some Early Paleozoic ophiolites and HP-UHP metamorphic rocks developed in East Asia similar to those Early Paleozoic orogens in Gondwana. However, some academic debates still remain on the boundaries of the Proto-Tethys Ocean and the nature, relationships and assembly processes of these continents/micro-continents to the Tarim-North China Continent to the north. These problems are important for revealing and reconstructing tectonic processes before the closure of the Proto-Tethys Ocean and the initial assembly of the Supercontinent Pangea. Not surprisingly, the Proto-Tethys tectonic domain is characterized by complex ocean-continent configurations, assemblies and dispersals of continents, from the rifting and drifting of the Supercontinent Rodinia to the assembly of the Supercontinent Pangea. Therefore, this paper mainly focuses on summarizing and discussing the northern part of the Proto-Tethys tectonic domain based on field geology, structural geology, magmatism, sedimentary formations, geochemical records, geochronology and tomography, in order to reveal three key aspects: 1) identifying the southern and northern boundaries of the Proto-Tethys Ocean; 2) establishing affinities of continents/micro-continents within the Proto-Tethys Ocean and its ocean-continent configuration; and 3) clarifying the temporal sequence and styles of micro-continental assembly and the closure of the Proto-Tethys Ocean. Integrated analysis results show that to the north the region is bounded by the paleo-Luonan-Luanchuan Suture (or Kuanping Suture) and its extension to West Kunlun; the southern boundary is marked by the Longmu Co-Shuanghu-Changning-Menglian Suture. The Tarim-Alax-North China Block to the north of the Proto-Tethys Ocean had a southward subduction polarity and collided with Gondwana along the northern margin of Gondwana in the Early Devonian. The southern branch of the Proto-Tethys Ocean may be closed, making the Greater South China Block, including the northern Qiangtang, Ruoergai, Yangtze and Cathaysia, Bureya-Jiamusi and Indochina blocks, southward subduction and accretion to the northern margin of Gondwana in the Early Devonian. The results also show that the North China Block had no clear affinity to Gondwana, whereas the other continental/micro-continental blocks, such as the Yangtze, Cathaysia, Tarim, Qaidam, Alax, North Qinling, Qilian, Oulongbuluke, South Qiangtang, Lhasa, Lanping-Simao and Indochina all have an affinity to Gondwana in the earlier part of the Early Paleozoic. During the interval 480–400 Ma these series of continental blocks/micro-continental blocks experienced gradual southward subduction and accretion to the eastern segment of the northern margin of Gondwana, resulting in the closure of the Proto-Tethys Ocean and formation of the supercontinent called Proto-Pangea. The Greater South China Block and the Tarim-North China Block separated and drifted from Greater Gondwana of the Supercontinent Proto-Pangea since 380 Ma, resulting in the formation of the Paleo-Tethys and the Mianlue oceanic crusts. After this minor adjustment and until 240–220 Ma, they assembled northward gradually to develop Laurasia, which in turn resulted in the final formation of the Supercontinent Pangea.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 184〈/p〉 〈p〉Author(s): Florian Scholz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Because of anthropogenic global warming, the world ocean is currently losing oxygen. This trend called ocean deoxygenation is particularly pronounced in low-latitude upwelling-related oxygen minimum zones (OMZs). In these areas, the temperature-related oxygen drawdown is additionally modulated by biogeochemical feedback mechanisms between sedimentary iron (Fe) and phosphorus release, water column nitrogen cycling and primary productivity. Similar feedbacks were likely active during past periods of global warming and ocean deoxygenation. However, their integrated role in amplifying or mitigating climate change-driven ocean anoxia has not been evaluated in a systematic fashion. Moreover, many studies on past (de)oxygenation events emphasize anoxic-sulfidic (i.e., euxinic) basins such as the Black Sea rather than upwelling-related OMZs as modern analogue systems.〈/p〉 〈p〉In this review, I summarize the current state of knowledge on biogeochemical processes in the water column and sediments of OMZs. Nitrate-reducing (i.e., nitrogenous) to weakly sulfidic conditions in the water column and Fe-reducing (i.e., ferruginous) to sulfidic conditions in the surface sediment are identified as key-features of anoxic OMZs in the modern ocean. A toolbox of paleo-redox proxies is proposed that can be used to identify OMZ-type biogeochemical cycling in the geological record. By using a generalized model of sedimentary Fe release and trapping, I demonstrate that the extent of Fe mobilization and transport in modern OMZs is comparable to that inferred for the euxinic Black Sea and ferruginous water columns in Earth history. Based on this result, I suggest that many sedimentary Fe enrichments in the geological record are broadly consistent with OMZ-type redox conditions in the water column and surface sediment, especially if enhanced chemical weathering and reactive Fe supply to the ocean during past periods of global warming are taken into account. Future studies on paleo-(de)oxygenation events with a combined focus on Fe, sulfur and nitrogen cycling may reveal that OMZ-type redox conditions were an important feature of the ocean through Earth's history.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 8 August 2017〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Robert A. Gastaldo, Johann Neveling, John W. Geissman, Jiawen Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The stratigraphic section at Bethulie, South Africa, is reported to contain the vertebrate-defined Permian–Triassic boundary succession in the terrestrial realm of the Karoo Basin. The model of vertebrate turnover, from the 〈em〉Daptocephalus〈/em〉 to 〈em〉Lystrosaurus〈/em〉 Assemblage Zones, tightly constrains the boundary sequence to a short stratigraphic interval where siltstone color begins to change from greenish gray to grayish red, the latter color interpreted to be a consequence of aridification. The biological response to this facies change has been termed “the Great Dying,” and the sedimentary rocks that are preserved are ascribed to a playa lake depositional setting. This drying event is believed to be contemporaneous across the basin, although previous studies have shown that the facies appears at multiple horizons at all purported Permian–Triassic boundary sections in the basin.〈/p〉 〈p〉Here, we report results of a multidisciplinary effort to characterize the vertebrate assemblage-zone boundary interval exposed at Bethulie using the lithostratigraphic, petrographic, geochemical, and rock magnetic properties of these rocks. In this stratigraphic succession at its “type” location, the 3-m thick assemblage-zone boundary interval is distinguished by thick beds of greenish-gray, greenish-gray mottled to grayish-red, and grayish-red siltstone, all of which change facies characteristics laterally along strike. Specifically, about 220 m to the southeast of the type section, sediments lose all grayish-red coloration, whereas the interval becomes laminated to the northwest. Petrographically, most siltstone is homogenized, with few burrows and small-scale cross-bedded structures with mudchips. There are no gypsiferous or calcareous beds, nor is there evidence of disturbed structures, authigenic breccia, or pseudomorphs associated with dessication. Mean elemental composition of both greenish-gray and grayish-red beds are indistinguishable, geochemically, and both are dominated by illite and chlorite clay species. Mössbauer spectroscopic analyses reveal the presence of a small concentration of fine-grained hematite in the grayish-red siltstone, with its presence mainly found as coatings on clay minerals. Rock magnetic experiments (isothermal remanent magnetization, acquisition and backfield DC demagnetization; magnetic hysteresis; susceptibility vs. temperature) yield data that demonstrate no essential differences between the different colored siltstones. And, both lithologies host mangnetite/maghematite and hematite. Our results do not support the previous interpretation that this inferred Permian–Triassic boundary interval represents the onset of playa lake deposits under conditions of aridification. Rather, our evidence supports the existence of a “wet” landscape at what is considered the 〈em〉Daptocephalus〈/em〉/〈em〉Lystrosaurus〈/em〉 assemblage-zone boundary.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Mihai N. Ducea, Alan D. Chapman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sedimentary rock units originally formed in subduction trenches are often found tectonically underplated directly below magmatic arc crustal sections along some segments of the ancient convergent margin of the North American Cordillera. During and immediately after tectonic underplating - which takes place during ultra-shallow subduction - magmatic arcs shut off completely or migrate suddenly inboard, thus leaving the underplated sections in the new forearc of the subduction system. A good modern equivalent is found in Southern Mexico where the Cocos plate subducts at shallow angle under North America. The process is episodic and corresponds to events of sudden trench inboard migration relative to the upper plate. If the trench sequence was dominated by quartz-rich material, the exposed rocks are schists; they display an inverse pressure-temperature path, suggesting that the crust collapsed and were exhumed immediately after the completion of this ablative process (Salinas type). If rich in feldspar, the trench-derived metasedimentary rocks are gneisses and display evidence for thermal relaxation-related heating and in some cases, partial melting (Skagit type). Feldspar-rich rocks presumably have a higher strength that precludes a quick gravitational collapse of the section. In both cases, this process leads to the complete reorganization of the crust with the addition of melt fertile, first cycle sedimentary materials in the deep crust of subduction systems.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Deepesh Machiwal, Madan Kumar Jha, Vijay P. Singh, Chinchu Mohan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increasing groundwater contamination across the globe triggered the concept of “〈em〉aquifer vulnerability〈/em〉”, which has been extensively used worldwide during past three to four decades by researchers and policy makers for protecting groundwater from pollution. However, only a few recent studies have focused on the performance evaluation of two or more vulnerability assessment methods. Some of these studies have resulted in contrasting findings. Given this fact and considering growing threat of groundwater contamination due to increasing human activities across the globe, it is necessary to critically review existing methods, understand current research trends, and identify major challenges associated with the assessment of aquifer vulnerability. Hence, the aim of this study is to present a comprehensive review of the methods and approaches used for the evaluation of aquifer vulnerability for ‘resource’ and ‘source’ protection. First, the concept and types of aquifer vulnerability along with the definitions evolved over the years are presented, and then the methods for assessing aquifer vulnerability are suitably classified and briefly discussed. Second, the concept of vulnerability assessment for ‘source’ protection is highlighted, and the evolution of groundwater vulnerability evaluation methods is presented with an enlightening block diagram. Third, current research trends and critiques on past studies are discussed. Fourth, the major challenges of vulnerability assessment are highlighted and a way forward is suggested. It is concluded that the progress of vulnerability evaluation methods has not kept pace with the advancement of knowledge and tools/techniques. There is an urgent need for developing a scientifically robust and somewhat versatile methodology for the evaluation of ‘intrinsic’ and ‘specific’ groundwater vulnerability for ‘resource’ and ‘source’ protection under varying hydrogeologic and hydro-climatic conditions. It is emphasized that more studies should be devoted to vulnerability assessment for ‘source’ protection using ‘Source-Pathway-Receptor/Target’ approach. Also, spatial decision support systems should be developed using modern tools/techniques including artificial intelligence to improve decision-making process for protecting vital groundwater resources.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): Guochun Zhao, Yuejun Wang, Baochun Huang, Yunpeng Dong, Sanzhong Li, Guowei Zhang, Shan Yu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Pangea is the youngest supercontinent in Earth's history and its main body formed by assembly of Gondwana and Laurasia about 300–250 Ma ago. As supported by voluminous evidence from reliable geological, paleomagnetic and paleontological data, configurations of major continental blocks in Pangea have been widely accepted. However, controversy has long surrounded the reconstructions of East Asian blocks in Pangea. To determine whether or not the East Asian blocks were assembled to join Pangea before its breakup, we carried out geological and paleomagnetic investigations on East Asian blocks and associated orogenic belts, supported by a NSFC Major Program entitle “Reconstructions of East Asian blocks in Pangea”. Our results indicate that the breakup of Rodinia around 750 Ma ago led to the opening of the Proto-Tethys and Paleo-Asian oceans in East Asia, with the former separating the South China, North China, Alex Qaidam and Tarim blocks from other East Asian blocks at the margins of Australia and India, whereas the Paleo-Asian Ocean existed between the East Asian blocks and Siberia-Eastern Europe. The Proto-Tethys Ocean closed in the early Paleozoic (500–420 Ma), leading to the collision of South China, North China, Alex, Qaidam and Tarim with other East Asian blocks at the northern margin of Gondwana. The subduction of the Paleo-Asian Ocean formed the Central Asian Orogenic Belt, the largest accretionary orogen in Earth's history, and its closure was diachronous, with its western, central and eastern segments closing at 310–280 Ma, 280–265 Ma and 260–245 Ma, respectively, leading the Tarim, Alex and North China blocks to join Eastern Europe-Siberia as part of Pangea. During the early Devonian (420–380 ma), the East Paleo-Tethys Ocean opened with two branches, of which the north branch is called the Mianlue Ocean that separated the Tarim-Qaidam-Central Qilian-Alex and North China blocks in the north from North Qiangtang-Indochina-South China in the south, and the south branch is the stricto sensu East Paleo-Tethys Ocean that separated North Qiangtang-Indochina-South China from the Sibumasu and South Qiangtang-Lhasa blocks at the northern margin of Gondwana. In the Triassic, the East Paleo-Tethys Ocean (stricto sensu) closed along the Longmu Co – Shuanghu – Changning – Menglian – Inthanon belt, leading to the collision of North Qiangtang-Indochina-South China with Sibumasu and South Qiangtang-Lhasa, forming a single southern continent, which then collided with the Tarim-Qaidam-Central Qilian-Alex and North China blocks to form a coherent East Asian continent that had become part of Pangea by 220 Ma, when the Mianlue Ocean closed, leading to the formation of the 〈em〉E〈/em〉-W-trending Central China Orogenic System.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): Maoliang Zhang, Zhengfu Guo, Jiaqi Liu, Guoming Liu, Lihong Zhang, Ming Lei, Wenbin Zhao, Lin Ma, Vincenzo Sepe, Guido Ventura〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The geodynamic significance of continental volcanoes located far from the plate boundaries remains highly controversial as exemplified by contrasting models that favor either a deep mantle plume rooted from the base of the mantle or, alternatively, the shallower subduction or lithospheric-related processes. The Changbaishan (also referred to as Paektusan or Baekdusan) volcanic field (CHVF), located in the interior of eastern Eurasian continent, provides a good opportunity to constrain the magma origin and geodynamic mechanism governing continental intraplate volcanism. Here, we review the volcanic geology, eruptive history, geochemical data on volcanic rocks and released gases and geophysical observations of the Changbaishan volcanoes with the aim to (a) reconstruct temporal and spatial evolution of eruptive activities, (b) identify source of the primary magmas, (c) delineate magma evolution in the crust, (d) highlight geodynamic significance of the CHVF volcanism, (e) characterize crustal magmatic structure, and (f) analyze recent dynamics with a focus on the 2002–2005 unrest episode at Tianchi caldera, the only active volcano in the area (last eruption in 1903 CE).〈/p〉 〈p〉The eruptive activities of the Changbaishan volcanoes can be divided into three main stages: (1) central vent and fissure eruptions of basaltic magmas started approximately in Pliocene and culminated in Early Pleistocene (ca. 5–1 Ma), forming a shield-like lava plateau; (2) multi-stage eruptions of voluminous silicic (and minor intermediate) magmas constructed cones of the polygenetic volcanoes (e.g., Tianchi, Wangtian'e and Namphothe) between Late Pliocene and Pleistocene (3.14–0.01 Ma); and (3) explosive silicic eruptions [e.g., the Millennium eruption (ME) in 946 CE] during Holocene dominated the Tianchi volcano and led to the formation of its summit caldera. Small-scale eruptions of basaltic magmas from monogenetic scoria cones (and minor fissures) were coeval with the Tianchi cone-construction stage (ca. 1–0.01 Ma). The elemental and Sr-Nd-Pb isotopic characteristics of the Changbaishan basalts indicate an enriched, heterogeneous mantle source with components from depleted mantle (DM), enriched mantle 1 (EM1) and subduction-related materials (e.g., recycled oceanic crust and sediments). The interaction between the DM-like peridotite and carbonatite melts released by subducted oceanic slab in the mantle transition zone (MTZ) led to the formation of carbonated peridotite characterized by low δ〈sup〉26〈/sup〉Mg values. By contrast, origin of the EM1-like components remains highly debated. The alkaline basalts and intermediate to silicic volcanic rocks from the polygenetic volcanoes constitute an integrated spectrum of magma composition controlled by closed system fractionation according to their element co-variations and uniform Sr-Nd-Pb isotopic compositions. Subordinate mingling between trachyte and comendite has been reported only for the ME at Tianchi caldera.〈/p〉 〈p〉The occurrence of a big mantle wedge (BMW) with a continuous stagnant Pacific slab in the MTZ is responsible for origin of the Changbaishan volcanoes. On the basis of subduction dynamics of the Pacific plate, we present a Late Cenozoic geodynamic framework of NE Asia, which can account for formation of the present-day BMW system via: (a) shallow-angle subduction (55–25 Ma), (b) slab rollback and sinking into the MTZ together with trench retreat (25–15 Ma), and (c) slab bottoming, thickening and flattening in the MTZ (15–0 Ma). Constraints from reconstructed plate motion history, numerical simulation and present-day geophysical observation of the BMW lend support to our geodynamic model, which reconciles well with the Izanagi slab break-off, development of the Japan Sea and Late Cenozoic continental intraplate volcanism in NE China. In response to the Rayleigh-Taylor instability, a MTZ-derived plume incorporating fragments of carbonated peridotite, EM1-like components and the Pacific slab-derived materials ascended and experienced decompression partial melting at shallow depths to feed the Changbaishan volcanism. From the perspective of magma origin and geodynamic mechanism, the Changbaishan volcanoes can shed light on the potential relationships between origin of continental intraplate volcanism and deep subduction of oceanic lithosphere.〈/p〉 〈p〉The spatial distribution of the Changbaishan volcanoes shows that the magmas ascended along a NW-SE trending, strike-slip fault oriented perpendicularly to the major faults delimiting the Songliao Basin, NE China. This interpretation is consistent with the 2009–2013 epicenters of tectonic earthquakes, also suggesting a NW-SE trending, buried and seismically active deep fault in the crust. Geophysical and petrological constraints indicate the presence of magma reservoirs at crustal depth beneath the active Tianchi volcano, which are likely to have high thermal state and act as the source of heat and material for shallow hydrothermal system. In consideration of magma origin from the MTZ-derived plume, the volatile outgassing from the Tianchi volcano associated with deep subduction of the Pacific plate represents an important mechanism for liberating volatile elements (especially carbon) from Earth's interior to the exosphere. Tianchi caldera suffered an unrest episode between 2002 and 2005, as evidenced by increased shallow seismicity, surface uplift and changes in chemical and isotopic composition of the hydrothermal gases. Such volcanic unrest was triggered by pressurization of a 2–6 km depth magma reservoir, from which magmatic volatiles were released into shallow hydrothermal system. Tianchi caldera shows different types of hazards related to volcanic, tectonic, geomorphological and hydrological processes. Further monitoring and additional volcanological data, especially those on eruptive dynamics of the past eruptions, should be collected to better constrain the potential hazards of future eruptions and to improve early warning management.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Ellen Wohl〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A channel head is the upstream-most point of concentrated water flow and sediment transport between definable banks with a longitudinally continuous channel downstream. A channel head can be a relatively diffuse feature, the identification of which is subjective, or a very discrete and prominent break in the surface associated with a headcut. As the formal start of the channel network, channel heads reflect the location of process thresholds and thus differentiate geomorphic process domains for water, solute, and sediment fluxes. Stream order derives from mapped channel networks and the accuracy of stream ordering thus depends on the accuracy of identifying channel heads and associated first-order streams. In the absence of mapped channel heads, remote methods that under- or over-estimate the contributing area necessary to form a channel head can significantly over- or under-estimate, respectively, the extent of first-order streams and erroneously estimate drainage density. This paper reviews the current state of knowledge of the processes that form channel heads, the influences on channel head stability, and the methods used to identify the location of channel heads within a landscape unit. Individual channel heads can result from distinctly different processes, including surface fluvial erosion, surface colluvial erosion, subsurface erosion, or the intersection of subsurface preferential flow with the surface. The location of any channel head over a period of years to decades and longer is best understood as an average location that can and does change through time. The magnitude of change in the location of a channel head over time periods of years to decades will reflect the disturbance regime of the hillslope and the speed with which hillslope-channel processes recover following disturbance. If channel heads form where overland flow exerts a boundary shear stress that exceeds the critical value for substrate erosion, the channel initiation threshold, 〈em〉C〈/em〉, can be expressed as the product of contributing catchment area, 〈em〉A〈/em〉, and hillslope gradient, 〈em〉S〈/em〉: 〈em〉AS〈/em〉〈sup〉〈em〉α〈/em〉〈/sup〉 ≥ 〈em〉C〈/em〉. An inverse relation between source area 〈em〉A〈/em〉 and local slope 〈em〉S〈/em〉 is present to a greater or lesser degree across diverse regions. Substantial variability in values of 〈em〉A〈/em〉 and 〈em〉S〈/em〉 reflects the influence of factors such as vegetation, slope aspect, surface versus subsurface flow paths, and substrate grain size. Analyses of published data suggest that channel head locations can be predicted with reasonable accuracy where surface runoff dominates channel initiation. Subsurface processes strongly influence the locations of many channel heads, however, and the area-slope relations for these channel heads are much less consistent and predictable. The challenges of channel heads are three-fold for any given drainage basin or portion of a drainage basin: to identify their geographic location, to predict their geographic location, and to determine the relative importance of potential control variables on the multiple processes that can create channel heads. In order to effectively address these challenges, additional research is needed to predict the regional characteristics likely to result in channel heads created by predominantly surface versus subsurface flow; develop envelope curves of 〈em〉A-S〈/em〉 relations for different regions; compare channel head locations predicted based on hillslope curvature versus actual channel head locations; evaluate the spatial consistency of channel heads through time; and develop 〈em〉A-S〈/em〉 relations for channel heads in little studied regions, including arid and hyperarid environments, karst and permafrost terrains, and grassland and savanna environments.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 184〈/p〉 〈p〉Author(s): D.C.P. Peacock, D.J. Sanderson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Seven distinct types of structural analysis can be defined, each with their own data and uses: (1) basic geological descriptions; (2) geometries and topology; (3) age relationships; (4) kinematics; (5) tectonics; (6) mechanics and (7) fluid flow. We illustrate these types of analysis using the example of faults and fractures, which typically form networks of interacting and connected segments. A framework for describing and characterising fault and fracture networks is presented for each of the structural analysis types.〈/p〉 〈p〉We suggest that any structural study be tailored to suit the desired outcome and that this scheme of analysis types should be used as a basis for the development of workflows, for the design of research projects and for testing hypotheses. For example, prediction of fluid flow through a fracture network must begin with the basic geological description of fracture types. Basic geological descriptions should be followed by measuring their geometries and topologies, understanding their age relationships, kinematic and mechanics, and developing a realistic, data-led model for related fluid flow. Missing steps can lead to fundamentally flawed interpretations.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 6 January 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): James G. Ogg〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Our knowledge of the history of our planet comes from deciphering the sedimentary record of biologic, ecologic, geochemical, climatic, physical and other systems using a vast array of tools and innovative techniques. To synthesize these trends and events into a coherent global history requires six inter-connected international efforts: (1) documentation and access to major research reference sections, including standardization of convenient and precise terminology for divisions of geologic time (e.g., Global Boundary Stratotype Section and Point (GSSPs) and within-stage levels), (2) inter-calibration of these marine and terrestrial records both within and among different regions to compile a global integrated scale, (3) improving and applying age models to understand cause-effect relationships and rates of processes, (4) public databases and syntheses, (5) international efforts and centers, and (6) Earth-systems geo-education that emphases relationships among fields in addition to training in particular specializations. In the past two decades, the careful analysis of the sedimentary records in China's marine and terrestrial basins have enabled major leaps in our understanding of Earth's history, such as major excursions of the carbon cycle during the Cambrian, “lethal” temperature excursions in Early Triassic, Cretaceous evolution of birds, and catastrophic impacts of large igneous eruptions. China has provided more reference sections for the international definition of GSSPs than any other country. It is vital to put those records from the China basins into a larger global context.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Jacopo Dal Corso, Piero Gianolla, Manuel Rigo, Marco Franceschi, Guido Roghi, Paolo Mietto, Stefano Manfrin, Béla Raucsik, Tamás Budai, Hugh C. Jenkyns, Claire E. Reymond, Marcello Caggiati, Giovanni Gattolin, Anna Breda, Agostino Merico, Nereo Preto〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 〈sup〉13〈/sup〉C-depleted CO〈sub〉2〈/sub〉 into the ocean–atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 23 August 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Alan Stebbins, Thomas J. Algeo, Christian Olsen, Hiroyoshi Sano, Harold Rowe, Robyn Hannigan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Smithian-Spathian substage boundary (SSB) in the Early Triassic was an important time interval during the protracted recovery of marine faunas and ecosystems following the end-Permian mass extinction event. Although some Tethyan SSB sections have been studied, little information is available regarding environmental conditions in the Panthalassic Ocean, which comprised ~85% of the Early Triassic global ocean, during the Smithian-Spathian transition. Understanding changes in the carbon and sulfur cycles during the Early Triassic is important for deciphering the pattern and controls on the marine recovery. Our understanding of the Early Triassic sulfur cycle, in particular, is incomplete. In this study, we report carbonate carbon and oxygen, carbonate-associated sulfate (CAS) sulfur and oxygen, and pyritic sulfur isotopic ratios from the Jesmond section, Cache Creek Terrane, western Canada. This section, which formed as a tropical carbonate atoll in the middle of the Panthalassic Ocean, spans the latest Smithian to middle Spathian. Both δ〈sup〉34〈/sup〉S〈sub〉CAS〈/sub〉 and δ〈sup〉18〈/sup〉O〈sub〉CAS〈/sub〉 increased through the SSB transition before decreasing in the early Spathian, matching variation in the δ〈sup〉13〈/sup〉C〈sub〉carb〈/sub〉 profile. We hypothesize that the sharp increase in δ〈sup〉34〈/sup〉S〈sub〉CAS〈/sub〉 and δ〈sup〉18〈/sup〉O〈sub〉CAS〈/sub〉 at the SSB reflects a global increase in the amount of microbial sulfate reduction (MSR) and pyrite burial. Driving this increase in MSR and pyrite burial were cooling temperatures, increasing primary productivity, and increasing organic matter availability. The decreasing trend immediately following the SSB indicates that these environmental changes reached maxima and began to diminish or reverse in the early Spathian. The difference between δ〈sup〉34〈/sup〉S〈sub〉CAS〈/sub〉 and δ〈sup〉34〈/sup〉S〈sub〉pyr〈/sub〉 values (Δ〈sup〉34〈/sup〉S〈sub〉CAS-pyr〈/sub〉) remained relatively stable from the latest Smithian through the middle Spathian. This stability provides an estimate of MSR sulfur-isotope depletion allowing us to estimate paleo-seawater sulfate concentrations. Using the “MSR-trend” method, we estimate that Early Triassic seawater sulfate concentrations were between 2.5 and 9.1 mM. These estimates are higher than previously published values for the Permian-Triassic boundary, suggesting an overall increase in seawater sulfate by the late Early Triassic.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Sebastián Oriolo, Klaus Wemmer, Pedro Oyhantçabal, Haakon Fossen, Bernhard Schulz, Siegfried Siegesmund〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Shear zones play a major role in the deformation of the crust at a variety of scales, as expressions of strain localization during orogeny and rifting, and also as reactivated structures. They influence the geometry and evolution of orogenic belts and rifts, crustal rheology, magma ascent and emplacement, and fluid flow. Consequently, assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere. The interpretation of thermochronologic data from shear zones is, however, not straightforward. In the first place, closure temperatures depend on a number of factors (grain size, cooling rate, mineral composition and pressure, among others). On the other hand, deformation-related processes such as dynamic recrystallization, neocrystallization and fluid circulation seem to be crucial for isotopic systems and, thus, the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks. For this reason, geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo- or recrystallization, fluid-assisted deformation and inheritance of the protolith age(s). In order to robustly reconstruct P-T-ε-t paths of long-term crustal-scale shear zones, structural, microstructural and petrologic data from mylonites need to be integrated with ages from different thermochronometric systems. In addition, geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications. One of the most challenging aspects that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored aspects of isotopic diffusion, particularly the coupling with deformation processes, based on natural, theoretical and experimental data. Future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): G. Cassinis, C. Perotti, G. Santi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In the Italian regions the stratigraphic successions of the Verrucano 〈em〉s.l.〈/em〉 consist essentially of continental alluvial plain to coastal-neritic siliciclastic redbeds, deposited at different times in the Alps (Mid? –Late Permian), the Northern Apennines (Mid?–Late Triassic 〈em〉p.p〈/em〉., locally in Southern Tuscany also followed by the Jurassic Pseudoverrucano Complex) and the ‘Calabro-Peloritani Arc’ (Mid?-Late Triassic, exceptionally reaching earliest Jurassic), whereas in Sardinia the recognition of the Verrucano succession is still a topic of discussion.〈/p〉 〈p〉The most typical metamorphic lithofacies, in the Pisan Mts. of Tuscany, is represented by the Verrucano 〈em〉s.s.〈/em〉 conglomerates and breccias, including quartz clasts and minor metamorphic and volcanic lithics, grading laterally and vertically to quartzitic sandstones and pelites.〈/p〉 〈p〉In the Pisa Symposium the term ‘Verrucano’ was suggested only for those detrital deposits laid down, in the Alpine-Mediterranean areas, after the final act of the Variscan orogeny, and also to use local geographical names. Consequently, the typical terms ‘Verrucano Toscano’, the ‘Verrucano Lombardo’, the ‘Verrucano Briançonnais’ and other similar deposits, being linked to the Variscan belt, were generally accepted.〈/p〉 〈p〉The ages of these ‘Verrucanos’, since they are devoid of fossils, can only be interpreted indirectly. The Verrucano Lombardo of central Southern Alps was recently ascribed to a Mid? –Late Permian interval (Late Guadalupian?–Lopingian 〈em〉p.p〈/em〉.), taking into account that the connected Val Gardena Sandstones of the nearby Venetian region are interdigitated with the Late Permian Bellerophon Fm. The Verrucano Briançonnais of the Maritime Alps is again mostly related to Late Permian, being covered by the Lower Triassic alluvial-deltaic quartzites. In the easternmost Ligurian Apennines, near La Spezia, the Mesozoic section of Punta Bianca, which begins with a fluvial conglomerate, transgressive and unconformable on a metamorphosed Paleozoic Variscan Basement, is composed of two main cycles, of which the upper one correlates to the typical Pisan Verrucano 〈em〉s.s〈/em〉. and the overlying Mt. Serra Quartzites, the latter yielding Carnian pelecypods and vertebrate footprints.〈/p〉 〈p〉The Verrucano from the Mid-Tuscan Ridge to Mt. Leoni and in the Argentario promontory is delimited above by the Tocchi Formation and presumably developed from Middle (Late? Ladinian) up to Late Triassic (Carnian) times; in contrast, in Calabria (〈em〉e.g.〈/em〉 the Longobucco unit of Sila Grande) and in Sicily (〈em〉e.g.〈/em〉 the Taormina-Longi Unit of Peloritani Mts.) the so-called (Pseudo-) Verrucano deposits pertain to Mid? –Late Triassic and are capped by a basal Jurassic succession, determined by the discovery of an Early Hettangian palynoflora.〈/p〉 〈p〉All over their distribution areas, the above-mentioned Alpine Verrucanos rest, through an unconformity marked by a gap of varying and imprecise duration, on Late Paleozoic volcanic/sedimentary successions or directly on the underlying Variscan metamorphic basement.〈/p〉 〈p〉Schematically, the post-Variscan succession in Italy can be subdivided into three main tectono-sedimentary megacycles: the first generally ranges from the Late Carboniferous to, or slightly above the Early Permian, the second from Mid? –Late Permian to Middle Triassic〈em〉,〈/em〉 while the third cycle begins with the Mid?-Late Triassic 〈em〉p.p.,〈/em〉 attaining the Jurassic in some parts of Southern Tuscany and the ‘Calabro-Peloritani Arc’.〈/p〉 〈p〉After the Late Carboniferous and Early Permian transtensional tectonics represented by many strike-slip continental basins (cycle I), widespread Middle Permian geodynamic reorganization (‘Mid-Permian Episode’ 〈em〉Auctt.〈/em〉) led to the development of a dominant extensional regime, and the birth of tectonic plates and oceans (Neotethys, Meliata-Maliak, etc.) between Africa and Europe. The erosion of the Variscan relief was followed by ingression from S-E sectors of shallow-marine branches of Neotethys (cycle II). The major rifting events that led to the Jurassic birth of the Ligurian-Piedmont Ocean started during the Middle–Late Triassic, and were related to the eastern opening of the Atlantic Ocean. These rifting events gave rise to the development of the Adria and Europe-Corsica-Sardinia conjugate passive margins, characterized by an asymmetric structural and sedimentary evolution. In this geological context, the Verrucano-like deposits of Italy can be interpreted as a discontinuous and asynchronous ‘tectofacies’ that marks the final dismantling of the SE border of the Variscan chain.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): Qing Ye, Lianfu Mei, Hesheng Shi, Giovanni Camanni, Yu Shu, Jing Wu, Lu Yu, Peng Deng, Gang Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Late Cretaceous is a significant geologic period in the South China Sea area, as it marks the tectonic transition from the early Paleo-Pacific Plate subduction to the subsequent Cenozoic rifting related to the opening of the SCS. However, the Late Cretaceous tectonic evolution of the South China Sea area is yet to be clearly defined, and it is at present largely debated in the literature. In this paper, mainly on the basis of ~240,000 km〈sup〉2〈/sup〉 newly acquired 3D seismic reflection data, 94 industrial wells and existing U〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Pb ages of basement granitoids, we carried out an integrated interpretation, mapping and analysis of the pre-Cenozoic (〉 66 Ma) structures within the basement of the Cenozoic rift basin in the northern South China Sea area, that can be crucial for a broad understanding of the Late Cretaceous tectonic evolution of this region. Results of this analysis suggest that three Late Cretaceous fault systems can be identified in the northern South China Sea margin: 1) the WNW-striking thrust system, 2) ENE-striking extensional fault system, and 3) ENE-striking thrust system. These three fault systems are considered to have developed in the Late Cretaceous since they are superimposed on the well dated Late Jurassic to Early Cretaceous (161.6–101.7 Ma) arc-related granitoids that define most of the basement of the Cenozoic rift basin within the study area. This new structural evidence, combined with a review of previous studies, led us to propose a renewed multi-phase geodynamic evolutionary model of the South China Sea area during the Late Cretaceous. The first tectonic event that can be recognized generated the WNW-striking thrust system and is, in this paper, interpreted to have formed as a result of a sinistral transpressional event that took place in the South China Sea area and adjacent areas around 100 Ma at the Early-Late Cretaceous boundary. This transpressional event was likely related to intense oblique convergence between the Paleo-Pacific Ocean Plate and the Eurasia Plate. The second tectonic phase that was identified in this paper (~100 Ma to ~72 Ma) is defined by an extensional event that generated the largely ENE-striking extensional fault systems and associated basins, which is interpreted to be related to the back-arc extension that took place in this period in response to the slab roll back and high-angle subduction of the Paleo-Pacific Plate. This extensional phase eventually led to the opening of the Proto-South China Sea on the SE margin of the proto-South China Block, and it should be distinguished from the Cenozoic rifting phases that are related to the opening of the South China Sea. The third and last tectonic phase that was recognized in this paper is a compressional event that took place in the late stage of the Late Cretaceous (~72 Ma to ~66 Ma) and was responsible for the development of the ENE-striking thrust system. We suggest that this post-subduction (post-Yanshanian) compressional event can be interpreted to have developed in response to process of ridge push related to the sea floor spreading of the Proto-South China Sea.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 2 July 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): C. Thomazo, A. Brayard, S. Elmeknassi, E. Vennin, N. Olivier, G. Caravaca, G. Escarguel, E. Fara, K.G. Bylund, J.F. Jenks, D.A. Stephen, B. Killingsworth, P. Sansjofre, P. Cartigny〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Early Triassic is generally portrayed as a time of various, high ecological stresses leading to a delayed biotic recovery after the devastating end-Permian mass extinction. This interval is notably characterized by repeated biotic crises (e.g., during the late Smithian), large-scale fluctuations of the global carbon, nitrogen and sulfur cycles as well as harsh marine conditions including a combination of ocean acidification, anoxia, extreme seawater temperatures and shifting productivity. Observations from different paleolatitudes suggest that sulfidic (H〈sub〉2〈/sub〉S-rich) conditions may have developed widely during the Early Triassic, possibly reaching up to ultra-shallow environments in some places. However, the existence and the spatio-temporal extent of such redox swings remain poorly constrained. In order to explore Early Triassic paleoceanographic redox changes and their potential influences on the biotic recovery, we analyzed multiple sulfur isotopes (〈sup〉32〈/sup〉S, 〈sup〉33〈/sup〉S, 〈sup〉34〈/sup〉S, and 〈sup〉36〈/sup〉S) of sedimentary pyrite and carbonate associated sulfate (δ〈sup〉34〈/sup〉S〈sub〉CAS〈/sub〉) from the Mineral Mountains section, Utah. Sediments from this section were mainly deposited in shallow waters and span the Smithian and lower Spathian. We report a 68‰ range of variations in δ〈sup〉34〈/sup〉S〈sub〉py〈/sub〉 associated with Δ〈sup〉33〈/sup〉S〈sub〉py〈/sub〉 varying from −0.01‰ to +0.12‰, whereas the δ〈sup〉34〈/sup〉S〈sub〉CAS〈/sub〉 varies between +19.5‰ and + 34.8‰. We interpret the observed signal of multiple sulfur isotopes as reflecting the operation of pore-water synsedimentary microbial sulfate reduction in open system with respect to sulfates before the late Smithian, evolving to a closed system, sulfate limited, Rayleigh-type distillation across the Smithian/Spathian boundary (SSB) and immediately after the SSB. We argue that this marked change is driven by the effectiveness of the connection between the sedimentary pore waters and the overlying water column, which is, in this case, controlled by the local sedimentological conditions such as the bioturbation intensity and the sedimentation rate. Therefore, our results suggest that changes in the sulfur cycle before and across the SSB at Mineral Mountains is probably a local consequence of the loss of the mixed sedimentary layer during the late Smithian extinction event, as opposed to reflecting the development of a lethal anoxic ocean at the global scale.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Mun Gi Kim, Yong Il Lee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The tectonic setting of the Okcheon Belt in the Korean Peninsula has long been regarded as one of the important topics in discussing East Asian tectonics. The controversial tectonic setting of the Okcheon Belt before the Triassic collision between North and South China limits proper understanding of the late Paleozoic tectonics of East Asia. Focusing on the upper Paleozoic to Lower Triassic Pyeongan Supergroup, coeval sedimentary records in different parts of the Okcheon Belt are reviewed. This study has a clear advantage over previous assessments that build upon comparison between (meta)sedimentary units of unknown age in the region. The Pyeongan Supergroup sediments show high similarity in both stratigraphy and detrital zircon U〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Pb ages throughout the Okcheon Belt. They are distinct from their age-equivalents in South China, while sharing characteristics with those in North Korea and North China. Critical criteria include marine influence and enrichment of organic materials at each time period, and relative proportion of Mesoproterozoic–Silurian components in detrital zircon age population. The combined results agree with the view that the entire Okcheon Belt was a single tectonic unit at least by the Late Carboniferous. The results of this study favor the idea of the Sino-Korean Block encompassing the whole Korean Peninsula, and cast doubts on the tectonic models that attribute the southern part of the Korean Peninsula to the South China Block. A retroarc foreland basin setting of the Okcheon Belt with detritus mainly provided from a subduction-related orogen in the continent-sided Japan is inferred from the provenance characteristics of the detrital zircons.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 184〈/p〉 〈p〉Author(s): Kyle W.R. Taylor, Pi Suhr Willumsen, Christopher J. Hollis, Richard D. Pancost〈/p〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): S.N. Pandey, Vikram Vishal, A. Chaudhuri〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Heat extraction from the geothermal reservoir is sensitive to reservoir properties, operating parameters and coupling among various processes. Due to complex reservoir structure, heat extraction performances and flow field behaviour in geothermal reservoirs are very different than the small scale laboratory model experiments. In recent past, significant progress in reservoir scale numerical modeling has been made for quantification of challenges in geothermal energy system development. In this paper, a comprehensive review of state of the art geothermal reservoir modeling for heat extraction is presented. Various numerical tools and approaches such as the finite difference method, finite element method, finite volume method, etc. to model the geothermal reservoir in the last four decades are discussed. The thrust of this paper is on a critical review of individual evaluation of coupling among all possible processes that are thermo, hydro, mechanical, and chemical processes on heat extraction performance. Future directions in developing better understanding on geothermal reservoir systems are proposed.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Zhen-Yu He, Reiner Klemd, Li-Li Yan, Ze-Ming Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Microcontinents with Precambrian basement have played an important role in the accretionary and amalgamation history of the Central Asian Orogenic Belt (CAOB). However, their geological evolution is only poorly constrained due to restricted exposure of the Precambrian rocks, which were extensively overprinted mainly by Paleozoic tectonic, metamorphic and magmatic events. In the present study, in situ zircon U–Pb age and Hf isotopic data of 64 Paleozoic and early Mesozoic (from 499 to 217 Ma) as well as 14 Mesoproterozoic and Neoproterozoic (from 1555 to 871 Ma) granitic samples from four major arc terranes of the Beishan orogen (southernmost CAOB) were compiled in order to assess the nature of their crustal basement as well as the subsequent Paleozoic tectonic evolution. Zircon 〈em〉ε〈/em〉〈sub〉Hf〈/sub〉(〈em〉t〈/em〉) values and calculated Hf model ages are similar for all arc terranes with Hf model age peaks at approximately 1.0–0.8 Ga and 2.0–1.8 Ga. We suggest that all of these Paleozoic arc terranes formed on a single, uniform Precambrian continental terrane. Furthermore, this continental terrane shows typical characteristics of Mesoproterozoic (~1.4 Ga) juvenile crustal growth, which may have been part of an extensive Mesoproterozoic continental terrane, now tectonically fragmented and located over a distance of more than a thousand kilometers in the southern CAOB. Among the cratons bordering the CAOB, Baltica displays most similarities with this continental terrane, while a Mesoproterozoic correlation with the Tarim Craton is rather questionable.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): W.M. van der Meij, A.J.A.M. Temme, H.S. Lin, H.H. Gerke, M. Sommer〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The ability of water to transport and transform soil materials is one of the main drivers of soil and landscape development. In turn, soil and landscape properties determine how water is distributed in soil landscapes. Understanding the complex dynamics of this co-evolution of soils, landscapes and the hydrological system is fundamental in adapting land management to changes in climate. Soil-Landscape Evolution Models (SLEMs) are used to simulate the development and evolution of soils and landscapes. However, many hydrologic processes, such as preferential flow and subsurface lateral flow, are currently absent in these models. This limits the applicability of SLEMs to improve our understanding of feedbacks in the hydro-pedo-geomorphological system. Implementation of these hydrologic processes in SLEMs faces several complications related to calculation demands, limited methods for linking pedogenic and hydrologic processes, and limited data on quantification of changes in the hydrological system over time.〈/p〉 〈p〉In this contribution, we first briefly review processes and feedbacks in soil-landscape-hydrological systems. Next, we elaborate on the development required to include these processes in SLEMs. We discuss the state-of-the-art knowledge, identify complications, give partial solutions and suggest important future development. The main requirements for incorporating hydrologic processes in SLEMs are: (1) designing a model framework that can deal with varying timescales for different sets of processes, (2) developing and implementing methods for simulating pedogenesis as a function of water flow, (3) improving and implementing knowledge on the evolution and dynamics of soil hydraulic properties over different timescales, and (4) improving the database on temporal changes and dynamics of flow paths.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): Guochun Zhao, Wenjiao Xiao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Pangea is the youngest supercontinent in Earth's history, forming about 300–250 Ma ago. As supported by large amounts of geological, paleomagnetic and paleontonlogical data, there is little debate on the positions of major continental blocks in Pangea. However, controversy has long surrounded the relations of East Asian blocks with Pangea. Most Pangea reconstructions assume that the East Asian blocks were not the components of Pangea but separated from Pangea by the Paleo-Tethys Ocean. These reconstructions were mainly based on geological and paleomagnetic data before the 1990's but did not fully consider recent data, especially for major orogenic belts that formed through the subduction and closure of the Proto-Tethys, Paleo-Asian and Paleo-Tethys oceans in East Asia. To determine where, when and how these oceans were closed, and whether or not the East Asian blocks were added to Pangea, the National Natural Science Foundation of China (NSFC) set up a NSFC Major Program entitled “Reconstructions of East Asian Continental blocks in Pangea”, which started in 2012 and was completed in 2016. In the past five years, the researchers of this project carried out extensive field-based geological and paleomagnetic investigations on the East Asian blocks and their intervening mountain belts, and produced large amounts of data and competing interpretations, which provide constraints on the paleogeographic evolution of the East Asian blocks from the breakup of Rodinia to the assembly of Pangea. This forms the justification for organizing this special issue in which we collected ten papers that timely summarize these new data and interpretations and present new models for the reconstructions of the East Asian continental blocks in Pangea.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): A.J.H. Reesink, D.R. Parsons, P.J. Ashworth, J.L. Best, R.J. Hardy, B.J. Murphy, S.J. McLelland, C. Unsworth〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The dunes that cover the beds of most alluvial channels change in size and shape over time and in space, which in turn affects the flow and sediment-transport dynamics of the river. However, both the precise mechanisms of such adaptation of dunes, and the hydraulic variables that control these processes, remain inadequately understood. This paper provides an overview of the processes involved in the maintenance and adaptation of dunes, provides new tools for the analysis of dune dynamics, and applies these to a series of bespoke experiments.〈/p〉 〈p〉Dunes that grow compete for space, and dunes that decay need to shed excess sediment. Therefore, dune adaptation necessarily involves the redistribution of sediment over and among dunes. The details of sediment redistribution are not captured by mean geometric parameters such as dune height and wavelength. Therefore, new analyses of dune kinematics, bed-elevation distributions, and dune deformation are presented herein that aid the identification and analysis of dune dynamics.〈/p〉 〈p〉Dune adaptation is often described as a morphological response to changes in water depth at a rate that depends on sediment mobility, which itself is a product of flow depth and velocity. However, depth and velocity are out-of-phase during the passage of flood waves, and they vary spatially across rivers from the thalweg to bar tops, and downstream along the river profile. In order to improve our understanding of the hydraulic controls on dune morphology and kinematics, a series of experiments was performed to investigate the response of dunes in fully-mobile sand (D〈sub〉50〈/sub〉 = 240 μm) to changes in flow depth and velocity.〈/p〉 〈p〉The experimental results illustrate that water depth and flow velocity have separate effects on the processes that control dune adaptation, and that the crests and troughs of dunes do not respond simultaneously to changes in flow. Trough scour increases with flow velocity, but superelevation of the dune crests appear to show only a weak relation with flow depth. Flattening-out of dune crests is related to decreasing depth and increasing flow velocity. Bedform superimposition, a key feature of bedform kinematics, was associated with increased flow depth, but was also systematically associated with local increases in the crest-to-crest distance following the dissipation of an upstream dune. Thus, local flow-form interactions have a significant effect on the manner in which sediment is redistributed over and among dunes. The splitting of dunes decreased in the downstream direction along the length of the flume, illustrating that the dunes continue to interact even after dune height has stabilised. Other processes, such as differential migration and dune merging, are ubiquitous during all flow conditions. These varied responses support the notion that the processes of dune adaptation vary over time and in space.〈/p〉 〈p〉Analysis of dune deformation through examination of the residuals of cross-correlations between successive dune profiles illustrates that local sources and sinks of sediment exist within mobile dune fields. These findings highlight that dune adaptation to changes in flow is a dynamic response involving multiple interconnected dunes. The redistribution of sediment that is required for dunes to change shape and adapt to new conditions is expected to be an important cause of variability in sediment transport. These detailed analyses and findings provide a foundation for further study of dune dynamics in different environments on Earth as well as other planetary bodies.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Jordon Bright, Andrew S. Cohen, Scott W. Starratt〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Brackish marine and brackish continental environments are fundamentally different from a compositional perspective. Brackish water is often defined as having salinity lower than that of standard seawater but higher than that of freshwater, but less regard is given to the origin of the salts involved. The simple dilution of standard seawater by freshwater in a coastal or estuarine setting constitutes a brackish environment, but so do lakes where continental fresh water is impounded and becomes more saline through a variety of solute evolution pathways. The range of potential compositions of brackish lake water is diverse and includes water with “seawater-like” compositions. Isolated brackish lake environments located hundreds of kilometers inland can evolve towards sodium chloride-dominated, low alkalinity environments that mimic the composition of brackish seawater environments. These types of lakes can harbor a variety of continentally invasive but typically marine organisms, including but not limited to algae, foraminifers, mollusks, diatoms, and crustaceans. Distinguishing brackish marine from brackish lake environments in the geologic record can be difficult. In this paper, the enigmatic late Miocene and early Pliocene southern Bouse Formation of southern Arizona and California, USA, considered by many to represent a marine transgression along the lower Colorado River corridor, is discussed within a broad framework that incorporates hydrochemical, biogeographical, and species niche concepts. A brackish lake interpretation provides a powerful platform that can comprehensively account for the enigmatic mixed marine and continental fossil assemblage and possible tidal rhythmites that feature prominently in the southern Bouse Formation controversy. A review of the broader regional (paleo)environmental context for the southern Bouse supports a sodium chloride-dominated, low alkalinity, mildly brackish (10-5 ppt) Colorado River-fed lake depositional environment that was populated by an intriguing but predictable array of euryhaline, opportunistic, and continentally invasive marginal marine organisms.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Zhanghua Wang, Yoshiki Saito, Qing Zhan, Xiaomei Nian, Dadong Pan, Long Wang, Ting Chen, Jianlei Xie, Xiao Li, Xuezhong Jiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Yangtze (Changjiang) mega-delta, China, has a high risk of coastal erosion owing to the recent high rate of relative sea-level rise and reduced sediment supply. The study of the Holocene evolution of the delta can provide information about its response to rapid sea-level rise and changes in sediment supply caused by climate or human activity, although this has yet to be fully explored because of the lack of integrated studies using age-constrained sedimentary records. Here we document stratigraphic architecture and morphological changes over the last 11,700 years and estimate the amount of sediment trapped in the delta region on a millennial scale using a dataset of 344 sediment cores, 658 radiocarbon and 28 optically stimulated luminescence (OSL) ages (of which we obtained 64 cores, 345 radiocarbon and 28 OSL ages, and the others we sourced from the literature). Using this dataset we present the temporal and spatial morphodynamic evolution of the entire Yangtze River mouth from its early Holocene transgressive estuary to a mid- to late-Holocene regressive delta, making it possible to produce a quantitative and sequential analysis of sediment deposition. A destructive phase of the river mouth region was identified at 10 to 8 cal. kyr BP, including significant coastal erosion of tidal flats and troughs within the estuary and of tidal ridge-and-trough topography offshore; these resulted from the reshaping of the river mouth morphology caused by rapid sea-level rise at that time. As a result, the rate of sediment trapping at the river mouth declined from an average of 224 Mt yr〈sup〉−1〈/sup〉 at 11.7–10 cal. kyr BP to 137 Mt yr〈sup〉−1〈/sup〉 between 10 and 8 cal. kyr BP. Since delta initiation 8000 years ago, a retreat of the subaqueous delta occurred and the sediment trapping rate declined from 151 Mt yr〈sup〉−1〈/sup〉 at 8–6 cal. kyr BP to 99–113 Mt yr〈sup〉−1〈/sup〉 between 6 and 2 cal. kyr BP, caused by the reduction in sediment supply linked to summer monsoon weakening ~6000 years ago. In the last 2000 years the sediment trapping rate has increased to 162 Mt yr〈sup〉−1〈/sup〉 due to intensified human activity. The present-day level of sedimentation in delta (49 Mt yr〈sup〉−1〈/sup〉 in 2003–2011), after the completion of the Three Gorges Dam, is far lower than the ‘natural’ range in the Holocene. We thus infer a potential for system regime shift in terms of coastal erosion and a transition to a new equilibrium in delta morphology in the near future.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Anita Bernatek-Jakiel, Jean Poesen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil erosion is not only a geomorphological, but also a land degradation process that may cause environmental damage affecting people’s lives. This process is caused both by overland and subsurface flow. Over the last decades, most studies on soil erosion by water have focused on surface processes, such as sheet (interrill), rill and gully erosion, although subsurface erosion by soil piping has been reported to be a significant and widespread process. This paper presents a state of art regarding research on soil piping and addresses the main research gaps. Recent studies indicate that this process (1) occurs in almost all climatic zones and in the majority of soil types, (2) impacts landscape evolution by changing slope hydrology, slope stability and slope-channel coupling, (3) is controlled by various factors including climate and weather, soil properties, topography, land use and land management. These issues are illustrated with various case studies from around the world. However, the majority of the reviewed studies used surface methods for soil pipe detection, although soil piping is a subsurface process. Surface methods, such as geomorphological mapping, may underestimate the piping-affected area by 50%. Moreover, most studies are limited to few case studies without presenting thresholds for soil pipe development in different environments. Subsurface erosion by soil piping is not represented in currently used soil erosion models. Therefore more research is needed to better understand the morphology and connectivity of soil pipes, their subsurface catchments, as well as soil erosion rates by piping in different environments. Knowledge of thresholds that induce erosion in pipes and subsequent initiation of gullies may help to improve models of hillslope hydrology and soil erosion that include pipeflow and piping erosion. The investigation of soil piping also requires improved methods that allow to better predict pipe development and collapses, and thus to detect piping-affected areas. Studies dealing with effective prevention and control measures of soil piping are scarce. Addressing these research gaps will help to improve our insights into subsurface erosion by soil piping, and thus help to better understand landscape evolution and hillslope hydrology, as well as to develop and improve effective piping erosion control techniques and strategies.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Sanzhong Li, Yanhui Suo, Xiyao Li, Bo Liu, Liming Dai, Guangzeng Wang, Jie Zhou, Yang Li, Yiming Liu, Xianzhi Cao, I. Somerville, Dunling Mu, Shujuan Zhao, Jinping Liu, Fan Meng, Libing Zhen, Lintao Zhao, Junjiang Zhu, Shengyao Yu, Yongjiang Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Any plate has a growth process from small to large. The micro-blocks or micro-plates are sometimes the precursors of large plates. The origin, growth, aborting, extinction and residual process of micro-blocks are of great significance for the study of plate tectonics and pre-plate tectonics. The micro-block can be divided into continental, oceanic and mantle micro-blocks according to their compositions. In this paper, the micro-blocks in the global oceans have been summarized according to the following five environments: mid-ocean ridge system, subduction system, transform fault system, deep-sea intraplate system and extension-rift system. We first propose a genetic classification of micro-blocks comprising: detachment-derived, rifting-derived, transform-derived, propagation-derived, ridge jumping-derived, subduction-derived, accretion-derived, collision-derived and delamination-derived micro-blocks. The different types of micro-block boundaries such as active or fossil detachment fault, subduction zone, mid-ocean ridge, transform fault, fracture zone, transfer fault, accommodation zone, lithosphere-scale strike-slip fault, pseudofault, intra-oceanic convergent zone, overlapping spreading centre, non-transform offset, rheological crustal or mantle discontinuity, are systematically discussed for different micro-blocks. Thus, the number of triple junctions will be more than the 16 in the traditional Plate Tectonic Theory. A stability analysis of these triple junctions is the key to understanding the causes of micro-blocks. However, the micro-block has no ultimate cause, so it is unnecessary to pursue one ultimate cause or initiation of plate tectonics. These micro-blocks within oceanic basins, along oceanic margins or within the deep mantle, can not only be used to develop deep ocean fine structural analysis and plate tectonic reconstruction, but also to explain the causes of micro-blocks in some orogens. This will enrich the research of more detailed pre-orogenic or syn-orogenic evolution of orogenic belts, and even extend to the study of early Precambrian pre-plate tectonic mechanisms. The micro-block can be a transition among microplate, plate and terrane under a plate tectonic regime. It can also be formed in inter-sphere tectonic processes. It helps better our understanding of regimes of cratonic basin formation and intra-continental deformation which are the difficulties faced by the Plate Tectonics Theory. We speculate that the Micro-block Tectonics Theory is a unified tectonic theory of cross-layer, cross-phase, cross-space-time scale and cross-planet.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 20 September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): A. Minissale, A. Donato, M. Procesi, L. Pizzino, S. Giammanco〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In recent years, two research projects specifically conceived by Italian Institutions of Research to promote the implementation of the use of geothermal energy in Southern Italy has allowed the review of most data on chemical and isotopic compositions of natural thermal manifestations in the territory of Italy. Two large databases, one for thermal springs and CO〈sub〉2〈/sub〉-rich springs, and a second one for fumarolic condensates and associated gas phase have been produced and are available on line, with data spanning in time from the early 70's to the present.〈/p〉 〈p〉We have used those data, after careful evaluation of the quality and reliability of them, to produce correlation diagrams and isodistribution maps of some relevant geochemical/geothermal parameters, such as: 〈em〉p〈/em〉CO〈sub〉2〈/sub〉 in thermal springs, %CO〈sub〉2〈/sub〉 and δ〈sup〉13〈/sup〉C in CO〈sub〉2〈/sub〉 of gas phases, 〈sup〉3〈/sup〉He/〈sup〉4〈/sup〉He ratio and %He. In this way, we have been able to delimit the areal patterns of thermal anomalies potentially related with geothermal reservoirs. The cross correlation among the many parameters (〉40) selected has allowed the overview on the circulation of fluids at shallow crust, in one of the most active tectonic boundary of the Earth between the African and the Eurasian continents.〈/p〉 〈p〉Shallow circulation of hot fluids is particularly active in the Roman Comagmatic Province, the Neapolitan area and Sicily (both at Etna, Aeolian Archipelago and Pantelleria island in the Sicily Channel) where active geothermal systems are already known, whose areal extension is probably much larger than what envisaged at present.〈/p〉 〈p〉The geothermometric evaluation of data has not allowed to clearly identity new areas apart from those already known but, nevertheless, some areas in the inner Apennines, as well as Sicily and Sardinia have shown anomalous 〈sup〉3〈/sup〉He/〈sup〉4〈/sup〉He values that point to the presence of mantle fluids located inside the crust.〈/p〉 〈p〉Being most of active volcanic islands likely much smaller than the thermal anomaly they are associated with, a futuristic perspective of utilizing geothermal fluids off shore is suggested. Moreover, the database and the proposed maps can be a useful tool both scientific community and stakeholders to perform geothermal favourability maps and to identify potential new areas interesting from a geothermal perspective.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 184〈/p〉 〈p〉Author(s): Francisco J. Rodríguez-Tovar, F. Javier Hernández-Molina〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The comments of G. Shanmugam concerning the paper “〈em〉Ichnological analysis of contourites: Past, present and future〈/em〉”, by Rodríguez-Tovar and Hernández-Molina (2018), imply that this study has tried to definitively resolve the issues of distinguishing contourites and differentiating them from other kinds of deposits. In reality, however, most of this reviewer's comments refer to issues that lie beyond of the scope of that contribution and therefore are not relevant to the paper. The criticisms of our work appear to be aimed at concepts and ideas from other authors.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Paul G. Albert, Victoria C. Smith, Takehiko Suzuki, Emma L. Tomlinson, Takeshi Nakagawa, Danielle McLean, Masataka Yamada, Richard A. Staff, Gordon Schlolaut, Keiji Takemura, Yoshitaka Nagahashi, Jun-Ichi Kimura, Suigetsu 2006 Project Members〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Accurately evaluating the tempo and magnitude of pre-historic eruptions is essential for hazard assessments. Here we demonstrate the importance of integrating records from locations close to the volcano with those in distal regions to generate more comprehensive event stratigraphies. The annually laminated (varved) and intensely radiocarbon dated lacustrine sediments of Lake Suigetsu (SG06 core), Japan are used to place chronological constraints on the tempo of volcanism at two stratovolcanoes located favourably upwind of the lake along the South-West Japan Arc, Sambe and Daisen. Major and trace element glass compositions are used to assign visible ash (tephra) layers preserved in the SG06 sediment core to past explosive eruptions from these volcanoes. Integrating these stratigraphies confirm that the ~150 ka long lake sequence records nine visible ash layers from Daisen and five from Sambe. The SG06 record captures two periods of closely spaced eruptions at Daisen volcano. The first period begins at ~61.1 ka with three explosive eruptions over ~10 ka, with two events separated by as little as 1.5 ka. One layer (SG06–4281), dated at 59.6 ± 5.5 ka (95.4% probability), relates to the large magnitude, and widely dispersed Daisen Kurayoshi Pumice (DKP) eruption. The other period of frequent activity began at 29,837 ± 96 IntCal13 yrs. BP (95.4% probability) with five widely dispersed ash fall events associated with explosive eruptions separated by approximately 6, 936, 5 and 438 years. The integrated proximal-distal event stratigraphy and the high-precision SG06 chronology provide unique insights into the timing and frequency of past explosive volcanism from Daisen and Sambe, which has implications for the prediction of future eruption scenarios.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 187〈/p〉 〈p〉Author(s): Tobias Heckmann, Marco Cavalli, Olivier Cerdan, Saskia Foerster, Mathieu Javaux, Elve Lode, Anna Smetanová, Damià Vericat, Francesco Brardinoni〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Indices of connectivity are critical means for moving from qualitative to (semi-)quantitative evaluations of material (e.g., water, sediment and nutrients) transfer across the building blocks of a terrestrial system. In geomorphology, compared to closely related disciplines like ecology and hydrology, the development of indices has only recently started and as such presents opportunities and challenges that merit attention. In this paper, we review existing indices of sediment connectivity and suggest potential avenues of development for meeting current basic and applied research needs. Specifically, we focus on terrestrial geomorphic systems dominated by processes that are driven by hydro-meteorological forcing, neglecting seismically triggered events, karstic systems and environments controlled by eolian processes.〈/p〉 〈p〉We begin by setting a conceptual framework that combines external forcings (drivers) and system (intrinsic) structural and functional properties relevant to sediment connectivity. This framework guides our review of response variables suitable for sediment connectivity indices. In particular, we consider three sample applications concerned with sediment connectivity in: (i) soil studies at the plot scale, (ii) bedload transport at the reach scale, and (iii) sediment budgets at the catchment scale. In relation to the set of response variables identified, we consider data availability and issues of data acquisition for use in indices of sediment connectivity. We classify currently available indices in raster based, object or network based, and indices based on effective catchment area. Virtually all existing indices address the degree of static, structural connectivity only, with limited attention for process-based, functional connectivity counterparts. Most recent developments in indices of sediment connectivity deal, to some extent, with different styles of anthropogenic and hydro-meteorological forcings and with the temporal variability of sediment connectivity, by incorporating additional variables and parameters in existing indices. We believe that, in order to use structural connectivity as explanatory or predictive tool, indices need to be interpretable in relation to geomorphic processes, material properties, and forcing styles and magnitude-frequency spectra. Improvements in this direction can be made through studies shaped to constrain structural-functional correlations across a range of hydro-meteorological scenarios, for example employing field-based techniques such as particle tracking and sediment provenance analysis, as well as numerical simulations.〈/p〉 〈p〉We further consider existing indices in relation to spatial and temporal scales. The latter have immediate implications on the distinction and application between indices and models of sediment connectivity. In this context, we suggest that sediment connectivity over millennial or longer time scales should be dealt with models, as opposed to indices.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 14 September 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Alan Stebbins, Thomas J. Algeo, Leopold Krystyn, Harold Rowe, Michael Brookfield, Jeremy Williams, Steven W. Nye Jr, Robyn Hannigan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Perturbations to the global carbon and sulfur cycles recurred episodically throughout the ~5-Myr-long Early Triassic, in the aftermath of the end-Permian mass extinction, the largest biocrisis in Earth's history. In this study, analyses of carbonate-associated sulfate (CAS) sulfur, CAS oxygen, and pyrite sulfur-isotope ratios in a continental shelf section from the southern Neo-Tethys Ocean (Spiti Valley, India) provide new insights into the Early Triassic marine sulfur cycle. Secular variation in CAS sulfur-isotope values at Spiti is similar to that in South China, suggesting that CAS was a robust recorder of a global seawater sulfate signal. The Spiti CAS and pyrite δ〈sup〉34〈/sup〉S profiles show that the highest rates of pyrite burial coincided with cooler sea-surface temperatures. We infer that climatic cooling steepened equator-to-pole temperature gradients, invigorating thermohaline overturning circulation, and enhancing upwelling of nutrients that stimulated marine productivity and organic carbon sinking fluxes. Enhanced productivity fueled and sustained microbial respiration, increased oxygen demand, and, within the southern Neo-Tethys, caused the zone of microbial sulfate reduction to migrate upwards and become more connected to the water column. Microbial sulfate reduction, under these conditions, was no longer limited by organic matter or sulfate availability, leading to burial of more 〈sup〉34〈/sup〉S-depleted pyrite and 〈sup〉34〈/sup〉S- and 〈sup〉18〈/sup〉O-enrichment of the oceanic sulfate pool. This environmental scenario suggests possible environmental stresses related to eutrophication during positive carbon-isotope excursions around the Griesbachian-Dienerian, Dienerian-Smithian, and Smithian-Spathian boundaries. Additionally, the difference between CAS and pyrite sulfur-isotope values, Δ〈sup〉34〈/sup〉S〈sub〉CAS-pyr〈/sub〉, slowly rose through the Early Triassic, reflecting a slow increase in seawater sulfate concentrations following a minimum close to the Permian-Triassic boundary.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Joost Frieling, Appy Sluijs〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉We explore a novel approach towards quantification of paleo-ecological signals from non-analogue microfossil assemblages by quantifying relations between assemblages and high-quality geochemical and sedimentological data from sedimentary archives. We test this approach using one group of microfossils, the organic cysts of dinoflagellates (dinocysts), which are widely used in shelf and open marine settings for biostratigraphy and reconstructions of past environments and environmental change. Similar to other microfossil groups, dinocysts can be used to reconstruct environments with relatively high confidence for recent time periods, as species affinities can be derived from observational and instrumental data. In the absence of such data, the ecology of extinct species is much less certain and as a result reconstructions in deep time are often limited to qualitative interpretations.〈/p〉 〈p〉To explore if quantitative empirical relations between extinct dinocysts and high-quality geochemical data can be established, we study a major event of climate change, the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma ago). The PETM is a particularly suitable period for this exercise as there is a multitude of large environmental perturbations associated with the transient global warming, such as deoxygenation, sea level rise and an accelerated hydrological cycle. The synthesized published dataset exhibits better spatial and temporal coverage compared to any other period in deep time. We extract empirical relations for the abundance of previously proposed paleoecological groups as a function of independent environmental proxies for example, sea surface temperature and terrestrial organic matter input.〈/p〉 〈p〉The results unequivocally illustrate that many dinocysts show relations to several of the reconstructed environmental variables. Notably, we show that one genus 〈em〉(Apectodinium)〈/em〉 and an ecogroup (epicystal Goniodomidae) required sea surface temperatures in excess of 20 °C, and 25 °C, respectively, while one species 〈em〉(Florentinia reichartii)〈/em〉 was only abundant between 30 and 35 °C. Other groups apparently favored either a limited (〈em〉Spiniferites〈/em〉) or high (〈em〉Senegalinium〈/em〉) terrestrial input to the study site, relating to salinity, nutrient levels or suspended sediment load (i.e. murkiness).〈/p〉 〈p〉Crucially, our work shows that the validation and quantification of ecological signals by independent environmental proxy data provides the opportunity to extract more quantitative information from a wide range of (non-analogue) microfossil assemblages. While this approach is not limited to any specific group of microfossils (or macrofossils), we stress that proper calibration datasets, high-quality sedimentological and geochemical proxy records, are needed and should ideally have decent geographical coverage and include one or more environmental perturbations. Using this approach such empirical relations can be established for a wide range of microfossil groups that have highly complementary geological records, which increases the value of existing data and ensures future application of microfossil-based paleoecology.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 185〈/p〉 〈p〉Author(s): Dirk Knaust, Roger D.K. Thomas, H. Allen Curran〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The trace fossil 〈em〉Skolithos〈/em〉, with its simple, vertical to very slightly inclined, tubular form, is widely recognized and globally distributed in early Cambrian to Holocene strata, representing deep-sea to continental paleoenvironments. The type species, 〈em〉Skolithos linearis〈/em〉, was first described in 1840 by Samuel S. Haldeman, based on his observations of early Cambrian quartzite at Chickies Rock, a well-known landmark on the east bank of the Susquehanna River, in Pennsylvania. The original description was meager; no illustrations were published, no holotype was established, and no specimens directly associated with Haldeman are known to exist today. A “neoholotype” proposed by Howell (1943) is invalid, as it does not conform to requirements of the International Code of Zoological Nomenclature. As a result, the iconic ichnogenus 〈em〉Skolithos〈/em〉 is inadequately characterized and some of the numerous ichnospecies that have subsequently been named are not unequivocally assignable to it. In order to stabilize this important ichnogenus and to provide a basis for the taxonomic revision it urgently requires, we have studied 〈em〉S. linearis〈/em〉 at its type locality. Our new material is described and illustrated here, and we have designated a neotype, accessioned by the U.S. National Museum of Natural History (Smithsonian Institution). The stratigraphy and regional geologic setting of Chickies Rock, the sedimentology and environment of deposition of cross-bedded quartzite with abundant 〈em〉S. linearis〈/em〉 constituting classic “pipe rock,” and the structural deformation of this fabric are reviewed〈em〉.〈/em〉 Given the simple morphology of 〈em〉Skolithos〈/em〉, disparate organisms in several phyla have been proposed as its maker〈em〉.〈/em〉 We concur in the general view that Cambrian trace fossils assigned to 〈em〉S. linearis〈/em〉 were most probably made by burrowing phoronids or polychaete annelids. The global abundance of largely monospecific pipe rock in analogous Cambro-Ordovician settings is recognized as a characteristic feature of the ecology of shallow-marine environments of that time. The stage has now been set for a thorough re-evaluation of all existing ichnospecies assigned and related to the ichnogenus 〈em〉Skolithos〈/em〉.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 7 November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Marc Leu, Hugo Bucher, Nicolas Goudemand〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In contrast to the benthos whose taxonomic recovery was lagging way behind that of the nekton, highly diverse Smithian conodont and ammonoid faunas were profoundly decimated during the late Smithian, ca. 2 Myr after the Permian-Triassic boundary mass extinction. As body size reduction is a common evolutionary response to heavy environmental stress, we investigate how the size of the P1 elements of different conodont clades responded during the late Smithian crisis based on three sections from the northern Indian Margin. A major and world-wide positive carbon excursion is also a consistent signature of the late Smithian time interval. Where adequate ammonoid biochronological control is lacking (i.e., Kashmir), a new carbonate carbon isotope record provides an independent age proxy for correlations with southern Tibet and the Salt Range. Assuming a positive correlation between the size of P1 elements and body size, we confirm that segminate conodonts underwent a size decrease during the late Smithian. However, segminiplanate conodonts consistently displayed a substantial size increase during the same time interval, thus highlighting clade specific, diverging answers and precluding any simplistic generalization of size responses to the same stress event. Additionally, a moderate but consistent size increase during the early Spathian is documented for both clades, thus obscuring any simple general relation between temperature stress and size among conodonts. Comparison of size time series with the oxygen isotopic composition of conodonts (a proxy for sea-water temperature) suggests that only the size of segminate P1 elements may correlate positively with temperature. Although at a slower pace, the size of segminiplanate P1 elements continued to increase during the early Spathian, when temperature rose again after the late Smithian cooling event. Therefore, temperature alone cannot explain the size variations of segminiplanate conodonts. The late Smithian was also a time of increasing burial of organic matter on continental shelves, but lateral variations of this factor also obscure any relation with the documented size changes. Last but not least, the stratigraphically more comprehensive study in Nammal reveals a segminiplanate gap during the middle Smithian thermal high. The biogeographical expansion of this clade towards the low latitudes during the Griesbachian, the early Smithian, the late Smithian and the early Spathian apparently occurred during the coolest intervals of the Early Triassic, in agreement with their supposed cooler habitat.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Claudia Troise, Giuseppe De Natale, Roberto Schiavone, Renato Somma, Roberto Moretti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Campi Flegrei caldera in Southern Italy is one of the most populated active volcanoes on Earth. It has an unprecedented record of historical unrest and eruption that dates back to 2.2 ka BP and provides key insights for understanding the dynamic evolution of large calderas. Since 1950, it has undergone four episodes of caldera-wide uplift and seismicity, which have raised the coastal town of Pozzuoli, near the centre of unrest, up to 4.5 m and triggered the repeated evacuation of some 40,000 people. After about 20 years of subsidence, following the uplift peak reached in 1984, the caldera started a new, low rate uplift episode, accompanied by low magnitude seismicity and marked geochemical changes in fumaroles. In this area it is crucial to discriminate episodes of shallow magma intrusion from hydrothermal perturbations, which are both able to generate unrest signals. In this paper, by a critical review of previous literature and some new results, we discriminate, in the unrest episodes, the relative contributions of hydrothermal effects and shallow magma intrusions. Our review is aimed also to show the different behavior of the largest unrest episodes, such as the 1982–1984, and the present, ungoing unrest characterized by smaller rate but longer lasting uplift. We show that for the former, larger uplift of the 80's, there is clear evidence for shallow magma intrusion, and we are able to compute the amount of intruded magma volume. For the present, on-going uplift, on the contrary, there is no evidence for magmatic activity at shallow depth. As a main result of our analysis, we demonstrate here the present unrest, characterized by much lower uplift rates and seismicity, is only interpretable as due to large gas fluxes coming from the deeper magma reservoir; without any appreciable contribution from shallow magma or recent magmatic intrusion. Our results shed new light on the interpretation of caldera unrest worldwide, and clearly indicate the most constraining data and the most rigorous procedures of data analysis for a correct interpretation of volcanic unrest.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Sarah Pederzani, Kate Britton〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Oxygen isotope analyses of skeletal remains (〈sup〉18〈/sup〉O/〈sup〉16〈/sup〉O, 〈em〉δ〈/em〉〈sup〉18〈/sup〉O) are a powerful tool for exploring major themes in bioarchaeology (the study of biological archaeological remains) and can aid in the reconstruction of past human-environment interactions, socio-cultural decisions and individual life histories. Making use of the preserved animal and human tooth and bone commonly found at archaeological sites, applications include the reconstruction of palaeoclimate and palaeoseasonality; animal husbandry and management practices; human and animal lifetime mobility and provenance; and cultural practices such as breastfeeding, weaning and even past culinary preparation techniques. With a range of other uses across the natural, physical, chemical and biological sciences, oxygen isotope analyses are also highly cross-disciplinary, with developments in the field of isotope bioarchaeology potentially feeding into other fields and 〈em〉vice-versa〈/em〉. The purpose of this paper is to provide a summary of the biogeochemical background of oxygen isotope systematics from the water cycle to human and animal skeletal tissues for archaeologists and other scientists, and to explore how these have been utilised in terrestrial bioarchaeological research. In this way, we aim to provide an overview resource for stable isotope analysts in archaeology and the wider earth science community, as well as for archaeological practitioners and consumers interested in specific applications. By providing a summary of fundamental isotope mechanics alongside a review of recent developments in the field, we hope to highlight the potential of oxygen isotope bioarchaeology to not only reveal environmental and ecological aspects of the past relevant to human groups using archaeological materials, but also to illuminate past human decisions and behaviours. Current limitations and caveats of the approaches used are also explored.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Dong-Xun Yuan, Shu-zhong Shen, Charles M. Henderson, Jun Chen, Hua Zhang, Quan-feng Zheng, Huaichun Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Lopingian is the uppermost series of the Paleozoic and it is bracketed by two major biological events, including the pre-Lopingian crisis and the end-Permian mass extinction (EPME). A high resolution temporal framework is essential to understand the patterns and causes of the extinction. Lopingian strata of South China have been intensively studied because three GSSPs have been defined in the region. Based on the review and updates to data from the Shangsi section as well as correlation with the Meishan section, the time framework for the Lopingian is revised, including biostratigraphy, chemostratigraphy, magnetostratigraphy, cyclostratigraphy and geochronology. The temporal framework is constrained by both precise geochronologic data and a high resolution conodont succession, and provides the possibility that the current high resolution marine international standard can also be applied to nonmarine strata by means of geochronology, magnetostratigraphy and cyclostratigraphy. The entire Lopingian high resolution conodont succession is for the first time, since the Lopingian Series was adopted as the international standard, recognized at a single section in South China and the succession correlates very well with the Lopingian GSSP sections at Penglaitan and Meishan. The Permian-Triassic boundary (PTB) of the Shangsi section is constrained to the basal 6 cm interval of Bed 28b in view of ammonoids, bivalves, conodonts, U-Pb ages and the EPME. The mass extinction interval is between Bed 27 and lower Bed 28a according to the EPME pattern at the Shangsi section, and the alternative interval between extinct Permian species and new Triassic species is from upper Bed 28a to lower Bed 28b. Unitary Association (UA) analysis of Lopingian conodonts reveals 15 unitary association zones (UAZs) based on seven important Lopingian sections of South China. Most of the UAZs correlate well with the standard biozonation, except for UAZ 3 to UAZ 5 and UAZ 12. The correspondence between UAZs and standard conodont biozones at the Shangsi section provides a practical example to understand controls on conodont UAZ determination. The Lopingian conodont succession is temporally calibrated by geochronologic ages, identified 405-kyr eccentricity cycles, and a Monte Carlo analysis at the Shangsi and Meishan sections. Updated ages for the base of the Lopingian and base of the Changhsingian are provided.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Aude Vincent, Sophie Violette, Guðfinna Aðalgeirsdóttir〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Catchments headed by temperate glaciers are severely impacted by climate change, and extensively studied from glaciological and surface hydrology perspectives. However groundwater in the same catchments is much more seldom mentioned, and even less studied.〈/p〉 〈p〉The few available studies found in the scientific literature tend to show a particularly high recharge of aquifers by glacial meltwater, a strong connection between surface and ground waters, and quite high hydraulic permeability in moraines and tills aquifers. New and more systematic studies could confirm and details these results. Such characteristics suggest that groundwater in coastal catchments headed by temperate glaciers could feed offshore fresh groundwater stocks. The role of potential deeper aquifers in fractured bedrock remains completely unknown.〈/p〉 〈p〉The numerous examples of natural hazards and of the sensitivity of water resources to the water cycle in catchments headed by temperate glaciers underline the importance of the study of hydrogeology, and of socio-economic aspects, in these catchments where population is glacier-dependant.〈/p〉 〈p〉The study of groundwater in catchments headed by temperate glaciers is just at the start and there is much to be studied.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Márton Veress〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The karren formation and karren features of bare slopes is studied. The occurrence of various karren features was measured on slopes with different inclination. The occurrence of various karren features on slopes has been presented according to slope inclination values. The slopes were put into slope categories and their karren features were given. Thus, the karren formation of the bare slopes of various karst types and karst features (glaciokarst, coastal karst, tropical karst, mediterranean karst, collapse dolines, gorges, caves etc.) can be described. It can be stated that on limestone with the increase of the inclination of the bearing slope, the diversity of karren features decreases and those of flow origin will be increasingly dominant. However, with the increase of slope inclination, features of flow origin will be increasingly simpler. On limestone, on slopes with a smaller dip and on slopes of less soluble rocks, the distribution of karren features of seepage origin increases. On glaciokarst, where bare slopes are widespread and of various inclination, karren are diverse and the distribution of various types is also considerable. In other karst areas, small-inclined slopes (coastal karst, tropical karst) or very large-inclined slopes (tropical karst, collapse dolines) are predominant and thus, the distribution of some karren features (e.g. rinnenkarren) is limited. The change of slope inclination may result in the change of karren formation. On glaciokarst, bare and subsoil karren formation are separated from each other, on mediterranean and tropical karst, they are less separated from each other and the latter prepares the former. On halite, the effect of slope inclination on karren formation may be modified by intensive dissolution. The karren formations of halite and tropical karst are partly similar which can be explained by intensive dissolution in both cases.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 16 November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Irina M. Artemieva〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉A new method for modeling the thermal structure of the lithosphere, termed thermal isostasy, is presented and used to calculate the lithosphere thickness and to predict geothermal heat flux in Europe and the adjacent off-shore regions. The method is based on analysis of topography deviations from the expected correlation between the Moho depth and topography. Anomalous topography is interpreted as caused by thermal anomalies in the lithosphere and by variations in the lithosphere thermal thickness. The new method allows for recovering the lithosphere thermal structure with a high lateral resolution and for testing the results by comparing the predicted and measured heat flux.〈/p〉 〈p〉The results for Europe, constrained by the regional seismic crustal model EUNAseis, demonstrate that the lithosphere thermal structure is controlled by both the geodynamic setting and the lithosphere age. The lithosphere of the East European craton ranges in thickness from ca. 140-180 km in the paleorifts to 200-220 km on average with local lithosphere roots down to ca. 300 km depth, such as in the south-central Proterozoic Finland, and local thinning to 〈100 km in the Peri-Caspian Basin and the Mezen rift system. Lithosphere thinning to 70-100 km beneath southern Norway may have caused its recent uplift. The craton to noncraton transition at depth roughly follows the geological boundary but with up to 200 km lateral deviations, which indicate reworking of the cratonic lithosphere along the craton edge. Paleoproterozoic – early Paleozoic Gondwana massifs of western Europe are distinct in having cold and thick lithosphere, typically 120-180 km thick, up to 200 km thick in the London-Brabant Massif, and only ca. 100 km in the Iberian Massif. The European Cenozoic Rift System is marked by a thin (〈80 km) and hot lithosphere that forms a linear belt from southern France to the North Sea. Lithosphere thinning to 50-60 km thickness beneath the Pannonian and Po basins may indicate the onset of oceanization. Cenozoic orogens of western Europe have lithospheric roots down to ca. 200-250 km associated with subducting lithospheric slabs, while a 80 km thick lithosphere beneath the Vrancea zone is in agreement with slab delamination. The Arctic shelf of the Barents Sea has a thick cratonic lithosphere with a sharp transition from a 120-150 km thick lithosphere of the western Barents Sea to a 175-230 km thick lithosphere of the eastern Barents Sea. The block with a ca. 150 km thick lithosphere in the North Atlantic region between the Aegir paleo-spreading and Norway may represent a continental terrane within the oceanic domain. The upper mantle temperature beneath the Bay of Biscay and the Black Sea is similar to the cratonic and is anomalously cold down to a 200 km depth.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0012825218304744-ga1.jpg" width="293" alt="Unlabelled Image" title="Unlabelled Image"〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Darrel G.F. Long〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The recognition of Archean fluvial deposits is complicated in many cases by post depositional deformation and metamorphism. Most surviving deposits can be categorized as deposits of alluvial fans with and without debris flows, and sand and gravel-bed braided rivers. Examples of possible intermediate to high sinuosity meandering systems have been tentatively identified in Africa, Australia and India: all lack clear evidence of lateral migration and can be reinterpreted in terms of esturine deposition, shallow tide-influenced marine, and deep-water mass-flow deposits respectively. Mudstone intervals in Archean fluvial strata are rare, and where present, are typically of silt grade. These may represent ponds developed within channel thalwegs, or where more extensive may be of lacustrine rather than floodplain origin. Prior to 3.2 Ga preserved fluvial deposits appear to be largely confined to the flanks of volcanic cones or plateau, perhaps reflecting globally high sea level combined with the small-scale of cratonic nuclei. The onset of modern style plate tectonics in the early Mesoarchean allowed for more extensive generation and preservation of fluvial strata: most of these are first cycle deposits, preserved in rift, strike-slip, and foreland basins, with rare examples accumulating in forearc and syn-tectonic piggy-back basins.〈/p〉 〈p〉This article is part of a special issue entitled: "Archean Earth Processes"; Edited by: Rajat Mazumder and Patrick Eriksson.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Kenneth A. Eriksson, Wilson S. McClung, Edward L. Simpson〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Climates during the Paleozoic varied from greenhouse to transitional to icehouse and siliciclastic successions deposited during those times have stratigraphic architectures consistent with magnitudes and frequencies of sea-level fluctuations at the time of deposition. Three Central Appalachian Basin Paleozoic successions, the Early Cambrian Chilhowee Group, the Late Devonian Foreknobs Formation, and the Early Pennsylvanian Breathitt Group, are compared and contrasted to develop models that relate stratigraphic architectures to greenhouse, transitional and icehouse conditions existing on Earth. Within the upper portion of the Early Cambrian Chilhowee Group, the Hampton and Erwin Formations represent a succession of 2 Myr (3rd-order) sequences consisting of stacked, 40–80 kyr (5th-order), marine parasequences that record low-magnitude, high-frequency sea-level changes consistent with greenhouse conditions. The Late Devonian Foreknobs Formation consists of a series of 0.8–1.0 Myr (3rd-order) composite sequences comprised of stacked unconformity-bounded, 225 to 450 kyr (4th-order) sequences, each containing 40 to 65 kyr (5th-order), marine parasequences. The bases of the unconformity-bounded sequences are marked by erosional surfaces (regressive surfaces of marine erosion, fluvial deposits, or paleosols) indicative of sea-level drops of 10 to 45 m consistent with a transitional greenhouse to icehouse climate. The Early Pennsylvanian Breathitt Group consists of stacked, unconformity-bounded, 100 kyr (4th-order) sequences that lack parasequences. Unconformity-bounded sequences are comprised of (from bottom to top): lowstand incised valley, braided alluvial deposits; transgressive tidal estuarine deposits; and progradational, highstand deltaic deposits. Depths of incised valleys and vertical transition into estuarine facies imply sea-level changes of 〉50 m consistent with icehouse conditions. This study demonstrates that siliciclastic successions preserve a record of sea-level changes consistent with greenhouse, transitional, and icehouse conditions on the Paleozoic Earth.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Guglielmo Stecca, Guido Zolezzi, D. Murray Hicks, Nicola Surian〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We analyse recent morphological evolution of braiding rivers of disparate regions of the Earth to develop and address the hypothesis that braiding of rivers tends to be reduced by human presence and related activities. Firstly, through a large-scale literature survey we observe generalised paths of bed degradation, channel narrowing and shift towards single-thread configuration in braided reaches due to multiple anthropogenic stressors. Secondly, we select three rivers from different geographic contexts characterised by complementary anthropic stressors for a detailed analysis (the lower Waitaki River in New Zealand, the middle Piave River in Italy and the lower Dunajec River in Poland) which shows that these rivers have undergone very similar trajectories of morphological change. In previous works, these morphodynamic changes have been related to the alteration of the fundamental physical processes of braided rivers, due to anthropogenic changes in constraints and controls. Here, a closer analysis of these alterations shows that analogous morphological evolutionary trajectories can result from very different paths of causation, i.e., from different management causes and different alteration of physical processes. Through the use of pattern predictors we analyse observed morphological trajectories and potential for recovery. We highlight the role of different geographic contexts as sources of constraints and drivers to the river evolution, with reference both to the physical and human environment, showing that the observed similar trajectories are the product of different local conditions and characteristics. These observations have implications for river management and restorations.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 1 November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Irina M. Artemieva〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Lithosphere thermal structure in Greenland is poorly known and models based on seismic and magnetic data are inconsistent, while growing awareness in the fate of the ice sheet in Greenland requires reliable constraints on geothermal heat flux (GHF) from the Earth's interior in the region where conventional heat flux measurements are nearly absent. The lithosphere structure of Greenland remains controversial, while its geological evolution is constrained by direct observations in the narrow ice-free zone along the coasts. The effect of the Iceland hotspot on the lithosphere structure is also debated.〈/p〉 〈p〉Here I describe a new thermal isostasy method which I use to calculate upper mantle temperature anomalies, lithosphere thickness, and GHF in Greenland from seismic data on the Moho depth, topography and ice thickness. To verify the model results, the predicted GHF values are compared to available measurements and show a good agreement. Thick (200–270 km) cratonic lithosphere of SW Greenland with GHF of ca. 40 mW/m〈sup〉2〈/sup〉 thins to 180–190 km towards central Greenland without a clear boundary between the Archean and Proterozoic blocks, and the deepest lithosphere keel is observed beneath the largest kimberlite province in West Greenland. The NW-SE belt with an anomalously thin (100–120 km) lithosphere and GHF of 60–70 mW/m〈sup〉2〈/sup〉 crosses north-central Greenland from coast to coast and it may mark the Iceland hotspot track. In East Greenland this anomalous belt merges with a strong GHF anomaly of 〉100 mW/m〈sup〉2〈/sup〉 in the Fjordland region. The anomaly is associated with a strong lithosphere thinning, possibly to the Moho, that requires advective heat transfer such as above active magma chambers, which would accelerate ice basal melting. The anomaly may extend 500 km inland with possibly a significant contribution of ice melt to the ice-drainage system of Greenland.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0012825218304847-ga1.jpg" width="352" alt="Unlabelled Image" title="Unlabelled Image"〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Juliane Hennig-Breitfeld, H. Tim Breitfeld, Robert Hall, Marcelle BouDagher-Fadel, Matthew Thirlwall〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Miri Zone in Sarawak contains thick Paleogene to Neogene sedimentary successions that extend offshore into the Sarawak Basin (Balingian and Central Luconia Provinces) and Sabah Basin. Exploration offshore has shown the Sarawak Basin in the South China Sea contains major hydrocarbon reservoirs. The sediments on land are age equivalents of the offshore successions and can be used to provide insights into their sedimentological and stratigraphic relations. However, because the rocks are found in mountainous regions covered by dense rainforest much of the stratigraphy in the Miri Zone is poorly known, as are timings and causes of major unconformities in the region that are essential for understanding the tectonic history, basin development, and sedimentary pathways. In this study we integrate fieldwork, U〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉Pb zircon dating, biostratigraphy, and light and heavy mineral analyses to present a revised stratigraphy for the region as well as paleogeographic maps, including major paleo-river systems for the main sedimentary basins. Rocks studied include parts of the Cretaceous to Eocene deep marine Rajang Group, fluvial to marginal marine sediments of the Oligocene to Early Miocene Tatau, Buan, Nyalau and Setap Shale Formations, and the Miocene sediments which are assigned to the Balingian, Begrih and Liang Formations in the Mukah-Balingian province, and the Belait Formation on Labuan.〈/p〉 〈p〉There is still much debate about the timings or even existence of some important unconformities offshore, such as the Middle Miocene Unconformity (MMU) and Deep Regional Unconformity (DRU). We propose to avoid the ambiguous time-based terminology that has been used for different events by different authors. Instead, our results from the on-land stratigraphy show two main unconformities in northern Sarawak; one at c. 37 Ma (Rajang Unconformity), marking the change from deep marine to fluvial – marginal marine sedimentation, and another one at c. 17 Ma (Nyalau Unconformity) which is related to widespread uplift in Borneo and changing river systems.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0012825218304835-ga1.jpg" width="500" alt="Unlabelled Image" title="Unlabelled Image"〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): María Isabel Arce, Clara Mendoza-Lera, María Almagro, Núria Catalán, Anna M. Romaní, Eugènia Martí, Rosa Gómez, Susana Bernal, Arnaud Foulquier, Michael Mutz, Rafael Marcé, Annamaria Zoppini, Giulia Gionchetta, Gabriele Weigelhofer, Rubén del Campo, Christopher T. Robinson, Alan Gilmer, Martin Rulik, Biel Obrador, Oleksandra Shumilova〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of fluvial networks. DRBs are often overlooked because they do not strictly belong to either domain of soil or freshwater science. Due to this dual character of DRBs, we suggest that concepts and knowledge from soil science can be used to expand the understanding of IRES biogeochemistry. Based on this idea, we propose that DRBs can be conceptually understood as early stage soils exhibiting many similarities with soils through two main forces: i) time since last sediment transport event, and ii) the development status of stabilizing structures (e.g. soil crusts and/or vascular plants). Our analysis suggests that while DRBs and soils may differ in master physical attributes (e.g. soil horizons vs fluvial sedimentary facies), they become rapidly comparable in terms of microbial communities and biogeochemical processes. We further propose that drivers of DRBs biogeochemistry are similar to those of soils and, hence, concepts and methods used in soil science are transferable to DRBs research. Finally, our paper presents future research directions to advance the knowledge of DRBs and to understand their role in the biogeochemistry of intermittent fluvial networks.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 186〈/p〉 〈p〉Author(s): 〈/p〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Rafael Marcé, Biel Obrador, Lluís Gómez-Gener, Núria Catalán, Matthias Koschorreck, María Isabel Arce, Gabriel Singer, Daniel von Schiller〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A large part of the world's inland waters, including streams, rivers, ponds, lakes and reservoirs is subject to occasional, recurrent or even permanent drying. Moreover, the occurrence and intensity of drying events are increasing in many areas of the world because of climate change, water abstraction, and land use alteration. Yet, information on the gaseous carbon (C) fluxes from dry inland waters is scarce, thus precluding a comprehensive assessment of C emissions including all, also intermittently dry, inland waters. Here, we review current knowledge on gaseous C fluxes from lotic (streams and rivers) and lentic (ponds, lakes, and reservoirs) inland waters during dry phases and the response to rewetting, considering controls and sources as well as implications of including ‘dry’ fluxes for local and global scale estimates. Moreover, knowledge gaps and research needs are discussed. Our conservative estimates indicate that adding emissions from dry inland waters to current global estimates of CO〈sub〉2〈/sub〉 emissions from inland waters could result in an increase of 0.22 Pg C year〈sup〉−1〈/sup〉, or ~10% of total fluxes. We outline the necessary conceptual understanding to successfully include dry phases in a more complete picture of inland water C emissions and identify potential implications for global C cycle feedbacks.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 190〈/p〉 〈p〉Author(s): Stephen R. Meyers〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉When Milankovitch cycles are preserved in the geologic record they provide a direct link between chronometer and climate change, and thus a remarkable opportunity to constrain the evolution of the surficial Earth System. The identification of such cycles has allowed exploration of the geologic record with unprecedented temporal resolution, and has spurred the development of a rich theoretical framework for climatic change. Accompanying these successes, however, has been a persistent skepticism: how does one reliably test for astronomical forcing/pacing in stratigraphic and paleoclimate data, especially when time is poorly constrained? From this perspective, it would seem that the merits and promise of astrochronology – a Phanerozoic time scale measured in 20,000 to 400,000 year increments – also serves as its Achilles heel, if the confirmation of such geologically short temporal rhythms defies rigorous hypothesis testing. The implications are substantial, since much of our understanding of paleoclimate change throughout the Cenozoic (and beyond) is firmly rooted in astrochronologic interpretation.〈/p〉 〈p〉In this study, a conceptual framework for assessing Earth System response to astronomical-insolation changes, and the propagation of that signal into the geologic record, is used as a guide to understand the nature of the problem of astrochronologic testing. This framework emphasizes three challenges – 〈em〉contamination, stratigraphic distortion〈/em〉, and 〈em〉temporal calibration〈/em〉. A statistical optimization method (TimeOpt; Meyers, 2015) is formulated as a solution to these three challenges, providing an approach for astrochronologic testing that objectively evaluates time scale uncertainty while simultaneously identifying an optimal model for climate and depositional system response to astronomical forcing. New extensions to the technique are presented, allowing explicit reconstruction of distortions to the primary forcing that are known to be omnipresent in the stratigraphic record. To illustrate the utility of this approach, it is applied to five well-studied stratigraphic series throughout the Phanerozoic, supporting their astronomical origin, and yielding constraints on the evolution of the Earth System and the astronomical solutions themselves. Future directions that build on this foundation are discussed, including the utility of process-based null models, approaches for Earth System transfer function reconstruction, and mapping out ancient Solar System behavior and Earth-Moon history using the geologic archive of Milankovitch cycles. The TimeOpt approach recognizes astronomy, geochronology, paleoclimatology and depositional system reconstruction as a unified geoscientific inverse problem.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Manuel Queißer, Mike Burton, Ryunosuke Kazahaya〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Geological CO〈sub〉2〈/sub〉 degassing is a fundamental Earth process but still quite poorly understood, since a thorough quantification with conventional measurement techniques is challenging. Optical remote sensing techniques have the potential to extend conventional measurement capabilities, enabling new insights into processes related to Earth’s CO〈sub〉2〈/sub〉 degassing. This article provides an integrated and pragmatic overview of existing and future remote sensing approaches suitable for geological CO〈sub〉2〈/sub〉 quantification and connects results from instrument research in optical remote sensing with possible applications in the Earth sciences. The paper aims to provide intercomparison by means of key parameters of very different remote sensing approaches. One of these parameters is the minimum detectable CO〈sub〉2〈/sub〉 flux, which is estimated for each remote sensing method herein. This may be used to identify a remote sensing platform for a specific Earth science problem related to CO〈sub〉2〈/sub〉 degassing. Six such prominent Earth science problems are detailed. Remote sensing technology for extraterrestrial CO〈sub〉2〈/sub〉 degassing is briefly examined. With respect to established in situ measurements, the main benefits of remote sensing include a safe measurement distance, spatially inclusive probing and swift measurements, while the main shortcomings include a generally lower measurement precision and the lack of commercially available turnkey solutions. While all six Earth science problems examined in this review will benefit to some extent from CO〈sub〉2〈/sub〉 remote sensing, remote sensing is unlikely to replace conventional in situ probing entirely in the near future, but can be seen as complementary to conventional measurement approaches. Earth science problems that could immediately benefit from CO〈sub〉2〈/sub〉 remote sensing include a comprehensive survey of the significant but highly uncertain CO〈sub〉2〈/sub〉 flux of the East African Rift System, comparing volcanic CO〈sub〉2〈/sub〉 concentrations from satellite borne remote sensing with ground-based remote sensing, and integration of CO〈sub〉2〈/sub〉 remote sensing data into automated volcanic unrest prediction.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Rajat Mazumder, Shuvabrata De, P.V. Sunder Raju〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉India has perhaps the richest Paleoarchean to Paleoproterozoic crustal components on Earth (Miller et al., 2018). Notwithstanding this, much of the Indian subcontinent remains unexplored compared to other ancient cratons in North America, Australia, Brazil and Africa. There are five Archean cratonic nuclei in India (the Aravalli, Bundelkhand, Singhbhum, Bastar and the Dharwar) with well-preserved Proterozoic supracrustal sequences. This paper critically reviews the Paleoarchean to Paleoproterozoic supracrustal record of the Indian subcontinent with special emphasis on the Archean-Paleoproterozoic transition, which is generally placed at ~2.5 Ga based on the emplacement age of the Great dyke of Zimbabwe. In general, the Archean-Paleoproterozoic transition in Indian cratonic blocks is associated with high continental freeboard condition. Unlike North America, South Africa and Western Australia, the Indian cratonic blocks (except Bastar) are devoid of Paleoproterozoic glacial diamictite (Mazumder et al., 2015). However, similar to the Pongola Supergroup of South Africa, there are evidences of Neoarchean glaciation in Dharwar (Ojakangas et al., 2014). In contrast to the global scenario of extensive development of BIF across the Archean-Paleoproterozoic transition, the Indian Paleoproterozoic successions are devoid of Banded Iron Formation (BIF) (except the 1.85 Ga old BIF in Bundelkhand). In contrast, the majority of the Indian BIFs are of Paleoarchean or Neoarchean age. Thus, the geodynamic and supracrustal data collected from five Indian Archean cratonic blocks do not correspond uniquely and precisely to a global change in tectonic style, onset of Neoarchean global magmatism and rifting, or lithostratigraphic and environmental changes suggested across the Archean-Paleoproterozoic transition (Van Kranendonk et al., 2012). Therefore, a revision and redefinition of the Archean-Proterozoic boundary is outstanding.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): Massimo Zecchin, Octavian Catuneanu, Mauro Caffau〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The wave-ravinement surface (WRS) is a surface of sequence-stratigraphic significance that forms in shallow-water settings during transgression. It develops progressively landward during shoreface retreat due to wave action, which erodes the substrate and leads to sediment bypass in the offshore direction. The WRS may rework previously formed surfaces, such as the maximum regressive surface (also known as the transgressive surface) and the subaerial unconformity, becoming a systems tract and/or sequence boundary. Due to the associated lithological contrast between underlying and overlying deposits and the presence of lags and/or shell pavements, the WRS has a very good appearance in both outcrop and cores and is often used as the boundary of shallow-marine stratigraphic sequences. The WRS, therefore, represents an important lithological and paleo-environmental break, and its recognition is significant for reconstructing stratigraphic architectures and the history of relative sea-level change, as well as for reservoir characterization. Several controlling factors govern the development of the WRS and of the associated deposits; they include the accommodation to sedimentation (A/S) ratio, environmental energy, topographic gradient, roughness and lithology of the substrate. Relatively low rates of relative sea-level rise and sediment supply, high wave energy, steep topographies and easily erodible substrates favor the development of the WRS. These factors interact, leading to a high variability in the amount of erosion, shape, length along depositional dip and deposits associated with these surfaces. WRSs may be classified based on either underlying or overlying deposits, or a combination of both. A classification based on the deposits that underlie the WRS helps to determine the location of the studied outcrop along depositional dip, whereas a classification based on the deposits that overlie the WRS afford insights into the physical conditions that accompanied its formation. However, the best description of the WRS in terms of location of a considered outcrop, physical conditions under which the WRS developed and their lateral variability, type of substrate, as well as its practical significance for reservoir modeling is achieved with a combination of the two criteria.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): José López-Gómez, Fidel Martín-González, Nemesio Heredia, Raúl de la Horra, José F. Barrenechea, Patricia Cadenas, Manuel Juncal, José B. Diez, Violeta Borruel-Abadía, David Pedreira, Joaquín García-Sansegundo, Pedro Farias, Carlos Galé, Marceliano Lago, Teresa Ubide, Gabriela Fernández-Viejo, Georges Gand〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Pyrenean-Cantabrian Orogen arose through the collision of the Iberian and Eurasian plates, mostly in Cenozoic times. This orogen comprises two main mountain ranges, the Pyrenees to the east, and the Cantabrian Mountains to the west. To date, the early Alpine tectono-sedimentary phases preserved in the Cantabrian Mountains, of Permian and Triassic age, have been considered independently from the same phases in neighbouring basins of SW Europe, and even from the eastern part of the same orogeny (the Pyrenean orogeny). In consequence, the beginning of the Alpine cycle in the Cantabrian Mountains has been interpreted within a specific geodynamic context, far from the general evolutionary phases of the western Peri-Tethys basins.〈/p〉 〈p〉Through detailed field work, including geological mapping, sedimentology, lithostratigraphy and petrology of volcanic rocks, and new palaeontological data, here we define several new lithostratigraphical formations and five new tectono-sedimentary cycles (TS I-V) for the initial phases of evolution of the Mesozoic Basque-Cantabrian Basin, interrupted by periods of tectonic stability. To complete this information, we include data from an onshore borehole (Villabona Mine) and two offshore boreholes constrained by 2D reflection seismic profiles acquired in the North Iberian continental platform. The main tectono-sedimentary cycles, related to the deposition of five major identified lithostratigraphic units, can be described as follows:〈/p〉 〈p〉TS I (late Gzelian-early Asselian), relating to the late Variscan deformation and preserved in a single outcrop in all the Cantabrian Mountains (San Tirso Formation). This formation is constituted by medium-distal alluvial fan deposits in which humid intervals predominate, forming some thin coal beds.〈/p〉 〈p〉TS II (Asselian-Sakmarian), a post-Variscan extensional phase with associated calc-alkaline magmatism, represented by profuse volcanic and volcanosedimentary intercalations in the early Permian sedimentary basins (Acebal Formation) and small plutons in surrounding areas.〈/p〉 〈p〉TS III (Kungurian), or reactivation of the post-Variscan extension leading to alluvial and lacustrine carbonate sedimentation in arid climate conditions, which do not change during the rest of the Permian and Triassic periods (Sotres Formation). A generalized karstification in the basin represents the end of Permian deposition, followed by an interruption in sedimentation longer than 30 Myr. The Permian tectono-sedimentary cycles (TS II and TS III) are contemporary with Variscan belt collapse and the basins are controlled by extensional reactivation of N〈em〉E〈/em〉-SW and E-W Variscan structures, and NW-SE late Variscan structures.〈/p〉 〈p〉TS IV (late Anisian–middle Carnian), renewed sedimentation in more extensive basins, precursors of the great Mesozoic Basque-Cantabrian Basin. This cycle is represented by fluvial deposits (Cicera Formation, or Buntsandstein facies), which are interrupted by the first Mesozoic marine ingression (Rueda Formation, or Muschelkalk facies).〈/p〉 〈p〉TS V (Norian-Rhaetian), or shallow marine carbonate deposits (Transición Formation) related to increasingly compartmentalized sub-basins, controlled by normal faults. This final TS is broadly connected with different basins of the western Peri-Tethys domain.〈/p〉 〈p〉The identification of units TS I-V in the Cantabrian Mountains along with the volcanic character of TS II, all indicate the development of a common post-Variscan to early Alpine tectono-sedimentary evolution for the whole Pyrenean-Cantabrian realm.〈/p〉 〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews, Volume 188〈/p〉 〈p〉Author(s): W. Krijgsman, A. Tesakov, T. Yanina, S. Lazarev, G. Danukalova, C.G.C. Van Baak, J. Agustí, M.C. Alçiçek, E. Aliyeva, D. Bista, A. Bruch, Y. Büyükmeriç, M. Bukhsianidze, R. Flecker, P. Frolov, T.M. Hoyle, E.L. Jorissen, U. Kirscher, S.A. Koriche, S.B. Kroonenberg〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Pontocaspian (Black Sea - Caspian Sea) region has a very dynamic history of basin development and biotic evolution. The region is the remnant of a once vast Paratethys Sea. It contains some of the best Eurasian geological records of tectonic, climatic and paleoenvironmental change. The Pliocene-Quaternary co-evolution of the Black Sea-Caspian Sea is dominated by major changes in water (lake and sea) levels resulting in a pulsating system of connected and isolated basins. Understanding the history of the region, including the drivers of lake level and faunal evolution, is hampered by indistinct stratigraphic nomenclature and contradicting time constraints for regional sedimentary successions. In this paper we review and update the late Pliocene to Quaternary stratigraphic framework of the Pontocaspian domain, focusing on the Black Sea Basin, Caspian Basin, Marmara Sea and the terrestrial environments surrounding these large, mostly endorheic lake-sea systems.〈/p〉〈/div〉 〈/div〉

Beschreibung: 〈p〉Publication date: Available online 17 October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Earth-Science Reviews〈/p〉 〈p〉Author(s): Feifei Zhang, Thomas J. Algeo, Ying Cui, Jun Shen, Huyue Song, Hiroyoshi Sano, Harry D. Rowe, Ariel D. Anbar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Smithian-Spathian boundary (SSB) was an interval characterized by a major global carbon cycle perturbation, climatic cooling from a middle/late Smithian boundary hyperthermal condition, and a major setback in the recovery of marine necto-pelagic faunas from the end-Permian mass extinction. Although the SSB has been linked to changes in oceanic redox conditions, key aspects of this redox variation (e.g., duration, extent, and triggering mechanisms) and its relationship to coeval climatic and biotic changes remain unresolved. Here, we report a high-resolution middle Smithian to middle Spathian U isotope (δ〈sup〉238〈/sup〉U) record based on marine carbonates of the Zuodeng (South China) and Jesmond (British Columbia) sections to investigate the timing and global extent of ocean-redox variation across the SSB. Our δ〈sup〉238〈/sup〉U record reveals values similar to or slightly heavier than modern seawater (-0.39‰) during the middle Smithian, a rapid negative shift to highly negative values during the early late Smithian, a positive shift at the SSB, and a rapid shift back to more negative values in the early-middle Spathian. A simple U-isotope mass balance modeling suggests that the global area of anoxic seafloor expanded strongly during the late Smithian and the early-middle Spathian (covering ~11% of total seafloor area), but that it contracted sharply during the SSB (~2%). The redox pattern documented by our δ〈sup〉238〈/sup〉U record shows a good first-order correspondence to tropical sea-surface temperature (SST) data for the Smithian-Spathian. In particular, peak anoxia coincided with the middle/late Smithian boundary hyperthermal event, and diminished anoxia with a pronounced decline in SSTs at the SSB. The temporal correlation between anoxia and low biodiversity levels of many marine clades (e.g., conodonts and ammonoids) during the late Smithian indicates that oceanic anoxia may have played a role in the SSB biocrisis.〈/p〉〈/div〉 〈/div〉