ALBERT

Description: The mechanisms of thinning of the lithosphere and destruction of the North China Craton have been debated in recent decades. Their causal link with regional tectonic extension is well exemplified by the exhumation of the Wulian metamorphic core complex (mcc), along the Sulu orogenic belt to the SE of the North China Craton. The Wulian mcc is a Cordilleran type mcc with a northwestward dipping low-angle master detachment fault zone (the Wulian detachment fault zone), an Early Cretaceous supradetachment basin (the Zhucheng Basin) and a lower plate of ultrahigh-pressure metamorphic rocks in the Sulu orogenic belt. Synthetic structural, fabric and thermochronological data suggest that tectonic extension is responsible for the exhumation of the lower plate and triggered syn- and post-tectonic magmatisms. A new cooling path for the lower plate rocks indicates that the lower plate was exhumed at a high rate of 2.0 km Ma –1 from before c . 128 Ma to 123 Ma and at a moderate rate of 0.35 km Ma –1 from 81 to 61 Ma. The rapid exhumation is consistent temporally with the sedimentation of terrestrial deposits of the Laiyang Group in the Zhucheng supradetachment basin. The post-kinematic granitic intrusions are dated as c. 122 Ma, which marks the cessation of rapid exhumation of the lower plate. Vast amount of andesitic volcanic rocks from 120 to 105 Ma in the Qingshan Group in the Zhucheng Basin may be related to the peak of lithospheric thinning in the Wulian area. These data highlight the importance of regional tectonic extension in the formation of the detachment fault zone and the exhumation of the Wulian mcc, and in triggering syn- and post-kinematic magmatisms. The scenario is consistent with the parallel extension tectonics model in which tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle, resulted in the loss of some of the subcontinental roots, gave rise to the exhumation of the mccs, and triggered plutonic emplacement and volcanic eruptions of hybrid magmas.

Description: New geochemical data for mafic intrusions within the Eocene Nisai Formation along the suture zone between the Indian and Eurasian plates are used to constrain their petrogenesis and assess the local tectonics and mantle dynamics. Petrological and geochemical data indicate that these alkalic intrusions have moderately enriched incompatible trace element compositions similar to ocean island basalt magmatism. Modelling suggests that these intrusions are the result of 1–5% melting of a deep, enriched, predominantly garnet lherzolite, with a small amount of subduction-derived fluids. These melts then underwent fractional crystallization at lithospheric depths of c . 30 km. Supplementary materials: Detailed information on each analysed sample including field notes and latitude and longitude, replicate analysis of standards, and fractional crystallization modelling are available at http://www.geolsoc.org.uk/SUP18893 .

Description: Composite hematite–silica structures recovered from a siltstone bed in the Elatina Formation of South Australia include (1) sub-circular to whorl-shaped forms, (2) elongate to half-moon-shaped forms and (3) and lozenge-shaped forms locally linked into chains. They range from 200 to 500 µm in diameter and are interpreted as eukaryote tests. Evidence for internal etching of a calcite core of some tests indicates that at least some of the hematite–silica fabrics were acquired through replacement. Carbon isotope values of –20 13 C are suggestive of precipitation by microbial activity, and imply a change in ambient fluid chemistry associated with a pH reduction. The tests occur within sandstone beds that were deposited on a tidally modulated braidplain during the Marinoan glaciation at the end of the Cryogenian. The quartz grains in the sandstone sample lack the typical textures (surface striae, internal fractures or irregular grain boundaries) expected for glacially transported material. Thus, on textural grounds we argue that the eukaryote tests represent a proglacial ecosystem during a late Cryogenian snowball Earth event. Supplementary material: Video files of digital X-ray tomographs (μCT) in the longitudinal and transverse planes are available at: https://doi.org/10.6084/m9.figshare.c.2209723 .

Description: Shetland occupies a unique central location within the North Atlantic Caledonides. Thirty-three new high-precision Rb–Sr mineral ages indicate a polyorogenic history. Ages of 723–702 Ma obtained from the vicinity of the Wester Keolka Shear Zone indicate a Neoproterozoic (Knoydartian) age and preclude its correlation with the Silurian Moine Thrust. Ordovician ages of c . 480–443 Ma obtained from the Yell Sound Group and the East Mainland Succession constrain deformation fabrics and metamorphic assemblages to have formed during Grampian accretionary orogenic events, broadly contemporaneously with orogenesis of the Dalradian Supergroup in Ireland and mainland Scotland. The relative paucity of Silurian ages is attributed to a likely location at a high structural level in the Scandian nappe pile relative to mainland Scotland. Ages of c . 416 and c . 411 Ma for the Uyea Shear Zone suggest a late orogenic evolution that has more in common with East Greenland and Norway than with northern mainland Scotland. Supplementary material: Detailed appraisal of biotite petrography is available at http://www.geolsoc.org.uk/SUP18887 .

Description: The Unst Ophiolite is the best exposed of a chain of early Ordovician ophiolites in the Scottish Caledonides and is widely regarded as having formed in a supra-subduction zone setting within the Iapetus Ocean. Reinterpretation of sheeted dykes suggests that it formed as an oceanic core complex, presumably during subduction roll-back immediately prior to obduction onto the Laurentian margin. A new U–Pb zircon age of 484 ± 4 Ma for development of the metamorphic sole places a lower limit on the timing of obduction, which was subsequently followed by regional-scale crustal thickening and Barrovian metamorphism during the Grampian orogenic event. Supplementary material: Analytical methods, CL images of representative zircon grains and an LA-ICP-MS U–Th–Pb zircon data table are available at www.geolsoc.org.uk/SUP18814 .

Description: Slip along low-angle normal faults is a mechanical paradox requiring activation of strain weakening mechanisms. Microstructures present in the slip zones of incipient low-angle normal faults cutting carbonates in the Southern Apennines of Italy show that slip was promoted by two weakening mechanisms producing a reduction of the friction coefficient: (1) high pore fluid pressures; (2) dynamic weakening related to thermal decomposition indicated by decarbonation microstructures and concomitant localized dynamic calcite recrystallization. Furthermore, as a consequence of thermal decomposition, nanoparticles occur as infilling of injection veins, suggesting that powder lubrication processes are active along the slip surface during seismic slip. Supplementary materials: A geological sketch of the study area, detailed field photographs of the studied faults and detailed micrographs are available at http://www.geolsoc.org.uk/SUP18806 .

Description: Vulcanian explosions generate some of the most hazardous types of volcanic phenomena, including pyroclastic density currents. Non-vertical directionality of an explosion promotes asymmetrical distribution of proximal hazards around the volcano. Although critical, such behaviour is relatively uncommon and has been seldom documented. Here we present, for the first time, evidence both from geophysical monitoring and field survey data that records the occurrence of such an event. Thermal imagery captures a Vulcanian explosion at Soufrière Hills Volcano, Montserrat, which occurred during a large partial lava dome collapse in February 2010, and was inclined at about 25° from the vertical in a northerly direction. Pyroclastic products were preferentially distributed to the north and included: an unusual pumice boulder deposit that we propose was formed by a dilute pyroclastic density current; pumice flow deposits; and a proximal lapilli and block fallout lobe. The inclined nature of the explosion is attributed to the asymmetric geometry around the vent. The explosion-derived pyroclastic density currents had notably lower velocities than those associated with lateral blasts, which, we suggest, result from a separate and distinct mechanism. These inclined explosions present an additional mechanism that is able to generate directed pyroclastic density currents, with consequent implications for hazard assessment.

Description: U–Pb detrital zircon data from the Baixo Alentejo Flysch Group in the South Portuguese Zone show significant age differences between formations. The Visean Mértola Formation and Serpukhovian to early Bashkirian Mira Formation are dominated by zircons in the 316–388 Ma age range, whereas the late Bashkirian to late Moscovian Brejeira Formation is dominated by zircons with an age range of 498–687 Ma. Detrital zircons spanning an age range of 0.9–1.1 Ga are present in the Brejeira Formation but are absent in the Mértola and Mira formations. Detrital zircon ages of the Mértola and Mira formations indicate provenance from an extra-basinal source (Ossa–Morena Zone) with a minor intra-basinal contribution (South Portuguese Zone). The abundant presence of detrital zircon with age ranges of 500–750 and 0.9–1.1 Ga in the Brejeira Formation suggests a sediment source from the Avalon–Meguma terranes with limited recycling from the SW Portugal Domain. The different inferred source areas for the Baixo Alentejo Flysch Group formations are attributed to the presence of a forebulge that was formed in Mid-Visean times during the foreland phase of the South Portuguese Zone. The forebulge acted as a physical barrier separating sub-basins that accumulated the Mértola–Mira and Brejeira sediments respectively.

Description: We propose a new volcanological interpretation of Santorini’s intracaldera fill deposits as revealed by seismic reflection profiles. This interpretation, along with supplementary gravity and geophysical studies, reveals three distinct volcaniclastic units (1–3). From top to bottom these units are attributed to (1) modern infilling sediment, (2) shallow marine phreatomagmatic volcanism associated with the relatively recent formation of the Kameni Islands, and (3) downfaulted ‘Minoan’ pyroclastic deposits, which formed during caldera collapse towards the end of the Bronze Age eruption. Estimates of the volumes of the seismic units and Kameni Islands yield a dense rock equivalent magma volume of 4.85 ± 0.7 km 3 . The average rate of volcanism over the past c . 3641 years is estimated at 1.3 x 10 –3 km 3 a –1 , and is similar to the rate since the AD 1707 eruption of 1.2 x 10 –3 km 3 a –1 based on historical lava volume estimates.

Description: The large palaeosinkholes located in the NW of Gozo (central Mediterranean Sea, Malta) offer excellent exposures that provide information on the geometry and kinematics of large karst-related collapse structures. Detailed geological analysis of these peculiar palaeosinkholes indicates that deep-seated evaporite dissolution is the most feasible hypothesis to explain their formation, according to the following evidence. (1) Several structures have been formed by progressive foundering of cylindrical blocks with limited internal deformation as revealed by the synsedimentary subsidence recorded by their Miocene sedimentary fill. This subsidence mechanism is more compatible with interstratal dissolution of evaporites than karstification and cave development in limestone formations. (2) The dimensions and deformation style of the palaeosinkholes are similar to those of other collapse structures related to deep-seated dissolution of salt-bearing evaporites. (3) The arcuate monocline associated with some of these collapse structures is also a characteristic feature of subsidence related to dissolution of evaporites. However, no major evaporite formations have been documented so far in the subsurface of the Malta Platform. Supplementary material: Detailed descriptions of the collapse structures of the island of Gozo (Malta, central Mediterranean Sea) are available at www.geolsoc.org.uk/SUP18808 .

Description: The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound top. Macroscopically the crusts form decimetre-sized, cone-shaped domal aggregates, stalactites and stalagmites. Microfabric and morphology identify them as microbially mediated speleothems in a dark environment. Combined Sr and C isotope values indicate a formation of the speleothems from meteoric waters without influence of a significant soil horizon. For the first time the age of the speleothems can be precisely constrained by 13 C whole-rock and brachiopod shell isotope data to the mid-Hirnantian. Repeated and/or prolonged subaerial exposure of the Boda mud mounds during the Hirnantian is evident from karst surfaces and early cements in the mound capping carbonates. The speleothems and the karst surfaces record an estimated sea-level fall in the range of 80–130 m within the time window of the Hirnantian Isotopic Carbon Excursion. This massive regression coincides with maximum ice sheet extent inferred from sections in West Gondwana. Supplementary material: 87 Sr/ 86 Sr isotope ratio of selected brachiopod shells and results of Energy-dispersive-X-ray spectroscopy are available from http://www.geolsoc.org.uk/SUP18809

Description: Systematic measured profiles on a regional scale are used to document the distribution of noritic and amphibolitic sills (787 in total) in the largely sedimentary latest Archaean–early Proterozoic succession of the Transvaal Supergroup in northeastern South Africa. An aggregate thickness of over 2.2 km of sills intruded this 12 km thick succession. The proportion of sill to sill plus sedimentary rock increases upward (average 16%), towards the overlying mafic phase of the Bushveld Complex. The average thickness of sills is 34 m, but increases in the same sense. The emplacement level of the Bushveld Complex transgresses across some 5 km of the stratigraphy of the upper formations of the Transvaal Supergroup. A node of maximum intensity of noritic sill intrusion is developed in these uppermost strata adjacent to the location where the transgressive relationship is most pronounced. The structural styles of the Transvaal Supergroup strata influence intensity of sill intrusion. Other factors being equal, maximum intrusion intensity is associated with areas of shallow homoclinal dip (〈20°) and minimum intensity with areas of steeper dip and folding. A lithological control on sill emplacement is also documented, with quartzite- and shale-dominated formations being more heavily intruded than dolomite and basaltic lava. Supplementary material: A spreadsheet including all 440 formation traverses including grid references, formation thicknesses, and number and thicknesses of every sill therein is available at http://www.geolsoc.org.uk/SUP18807 .

Description: Volcanism across the North Tanzanian Divergence Zone (NTD), part of the East African Rift System, occurred episodically from the late Miocene to Recent. Here, we present a summary of previously published K–Ar and 40 Ar/ 39 Ar ages, new 40 Ar/ 39 Ar ages, and geochemical and Sr–Nd–Pb isotopic analyses on samples collected from several volcanoes distributed across the NTD: Burko, Monduli, Tarosero, Ketumbeine, Gelai, Kerimasi and Meru. The locus of volcanism over this period progressed from the southwestern portion of the NTD to the north and east, with a main pulse occurring at about 2.3 Ma, possibly marking the inception of a main rifting event. We model the source of the NTD volcanic rocks as a metasomatized subcontinental lithospheric mantle that includes minor and variable amounts of garnet and amphibole. REE data indicate variations in residual garnet content, consistent with varying depth of melt separation. Radiogenic isotopic data show systematic variations requiring the involvement of up to three components. Two alternative but not exclusive tectonic scenarios are proposed: one requiring the involvement of contributions from recent plume-related fluids, and one explaining the observed geochemical variations by melting of a lithosphere layered by multiple metasomatic events. Supplementary material: Details of analytical methods, operating system and calibration methods, a summary table of the recalculated 40 Ar/ 39 Ar and K–Ar NTD ages, a complete set of detailed release spectra analysis and dating figures, 40 Ar/ 39 Ar incremental heating data and analytical conditions, and examples of NTD calculated fractional crystallization modes are available at http://www.geolsoc.org.uk/SUP18813 .

Description: The temporal change of redox conditions of the Yangtze ocean has been revealed by investigating the Ediacaran–Cambrian transition section at Zhalagou, South China. During the earliest Cambrian, cherts and shales were deposited under an anoxic and ferruginous bottom water with significantly increasing total organic carbon and P contents, and negative shift in kerogen 13 C values in the lowest part of the section. Euxinic bottom water conditions occurred during the earliest Cambrian Stage 2, with the surface water dominated by N 2 utilization by cyanobacteria or sulphur bacteria leading to negative kerogen 15 N values. During Stage 3, dissolved oxygen and sulphate concentrations were significantly increased, and thus the oxidized surface water and the redox transition zone overlying a euxinic bottom water may have been expanded, resulting in an increase in kerogen 15 N increasing to 2–4, a decrease in pyrite 34 S decreasing to as low as –24.6 and differences in 34 S values between kerogen and pyrite as high as 37. This period coincided with the abrupt appearance of large-body metazoans. Thus, the expanding oxic surface water may have reinforced the evolution of animals or vice versa. Interestingly, kerogen 34 S values show negative relationships to FePy/FeHR ratios and pyrite sulphur contents, indicating that they can be used to reflect redox conditions, with the lightest values being obtained from euxinic environments.

Description: Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion: Ediacaran–Cryogenian ( c . 0.55–0.8 Ga), Tonian–Stenian (0.85–1.2 Ga), Palaeoproterozoic ( c . 1.8–2.2 Ga) and Archaean ( c . 2.5–3.3 Ga). Five samples contain very minor Palaeozoic (Cambrian) zircons and six samples contain minor but significant zircons of Middle and Early Mesoproterozoic (Ectasian–Calymmian, 1.6–1.8) age. These data highlight the transition from an arc environment to a stable platform following the opening of the Rheic Ocean. Variations in detrital zircon populations in Middle–Late Devonian times reflect the onset of Variscan convergence between Laurussia and Gondwana. The presence of a high proportion of zircons of Tonian–Stenian age in Devonian sedimentary rocks may be interpreted as (1) the existence of a large Tonian–Stenian arc terrane exposed in the NE African realm (in or around the Arabian–Nubian Shield), (2) the participation, from the Ordovician time, of a more easterly alongshore provenance of Tonian–Stenian zircons, and (3) an increase in the relative proportion of Tonian–Stenian zircons with respect to the Ediacaran–Cryogenian population owing to the drift of the Avalonian–Cadomian ribbon continent, or the progressive burial of Ediacaran–Cryogenian rocks coeval with the denudation of older source rocks from the craton interior. Supplementary material: Tables with the analytical data and the geochronological results are available at http://www.geolsoc.org.uk/SUP18812 .

Description: In the southern winter of 1970, a phreatomagmatic eruption occurred in the northern part of Deception Island (South Shetland Archipelago, Antarctic Peninsula). The eruption, with no eye-witnesses to the event, occurred in the same general area as the 1967 eruption, but with new, more widely distributed vents. Two contrasting groups of craters were formed in the 1970 eruption, showing that different active fissures and eruptive dynamics were operating. One group consists of ‘maar-like’ craters, whereas the other comprises conical edifices. The 1970 eruption can be classified as volcanic explosivity index (VEI) 3, with mainly phreatomagmatic phases that generated a bulk volume of about 0.1 km 3 of pyroclastic material and an eruptive column at least 10 km high, from which fallout deposits are recognized more than 100 km to the NE. The 1970 eruption was similar to that of 1967 and together these two eruptive events show how eruption dynamics can be controlled by the uppermost part of the volcano substrate and the width and orientation of the eruptive fissure. These influence magma–water interaction and hence may imply different eruptive phases and associated volcanic hazards. Supplementary material: Granulometric and component histograms of the samples that are not shown in Figure 4 are available at http://www.geolsoc.org.uk/SUP18761 .

Description: Neoproterozoic oceans provided the setting for the rise of animals, yet little is known of their chemical composition. Marine carbonates from the Cryogenian Oodnaminta Reef Complex, South Australia, reveal the chemical structure of a Neoproterozoic ocean. Pseudo-depth profiles from shallow- to deep-water reef facies have been constructed from geochemical and sedimentological analysis of marine cements. Evidence suggests that under a peritidal oxic–anoxic chemocline, the water column was largely anoxic, strongly ferruginous and had a chemistry profoundly different from that of modern seawater. These geochemical data suggest early Archaean-like conditions for this late Cryogenian ocean, posing problems for metazoan evolution in extremely anoxic conditions. Supplementary material: Detailed methods and data tables are available at www.geolsoc.org.uk/SUP18764 .

Description: U–Pb ages and Hf isotope data were obtained for zircon from amphibole-rich mafic to ultramafic rocks from the Adamello batholith and the Bergell pluton, the largest Palaeogene intrusions of the Alpine Orogen. The 206 Pb/ 238 U age pattern of U–Pb concordant dates from the Adamello mafic rock shows a major crystallization event at c . 41 Ma and older age peaks at c . 50 and c . 45 Ma. Hornblendite and amphibole gabbro samples of the Adamello batholith have zircon with initial Hf of c . +9.0 and c . +7.0, respectively. Amphibole gabbro and diorite samples of the Bergell pluton yield a younger age of c . 31 Ma and have zircon with lower initial Hf ( c . +4.0). We propose that the amphibole-rich rocks from the Adamello batholith originated from a depleted mantle source activated by the subduction of the Ligurian–Piedmontese Basin. The amphibole-rich rocks from the Bergell pluton formed 10–15 Ma later than the Adamello counterparts by melts derived from a mantle sector metasomatized by the subduction of the Valais Basin. The enriched Hf isotopic signature of the amphibole-rich rocks from the Bergell pluton is therefore interpreted to reflect the peculiar lithostratigraphy of the Valais Basin or a primary feature of the newly activated mantle source. Supplementary material: (1) A map showing the location of analysed samples and table with GPS coordinates of the samples, (2) data tables for U–Pb in zircon determined by LA-ICP-MS, (3) data tables for Hf isotopes in zircon, (4) U–Pb and Hf isotope analytical methods, (5) cathodoluminescence images of analysed zircon from the amphibole-rich mafic rocks of the Adamello and Bergell intrusions, and (6) a U–Pb concordia diagram for zircon of the Adamello amphibole gabbro are available at www.geolsoc.org.uk/SUP18763 .

Description: The only place where Neogene–Quaternary rocks crop out for the entire Tuscan Archipelago in the Northern Tyrrhenian Sea is the island of Pianosa. In particular, the Miocene deposits record the depositional and tectonic evolution of the Northern Tyrrhenian region during this time period. These deposits are subdivided into two successions separated by a low-angle unconformity. The older, middle Burdigalian succession represents a calciturbidite shallow marine system, whereas the younger late Tortonian–early Messinian succession comprises a continental alluvial system that evolves upwards into a lagoonal–marginal marine environment. Here we present sedimentological, palaeontological and petrographical data that support a new stratigraphic and palaeogeographical framework for reconstructing the opening of the Northern Tyrrhenian back-arc basin. The early Miocene succession records a pre-rift marine depositional phase followed by a late Burdigalian–Langhian erosional phase. This was followed by a period of synrift continental-marginal deposition, as recorded by the late Miocene succession, terminated by an important phase of uplift, probably induced by the start of magmatic activity in the Tuscan Archipelago area.

Description: Microbial carbonates contain valuable chemical, isotopic and molecular information regarding the Precambrian Earth. They record shallow-water information complementary to deep ocean proxies, such as banded iron formation and black shale. Six groups of well-preserved stromatolites illustrate how the rare earth elements (REE) are used for chemical investigation. The first task is to test whether the REE inventory of carbonate is compromised by clastic, volcanic, or diagenetic contaminants. Once the cleanliness has been verified, the shale-normalized REE pattern can be used to distinguish between marine and lacustrine settings. For marine carbonates, it is possible to distinguish between restricted basin and open marine settings and for thick platform limestones the relative water depth can be inferred from REE systematics. The studied shallow-water stromatolites range in age from 2.52 to 3.45 Ga. They contain no evidence from the behaviour of the redox-sensitive element cerium that free oxygen levels in the shallow sea approached concentrations beyond a trace gas by 2.52 Ga. Compared with abiotic early diagenetic marine carbonate cements, microbial carbonate is strongly enriched in REE. This may itself not yet serve as a biomarker, but it is regarded as a necessary prerequisite for a sample to qualify for biomarker studies.

Description: A new structural examination of Palaeoproterozoic high- P granulites on South Harris, NW Scotland, when integrated with previous geochronological, structural and metamorphic studies on key areas of the Lewisian Complex, suggests the existence of two distinct tectonothermal cycles within the Palaeoproterozoic ‘Laxfordian Event’, which on South Harris are separated by a 〉100 myr hiatus in deformation. The older cycle, from c . 1.91 to 1.85 Ga, records the development of an active continental margin on the Archaean gneisses that dominate the Complex, and the subsequent onset of continent–continent collision; this represents the continuation of the Nagssugtoqidian orogen of Greenland. Evidence for this is concentrated in allochthonous slivers of the former active continental margin displaced during the younger cycle. The younger cycle, around 1.75–1.65 Ga, began with thrust-related crustal thickening that initiated regionally extensive amphibolite-facies metamorphism and ductile deformation, which dominates the preserved ‘Laxfordian’ deformation history. This may be the peripheral expression of the accretion of the Malin block to the SW of the Lewisian, and represents the lateral continuation of the Labradorian–Ketilidian orogen of North America. Supplementary Material: Additional figures are available at http://www.geolsoc.org.uk/SUP18863 .

Description: Microbial mats are thought to have been widespread in marine settings before the advent of bioturbation, and the range of their influence on sediments is gradually becoming recognized. We propose that mat sealing can dynamically affect porewater conditions, and allow the build-up of overpressure that can drive dewatering and degassing to produce a suite of atypical fluid-escape features. Finely bedded silty and sandy laminae from the c . 560 Ma Burway Formation of the Longmyndian Supergroup, Shropshire, England, reveal evidence for sediment injection, including disrupted bedding, clastic injections, sill-like features and sediment volcanoes at sub-millimetre scale. These features are associated with crinkly laminae diagnostic of microbial matgrounds. Matground-associated sediment injection can explain the formation of several types of enigmatic discoidal impressions, common in rocks of this age, which have previously been attributed to the Ediacaran macrobiota. Serial grinding of Longmyndian forms previously described as Medusinites aff. asteroides and Beltanelliformis demonstrates that such discoidal features can be fully explained by fluid escape and associated load structures. Our observations emphasize the non-actualistic nature of shallow-marine Ediacaran sediments. Matground-associated sediment injection features provide a new insight into the interpretation of Proterozoic rocks and the biogenicity of their enigmatic discoidal markings. Supplementary materials: A document containing further images of fluid escape and loading features observed in the upper Burway Formation at Ashes Hollow, together with an annotated diagram of features appearing in one typical vertical cross-section, is available at www.geolsoc.org.uk/SUP18870 .

Description: U–Pb and Lu–Hf signatures of detrital zircon from conglomerates and sandstones of the Ordovician Natal Group, South Africa were determined using laser ablation inductively coupled plasma mass spectrometry. The basal conglomerates are dominated by Palaeo- to Mesoarchaean detrital zircon with Hf values from +3 to –4 with minor Mesoproterozoic input, indicating a proximal source in the Kaapvaal Craton and minor input from rocks of the Natal Sector of the Mesoproterozoic Namaqua–Natal Province. The sandstones are all dominated by a combination of juvenile Mesoproterozoic zircon and Neoproterozoic zircon derived from Mesoproterozoic rocks that were reworked during the Pan-African Orogeny. Several sedimentary sequences from former Gondwana with Neoproterozoic to Permian depositional ages show similar detrital zircon signatures. Sedimentary sequences of such vast temporal and geographical distribution are unlikely to have been fed by a single source, making it more likely that these sequences were fed by several different (Pan-Gondwana) source terranes with closely similar U–Pb and Lu–Hf zircon signatures. The results show that source terrane non-uniqueness can make ascertaining sedimentary provenance from detrital zircon impossible, and should be taken as a reminder when using detrital zircon as evidence for far-reaching conclusions in basin evolution studies and palaeogeography. Supplementary materials: U–Pb and Lu–Hf data are available at http://www.geolsoc.org.uk/SUP18880 .

Description: This work investigates how anisotropy of magnetic susceptibility (AMS) recorded the strain related to the Early Cretaceous extensional processes in synrift sediments of the Maestrat basin (eastern Spain). Forty-two sites, distributed throughout the Lower Cretaceous sequence with dominant gentle dips, were sampled. Minerals contributing to the AMS are mainly phyllosilicates. The parallelism between magnetic and sedimentary foliation seems to indicate that a primary (synsedimentary and early diagenetic) magnetic fabric was preserved at 84% of sites. Consequently, preferred orientations of magnetic lineations are interpreted to record the effect of extensional processes coeval with sedimentation and diagenesis during this period. At these 35 sites, two main magnetic lineation orientations are found, delimiting two large domains: a NE–SW orientation prevailing in the NW sector of the basin (parallel to the extension direction of the Iberian basin), and NW–SE to NNW–SSE orientations to the SE (parallel to the extension direction controlling the western Tethys margin). Directional variability demonstrates that the Maestrat basin is located at the boundary between two domains (Iberian and Tethyan) undergoing different plate-scale extensional processes. The subsequent Cenozoic tectonic inversion affected the synsedimentary magnetic fabrics at only a few sites at the borders of the basin, where compressive features are more developed.

Description: The Permian Tarim magmatic province has 118 published ages, ranging from 358 to 205 Ma, but the timing of mafic magmatism is not well constrained. We report two new secondary ion mass spectrometry U–Pb zircon dates on the Halahatang trachydacite and Wajilitag olivine clinopyroxenite, which are 287.2 ± 2.0 Ma and 283.2 ± 2.0 Ma, respectively. The trachydacite overlies the uppermost basalt and constrains the latest eruption age of basalt in northern Tarim. The latter is the first high-resolution date for the Wajilitag mafic layered intrusion. By screening all published ages, we identified 22 robust ages, ranging from 290.9 ± 4.1 to 261.7 ± 1.8 Ma. The robust ages together with our new data reveal a protracted period of mafic magmatism at c . 283 and c . 267 Ma. Silicic magmatism occurred from 291 to 272 Ma. Although the current known volume of Tarim basalt is too small to qualify as a large igneous province, the eroded and intrusive components, as well as pyroclastic deposits and silicic lavas, may increase the estimated volume. Further work is required to refine the duration of magmatism and the volume estimate of the province. Supplementary material: A list of all the published dates, raw data of published 40 Ar– 39 Ar dates, raw data of published U–Pb dates, published geochemistry data used for calculation and complete details of the data evaluation are available at http://www.geolsoc.org.uk/SUP18862 .

Description: The use of sedimentary structures as indicators of flow and sediment morphodynamics in ancient sediments lies at the very heart of sedimentology, and allows reconstruction of formative flow conditions generated in a wide range of grain sizes and sedimentary environments. However, the vast majority of past research has documented and detailed the range of bedforms generated in essentially cohesionless sediments that lack the presence of mud within the flow and within the sediment bed itself. Yet most sedimentary environments possess fine-grained sediments and recent work has shown how the presence of this fine sediment may substantially modify the fluid dynamics of such flows. It is increasingly evident that understanding the influence of mud, and the presence of cohesive forces, is essential to permit a fuller interpretation of many modern and ancient sedimentary successions. In this paper, the present state of knowledge on the stability of current- and wave-generated bedforms and their primary current stratification is reviewed, and a new extended bedform phase diagram is presented that summarizes the bedforms generated in mixtures of sand and mud under rapidly decelerated flows. This diagram provides a phase space using the variables of yield strength and grain mobility as the abscissa and ordinate axes, respectively, and defines the stability fields of a range of bedforms generated under flows that have modified fluid dynamics owing to the presence of suspended sediment within the flow. Our results also present unique data on a range of bedforms generated in such flows, whose recognition is essential to help interpret such deposits in the ancient sedimentary record, including the following: (1) heterolithic stratification, comprising alternating laminae or layers of sand and mud; (2) the preservation of low-amplitude bed-waves, large current ripples and bed scours with intrascour composite bedforms; (3) low-angle cross-lamination and long lenses and streaks of sand and mud formed by bed-waves; (4) complex stacking of reverse bedforms, mud layers and low-angle cross-lamination on the upstream face of bed scours; (5) planar bedding comprising stacked mud–sand couplets. Furthermore, the results shown herein demonstrate that flow variability is not required to produce deposits consisting of interbedded sand and muds, and that the nature of flaser, wavy and lenticular bedding ( sensu Reineck & Wunderlich 1968) may also need reconsideration in the deposits of such sediment-laden flows.

Description: In this study field data from mesoscopic-scale brittle structures (faults) are used to decipher palaeostress and relate it to regional-scale kinematics. Fault-slip data from oblique-slip normal faults in granite (Mulgund, West Dharwar Craton, southern India) are analysed in three steps: (1) determination of palaeostress direction using fault-slip data; (2) kinematic interpretation of fault data; (3) fitting the kinematic model to the regional far-field stress. Palaeostress analysis of two sets of faults (left-lateral and right-lateral oblique-slip normal faults) reveals that both formed under the same compression direction (ENE–WSW). It is shown that inferring the faults to be R, P, R' and X shears of a Riedel shear system explains their kinematic evolution within the granite. The Riedel shears developed as a result of sinistral movement along the 305°-oriented contact between the granite and the surrounding gneisses. Riedel shear kinematics is interpreted as being a consequence of deformation partitioning, which was favoured by the rheological contrast between the above lithologies, during the late stage of a third phase of deformation under 315–135°-directed ( S Hmax ) far-field stress.

Description: The Sudbury impact structure is one of only a few terrestrial impact craters capable of providing insight into large impact processes. However, despite more than a century of study, no consensus exists regarding its depths of excavation and melting. This study presents 3920 U–Pb zircon dates for target lithologies and the crater-fill as well as new Pb-isotope data for target lithologies in an attempt to further constrain these depths and understand the behaviour of zircon in large impacts. Only 1.5% of the crater-fill zircons have dates within uncertainty of the 1.85 Ga impact event, with most seeming to preserve their pre-impact U–Pb systematics. The preponderance of undisturbed zircon in the crater-fill suggests that this mineral is an effective means of tracing target lithologies in impact basins. A significant fraction of crater-fill zircon was dated between 2.50 and 2.61 Ga, which is negligible amongst known target lithologies, and therefore identifies previously unrecognized target rocks. The Pb-isotope systematics are compatible with the proposal that the 2.6 Ga rock represents typical mid- to lower-crustal basement and could have been an important contributor to the melt-sheet. The combined data argue against a shallow melting scenario. With regard to Hadean terrestrial zircon, the lesson from Sudbury is that zircon can be recycled through multiple large impact events and still preserve the age of the original crust. Supplementary materials: Sample information, trace element and Pb-isotope data for granitoid and gneiss feldspar, Pb modelling parameters, U–Pb zircon data, concordia diagrams and airborne radiometric images are available at http://www.geolsoc.org.uk/SUP18881 .

Description: The Annieopsquotch Accretionary Tract comprises a tectonic collage of Ordovician peri-Laurentian terranes that formed during closure of Iapetus Ocean and imbricated beneath the composite margin of Laurentia. New zircon U–Pb geochronological data ( n = 8) for felsic volcanic rocks representing three distinct tectonostratigraphic units (the Mary March Brook group, the Buchans Group and the Red Indian Lake Group) indicate deposition over a short interval between 465 and 462 Ma. These tectonostratigraphic units are characterized by submarine mafic and felsic magmatism, and sedimentation typical of intra-oceanic arc systems. New and compiled whole-rock geochemical ( n = 315) and Sm–Nd isotopic ( n = 33) data for mafic and felsic volcanic rocks indicate that these tectonostratigraphic units formed in tholeiitic island arc to calc-alkaline arc settings. Isotopic ( Nd –11.2 to +6; T DM 1.0–2.4 Ga) and zircon inheritance data (0.5–3.4 Ga) are consistent with presence of Laurentian continental crust in the basement. Relationships within and between these and adjacent tectonostratigraphic units in the Annieopsquotch Accretionary Tract suggest that they represent imbricated slices of a submarine arc that experienced disorganized arc rifting, similar to sectors of the modern Tonga–Kermadec and Izu–Bonin–Mariana arcs. The recognition of disorganized spreading in the Annieopsquotch Accretionary Tract has significant implications for along-strike correlations within the Appalachian orogen, as the nature of the arc systems is expected to differ significantly along-strike. The presence of a clear isotopic and inheritance signature of peri-Laurentian continental crust within the Annieopsquotch Accretionary Tract submarine arc system is consistent with the discoveries of older arc and continental basement in modern intra-oceanic arc systems. Supplementary materials: Geochronological analytical procedures and data, summary of geochemical data and isotopic data are available at http://www.geolsoc.org.uk/SUP18860 .

Description: Turbidite sandstones and related deposits commonly contain deformation structures and remobilized sediment that might have resulted from post-depositional modification such as downslope creep (e.g. slumping) or density-driven loading by overlying deposits. However, we consider that deformation can occur during the passage of turbidity currents that exerted shear stress on their substrates (whether entirely pre-existing strata, sediment deposited by earlier parts of the flow itself or some combination of these). Criteria are outlined here, to avoid confusion with products of other mechanisms (e.g. slumping or later tectonics), which establish the synchronicity between the passage of overriding flows and deformation of their substrates. This underpins a new analytical framework for tracking the relationship between deformation, deposition and the transit of the causal turbidity current, through the concept of kinematic boundary layers. Case study examples are drawn from outcrop (Miocene of New Zealand, and Apennines of Italy) and subsurface examples (Britannia Sandstone, Cretaceous, UK Continental Shelf). Example structures include asymmetric flame structures, convolute lamination, some debritic units and injection complexes, together with slurry and mixed slurry facies. These structures may provide insight into the rheology and dynamics of submarine flows and their substrates, and have implications for the development of subsurface turbidite reservoirs.

Description: Jurassic dykes ( c . 182 Ma) are widespread across the Falkland Islands and exhibit considerable geochemical variability. Orthopyroxene-bearing NW–SE-oriented quartz-tholeiite dykes underwent fractional crystallization at 〉1 GPa, and major element constraints suggest that they were derived by melting of a pyroxenite-rich source. They have Nd 182 in the range –6 to –11 and 87 Sr/ 86 Sr 182 〉0.710 and therefore require an old lithospheric component in their source. A suite of basaltic-andesites and andesites exhibit geochemical compositions transitional between Ferrar and Karoo magma types, and are similar to those seen in the KwaZulu-Natal region of southern Africa and the Theron Mountains of Antarctica. Olivine-phyric intrusions equilibrated at 〈0.5 GPa, and have isotopic compositions (Nd 182 1.6–3.6 and 87 Sr/ 86 Sr 182 0.7036–0.7058) that require limited interaction with old continental lithosphere. A suite of plagioclase-phyric intrusions with 87 Sr/ 86 Sr 182 c . 0.7035 and Nd 182 c . +4, and low Th/Ta and La/Ta ratios ( c . 1 and c . 15, respectively) also largely escaped interaction with the lithosphere. These isotopically depleted intrusions were probably emplaced synchronously with Gondwana fragmentation and the formation of new oceanic lithosphere. Estimates of mantle potential temperature from olivine equilibration temperatures do not provide unequivocal evidence for the presence of a plume thermal anomaly beneath the Falkland Islands at 182 Ma. Supplementary materials: Mineralogical data, XRF major and trace element data and Ar-Ar results for Falkland Islands intrusions are available at http://www.geolsoc.org.uk/sup18873 .

Description: The Faroe–Shetland region of the NE Atlantic continental margin contains a number of complexly structured Mesozoic–Palaeogene-age rift basins, but in comparison with the contiguous British Isles and North Sea Basin, the state of crustal stress in the Faroe–Shetland region is poorly understood. The orientation of maximum horizontal compressional stress ( Hmax ) across most of NW Europe is roughly NW–SE, which is considered to be controlled by forces acting at the plate boundaries. We have determined 16 B–D quality Hmax orientations based on borehole breakouts interpreted in petroleum wells, and define three distinct stress provinces within the Faroe–Shetland region. Stress orientations in the NE are roughly NW–SE, consistent with the regional pattern of stresses in NW Europe and local neotectonic structural trends. However, contemporary stress orientations in the central and SW of the Faroe–Shetland region exhibit short-wavelength (distances 〈10–50 km) variation, with NE–SW, north–south and east–west orientations that are parallel or subparallel to underlying structural trends. This variation is interpreted in terms of stress deflections towards weak faults that downthrow the Mesozoic–Cenozoic sedimentary successions against basement highs. These local-scale sources are superimposed on a background roughly WNW–ESE Hmax orientation that is controlled by both plate boundary forces and regional-scale sources of stresses.

Description: The Late Triassic climate is characterized by arid conditions interrupted by a humid phase known as the Carnian Pluvial Event (CPE). This wet phase is well documented in the Tethyan realm, but evidence from the Boreal realm is scarce. Here we present evidence from quantitative palynology for the CPE from the Kapp Toscana Group on central Spitsbergen integrated with organic carbon isotope data linked to the geomagnetic polarity time scale. Our data reveal an early to mid-Julian-1 age for the Tschermakfjellet Formation. The transition to the Julian-2 is located in the De Geerdalen Formation and the Isfjorden Member is confirmed as mostly Tuvalian-3 in age. The Aulisporites astigmosus pollen assemblage zone that marks the base of the CPE in the Tethys realm at the base of the Julian-2 is assigned to the Julian-1 in the Boreal region. Palaeoclimate proxy data inferred from principal component analysis indicate wetter conditions from the Julian-2 onwards, which is in agreement with the establishment of local swamp vegetation on top of a delta plain. The palaeotemperature curve indicates a period of cooler climate during the early Julian-1 followed by warming during the late Julian-1. Supplementary materials: A list of all identified morphotaxa of pollen, spores and aquatic palynomorphs is available at http://www.geolsoc.org.uk/SUP18879 .

Description: Fluvial discharge fluctuations are a fundamental characteristic of almost all modern rivers and can produce distinctive deposits that are rarely described from ancient fluvial or mixed-energy successions. Large-scale outcrops from the Middle Jurassic Lajas Formation (Argentina) expose a well-constrained stratigraphic succession of marginal-marine deposits with a strong fluvial influence and well-known tidal indicators. The studied deposits show decimetre-scale interbedding of coarser- and finer-grained facies with mixed fluvial and tidal affinities. The alternation of these two types of beds forms non-cyclic successions that are interpreted to be the result of seasonal variation in river discharge, rather than regular and predictable changes in current velocity caused by tides. Seasonal bedding is present in bar deposits that form within or at the mouth of minor and major channels. Seasonal bedding is not preserved in channel thalweg deposits, where river flood processes were too powerful, or in floodplain, muddy interdistributary-bay, prodelta and transgressive deposits, where the river signal was weak and sporadic. The identification of sedimentary facies characteristic of seasonal river discharge variations is important for accurate interpretation of ancient deltaic process regime.

Description: 〈span〉〈div〉Abstract〈/div〉In Northern Apennines, upper Lutetian-Bartonian sedimentary mélanges, corresponding to ancient mud-rich submarine mass transport deposits, are widely distributed along the exhumed outer part of the External Ligurian accretionary wedge (ELAW), over an area of ∼300 km long and tens of kilometres wide. The occurrence of CH〈sub〉4〈/sub〉-derived carbonate concretions (septarians) in a specific tectono-stratigraphic position below sedimentary mélanges, allows us to document the relationships between a significant period of regional-scale slope failure, climate change (Early and Middle Eocene Optimum stages; EECO and MECO), gas hydrates dissociation, and accretionary tectonics during the Ligurian Tectonic Phase (early-middle Lutetian). The distribution of septarians at the core of thrust-related anticlines documents that gas hydrates dissociation was triggered by accretionary tectonics rather than climate changes. The different ages of slope failure emplacement and septarians formation support that gas hydrates dissociation was not the most important triggering for slope failure. The latter occurred during a tectonic quiescence stage associated with a depositional regressive trend, and probably minor residual tectonic pulses, which followed the Ligurian Tectonic Phase, favoring the dynamic re-equilibrium of the ELAW. Our findings provide useful information for better understanding factors controlling giant slope failure events in modern accretionary settings, where they may cause tsunamis.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Latest Oligocene-Pleistocene basic sheet intrusions in the Late Oligocene-Pliocene Wichianburi Sub-basin (onshore Thailand), and Eocene intrusions of the Ceduna Sub-basin (offshore southern Australia) provide examples of igneous intrusion architecture in rift and post-rift basin settings, respectively that have been imaged on 3D seismic reflection data. These examples indicate rift-related intrusions are overall smaller, have a higher aspect ratio, and tend to be more planar or transgressive in a single direction, than the saucer-shaped sills which dominate in the post-rift setting of the Ceduna Sub-basin. The long axis trend and dip-direction of most sills in the rift setting investigated tend to conform with rift structure (i.e. fault strike-directions and bedding dip and strike directions), and give a strong orientation bias, whereas orientations in the post-rift basin are more varied. The few saucer-shaped sills that formed in the Wichianburi Sub-basin are asymmetric and incompletely developed. A third area, the Kora region of the Taranaki Basin is a region where intrusions are related to a volcanic centre. This gives the intrusions a mixture of circumferential and radial intrusions related to magmatic processes (e.g. loading by the volcanic edifice, magma chamber pressure) and rift-related influences. Rift-related sills commonly form stacked arrays. Fundamental factors that affect the morphology of sills include: magma composition, volume, reservoir pressure, and the mechanical stratigraphy of the host rocks. In rifts extra complexities affecting some sills, or parts of sills include: rift structure (faults, rotated, folded bedding), basin size and morphology, stress distribution and sedimentary architecture.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4620101"〉https://doi.org/10.6084/m9.figshare.c.4620101〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Widespread wrench tectonics has been described along the Northern Andes. The Bucaramanga fault, described as sinistral strike-slip, bounds the high Santander Massif. We combine structural and thermochronologic data at the central-southern portion of the fault, in order to investigate the vertical displacement.Structural survey data shows: 1) old phases of activity preserved in the host rocks along the fault trace, with superimposition of different slickenlines generations; and 2) both strike- and dip-slip kinematics indicators. New and previous thermochronologic data show that differential exhumation of the fault walls has been ongoing from 50 Ma. The hangingwall, the Santander Massif, records: 1) in the central portion, decreasing exhumation rates from the early Miocene to the middle-late Miocene; and 2) in the southern portion, constant rates through the Late Oligocene to the Pliocene.Combining such observations, the thermochronologic offset resulting from the relative motion of the two fault walls is comparable with the observed elevation drop across the fault, suggesting that the present topography of the Santander Massif is related to the vertical movement along the Bucaramanga fault. We infer that the fault has a significant Neogene reverse component, consistent with present-day horizontal GPS vector data, long-term exhumation rates and the structural assemblage.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4620140"〉https://doi.org/10.6084/m9.figshare.c.4620140〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Asbestos nucleation and concentration in rocks are mostly associated with mechanisms of fibre formation, combined with the water-dependent mineralogical alteration produced during serpentinisation of ultramafic masses. Very little is known about the structural settings and tectonic histories that influence and control asbestos occurrence in non-serpentinised rocks, which are diffusely embedded within tectonised ophiolitic suites. Focussing on a case history provided by a tectonised metagabbro from the Ligurian Alps (northern Italy), a multiscale structural-petrographical approach is used to investigate the relationships between rock fabric and fibrous amphibole growth within the metagabbro. Meso- to micro-structural observations are used to document the role of structurally controlled fluid-rock interactions in localising the fibrous amphibole growth during ductile-to-brittle shearing (mylonitic foliation to shear veins). A qualitative structural scenario is here provided for illustrating the growth of asbestos amphiboles in shear veins during the progression of shear deformation towards semi-brittle rheological conditions. The mechanisms of structurally controlled growth of fibrous amphibole in non-serpentinised rocks imply an examination of the tectonic boundary conditions that are at the origin of the asbestos concentration in ophiolitic rocks involved in orogenic belt construction.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Upper Lutetian–Bartonian sedimentary mélanges, corresponding to ancient mud-rich submarine mass transport deposits, are widely distributed over an area 〈span〉c.〈/span〉 300 km long and tens of kilometres wide along the exhumed outer part of the External Ligurian accretionary wedge in the Northern Apennines. The occurrence of methane-derived carbonate concretions (septarians) in a specific tectonostratigraphic position below these sedimentary mélanges allows us to document the relationships among a significant period of regional-scale slope failure, climate change (the Early and Mid-Eocene Optimum stages), the dissociation of gas hydrates and accretionary tectonics during the Ligurian Tectonic Phase (early–mid-Lutetian). The distribution of septarians at the core of thrust-related anticlines suggests that the dissociation of gas hydrates was triggered by accretionary tectonics rather than climate change. The different ages of slope failure emplacement and the formation of the septarians support the view that the dissociation of gas hydrates was not the most important trigger for slope failure. The latter occurred during a tectonic quiescence stage associated with a regressive depositional trend, and probably minor residual tectonic pulses, which followed the Ligurian Tectonic Phase, favouring the dynamic re-equilibrium of the External Ligurian accretionary wedge. Our findings provide useful information for a better understanding of the factors controlling giant slope failure events in modern accretionary settings, where they may cause tsunamis.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Geochronological, elemental and Sr-Nd-Hf isotopic data for intermediate- acid volcanic sequences from the western North Huaiyang Belt of the Dabie Orogen, China, provide new constraints for the nature of the lithosphere and the potential involvement of the subducted Yangtze crust. These rocks are calc-alkaline andesite, trachyandesite and dacite. They were dated at 129∼127 Ma and show the geochemical affinity to arc volcanics. (87Sr/86Sr)i ratios and εNd(t) values range from 0.7065 to 0.7080 and −16.9 to −13.2, respectively. Zircon in-situ εHf(t) values range from –29.4 to –20.2 and Hf model ages from 3.03 Ga to 2.46 Ga. These volcanics might be derived from a hybridized source of NCC enriched lithosphere with the deep-recycled Yangtze continental crust. Our data, along with geological observations of the early Cretaceous igneous rocks, suggest an east-west extensional magmatic pulse at 130-120 Ma along the whole North Huaiyang Belt. From east to west, the recycled Yangtze continental crust has been decreasingly involved in the NCC enriched lithosphere in response to its Triassic northwardly deep subduction and subsequent exhumation. The lithospheric extension might induce the unrooting of previously-thickened lithosphere at early Cretaceous, resulting in the generation of the synchronous Cretaceous volcanics along the North Huaiyang Belt.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4611911"〉https://doi.org/10.6084/m9.figshare.c.4611911〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Palaeozoic sedimentary successions in northern Ethiopia contain evidence for two Gondwana glaciations during the Late Ordovician and Carboniferous–Permian. We compare sediments of the two glaciations regarding their detrital zircon U–Pb ages. The main age group for both formations is Pan-African (〈span〉c〈/span〉. 550–700 Ma). However, the remaining spectra are different: The Upper Ordovician–Lower Silurian Enticho Sandstone is characterised by a Stenian–Tonian (〈span〉c.〈/span〉 1 Ga) zircon population. The Carboniferous–Permian Edaga Arbi Glacials contain a prominent 〈span〉c.〈/span〉 800 Ma population. The Stenian–Tonian zircons are likely derived from the centre of the East African Orogen and were supplied via the Gondwana super-fan system. This material was transported by the Late Ordovician glaciers and formed the Enticho Sandstone. Tonian (〈span〉c.〈/span〉 800 Ma) zircons are abundant in the Ethiopian basement and represent the earliest formation stage of the southern Arabian–Nubian Shield. Glaciers of the Late Palaeozoic Ice Age must have cut deeply into the basement for efficient erosion. No recycling of the Enticho Sandstone by the Edaga Arbi Glacials took place on a grand scale — probably because sedimentation of the former was limited to northern Ethiopia, whereas the source area for the latter was to the south.〈strong〉Supplementary material:〈/strong〉 A detailed description of the analytical parameters and supplementary data are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4605548"〉https://doi.org/10.6084/m9.figshare.c.4605548〈/a〉.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Studies of the submerged Pleistocene conglomerate cored and dredged in the English Channel show that it resulted from the cementation of stony beaches under a loess blanket. Although the loess cover was later washed out by younger transgressions, the northern limit of the conglomerate corresponds to the original offshore extension of the loess deposits. Compilation of offshore and onshore altitudes of the limits of these deposits shows that loess was deposited by low-level wind fields never thicker than 200 m. Mapping surveys show that the present limits of loess are probably close to their original boundaries. The past proximity of the British Ice Sheet, the accumulation of dusty sediments coating north-facing cliffs of Brittany originating in the outwash of the British–Irish Ice Sheet and in the palaeo-rivers of the English Channel, as well as the southeastward orientation of the palaeo-winds deduced from particle size analysis and heavy minerals distribution, suggest that large volumes of loess were transported by strong katabatic winds blowing from the northern ice-covered regions towards Brittany and Normandy. The existence of katabatic winds is also consistent with the drift of ice rafts that transported Icelandic basalts now grounded in Brittany and possibly with the orientation of 〈span〉Homo neandertalensis〈/span〉 shelters.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Structural geometry and kinematics are important to understand the growth of the Tibetan Plateau margins. In this study, several high-resolution seismic reflection profiles were combined with well data and the fault-bend fold theory to determine the geometric and kinematic characteristics of the Pengxian buried structures located in the piedmont of central Longmen Shan (LMS). Seismic interpretations indicate that the Pengxian buried structures were involved in multi-period, superimposed deformation during the Cenozoic. The structural deformation of the frontal LMS was controlled by a Triassic detachment fault (f2), which extended forward at a gentle angle, and formed a fault-bend fold during the Late Miocene. The steep-angle Pengxian blind fault developed on the f2 with a few offsets during the Pleistocene. 3D imaging of the Pengxian buried structures shows that the f2 horizontally propagated into the western Sichuan Basin with a fault slip of approximately 3.3–3.5 km. The Longquan Shan (LQS) anticline has a total slip of approximately 3.0 km since its initiation. Our study suggests that the average slip rate of the f2 is 〈0.4 mm/yr in the central LMS front. The Pengxian buried structures and the LQS anticline have been slowly shortening since the Late Cenozoic.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Benin continental margin was formed during the breakup of Gondwana through oblique rifting along transform faults. The evolution of topography following breakup directly affects the evolution of sedimentary basins, which has major implications for hydrocarbon exploration in the region. Quantitative constraints on erosion across Benin are limited to the Cenozoic, based on analysis of dissected lateritic palaeolandscapes. To resolve the Mesozoic erosion history, we have obtained apatite fission-track and single-grain (U–Th–Sm)/He data from 18 samples collected across a 600 km long transect through Benin. We invert these data, including available geological and geomorphological constraints, to obtain time–temperature paths, which are used to estimate magnitudes of denudation over the last 200 myr. Our study suggests that denudation was focused over a 〈span〉c.〈/span〉 300 km long seaward sloping limb of the marginal upwarp and at the southern margin of the interior Iullemmeden Basin from 140 to 100 Ma with lower magnitudes of denudation characterizing the continental interior and post-Cretaceous evolution of the margin. Models are consistent with modest burial (〈span〉c.〈/span〉 1 km) of the Iullemmeden Basin between 120 and 85 Ma, and of the continental margin between 85 and 45 Ma. By the Eocene the first-order relief of Benin had developed, with regional erosion rates 〈20 m Ma〈sup〉−1〈/sup〉 since then.〈strong〉Supplementary information:〈/strong〉 Full details of the analytical data and modelling results, including the various constraints, and further data on denudation and burial magnitudes and rates are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4220804"〉https://doi.org/10.6084/m9.figshare.c.4220804〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The discovery of the Carnian Pluvial Episode arose through a chance conversation bringing together two seemingly unrelated strands of research: the extinction of some Triassic crinoids and the stratigraphy of the non-marine Mercia Mudstone Group. Investigations revealed a hitherto unrecognized period of climate change seemingly linked to a largely overlooked episode of biotic turnover. Ignored for more than a decade, an upsurge of interest in recent years has validated our original findings and answered some of the key questions concerning its extent and ultimate cause.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉In May 2017, in the delightful town of Delmenhorst (Lower Saxony, Germany), the first meeting on the Carnian Pluvial Episode (CPE) was hosted by the Hanse-Wissenschaftskolleg, Institute for Advanced Study. This was a milestone event. For the first time researchers from around the world met to discuss this still poorly known episode of early Late Triassic global environmental and biological change. This thematic set originates from discussions at this first meeting, and includes state-of-the-art research on the CPE, with the most recent discoveries on the complex phenomena that happened during this fascinating interval in Earth's history.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Spongtang ophiolite (Ladakh, NW India) constrains the nature of oceanic lithosphere before Indo-Asia collision and key stages in the development of the Himalayas. We report whole-rock 40Ar/39Ar and in-situ zircon 238U-206Pb ages from its crustal, upper and lower mantle sequences. Major and trace elements from harzburgite minerals suggest the ophiolite formed at a mid-ocean ridge-type spreading center, whereas published spinel compositions from Spongtang dunites are consistent with a supra-subduction zone setting. Rare Earth Element-in-two-pyroxene thermometry for the harzburgite yields 1058±13°C whereas temperature from solvus-based two-pyroxene and olivine-spinel thermometry is lower (to 656°C). The distribution suggests the mantle section of the ophiolite cooled at rates of 100°/Myr or slower. Based on ages, major and trace element geochemistry, and geospeedometric estimates, we model the origin of the Spongtang ophiolite as forming within a mid-ocean ridge-type spreading center with a spreading rate 〉2cm/y in the Neo-Tethyan Ocean, possibly from the Late Triassic to Jurassic. By Early Cretaceous, the ridge experienced increasing influence of subduction beneath the Spongtang oceanic lithosphere owing to a subduction polarity reversal. Based on 238U-206Pb ages of the youngest Cenozoic zircon grain, latest obduction occurred between 64.3±0.8 Ma to 42.4±0.5 Ma, in accordance 56.7±5.2 Ma whole-rock 40Ar/39Ar ages.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4261856"〉https://doi.org/10.6084/m9.figshare.c.4261856〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The upper Beetaloo Sub-basin of the McArthur Basin, Northern Territory, Australia, records over 500 million years of tectonic history of the North Australian Craton from ca. 1.45 to 0.9 Ga. The basin sequences include shallow-water clastic sedimentary rocks that preserve the oldest global commercial hydrocarbon reserves. New detrital zircon U–Pb age and Lu–Hf isotopes, compiled with published data, provide constraints on the basin provenance and reveal the dynamic tectonic evolution of Mesoproterozoic northern Australia.Data from the oldest formation examined, the ca. 1.4 Ga Bessie Creek Sandstone, suggest provenance from (present-day) eastern sources (e.g. the Mount Isa Province and the palinspastically adjacent Curnamona and Georgetown provinces) with considerable spatial heterogeneity. These eastern source regions are interpreted as uplifted rift-shoulder highs, formed by contemporaneous extension between Proterozoic Australia and Laurentia. Progressively younger formations (the Velkerri Formation, the Moroak Sandstone and the Kyalla Formation) demonstrate a rapid swamping of the basin by detritus from southerly sources (e.g. the Arunta Region) that occurred at ca. 1.4–1.3 Ga. This is particularly characterised by the up-section reduction of ca. 1.6 to 1.5 Ga detrital zircon grains. This change in provenance is interpreted to relate to closure of an ocean basin during the period 1.35 to 1.25 Ga, which resulted in uplift of the southern margin of North Australia Craton. Three ungrouped latest Mesoproterozoic to Neoproterozoic sedimentary units, the lower and upper Jamison sandstone and the Hayfield mudstone, were deposited after the emplacement of the Warakurna Large Igneous Province and are sourced from the Musgrave Province.Detrital zircon U–Pb and Hf isotope affinities between the lower and upper Jamison sandstone and the Hayfield mudstone, and the latest Mesoproterozoic to early Neoproterozoic successions along the eastern margin of the North China Craton, suggest that they share a similar provenance. This supports correlations between the Mesoproterozoic of the North China Yanshan Basin and the greater McArthur Basin.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4444790"〉https://doi.org/10.6084/m9.figshare.c.4444790〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Two Cenozoic magmatic cycles occurred in Sardinia separated by a 5 Ma gap: Oligo-Miocene (OM) subduction-related calc-alkaline magmatism associated with Sardinia migrating from the European continental margin to its current location, and Plio-Pleistocene (PP) intraplate alkaline magmatism associated with the opening of the southern Tyrrhenian basin. Based on an integration of new and published geochemical data on the Cenozoic volcanic rocks of Sardinia, and regional tectonics, we propose that a northward propagating slab tear formed south of Sardinia at the end of the OM cycle. This was responsible for the transition from subduction-controlled calc-alkaline to extension-controlled mildly alkaline to peralkaline magmatism in the Sulcis area (SW Sardinia), and for the end of the OM magmatism. The inflow of hotter material from the European Asthenospheric Reservoir (EAR) through the slab window could have produced the minor EAR-type alkaline lavas that erupted at the end of the OM cycle and at the beginning of the PP cycle. The dominant younger PP lavas with EMI-type compositions likely formed from decompression melting of a shallower lithospheric mantle with little influence from the EAR-forming event.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4447802"〉https://doi.org/10.6084/m9.figshare.c.4447802〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The valence of carbon is governed by the oxidation state of the host system. The subducted oceanic lithosphere contains considerable amounts of iron so that Fe〈sup〉3+〈/sup〉/Fe〈sup〉2+〈/sup〉 equilibria in mineral assemblages are able to buffer the (intensive) 〈span〉f〈/span〉O〈sub〉2〈/sub〉 and the valence of carbon. Alternatively, carbon itself can be a carrier of (extensive) ‘excess oxygen’ when transferred from the slab to the mantle, prompting the oxidation of the sub-arc mantle. Therefore, the correct use of intensive and extensive variables to define the slab-to-mantle oxidation by C-bearing fluids is of primary importance when considering different fluid/rock ratios. Fluid-mediated processes at the slab–mantle interface can also be investigated experimentally. The presence of CO〈sub〉2〈/sub〉 (or CH〈sub〉4〈/sub〉 at highly reduced conditions) in aqueous COH fluids in peridotitic systems affects the positions of carbonation or decarbonation reactions and of the solidus. Some methods to produce and analyse COH fluid-saturated experiments in model systems are introduced, together with the measurement of experimental COH fluids composition in terms of volatiles and dissolved solutes. The role of COH fluids in the stability of hydrous and carbonate minerals is discussed comparing experimental results with thermodynamic models and the message of nature.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Potassium feldspar present in global mineral aerosol (〈5%) plays a disproportionate role in modulating the microphysics of mixed-phase cloud. Via exceptional ice nucleation properties, it is capable of changing cloud properties and behaviour. Here we identify times of substantial and abrupt change in the global availability of potassium feldspar since 600 Ma. Normally, weathering and vegetation cover contribute to low availability, with clay dominating mineral aerosol. Periods of maximum availability are reasoned to follow the emplacement and remobilization of ejecta blankets from major meteorite impact events, before returning to background after some hundreds to thousands of years. We review the 44 largest confirmed craters and evaluate the potassium feldspar content of their target rocks, which range from 〈span〉c.〈/span〉 0 to 〉30%. By combining crater size and tectonic reconstructions, we are able to provide a quantitative and self-consistent assessment of changes to global potassium feldspar availability. Considerable differences in potassium feldspar availability following meteorite impact events are revealed. Different impact events generated dust containing different amounts of potassium feldspar. Differing levels of influence upon climate are hypothesized, and should now be tested by looking at stratigraphic records of these events to reveal the sensitivity of climate to different dust mineralogy.〈strong〉Supplementary material:〈/strong〉 Figures showing palaeolatitude determinations using various methods and reconstruction models, and estimates of alkali feldspar abundance and distribution across contemporary continental landmasses for meteorite impact events are available at: 〈a href="https://doi.org/10.6084/m9.figshare.c.4253312"〉https://doi.org/10.6084/m9.figshare.c.4253312〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉We present a regional synthesis of the structural architecture and tectonic evolution of the Western Alpine Ophiolites (WAO), exposed in NW Italy. The WAO represent the remnants of Alpine Tethys (Ligurian–Piedmont Ocean) that opened between Europe and Adria, and developed in four stages from the Middle Jurassic to Early Cretaceous. Emplacement of gabbroic intrusions into the extending lithospheric mantle of Europe–Adria marked the main magmatic event (Stage 1). Coalescent shear zones in the fossil upper mantle form lithospheric-scale detachment faults, which led to the exhumation of upper mantle peridotites and gabbros on the seafloor, and extensive serpentinization (Stage 2). Detachment faults, and serpentinized peridotites–gabbros in their footwalls, represent preserved fossil oceanic core complexes within the WAO. Emplacement of ophiolitic breccias and basaltic lava flows marked the syn-extensional phase (Stage 3). Radiolarian chert and limestone were deposited unconformably on this syn-extensional volcanic–sedimentary sequence, marking the post-extensional phase (Stage 4). Magmatic ages of gabbroic intrusions and mafic–felsic dykes, and depositional ages of post-extensional sequences in the WAO constrain the timing of the opening of the Ligurian–Piedmont Ocean to the Middle Jurassic (〈span〉c.〈/span〉 170–168 Ma), followed by a tectonic quiescence stage in the Late Jurassic–Early Cretaceous.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The early Paleozoic Kwangsian event, the first compressive orogeny after the Rodinia assemblage in the South China Block (SCB), is characterized by the angular unconformity between the Devonian and pre-Devonian sequences and widespread granitoids and small-volume mafic rocks. However, the mechanism triggering this event is highly debated and the associated mantle source is poorly known. Our recent investigations identified the occurrence of early Silurian high-Mg basalt–andesite–dacite in the Dashuang area along the northwestern Yunkai Domain in the SCB. This study presents a set of new zircon U–Pb geochronological, whole-rock geochemical and Sr–Nd isotopic data for these volcanic rocks. They yield weighted mean 〈sup〉206〈/sup〉Pb/〈sup〉238〈/sup〉U ages of 〈span〉c.〈/span〉 430–443 Ma, similar to the age-peaks of early–middle Paleozoic magmatism and metamorphism in the SCB. These volcanic rocks have high MgO, Cr and Ni contents and Mg-numbers. They also exhibit arc-like geochemical affinities with crustal-like Sr–Nd isotopic compositions, similar to the Neoproterozoic high-Mg basalt–andesite in the eastern SCB. Such signatures, combined with other geological observations, suggest that the Dashuang high-Mg rocks were derived from an ancient (probably early Neoproterozoic) mantle wedge source. The early Paleozoic intra-continental reactivation in response to late-orogenic extension triggered the melting of this palaeosubduction-modified mantle, which led to the formation of these volcanic rocks.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The discovery of the Carnian Pluvial Episode arose through a chance conversation bringing together two seemingly unrelated strands of research: the extinction of some Triassic crinoids and the stratigraphy of the non-marine Mercia Mudstone Group. Investigations revealed a hitherto unrecognized period of climate change seemingly linked to a largely overlooked episode of biotic turnover. Ignored for more than a decade, an upsurge of interest in recent years has validated our original findings and answered some of the key questions concerning its extent and ultimate cause.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉This study examines rainfall variations of the Mid-Carnian Pluvial Episode (CPE) based on the continental fluvial sedimentology, palaeosol and clay mineralogy records of the Stable Meseta (eastern Spain). In the formation examined, the Manuel Fm or K2 Fm, the CPE is represented by three regressive–transgressive sequences, or subunits K2.1, K2.2 and K2.3, from base to top. Each subunit broadly consists of a genetic stratigraphic sequence bearing well-developed highstand, lowstand and transgressive systems tracts. Hydromorphic features in the palaeosols suggest changes in the activity of both groundwater and surface water. The clay mineral assemblage is dominated by illite, with a minor presence of kaolinite and traces of smectite in some samples. After ruling out tectonism in the study area, climate and eustatism emerge as the main allogenic controls in the sedimentary record. Differentiated sedimentary facies and architectural elements in the K2.2 subunit were probably controlled by both a more humid climate and source area, whereas K2.1 and K2.3 were more related to base-level changes and eustatic control. The presence of more waterlogged pedotypes and of kaolinite and traces of smectite in the clay mineral assemblage of K2.2 also indicates increased humidity. Notwithstanding, our data do not point to intense rainfall periods for the CPE in eastern Spain.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉New biostratigraphic (ammonoids and conodonts) and geochemical data (carbonate carbon and oxygen stable isotopes, and organic carbon stable isotopes) are presented for the Carnian (Upper Triassic) marine succession of Ma'antang, Jiangyou County, in the Upper Yangtze Block (NW margin of the Sichuan Basin, China). In this locality, the Ma'antang Formation lies on top of the Tianjingshan Formation, which is identified by the occurrence of peritidal cycles with stromatolite layers, and includes a distinct karst surface in its upper part. Below the karst surface, negative trends in carbonate carbon and oxygen isotopes can be interpreted as the result of meteoric diagenesis. Above, the Ma'antang Formation is subdivided into five units. The lower part (Units 1–3) mostly consists of bioclastic limestones with thin clayey siltstone intercalations, but at least three intervals of terrigenous deposits are present. A lithological change from mainly carbonates to terrigenous clastic rocks occurs between Units 3 and 4. This interval is biostratigraphically well constrained by the occurrence of ammonoids from the clayey siltstone of Unit 4, suggesting a Julian 2 age (Early Carnian), and conodont associations allow us to place the Julian–Tuvalian boundary at 195 m, the upper part of Unit 4. A wide negative carbon isotope oscillation of about 2‰ occurs in Units 1 and 2, which should be dated to the early Carnian and could be correlated to similar perturbations in western Tethys and in the Nanpanjiang Basin, South China. These correlated carbon isotopic oscillations were attributed to the onset of the Carnian Pluvial Episode (CPE). The two known Chinese records of the CPE both display a broad negative carbon isotopic excursion that encompasses a significant part of the Carnian, whereas the western Tethys records feature possibly multiple, short-lived isotopic excursions. The present isotopic data show that the CPE began roughly contemporaneously with the first terrigenous input at Ma'antang. It is unclear whether the minor siliciclastic intervals within Units 1–3 at Ma'antang could be correlated to similar terrigenous episodes in the western Tethys region. So far, Ma'antang is the only locality of the Sichuan Basin where the carbon isotopic perturbation related to the Carnian Pluvial Episode has been documented.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The break-up of continents at magma-poor rifted margins is a complex yet little understood process accounting for intricate interactions between tectonic and magmatic processes. Whereas high-resolution seismic data may resolve the first-order architecture of ocean–continent transitions (OCTs), direct access to rocks remains limited to deep-sea drilling. In this study, we combine seismic observations from the East Antarctica margin (Geoscience Australia Survey 228) with field observations from the Bracco–Levanto area (Northern Apennines, Italy), representing modern and fossil examples of ultra-distal magma-poor rifted margins respectively. The combination of detailed structural mapping and petrological studies from fossil examples with architectural features observed in seismic sections from present-day OCTs enables to bridge the different observation scales. Field evidence indicates that the magmatic budget is not zero, as magma is present throughout the exhumation process. Extensional detachment faults that exhumed serpentinized mantle and deep-seated gabbro intrusions are truncated by later high-angle normal faults, which most probably acted as feeders for the emplacement of massive syn-extensional basalts. These observations suggest a polyphase tectonic and magmatic evolution of the ultra-distal margin prior to the formation of the first true oceanic crust, which can be studied in detail only by combining seismic and outcrop observations.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Sanandaj–Sirjan Zone (SaSiZ) is a magmatic terrane within the Zagros Orogen, western Iran, marking the Tethyan suture zone between the Afro-Arabian Plate and the Central Iran Micro-Continent. Mafic–intermediate dyke swarms with Middle Jurassic (Group 1: hornblende gabbro and diorite) and Late Eocene (Group 2: hornblende–pyroxene gabbro) ages are recognized in the Malayer–Boroujerd Plutonic Complex of the northern SaSiZ. Group 1 dykes have elemental and isotopic signatures consistent with melting of a mantle source modified during Neo-Tethyan subduction. Some Group 1 magmas evolved to intermediate compositions through assimilation and fractional crystallization. Group 2 dykes have within-plate trace element geochemical signatures, modelled as deriving from low-degree melting of asthenospheric mantle without a subduction influence. Published models postulate either a Cretaceous–Eocene Neo-Tethyan flat-slab scenario or a Latest Cretaceous–Paleogene Neo-Tethyan break-off event beneath the SaSiZ. Such models do not reconcile with the Late Eocene presence of within-plate magmatism in westernmost Iran, very close to the Zagros Suture. We argue that a period of flat-slab subduction concluded with sub-parallel subduction of a Neo-Tethyan ridge to the trench. The resulting slab break-off event in the Late Eocene is responsible for generation of the distinct Mesopotamia and Zagros slabs in mantle tomography models. Break-off was followed by small-volume within-plate type magmatism before short-lived re-establishment of Tethyan subduction prior to the final Arabia–Eurasia collision.〈strong〉Supplementary material:〈/strong〉 Field photographs, photomicrographs, additional geochemical plots, descriptions of analytical methods and tables of geochemical modelling parameters are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4126196"〉https://doi.org/10.6084/m9.figshare.c.4126196〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Lake sediments commonly contain detrital layers that record events such as floods or earthquakes, but these may be disturbed or partially destroyed by bioturbation. Here we use a novel combination of techniques to relate microscopic sediment fabric features to processes at the lake basin scale. X-radiography and micro-X-ray fluorescence analysis of cores are complemented by back-scattered electron imagery and energy-dispersive X-ray microanalysis of resin-embedded sediment. Together, the microfabric and geochemical methods enable the identification of clay layer mass transport deposits despite bioturbational mixing of the original end-members. Two cores with robust radionuclide chronologies contain correlative clay layers dated to 1979 (1974–1982) and 1979–1980 (1973–1986), respectively. These clay layers probably represent the distal turbidite generated by a major mass flow deposit identified from multi-beam swath bathymetry and sediment grab sampling. A probable trigger for the mass flow and associated turbidity current is the 4.7 M〈sub〉L〈/sub〉 1979 Carlisle earthquake. The lake basin slope was probably preconditioned for failure by increased sedimentary biogenic gas production and sediment in-wash as a result of anthropogenic activities, coupled with sediment disruption and dredging. This study highlights the effectiveness of microstratigraphic techniques in the recognition and characterization of event layers in sediments where bioturbative disruption has occurred.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Winneshiek Shale (Middle Ordovician, Darriwilian) was deposited in a meteorite crater, the Decorah impact structure, in NE Iowa. This crater is 5.6 km in diameter and penetrates Cambrian and Ordovician cratonic strata. It was probably situated close to land in an embayment connected to the epicontinental sea; typical shelly marine taxa are absent. The Konservat-Lagerstätte within the Winneshiek Shale is important because it represents an interval when exceptional preservation is rare. The biota includes the earliest eurypterid, a giant form, as well as a new basal chelicerate and the earliest ceratiocarid phyllocarid. Conodonts, some of giant size, occur as bedding plane assemblages. Bromalites and rarer elements, including a linguloid brachiopod and a probable jawless fish, are also present. Similar fossils occur in the coeval Ames impact structure in Oklahoma, demonstrating that meteorite craters represent a novel and under-recognized setting for Konservat-Lagerstätten.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Kalkarindji flood basalt province of northern Australia erupted in the mid-Cambrian. Today, the province consists of scattered volcanic and intrusive suites, the largest being the Antrim Plateau Volcanics (APV) in Northern Territory. Accurate dating of the Kalkarindji flood basalt province has proved challenging, with previous studies focused on minor volcanic rocks and intrusive dykes in Northern Territory and Western Australia. These previously published data, corrected to the same decay constants, range from 512.8 to 509.6 ± 2.5 Ma [2σ], placing the Kalkarindji flood basalt province in apparent synchronicity with the Cambrian Stage 4–5 biotic crisis at 510 ± 1 Ma. This study utilizes 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar dating of basalts from the APV to accurately date the major volcanic eruptions in this province. The results yield an age of 508.0–498.3 ± 5.5 Ma [2σ], indicating that the APV is younger than the intrusive rocks. These dates allude to a relative timing discrepancy, where intrusive activity in the North Australian Craton preceded the eruption of the APV as the last magmatic activity in the region. The determination of these largest eruptions to be later than 510 Ma effectively disassociates the Kalkarindji lavas from being a major cause of the 510 Ma biotic crisis, but cannot definitively discount any deleterious effects on the fragile Cambrian ecosystem.〈strong〉Supplementary material〈/strong〉: 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar analysis data tables, XRF geochemical data, alteration study and photomicrographs of all five samples are available at: 〈a href="https://doi.org/10.6084/m9.figshare.c.4176674"〉https://doi.org/10.6084/m9.figshare.c.4176674〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Hindu Kush–Kohistan–Karakoram region is critical to understanding the long-term accretion history of the south Asian margin pre- and post-India–Asia collision and the impact of these collisions on the development of high topography. However, knowledge about this region remains incomplete owing to sparse studies. Here, we present a study comprising detrital zircon U–Pb geochronology, detrital muscovite 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar thermochronology and numerical modelling on 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar dates. The study identifies zircon U–Pb age peaks at 200, 110–130, 60–80 and 28–40 Ma, supporting the polyphase collisions and crustal growth in the south Asian margin. The modelling study reveals fast cooling–erosion at 115–129, 69–71, 27–35 and 〈8 Ma, synchronous with collision-related crustal growth, indicating the significant impact of accretion both prior to and post-India–Asia collision. This study, along with studies in eastern Karakoram, reveals along-strike variations in erosion and exhumation with young (since late Miocene) intense erosion focusing on the east–central Karakoram. We suggest that this east–west spatial variation in exhumation may have been associated with more intense crustal shortening, and thus the greater crustal thickness, topographic relief and altitude observed in the eastern compared with the western Karakoram.〈strong〉Supplementary material:〈/strong〉 Detrital zircon U–Pb ages, detrital muscovite single-crystal 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar ages and modelling results are available at: 〈a href="https://doi.org/10.6084/m9.figshare.c.4124573"〉https://doi.org/10.6084/m9.figshare.c.4124573〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The enigmatic biotic and environmental changes during the Carnian Humid Episode (CHE) have been investigated in South China. The body size of conodonts, assessed as length of P1 elements, and their diversity show substantial changes in the mid-Carnian. The well-dated Long Chang, Yongyue and Caizitang sections in southwestern China record a change of palaeoenvironments from shallow-marine carbonate platforms to deeper, euxinic basins. All sections show a major loss of conodont diversity and abundance late in the Julian 1 at a time of rapid warming and marine anoxia. Conodont size saw a reduction in maximum, mean and minimum size during the Julian 2 to Tuvalian 2 interval caused by the short-lived appearance of small species and a size decrease of the survivors. Conodont mean size reduction coincided with marine euxinia or anoxia and temperature fluctuations during the Julian 2 to Tuvalian 2 interval. Carnian conodonts thus follow Bergmann's Rule: element size is inversely correlated to the temperature. Climate warming with the consequential development of marine anoxia or euxinia is probably directly responsible for biotic changes at this time.〈strong〉Supplementary material:〈/strong〉 Conodont length data from the Long Chang (LC), Yongyue (NR) and Caizitang (CZ) sections and data for the cross plot between estimated temperature and conodont mean size in the Long Chang section are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4114424"〉https://doi.org/10.6084/m9.figshare.c.4114424〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Late Triassic Carnian wet episode was an interval of humid climate evident in the lowermost strata of the Upper Triassic Chinle Group in the western USA. Chinle deposition began with the development of major river systems of the Shinarump Formation and equivalents, laterally equivalent to and/or overlain by floodplain deposits containing kaolinitic gleyed to spodic palaeosols and local coal beds. The Chinle strata immediately above these wet episode strata are deposits of smaller rivers that lack coal or carbonaceous strata and contain non-kaolinitic palaeosols that are locally calcareous and vertic, indicative of drier but strongly seasonal climates. The lowermost Chinle strata contain fossil tetrapods, palynomorphs and conchostracans that are consistent with other data that indicate that the basal Chinle strata are of Julian age and immediately overlying lower Chinle strata are early Tuvalian, so these strata are the age of the Carnian wet episode. Identification of a ‘long Norian’ Stage places the Norian base in the Chinle Group near the top of the strata of the wet episode, which means that Norian strata sit directly on early Carnian strata, but there is no unconformity at this level to support recognition of such a long Norian in the Chinle section.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉We present new evidence for a major inflection point in the history of tetrapods on land, a jump in the diversification of archosauromorphs, primarily dinosaurs, at 232–230 Ma. This corresponds to a long-noted changeover in Triassic terrestrial tetrapod faunas from those dominated by synapsids, many of them holdovers from the Permian, to those dominated by dinosaurs. The dinosaur explosion is shown here to correspond in timing to the Carnian Pluvial Episode (CPE), dated at 232 Ma, a time of increased rainfall and perturbation of oceans and atmospheres, followed by substantial aridification. The rock record through the CPE confirms that this event shared many characters with other mass extinctions driven by eruption of large igneous provinces, in this case the Wrangellia flood basalts of the west coast of North America. If this was a catastrophic extinction event, then the environmental perturbations of the CPE explain the sharp disappearance of various terrestrial tetrapods, and the subsequent sharp rise of dinosaurs and perhaps other clades too, especially those that constitute much of the modern terrestrial faunas, such as lissamphibians, turtles, crocodiles, lizards and mammals.〈strong〉Supplementary material:〈/strong〉 The sampled tetrapod faunas, geological ages, and details of the R code method and results are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4111439"〉https://doi.org/10.6084/m9.figshare.c.4111439〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Palaeoenvironmental and palaeoclimatic changes during the Toarcian Oceanic Anoxic Event (T-OAE) are reported from two successions deposited in the Andean Basin (Chile), based on a high-resolution biostratigraphic (calcareous nannofossils), sedimentological, mineralogical and geochemical analysis. A large negative carbon-isotope excursion was identified in a lower Toarcian storm-dominated marl–limestone alternation, underlining the global extent of the carbon-cycle perturbation and the occurrence of episodic high-energy conditions during the T-OAE. Low total organic carbon content and absence of redox-sensitive trace-element enrichment indicate that the dynamic depositional conditions did not favour the development of oxygen-depleted conditions and the preservation of organic matter. The decrease in kaolinite reflects a shift to more arid conditions, whereas the increase in the chemical index of alteration at the onset of the T-OAE is probably related to a change in the sediment source. Less hydrolytic activity probably promoted a decrease in nutrient input in the Andean Basin. Mercury anomalies support the link between the onset of the Karoo–Ferrar large igneous province activity, the carbon cycle perturbation and the generated environmental change. This paper presents one of the most complete T-OAE studies from the southern hemisphere, and reveals that regional conditions strongly modulated the expression of this global event in the Andean Basin.〈strong〉Supplementary material:〈/strong〉 the complete dataset, the coefficient of correlation (〈span〉r〈/span〉) for major and trace elements, and the nannofossil assemblages are available at: 〈a href="https://doi.org/10.6084/m9.figshare.c.4133687"〉https://doi.org/10.6084/m9.figshare.c.4133687〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉As the junction of the Silk Roads, the Tarim Basin played a critical role in human migration and cultural interaction between the East and the West. Recently, population migration patterns have been increasingly reconstructed from strontium isotope ratios (〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr) in archaeological human skeletons, and further constraints on their provenance require a bioavailable 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr map across the basin. Based on measurement data from 44 river samples in this study and 29 samples from published data, we generate the first map of bioavailable 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr values across the Tarim Basin and the neighbouring area. From the baseline map, three geologically distinct regions can be identified: (1) the Yili Block, Tian Shan orogenic belt and northern Tarim Block with lower ratios (0.7105 ± 0.0007 (1σ), 〈span〉n〈/span〉 = 25); (2) the southern Tarim Block with higher ratios (0.7118 ± 0.0008, 〈span〉n〈/span〉 = 29); and (3) the eastern Pamir Block with diverse values (0.7110 ± 0.0009, 〈span〉n〈/span〉 = 19). This map is a promising tool for recognizing the origins of immigrants in the Tarim Basin and may aid understanding of the migration patterns and cultural communication along the Silk Roads.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Fault geometry exerts a dominant structural control on the deformation of hanging wall sequences during extension and contraction. Numerical, kinematic and sandbox modelling studies have demonstrated that characteristic anticline–syncline pairs are produced during the extension of ramp-flat faults. These features are commonly recognized in smaller fault-scale structures, but remain underappreciated in larger, basin-scale settings. The Lewis Trough, situated within the Northern Carnarvon Basin, Western Australia, is a basin-scale, largely unfaulted syncline with an associated anticline along its western flank, rather than the fault-related graben typical of the region. We present kinematic models demonstrating that a SE-dipping, ramp-flat fault geometry can produce relative highs and lows in Jurassic strata as well as honouring the asymmetrical onlap pattern within the Lewis Trough. This study indicates that the Lewis Trough formed during the Early Jurassic, a period typically associated with high rates of extension and not during the Late Triassic Fitzroy Compression Event. This study also highlights the importance of the Locker Shale in partitioning deformation of the Permian and Mesozoic fault systems and as a diffuse zone that variably partitions displacement between stacked Permian and Mesozoic fault systems.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Carbon is found in nature in a huge variety of allotropic forms and recent research in materials science has encouraged the development of technological materials based on nanocarbon. Carbon atoms with 〈span〉sp〈/span〉〈sup〉2〈/sup〉 or 〈span〉sp〈/span〉〈sup〉3〈/sup〉 hybridization can be thought of as building blocks. Following a bottom-up approach, we show how graphene and diamond molecules are built up and how their properties vary with size, reaching an upper limit with bulk graphite and diamond. Carbon atoms with 〈span〉sp〈/span〉〈sup〉2〈/sup〉 hybridization give rise to an impressive number of different materials, such as carbon nanotubes, graphene nanoribbons, porous carbon and fullerene. As in any crystalline phase, the crystal structures of natural carbon allotropes (i.e. graphite and diamond) contain various types of imperfections. These so-called lattice defects are classified by their dimensions into 0D (point), 1D (line), 2D (planar) and 3D (volume) defects. Lattice defects control the physical properties of crystals and are often a fingerprint of the geological environment in which they formed and were modified. Direct observations of lattice defects are commonly accomplished by transmission electron microscopy. We present and discuss the ideal and real structures of carbon allotropes, the energetics of lattice defects and their significance in understanding geological processes and conditions.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉In May 2017, in the delightful town of Delmenhorst (Lower Saxony, Germany), the first meeting on the Carnian Pluvial Episode (CPE) was hosted by the Hanse-Wissenschaftskolleg, Institute for Advanced Study. This was a milestone event. For the first time researchers from around the world met to discuss this still poorly known episode of early Late Triassic global environmental and biological change. This thematic set originates from discussions at this first meeting, and includes state-of-the-art research on the CPE, with the most recent discoveries on the complex phenomena that happened during this fascinating interval in Earth's history.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Amber (fossil resin) is not common throughout the fossil record, and previously the only globally significant deposits were thought to occur during the Cretaceous, Eocene, Oligocene and Miocene periods. Recent finds of Late Triassic (Carnian) ambers highlight a significantly older set of deposits. Here we review these ambers that appear coincident with the Carnian Pluvial Episode, a time interval of major climate change and biotic turnover. Much of the amber is found in a palaeolatitudinal belt between 5° and 30° N, and covers Italian, Austrian, Swiss, Hungarian, Spanish and Arizona (USA) deposits, with one exception from Lesotho, Southern Africa (〈span〉c.〈/span〉 40° S). Most deposits are small and allochthonous, with the major exception of the autochthonous–parautochthonous amber deposit found as droplets in a palaeosol from the Dolomites (Italy). In some of these deposits there is even direct evidence of the source plants that produced the preserved resin. The oldest confirmed organisms found preserved in amber are from Carnian droplets from the Dolomites in Italy and include arthropods and microorganisms. The occurrence of amber in different localities and within the same time interval suggests a widespread stressed flora, and major biological turnover in the terrestrial ecosystems during the Carnian Pluvial Episode.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Middle Jurassic Rattray Volcanic Province is located at the triple junction of the North Sea continental rift system. It has previously been thought to be sourced from three large central volcanoes: the Glenn, Fisher Bank and Ivanhoe Volcanic Centres. Re-interpretation using 3D seismic and well data shows that no volcanic centres are present and the Rattray Volcanics were instead sourced in fissure eruptions from linear vents including the Buchan-Glenn Fissure System, a ~25km-long zone of WSW-ENE striking linear fissure vents and associated small volcanic edifices across the Buchan-Glenn Horst. The orientation of the fissures is broadly parallel to the Highland Boundary Fault which intersects the Rattray Volcanics at the Buchan-Glenn Fissure System, implying that Middle Jurassic magmatism exploited pre-existing crustal structural anisotropies established during the Caledonian Orogeny. The lack of large intrusive complexes beneath the Rattray Volcanics indicates pre-Middle Jurassic sedimentary sequences (e.g. Devonian-Carboniferous Old Red Sandstone Group, Permian Rotliegend and Zechstein Groups and Triassic Skagerrak Formation) extend further than previously supposed, and therefore the presence of possible sub-volcanic reservoir and source rock units may have been overlooked within the triple junction of the Central North Sea.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Before the India–Asia collision, Neotethyan subduction gave rise to an Andean-type convergent margin on the southern margin of Asia. To investigate the spatial and temporal distribution of the subduction-related magmatism, we undertook a combined determination of zircon U–Pb ages and Hf isotopes of Mesozoic to Paleogene intrusive and volcanic rocks from southern Tibet to Myanmar to characterize the two parallel magmatic belts that have previously been considered separately. One belt extends from the Gangdese Batholith in the Southern Lhasa sub-terrane to the Lohit Batholith, the Sodon Pluton and the Popa–Loimye Arc in the West Burma Block, and the other from the Central Lhasa Plutonic Belt to the Bomi–Chayu Batholith, the Dianxi Batholith and the Shan Scarps Batholith in central Myanmar. The Gangdese belt, as the main arc component, consists typically of I-type granitoids that contain magmatic zircons showing positive ε〈sub〉Hf〈/sub〉(〈span〉t〈/span〉) values. In contrast, the Central Lhasa Plutonic Belt belt is dominated by S-type granites in which most zircons show negative ε〈sub〉Hf〈/sub〉(〈span〉t〈/span〉) values suggesting the involvement of older continental crust in their petrogenesis. The distinct geochemical characteristics indicate not only distinct tectonic settings of their genesis but also the diverse nature of the crust forming the exotic continental ribbons amalgamated to Asia.〈strong〉Supplementary material:〈/strong〉 Details of sample locations and analytical results are available at: 〈a href="https://doi.org/10.6084/m9.figshare.c.4311485"〉https://doi.org/10.6084/m9.figshare.c.4311485〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Middle Jurassic Rattray Volcanic Province is located at the triple junction of the North Sea continental rift system. It has previously been thought to be sourced from three large central volcanoes: the Glenn, Fisher Bank and Ivanhoe volcanic centres. Re-interpretation using 3D seismic and well data shows that no volcanic centres are present and the Rattray Volcanics were instead sourced in fissure eruptions from linear vents, including the Buchan–Glenn Fissure System, a 〈span〉c.〈/span〉 25 km long zone of WSW–ENE-striking linear fissure vents and associated small volcanic edifices across the Buchan–Glenn Horst. The orientation of the fissures is broadly parallel to the Highland Boundary Fault, which intersects the Rattray Volcanics at the Buchan–Glenn Fissure System, implying that Mid-Jurassic magmatism exploited pre-existing crustal structural anisotropies established during the Caledonian Orogeny. The lack of large intrusive complexes beneath the Rattray Volcanics indicates that the pre-Middle Jurassic sedimentary sequences (e.g. the Devonian–Carboniferous Old Red Sandstone Group, the Permian Rotliegend and Zechstein groups and the Triassic Skagerrak Formation) extend further than previously supposed and therefore the presence of possible subvolcanic reservoir and source rock units within the triple junction of the Central North Sea may have been overlooked.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Ordovician peri-Laurentian Grangegeeth Terrane in eastern Ireland and the adjacent Katian to Wenlock Rathkenny Tract are together a relic of the closing Iapetus Ocean. The Rathkenny Tract succession is part of the Laurentian Southern Uplands-Down-Longford Terrane accretionary prism, but the contact between the Rathkenny and Grangegeeth terranes is cryptic.Two cores of Lower Paleozoic strata along a buried projection of the Rathkenny - Grangegeeth outcrops contain volcaniclastic units within a succession of mudstone and siltstone. LA-ICPMS U-Pb dating of zircon from volcanogenic horizons yielded a maximum depositional age of c. 450 Ma. Nearly 98% of zircon ages are 445 – 480 Ma, indicating a proximal volcanic source. Trace element geochemistry of Ordovician zircon indicates host magma sourced in continental crust. A diverse ostracod fauna in mudstone suggests a Katian age, and includes species with Baltic, Laurentian and Avalonian affinities.We propose a paired-subduction-zone model for emplacement of the Grangegeeth/Rathkenny succession, with the Rathkenny strata deposited on an oceanic plate between the Laurentian-margin accretionary prism and the 480-450 Ma Grangegeeth peri-Laurentian micro-continental arc. Volcaniclastic detritus fed into the Rathkenny basin was then incorporated into the accretionary prism. The mixed fauna indicates that the Iapetus Ocean was narrow by Katian time.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4358243"〉https://doi.org/10.6084/m9.figshare.c.4358243〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Structural field relationships, petrography and geochemical features of plagiogranites and associated intermediate (diorite) to mafic rocks (basalt and gabbro) of the Habana–Matanzas ophiolites in northern Cuba suggest that these felsic and mafic rock units represent a boundary case between forearc and volcanic arc ophiolite types. Subduction-related basalts can be subdivided into back-arc, back-arc to forearc, forearc and volcanic arc types. The majority of the basalts plot in the oceanic arc (as well as joint oceanic arc–continental arc) field of the Th/Yb–Nb/Yb diagram. The samples that classify as volcanic arc basalts plot in the continental arc field of the Th/Yb–Nb/Yb diagram and within the island arc tholeiite and boninite fields in the V–Ti diagram. The Habana–Matanzas plagiogranites and associated basalts, diabases and gabbros display significantly negative Ta–Nb anomalies and are depleted in heavy rare earth elements. 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar whole-rock plateau ages of these plagiogranites reveal minimum crystallization ages of 98.11 ± 0.50 Ma, providing the first important time constraint for suprasubduction zone oceanic crust formation on the island of Cuba. Based on our petrogenetic modelling and geochemical characterization, we conclude that magmas of the plagiogranites and associated intermediate rocks of the Habana–Matanzas ophiolites were derived from partial melting of highly depleted, pre-existing crustal rocks (basalt and/or gabbro).〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉We have used clumped isotope thermometry to study a fault-hosted hydrothermal calcite vein associated with the Mississippi Valley Type (MVT) mineralization on the Derbyshire Platform in the southern Pennines, UK. This is the first published dataset obtained using a new mass spectrometer, MIRA, optimized for clumped isotope analysis and an associated clumped isotope–temperature calibration. We analysed multiple generations of vein growth at high spatial resolution in two transects across the vein. The vein grew episodically at temperatures between 40 and 100°C. We interpret each episode of growth as being associated with an increasing flux of formation waters from deep sedimentary basins next to the mineralized platform and an accompanying increase in the precipitation temperatures. Heat is conserved in the fluid as it ascends along the fault surface and, thus, flow must have been fast and restricted to short-lived pulses. The flux could have been driven by high pore pressures associated with rapid sedimentation, hydrocarbon generation and diagenesis in the basinal facies of the Visean Bowland–Hodder group. Natural hydraulic fracturing of shale units and failure of capillary seals, possibly triggered by uplift, allowed the release of fluids into aquifers within the sediment pile. The transmission of high pore fluid pressures from the shales to the fault zone, aided by the compressibility of the gas phase in two-phase pore fluids, may have resulted in fault rupture, accompanied by enhanced fracture permeability and rapid fluid flow. Vein growth ceased as pore pressures dissipated. Such behaviour is closely related to a seismic valve type model for mineralization.〈strong〉Supplementary material:〈/strong〉 Details of the methods and equipment are available at 〈a href="https://dx.doi.org/10.6084/m9.figshare.3808329.v9"〉https://dx.doi.org/10.6084/m9.figshare.3808329.v9〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Here we present the second part of the special thematic issue on the Carnian Pluvial Episode (CPE). In this issue, two works on terrestrial sedimentological and floral changes linked to the CPE, and new carbon isotope records from Oman and China are presented. The papers published in this issue complement those contained in volume 175 issue 6; they altogether give an almost complete vision of the state-of-the-art about the CPE, including the many conundrums.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The preservation of ultra-high-pressure and super-reducing phases in the Neotethyan Luobusa ophiolite in Tibet suggests their deep origin near the mantle transition zone. Dunite and harzburgite core samples from the Luobusa Scientific Drilling Project show supra-subduction zone geochemical signatures and equilibration temperatures of 〈span〉c.〈/span〉 950–1080°C. Olivine shows A-, B-, C- and E-type fabrics, and combinations of A- and E-type or B- and E-type fabrics. Transmission electron microscopy observations show straight dislocations and the activation of multiple slip systems [100](010), [001](010), [001](100) and [100](001) in olivine. The mean water content in olivine, orthopyroxene (Opx) and clinopyroxene (Cpx) from 24 peridotite samples was 16 ± 5, 90 ± 21 and 492 ± 64 ppm, respectively, which is different from the water content of hydrated peridotites above the mantle wedge. The trace element compositions of Cpx exclude significant metasomatism after melt extraction. The high hydrogen partition coefficient between Cpx and Opx (〈span〉D〈/span〉〈sub〉H〈/sub〉〈sup〉Cpx/Opx〈/sup〉 = 5.56 ± 0.96) implies equilibrium at high pressures and rapid exhumation. Based on deformation experiments, the B- and C-type fabrics could be formed in a subduction zone at depths 〉200 km, whereas the A- and E-type fabrics were produced in the shallow mantle. In a process triggered by slab rollback, the Luobusa peridotites may have been rapidly exhumed within a subduction channel and mixed with the lithospheric mantle of the forearc.〈strong〉Supplementary material:〈/strong〉 Major oxide contents in Opx, Cpx and spinel, trace element concentration in Cpx, micrographs and TEM images of peridotite are available at 〈a href="https://doi.org/10.6084/m9.figshare.c.4307828"〉https://doi.org/10.6084/m9.figshare.c.4307828〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Herefordshire Lagerstätte (〈span〉c〈/span〉. 430 Ma) from the UK is a rare example of soft-tissue preservation in the Silurian. It yields a wide range of invertebrates in unparalleled three-dimensional detail, dominated by arthropods and sponges. The fossils are exceptionally preserved as calcitic void infills in early diagenetic carbonate concretions within a volcaniclastic (bentonite) horizon. The Lagerstätte occurs in an outer shelf/upper slope setting in the Welsh Basin, which was located on Avalonia in the southern subtropics. The specimens are investigated by serial grinding, digital photography and rendering in the round as ‘virtual fossils’ by computer. The fossils contribute much to our understanding of the palaeobiology and early history of the groups represented. They are important in demonstrating unusual character combinations that illuminate relationships; in calibrating molecular clocks; in variously linking with taxa in both earlier and later Paleozoic Lagerstätten; and in providing evidence of the early evolution of crown-group representatives of several groups.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Spence Shale Member of the Langston Formation is a Cambrian (Miaolingian: Wuliuan) Lagerstätte in northeastern Utah and southeastern Idaho. It is older than the more well-known Wheeler and Marjum Lagerstätten from western Utah, and the Burgess Shale from Canada. The Spence Shale shares several species in common with these younger deposits, yet it also contains a remarkable number of unique species. Because of its relatively broad geographic distribution, and the variety of different palaeoenvironments and taphonomy, the fossil composition and likelihood of recovering weakly skeletonized (or soft-bodied) taxa varies across localities. The Spence Shale is not only widely acknowledged for its collection of soft-bodied taxa, but also for its abundant trilobites and hyoliths. Recent discoveries from the Spence include problematic taxa and insights about the nature of palaeoenvironmental and taphonomic variation between different localities.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4423145"〉https://doi.org/10.6084/m9.figshare.c.4423145〈/a〉〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Carbon is subducted to depths where metamorphism liberates water-bearing fluids. The C-bearing fluids facilitate partial melting of the upper mantle, generating magmas that may erupt as arc volcanics. Degassing of the magmas releases CO〈sub〉2〈/sub〉 and other volatile species to the atmosphere. Over geological time, this process contributes to the composition of the atmosphere and planetary habitability. Here I summarize the background needed to carry out theoretical geochemical modelling of fluids and fluid–rock interactions from surficial conditions into the upper mantle. A description of the general criteria for predicting equilibrium and non-equilibrium chemical reactions is followed by a summary of how the thermodynamic activities of species are related to measurable concentrations through standard states and activity coefficients. Specific examples at ambient conditions involving dilute water are detailed. The concept of aqueous speciation and how it can be calculated arises from this discussion. Next, I discuss how to calculate standard Gibbs free energies and aqueous activity coefficients at elevated temperatures and pressures. The revised Helgeson–Kirkham–Flowers equations of state are summarized and the revised predictive correlations for the estimation of equation of state coefficients in the Deep Earth Water (DEW) model are presented. Finally, the DEW model is applied to the solubility and speciation of aqueous aluminium.〈/span〉

Description: Crack-seal texture within fracture cements in the Triassic El Alamar Formation, NE Mexico, shows that the fractures opened during precipitation of quartz cements; later, overlapping calcite cements further occluded pore space. Previous workers defined four systematic fracture sets, A (oldest) to D (youngest), with relative timing constrained by crosscutting relationships. Quartz fluid inclusion homogenization temperatures are higher within Set B (148 ± 20°C) than in Set C (105 ± 12°C). These data and previous burial history modelling are consistent with Set C forming during exhumation. Fluid inclusions in Set C quartz have higher salinity than those in Set B (22.9 v. 14.2 wt% NaCl equivalent, respectively), and Set C quartz cement is more enriched in 18 O (20.2 v. 18.7 VSMOW). Under most assumptions about the true temperature during fracture opening, the burial duration, the amount of cement precipitated and fluid-flow patterns, it appears that the fracture fluid became depleted in 18 O and enriched in 13 C. This isotopic evolution, combined with increasing salinity, suggests that throughout fracture opening there was a gravity-driven influx of fluid from upsection Jurassic evaporites, which form a regional décollement. Fracture opening amid downward fluid motion suggests that fracturing was driven by external stresses such as tectonic stretching or unloading, rather than increases in fluid pressure.

Description: Calcite pseudomorphs have replaced euhedral ikaite (CaCO 3 .6H 2 O) porphyroblasts in Dalradian calcareous slates and metadolostones of western Scotland, with a volume decrease of at least 47%. Porphyroblast–fabric relationships indicate that the initial growth of ikaite post-dates a penetrative tectonic fabric developed during upright folding. This is the first reported occurrence of metamorphic ikaite porphyroblasts and points towards growth within the slates during an ultra-low-temperature metamorphism with an exceptionally low geothermal gradient. This event is associated with the penetration of long-lived and extreme permafrost deep into subaerially exposed bedrock during Neoproterozoic glaciation. The presence of the well-preserved pseudomorphs within the Easdale slates of the Argyll Group implies that a Neoproterozoic orogenic unconformity exists above the stratigraphic position of these rocks.

Description: The addition of crustal sulphur to magma can trigger sulphide saturation, a process fundamental to the development of some Ni–Cu–PGE deposits. In the British Palaeogene Igneous Province, mafic and ultramafic magmas intrude a thick sedimentary sequence offering opportunities to elucidate mechanisms of magma–crust interaction in a setting with heterogeneous S isotope signatures. We present S-isotopic data from sills and dykes on the Isle of Skye. Sharp contrasts exist between variably light 34 S in Jurassic sedimentary sulphide (–35 to –10) and a local pristine magmatic 34 S signature of –2.3 ± 1.5. Flat-lying sills have restricted 34 S (–5 to 0) whereas steeply dipping dykes are more variable (–0 to –2). We suggest that the mechanism by which magma is intruded exerts a fundamental control on the degree of crustal contamination by volatile elements. Turbulent flow within narrow, steep magma conduits, discordant to sediments, and developed by brittle extension or dilation have maximum contamination potential. In contrast, sill-like conduits emplaced concordantly to sediments show little contamination by crustal S. The province is prospective for Ni–Cu–PGE mineralization analogous to the sill-hosted Noril’sk deposit, and Cu/Pd ratios of sills and dykes on Skye indicate that magmas had already reached S-saturation before reaching the present exposure level. Supplementary material: Details of the whole-rock chemical sulphur extraction method; simplified geological maps of the Isle of Skye, a geological cross-section of part of southern Skye, and a stratigraphic log of the Mesoproterozoic and Mesozoic sediments of western Scotland; trace element diagrams of sills and dykes used in this study; and tables for QA/QC of S-isotope results, sample location information, and whole-rock major and trace element results for sill and dyke samples and for Jurassic mudrocks are available at http://www.geolsoc.org.uk/SUP18834 .

Description: Mass-balance calculations indicate that a massive amount of 13 C-depleted carbon was released into the early Danian atmosphere in volumes comparable with the younger Paleocene–Eocene Thermal Maximum (PETM). This Danian hyperthermal event (the Dan-C2) has been documented from the fill of the Boltysh meteorite crater, Ukraine. Palynofloras recovered from the Boltysh crater fill show a trend from mesic forest to savannah ecosystem dominance on a millennial scale across the hyperthermal inception with no abrupt compositional shift. This longer-term trend is overprinted by moisture availability oscillations reflecting orbital forcing. Forcing is not directly tracked by the oscillations, which are composed of mesic forest and savannah palynofloras separated by rapid critical transitions. The absence of an ecological collapse at the Dan-C2 indicates that plant ecosystems experienced dominant forcing from orbital cyclicity, rather than a stochastic temperature rise.

Description: The Plio-Quaternary magmatism in the Tyrrhenian Sea area exhibits wide compositional variations, which cover almost entirely those observed for volcanic rocks worldwide. Some volcanoes (Etna, Iblei, Sardinia, etc.) range from tholeiitic to Na-alkaline, and display elemental and isotope signatures typical of FOZO and EM-1 ocean-island basalts (OIB). Other volcanoes (Aeolian Arc, Italian peninsula) range from calc-alkaline–shoshonitic to K-alkaline, exhibit typical ‘subduction-related’ trace element signatures (low Ta–Nb, high Rb–Cs–LREE), and show a large range of radiogenic isotope ratios, from mantle-like in the Aeolian Arc to crustal-like in central Italy. Geochemical data suggest that OIB-type magmatism originated in lithosphere–asthenosphere sources that were unaffected by recent subduction. In contrast, subduction-related magmas come from mantle sources that underwent Eocene to present mixing with various amounts and types of subducted crustal components. Fluxing of the mantle wedge by water-rich fluids from a mid-ocean ridge basalt-type slab occurred in the southern Tyrrhenian Sea, whereas interaction between peridotite and various types of sediments occurred in central Italy. These contrasting styles of mantle contaminations relate to the nature (oceanic or continental) of the foreland, slab geometry and pre-metasomatic mantle compositions, which vary greatly along the Apennine arc and are the reason for the formation of the wide variety of orogenic magmas in Italy.

Description: A characteristic association of crustal and mantle rocks is commonly used to decipher processes at the mantle–crust interface of HP–UHP collisional orogenic systems. Also, in the Variscan orogenic root of the Bohemian Massif (the Moldanubian Zone), high-pressure felsic granulites are often accompanied by spinel or garnet peridotites. This association was investigated using petrography, zircon geochronology and whole-rock geochemical data from the Náměšť Granulite Massif. The geochemical signature of the granulite is the same as for other Moldanubian occurrences, suggesting nearly isochemically metamorphosed felsic metaigneous rocks of Saxothuringian provenance. SHRIMP zircon dating yielded two main age maxima, at 395.2 ± 4.4 and 337.2 ± 1.7 Ma, reflecting an Early Devonian protolith and Visean HP metamorphism. As shown by Sr–Nd isotopic data, the variably refertilized harzburgite or depleted lherzolite was variously contaminated by mature crustal material resembling the studied granulites. To account for the origin of these HT–HP rock associations we suggest a new geotectonic model. An eastward continental subduction of Early Palaeozoic felsic metaigneous material of Saxothuringian origin was followed by its relamination at the bottom of the autochthonous lower crust. Ascending felsic granulites derived from the relaminated lower plate material sampled refertilized harzburgites originally formed in a back-arc. The complete assemblage was subsequently exhumed, forming large, diapir-like bodies. Supplementary material: Sample coordinates from the Náměšť Granulite Massif, analytical techniques, SHRIMP age measurements on zircon grains and whole-rock geochemical data are available at http://www.geolsoc.org.uk/SUP18833 .

Description: Cambrian to middle Ordovician schists and phyllites in southwestern Baltica, now exposed in the (par-)autochthon to Lower Allochthon nappes of the Scandinavian Caledonides in southern Norway, contain previously unrecognized far-travelled detrital zircons with ages in the intervals 0.47–0.8 and 1.85–3.2 Ga and Hf in the range –27 to +18. These ages are assigned to Timanian and Fennoscandian Shield sources respectively and contrast with the locally derived detritus with zircon ages of c . 0.9–1.8 Ga and Hf values c . –13 to +10. The far-travelled zircons provide evidence that a steady, long-haul, source-to-sink drainage system existed from the northeastern fringe of Baltica to the SW passive margin across the whole palaeocontinent ( c . 2000 km) since c . 521 Ma, and that the Timanian orogen shed detritus across large distances towards both its foreland (Baltica) and hinterland (Arctica). There are several arguments against an Avalonian source for these zircons. Recycling of the detrital zircon from the Cambrian to middle Ordovician sediments is probably responsible for the presence of Cryogenian to Middle Ordovician zircon ages in younger sedimentary sequences of southwestern Baltica. The development of an ophiolitic mélange associated with Ordovician phyllites underlying the Jotun Nappe Complex seems to mark the change to an active continental margin in the middle Ordovician, heralding the Caledonian orogeny. The study demonstrates that detrital zircon-poor fine-grained (siltstone to mudstone) sediments are an extremely valuable indicator for distal sources and favourably complement zircon-rich coarser sandstone in provenance analysis. Supplementary material: Results of LA-ICP-MS and SIMS U–Pb–Hf analyses of zircons with details of analytical methods and the collection of CL images of the youngest (〈500 Ma) detrital zircon grains are available at http://www.geolsoc.org.uk/SUP18827 .

Description: A petrological and metamorphic comparison of Mesoproterozoic metabasic rocks was conducted on the eastern margin of the Archaean Kaapvaal–Grunehogna Craton and the adjacent westernmost Maud Belt (western H.U. Sverdrupfjella), across a major structural discontinuity known as the Pencksökket–Jutulstraumen Discontinuity. Thermodynamic phase diagram modelling of the low- and high-grade metabasaltic assemblages on either side of the discontinuity revealed a difference in peak metamorphic conditions from T = 340 ± 25 to 700 ± 30°C and P = 0.29 ± 0.08 to 0.90 ± 0.10 GPa over an extrapolated orthogonal distance of 32 km across the strike of the discontinuity. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of titanite in a hornblende–plagioclase–quartz corona around garnet yielded a late Pan-African age of 491 ± 27 Ma for high-grade metamorphism in the western H.U. Sverdrupfjella of the Maud Belt. The new petrological and geochronological constraints indicate that peak upper amphibolite-facies conditions were achieved in the western H.U. Sverdrupfjella at c . 500 Ma; namely, c . 70–80 Ma after peak eclogite–high-pressure granulite-facies metamorphism in the eastern H.U. Sverdrupjella. The U–Pb age data argue against previous models that invoke only late Mesoproterozoic ( c . 1060–1030 Ma) granulite-facies metamorphism in the western H.U. Sverdrupfjella and Kaapvaal–Grunehogna Craton margin, and support the concept of a major diachronous Pan-African orogenic episode. A new geodynamic model is presented for western Dronning Maud Land, involving earliest Pan-African eclogite–high-pressure granulite- and upper amphibolite-facies metamorphism in a separate eastern H.U. Sverdrupjella terrane between c . 565 and 540 Ma, followed by later diachronous tectonic accretion of the eastern H.U. Sverdrupjella arc segment onto the western H.U. Sverdrupfjella crustal segment (including the easternmost Kaapvaal–Grunehogna Craton margin) that involved only upper amphibolite-facies metamorphism at c . 500 Ma. The new petrological data indicate that the inferred sub-glacial boundary (Pencksökket–Jutulstraumen Discontinuity) between the Kaapvaal–Grunehogna Craton and the western H.U. Sverdrupfjella region represents a major cratonic Pan-African thrust, which was subsequently reactivated by normal faulting during Gondwana break-up. Supplementary materials: Analytical details, representative mineral compositions, and geothermometry and geobarometry results are available at http://www.geolsoc.org.uk/SUP18832 .

Description: We infer system-scale fluid flow in the Late Jurassic Salt Wash fluvial succession (SW USA) by plotting uranium deposit distribution against sedimentological data, using uranium distribution as a proxy for subsurface fluid flow. More than 90% of uranium deposits in the Salt Wash occur where sandstone forms 40–55% and sand-rich channel-belts form 20–50% of the succession, which coincides with changes in channel-belt connectivity and gross-scale architecture. The paucity of uranium below these cut-off values suggests that fluid flow is related directly to predictable downstream fining and facies variations in distributive fluvial systems. Supplementary material: A summary table of location data, key trends and the amalgamation ratio method is available at https://doi.org/10.6084/m9.figshare.c.2849581 .