ALBERT

Description: Middle to Late Jurassic belemnites from the Spiti and Zanskar valleys in the Indian Himalayas were used for stable isotope (δ13C, δ18O) and element (Mg/Ca, Sr/Ca) analyses. Although the Himalayan orogeny deformed and altered a large portion of the collected fossils, cathodoluminescence and scanning electron microscopy in combination with analyses of iron and manganese contents allowed the identification of belemnites believed to still retain their original chemical composition. Results indicate a long-term temperature decrease from the Middle Callovian–Oxfordian to the Tithonian, which is proposed to have been caused by a concomitant drift of eastern Gondwana into higher palaeolatitudes. Reconstructed absolute temperatures depend on the used equation and assumed δ18O value of seawater, but most likely varied between 17.6 °C to 27.6 °C in the Kimmeridgian and Tithonian with average values between 22 °C to 24 °C. This way, temperatures were similar to slightly warmer than today at comparable latitudes. The reconstruction of absolute temperatures for the Middle Callovian–Oxfordian was hindered by a larger number of poorly preserved belemnites representing this time interval.

Description: Deltas constitute complex depositional systems formed when a land-derived gravity-flow (carrying water and sediments) discharges into a marine or lacustrine standing body of water. However, the complexity of deltaic sedimentary environments has been oversimplified by geoscientists over the years, considering just littoral deltas as the unique possible type of delta in natural systems. Nevertheless, a rational analysis suggests that deltas can be much more complex. In fact, the characteristics of deltaic deposits will depend on a complex interplay between the bulk density of the incoming flow and the salinity of the receiving water body. This paper explores the natural conditions of deltaic sedimentation according to different density contrasts. The rational analysis of deltaic systems allows to recognize three main fields for deltaic sedimentation, corresponding to (1) hypopycnal (2) homopycnal and (3) hyperpycnal delta settings. The hypopycnal delta field represents the situation when the bulk density of the incoming flow is lower than the density of the water in the basin. According to the salinity of the receiving water body, three different types of hypopycnal littoral deltas are recognized: hypersaline littoral deltas (HSLD), marine littoral deltas (MLD), and brackish littoral deltas (BLD). The basin salinity will determine the capacity of the delta for producing effective buoyant plumes, and consequently the characteristics and extension of prodelta deposits. Homopycnal littoral deltas (HOLD) form when the density of the incoming flow is roughly similar to the density of the water in the receiving basin. This situation is typical of clean bedload-dominated rivers entering freshwater lakes. Delta front deposits are dominated by sediment avalanches. Typical fallout prodelta deposits are absent or poorly developed since no buoyant plumes are generated. Hyperpycnal deltas form when the bulk density of the incoming flow is higher than the density of the water in the receiving basin. The interaction between flow type, flow density (due to the concentration of suspended sediments) and basin salinity defines three types of deltas, corresponding to hyperpycnal littoral deltas (HLD), hyperpycnal subaqueous deltas (HSD), and hyperpycnal fan deltas (HFD). Hyperpycnal littoral deltas are low-gradient shallow-water deltas formed when dirty rivers enter into brackish or normal-salinity marine basins, typically in wave or tide-dominated epicontinental seas or brackish lakes. Hyperpycnal subaqueous deltas represent the most common type of hyperpycnal delta, with channels and lobes generated in marine and lacustrine settings during long-lasting sediment-laden river-flood discharges. Finally, hyperpycnal fan deltas are subaqueous delta systems generated on high-gradient lacustrine or marine settings by episodic high-density fluvial discharges.

Description: The underpinning problems of deep-water facies still remain unresolved. (1) The Tb, Tc, and Td divisions of the turbidite facies model, with traction structures, are an integral part of the “Bouma Sequence” (Ta, Tb, Tc, Td, Te). However, deposits of thermohaline contour currents, wind-driven bottom currents, deep-marine tidal currents, and baroclinic currents (internal waves and tides) also develop discrete rippled units, mimicking Tc. (2) The application of “cut-out” logic of sequences, which was originally introduced for the “Bouma Sequence”, with sharp basal contacts and sandy divisions containing well-developed traction structures, to muddy contorts with gradational basal contacts and an absence of well-developed traction structures is incongruent. (3) The presence of five internal divisions and hiatus in the muddy contoured facies model is in dispute. (4) Intersection of along slope contour currents with down slope sediment-gravity flows, triggering hybrid flows, also develops traction structures. (5) The comparison of genuine hybrid flows with down slope flow transformation of gravity flows is inconsistent with etymology of the term “hybrid”. (6) A reexamination of the Annot Sandstone at the Peira Cava type locality in SE France fails to validate either the orthodoxy of five internal divisions of the “Bouma Sequence” or their origin by turbidity currents. For example, the “Ta” division is composed of amalgamated units with inverse grading and floating mudstone clasts, suggesting a mass-transport deposit (MTD). The “Tb” and “Tc” divisions are composed of double mud layers and sigmoidal cross bedding, respectively, which suggest a tidalite origin. (7) Although it was reasonable to introduce a simplistic “Bouma Sequence” in 1962, at a time of limited knowledge on deep-water processes, it is obsolete now in 2021 to apply this model to the rock record amid a wealth of new knowledge. (8) The disconnect between 12 observed, but questionable, modern turbidity currents and over 10,000 interpreted ancient turbidites defies the doctrine of uniformitarianism. This disconnect is attributed to routine application of genetic facies models, without a pragmatic interpretation of empirical data. (9) A suggested solution to these problems is to interpret traction structures in the sedimentary record pragmatically on the basis of empirical field and experimental evidence, without any built-in bias using facies models, such as the “Bouma Sequence”. (10) Until reliable criteria are developed to distinguish traction structures of each type of bottom currents based on uniformitarianism, a general term “BCRS” (i.e., bottom-current reworked sands) is appropriate for deposits of all four kinds of bottom currents.

Description: As a type of non-laminated microbial carbonates, dendrolites are dominated by isolated dendritic clusters of calcimicrobes and are distinct from stromatolites and thrombolites. The dendrolites in the upper part of the Miaolingian Zhangxia Formation at Anjiazhuang section in Feicheng city of Shandong Province, China, provide an excellent example for further understanding of both growth pattern and forming mechanism of dendrolites. These dendrolites are featured by sedimentary fabrics and composition of calcified microbes as follows. (1) The strata of massive limestones, composed of dendrolites with thickness of more than one hundred meters, intergrade with thick-bedded to massive leiolites, formimg the upper part of a third-order depositional sequence that constitutes a forced regressive systems tract. (2) A centimeter-sized bush-like fabric (shrub) typically produced by calcified microbes is similar to the mesoclot in thrombolites but distinctive from clotted fabrics of thrombolites. This bush-like fabric is actually constituted by diversified calcified microbes like the modern shrub as a result of gliding mobility of filamentous cyanobacteria. Such forms traditionally include: the Epiphyton group (which actually has uncertain biological affinity), the Hedstroemia group which closely resembles modern rivulariacean cyanobacteria, and the possible calcified cyanobacteria of the Lithocodium–Bacinella group. (3) Significantly, dense micrite of leiolite is associated with sponge fossils and burrows, and is covered by microstromatolite. The Lithocodium–Bacinella group is a controversial group of interpreted calcified cyanobacteria in the Cambrian that has also been widely observed and described in the Mesozoic. Therefore, dendrolites with symbiosis of leiolites in the studied section provide an extraordinary example for further understanding of growing style of bush-like fabrics (shrubs) of the dendrolites dominated by cyanobacterial mats. Furthermore, the present research provides some useful thinking approaches for better understanding of the history of the Early Paleozoic skeletal reefs and the microbe–metazoan transitions of the Cambrian.

Description: This contribution focuses on a multidisciplinary research showing the geomorphological evolution and the beach sand composition of the Tyrrhenian shoreline between Capo Suvero promontory and Gizzeria Lido village (Calabria, southern Italy). The aim of the geomorphological analysis was to reconstruct the evolutionary shoreline stages and the present-day sedimentary dynamics along approximately 6 km of coastline. The results show a general trend of beach nourishment during the period 1870–2019. In this period, the maximum shoreline accretion value was estimated equal to + 900 m with an average rate of + 6.5 m/yr. Moreover, although the general evolutionary trend is characterized by a remarkable accretion, the geomorphological analysis highlighted continuous modifications of the beaches including erosion processes. The continuous beach modifications occurred mainly between 1953 and 1983 and were caused mainly by human activity in the coastal areas and inside the hydrographic basins. The beach sand composition allowed an assessment of the mainland petrological sedimentary province and its dispersal pattern of the present coastal dynamics. Petrographic analysis of beach sands identified a lithic metamorphi-clastic petrofacies, characterized by abundant fine-grained schists and phyllites sourced from the crystalline terrains of the Coastal Range front and carried by the Savuto River. The sand is also composed of a mineral assemblage comparable to that of the Amato River provenance. In terms of framework detrital constituents of QFL (quartz:feldspars:aphanitic lithic fragments) and of essential extraclasts, such as granitoid:sedimentary:metamorphic phaneritic rock fragments (Rg:Rs:Rm), sand maturity changes moderately from backshore to shoreface, suggesting that transport processes had a little effect on sand maturity. Moreover, the modal composition suggests that the Capo Suvero promontory does not obstruct longshore sand transport from the north. Indeed, sands displaced by currents driven by storm-wave activity bypass this rocky headland.

Description: This study provides an overview and discussion of controls on the distribution of organic reefs during the Early Ordovican Period, in the Yangtze Platform, a region of epicontinental sedimentary rocks in South China. The Yangtze Platform was located in low latitudes during the Early Ordovician and recorded rich and diverse reefs through that time. During the late Tremadocian Epoch, dolomitic and stratiform stromatolites were common in supratidal to intertidal zones of the western Yangtze Platform, while columnar stromatolites formed in deeper waters of the eastern Yangtze Platform. Skeletal-dominated reefs occurred in upper subtidal settings of the central Yangtze Platform. A transition from microbial-dominated to metazoan-dominated reefs with shallowing-upward cycles was evident, indicating that the composition of the main reef-builders was driven mainly by water depth. Increasing metazoan competition during the Great Ordovician Biodiversification Event reduced the abundance of microbial reefs. Sufficient nutrient supply is interpreted to have promoted development of skeletal-dominated reefs locally in shallow settings in the central Yangtze Platform, especially represented by the expansion of abundant solitary fossils of lithistid sponges and Calathium. High salinity environmental settings facilitated the bloom of stromatolites in near-shore locations. Low oxygen content in deep subtidal settings may have led to the absence of skeletal reefs in these habitats, so the mass occurrences of stromatolites was located in the shallower-water central and eastern platform. No keratose sponge-bearing stromatolite can be confirmed across the platform during this interval.

Description: This study provides a combined analysis on the palynology, fossil charcoal and biomarkers of the subsurface coal deposits from a borehole RMB #2 drilled at the Dhulia Coal Block, Rajmahal Basin, India, in attempts to establish the chronology of sedimentation and to propose palaeobotanical as well as geochemical evidence for the occurrence of wildfires in these sediments. The palynological investigation suggests a Scheuringipollenites barakarensis palynoassemblage from the lower Barakar Formation, dated as Artinskian (Early Permian) in age. This assemblage reveals the dominance of Glossopteridales and sub-dominance of taxa belonging to Cordaitales and Coniferales. Fossil charcoal in sediments is usually recognized as a direct indicator for the occurrence of palaeo-wildfires. More data involving the anatomical features of fossil charcoal analyzed by Field Emission Scanning Electronic Microscope broaden our knowledge on Early Permian wildfires from the peninsula of India. The studied macroscopic charcoal fragments exhibit anatomical details such as homogenized cell walls, uniseriate simple and biseriate alternate pitting on tracheid walls and rays of varying heights pointing to a gymnospermous wood affinitity. The excellent preservation of charcoal fragments, shown by their large sizes and almost unabraded edges, suggests a parautochthonous origin. The embedded biomarker study performed for charcoal sediments and its characterization demonstrate the presence of n-alkanes, isoprenoids, terpenoids and aromatic compounds. A bimodal distribution pattern of n-alkanes with a Cmax at n-C25 is identified. Diterpenoids and pentacyclic terpenoids are identified, indicating the input of an early conifer vegetation and bacterial activity, respectively. The identified polyaromatic hydrocarbon (PAH) compounds, together with the charcoal fragments, clearly suggest that repeated wildfire events occurred during the deposition of these Artinskian sediments in the Rajmahal Basin.

Description: A new type of polyhalite potassium ore (NTPPO) was found in the Lower Triassic Jialingjiang Formation, NE Sichuan Basin, SW China. It is water soluble, therefore can be exploited using the water-solution method, and is of great potential of economic value and research significance. Based on cores, thin sections, energy spectrum and SEM analyses, its microfeatures, macrofeatures and origin are discussed, and a genetic model is established to provide a scientific basis for future evaluation, prediction and exploration of potassium ore in the Sichuan Basin. It is proposed that the NTPPO was caused by storm activities: (1) the storm broke the original sedimentary polyhalite–gypsum beds, whose fragments were transported into the salt basin with high content of K+ and Mg2+; (2) in the basin, the polyhalite continued to be formed from gypsum by metasomatism with K- and Mg-rich brine; (3) during diagenesis, under high temperature and high pressure, K–Mg-rich brine from halite continued to replace anhydrite (or gypsum) to form polyhalite.

Description: An amendment to this paper has been published and can be accessed via the original article.

Description: Rising sea-levels in tectonically active epicontinental basins often lead to varied depositional settings and palaeogeography, mostly influenced by the net accommodation resulting from mutual interference of the extent and nature of landward encroachment by the sea and the net sedimentation. The Cenomanian Nimar Sandstone Formation, Bagh Group, Narmada rift basin, uniquely portrays the effect of sea-level rise within an intra-cratonic setting and attributes to the corresponding palaeogeographic changes in west-central India. An integrated sedimentological–sequence-stratigraphic study of the broadly fining-upward Nimar Sandstone Formation (thickness ~ 20–30 m) depicts the actual nature of changeover from a fluvial to a marine-dominated transitional depositional setting. Detailed sedimentological study reveals total seventeen facies, grouped in five facies associations, viz., the channel-fill facies association (FA-1), the overbank facies association (FA-2), the fluvial-dominated fluvio-tidal facies association (FA-3), the tide-dominated fluvio-tidal facies association (FA-4), and the shoreface facies association (FA-5). Overall facies architecture indicates a west-to-eastward marine encroachment, resulting in stacking of three distinct palaeo-depositional conditions: (i) an initial fluvial system with channel and overbank, changing into a tide-influenced fluvial bay-head delta in the inner estuary, followed by (ii) marine encroachment leading to a tide-dominated central estuary with inter- to sub-tidal settings, and finally, (iii) with further intense marine encroachments, a wave-reworked open shore condition in the outer estuary zone. The overall fining-up succession with a systematic change from fluvial to marine-dominated depositional systems points to a landward shift of the shoreline, signifying a major transgressive event correlated to the Cenomanian global sea-level rise. Characteristic stratal stacking patterns point to four coarsening- and fining-up hemicycles, embedded within the major transgressive succession. These high-frequency cycles attest to the varied interplay of sedimentation, tectonics and sea-level changes, and the resultant net accommodations. A palaeogeographic model is proposed based on the high-frequency transgressive–regressive hemicycles, which envisages the evolution of the depositional environments in relation to the Cenomanian eustatic rise in the intra-cratonic riftogenic fluvio-marine transitional basinal setup.