Shallow Marine Environment Research Articles

Effects of interface roughness and layer thickness on the cracking characteristics of fine-grained coral soil

Fine-grained coral soil, prevalent in tropical shallow marine environments, demonstrates significant potential as a natural engineering material. This study presents laboratory experiments employing digital image technology to investigate the effects of soil layer thickness and interface roughness on its cracking characteristics. By analyzing soil particle displacement during the cracking process, we examined the relationship between particle movement and the observed macroscopic crack patterns. The results indicate that both interface roughness and soil thickness substantially influence crack development and morphology. Increased interface roughness accelerates the cracking rate and transforms the pattern from overall contraction to multi-directional expansion, resulting in dense crack networks. Thinner soil layers facilitate more intricate crack formations, whereas thicker layers lead to more pronounced settling, longer and wider cracks, reduced horizontal cracking, and a simplified overall cracking pattern. This study elucidates the impact of interface roughness and soil layer thickness on the cracking behavior of fine-grained coral soil, providing valuable insights for its potential engineering applications.

High-sensitivity optical fiber seawater temperature and pressure sensor with a low-error demodulation method.

Using a single optical microfiber (OM) sensor for multi-parameter sensing can lead to significant demodulation error due to ill-conditioned matrices and nonlinear response characteristics. To address these issues, this paper proposes a novel specially packaged optical microfiber coupler combined with a silver mirror (OMCM). OMCM is combined with a mechanically enhanced sensitivity fiber Bragg grating (FBG) to form a temperature-pressure sensor. The temperature sensitivity exceeds -1.7 nm/°C while the pressure sensitivity reaches 53.435 nm/MPa, with a depth resolution of 0.935 cm. According to the characteristics of the sensor spectrum, this paper proposes a new demodulation method, which combines machine learning methods with a traditional wavelength-tracking method to achieve low demodulation error. For temperature and pressure, the mean absolute percentage errors are 0.04% and 1.31%, respectively. This feature facilitates the detection of minute changes in shallow marine environments, lacustrine systems, and other aquatic habitats, thus making it highly suitable for applications such as underwater aquaculture and marine monitoring.

Geochemical and Mineralogical Insights into Organic Matter Preservation in the Gondwana and Post-Gondwana Shale of the Lesser Himalayas, Nepal

The depositional environments, weathering and provenance, organic matter enrichment, and preservation in the Gondwana and post-Gondwana units of the Lesser Himalayas, Nepal, are studied through geochemical and mineralogical analyses using petrography, X-ray diffraction, XRF, and ICP-MS. Mineralogical findings indicate that shales comprise 55% to 72% clay, 25% to 55% quartz, and less than 10% carbonate minerals, with a significant presence of illite, suggesting a transition from fluvial to shallow marine environments during post-Gondwana deposition. The thin sections of the post-Gondwana sandstone reveal an increase in quartz, feldspar, and plagioclase content, with rounded to sub-angular quartz grains indicating moderate transportation before lithification, resulting from the Indo-Asian collision. Geochemical data, including major, trace, and rare earth elements (REE), along with bivariate discrimination diagrams, reveal distinct environmental changes; Gondwana sediments exhibit oxic, arid conditions with continental provenance, while post-Gondwana deposits indicate humid environments favorable for organic matter enrichment, primarily sourced from felsic-intermediate igneous rocks. The TOC is less than 1 wt.% in the Gondwana and is 0.75 to 2 wt.% in the post-Gondwana shale, indicating better organic matter preservation. The existing geological structural data and the research findings highlight the pivotal role of Himalayan tectonism in enhancing the thermal maturity and hydrocarbon generation potential of organic-rich post-Gondwana shales, attributed to their substantial organic matter content.

The record of the Early Late Paleocene Event (ELPE, 59.5 Ma) in shallow-water Tethys Himalayan carbonates (Zongpu Formation, South Tibet)

ABSTRACT The Early Late Paleocene Event (ELPE, 59.5 Ma) was a short-lived climatic perturbation accompanied by prominent biotic changes. Although the ELPE has been widely recognized from pelagic and continental archives, shallow-marine records remain scarce and poorly documented. To constrain the pattern and magnitude of the ELPE and associated environmental changes, we here present a detailed sedimentologic, biostratigraphic, and stable-carbon-isotope study of upper Paleocene platform carbonates continuously exposed in the Jiajin section of southern Tibet. Two distinct negative carbon-isotope excursions (CIEs) are documented: the first one occurred during shallow benthic zone (SBZ) 3 with a magnitude of ∼ 1.0‰, the second one began near the SBZ3–SBZ4 boundary with a magnitude of ∼ 1.5‰. Carbonate microfacies dominated by packstones with rotaliids and/or dasycladacean algae testify to an open shallow-marine environment. Neither a significant change in paleo–water depth nor evidence of early diagenetic dissolution are documented across the ELPE. The microfacies change observed during the ELPE, characterized by a decrease in the abundance of larger benthic rotaliid foraminifera relative to calcareous green algae, is related to environmental perturbations and increased nutrient supply. The changed trophic level may have resulted from intensified continental weathering promoted in turn by global warming. Compared with biocalcification crises observed in deep-water sedimentary records, shallow-water carbonate production remained relatively unaffected by changes in ocean-water chemistry.

Rotularia (Annelida: Sabellida: Serpulidae) attached to the mid-Cretaceous Burmese amber

Rotularia Defrance is a common extinct genus of planispirally coiled fossil polychaete worms in the family Serpulidae from shallow marine environment. Here, we describe a large collection of Rotularia specimens attached to mid-Cretaceous Burmese amber. The fossil record of Rotularia serves as a valuable tool for calibrating polychaete evolution and suggests that the Burmese amber forest was likely situated not far from the seashore.

Were early Archean carbonate factories major carbon sinks on the juvenile Earth?

Abstract. Paleoarchean carbonates in the Pilbara Craton (Western Australia) are important archives for life and environment on early Earth. Amongst others, carbonates occur in interstitial spaces of ca. 3.5–3.4 Ga pillow basalts (North Star, Mount Ada, Apex, and Euro Basalt, Dresser Formation) and are associated with bedded deposits (Dresser and Strelley Pool Formation, Euro Basalt). This study aims to understand the formation and geobiological significance of those early Archean carbonates by investigating their temporal–spatial distribution, petrography, mineralogy, and geochemistry (e.g., trace elemental compositions, δ13C, δ18O). Three carbonate factories are recognized: (i) an oceanic crust factory, (ii) an organo-carbonate factory, and (iii) a microbial carbonate factory. The oceanic crust factory is characterized by carbonates formed in void spaces of basalt pillows (referred to as “interstitial carbonates” in this work). These carbonates precipitated inorganically on and within the basaltic oceanic crust from CO2-enriched seawater and seawater-derived alkaline hydrothermal fluids. The organo-carbonate factory is characterized by carbonate precipitates that are spatially associated with organic matter. The close association with organic matter suggests that the carbonates formed via organo-mineralization – that is, linked to organic macromolecules (either biotic or abiotic), which provided nucleation sites for carbonate crystal growth. Organo-carbonate associations occur in a wide variety of hydrothermally influenced settings, ranging from shallow marine environments to terrestrial hydrothermal ponds. The microbial carbonate factory includes carbonate precipitates formed through mineralization of extracellular polymeric substances (EPSs) associated with microbial mats and biofilms. It is commonly linked to shallow subaquatic environments, where (anoxygenic) photoautotrophs might have been involved in carbonate formation. In the case of all three carbonate factories, hydrothermal fluids seem to play a key role in the formation and preservation of mineral precipitates. For instance, alkaline Earth metals and organic materials delivered by fluids may promote carbonate precipitation, whilst soluble silica in the fluids drives early chert formation, delicately preserving authigenic carbonate precipitates and associated features. Regardless of the formation pathway, Paleoarchean carbonates might have been major carbon sinks on the early Earth, as additionally suggested by carbon isotope mass balances indicating a carbon flux of 0.76–6.5 × 1012 mol yr−1. Accordingly, these carbonates may have played an important role in modulating the carbon cycle and, hence, climate variability on the early Earth.

A review of the Neogene formations and beds in Slovenia, Western Central Paratethys

Neogene sedimentary successions are found in eastern and northeastern Slovenia. Their formation was closely related to the evolution of the western part of the Pannonian Basin System and the Central Paratethys; it was influenced by global transgressive and regressive cycles as well as by global, regional and local tectonics. Several formations and beds were defined within the Neogene sedimentary successions which can be found in three separate areas. The first one includes the formations north of two major fault systems, the Periadriatic Fault System and the Mid-Hungarian Zone, which were associated with the Mura-Zala and the Styrian Basins, respectively. Successions south of these major faults are not formally connected to any of the major basins and developed in two distinct parts: a strip between Tunjice and Kozjansko to the north and the Krško area to the south. From the Egerian to the early Badenian, different areas exhibit different types of sedimentation, whereas from the middle Badenian onwards, sedimentation in different zones is partly comparable, depending on the type of depositional environment. Egerian and Eggenburgian sediments are only found south of the above-mentioned major fault zones, whereas Karpatian sedimentation only occurred north of them. Sediments in both areas are characterized by alternation of shallow marine, brackish and terrestrial sedimentation. In contrast, sedimentary environment in the Badenian evolved from a terrestrial, mainly fluvial environment with alluvial fans, through a transitional stage (delta and lagoon) to a shallow and deep marine environment. The Sarmatian sequences reflect a brackish environment with decreasing salinity and continue into extensive Pannonian delta systems that gradually fill the basins from west to east. The formations that correspond to the Pannonian in the Mura-Zala Basin can be correlated with the formations in the Krško area. The Pliocene is characterized by terrestrial sedimentation with the formation of rivers and lakes in the newly established intramontane basins.

Quantifying the rise of animals during the Ediacaran–Cambrian using ichnodissimilarity

Abstract The trace fossil record provides important insights into the evolution of early animals during the Ediacaran/Cambrian transition, with changes in ichnodiversity through time and between environments informing on the diversification of major body plans, behaviors, and niches. To quantify variation in the diversity of trace fossils across this critical interval, we propose a measure of trace fossil dissimilarity (ichnodissimilarity) based on vector calculation. Furthermore, by comparing discrepancies between the angular bisector and mean vector of two sets of vectorized fossil data, we are able to weigh the relative contribution of increases and decreases in the variation of occurrences of taxa. We used this metric to analyze an expansive dataset of Ediacaran/Cambrian trace fossils. The results allowed us to quantify the diversification of traces across this transition, informing on the timing of first appearance of different behaviors (e.g., foraging, grazing, and resting) and functional groups. By interpreting the results in the context of environmental changes and advancements in motility and sensory capabilities, we were able to pinpoint the onset and sequence of the Fortunian diversification event, Cambrian information revolution, and agronomic revolution, shedding light on the evolution of organismal body plans, behaviors, and locomotion during the Ediacaran/Cambrian transition. We identified two phases of origination and expansion during the divergence of early animal traces. Furthermore, by analyzing shallow- and deep-marine trace fossils, we were able to uncover evidence for a more rapid diversification of traces in shallow-marine environments, with progressive niche partitioning through the Ediacaran to Cambrian.

Paleoproterozoic Mississippi Valley-type mineralization at Black Angel, Greenland: evidence from sulfide δ66Zn and rhenium-osmium geochronology

AbstractWe provide timestamps for the major zinc-lead (Zn-Pb) Mississippi Valley-type Black Angel deposit (Greenland) based on new pyrite rhenium-osmium (Re-Os) isotope geochemistry data: (1) a Re-Os isochron age 1,884 ± 35 million years ago (Ma – 2σ, 1.8%) for subhedral pyrite cemented by sphalerite ± galena in dolomitized clean limestone, and, (2) a Re-Os model age 1,828 ± 16 Ma (2σ, 0.9%) for epigenetic massive pyrite in siltstone/mudstone cap rock. Zinc-lead mineralization in evaporite-bearing carbonates in the Karrat Basin took place ca. 1,884 Ma at the time of far-field fluid flow associated with back-arc spreading ca. 1,900–1,850 Ma. Mineralization predates the development of the Rinkian foreland basin (ca. 1,850 – < 1,800 Ma) and a collisional stage (ca. 1,830 – < 1,800 Ma) in the context of the telescoping Rinkian and the Nagssugtoqidian Orogens. Replacement of clean carbonate and sustained acid neutralization led to significant sphalerite precipitation ca. 1,884 Ma. Conversely, precipitation of epigenetic massive pyrite in the cap rock ca. 1,828 Ma may signal (1) the lack of chemical reactivity of the cap rock for the pH-buffered conditions needed for Zn-Pb mineralization, and (2) the unfavorable impact of incipient regional Rinkian metamorphism (ca. 1,830–1,800 Ma) and tectonic compression on aquifer permeability and continued brine migration. The initial 187Os/188Os ratio (Osi-pyrite = 1.07 ± 0.32) from isochron regression identifies a crustal origin for Os and, by corollary, other metals in the ca. 1,884 Ma Zn-Pb mineralization. Although the Rae Craton basement rocks comprise the dominant source for metals (based on our Osi-pyrite and δ66Znpyrite/sphalerite data), we identify a complementary contribution in Zn (maximum 12–24%) from Paleoproterozoic sedimentary carbonate. This source of Zn in sedimentary calcite is deemed possible in the context of Paleoproterozoic seawater at high Na/Cl ratio and in the absence of Zn-based eukaryotic metabolism in shallow marine environment.

Karang Panganten as a Geological Education Facilities in West Bandung Regency

Abstract Karang Panganten is an integral part of the Citatah Karst Area, known for its geological uniqueness and richness. This area reflects traces of complex geological dynamics, especially related to fault activities and other geological structures. In the Miocene era, about 25 million years ago, the Karang Penganten area was a shallow marine environment. The subsequent orogenesis activity lifted these limestone rocks to the surface, forming a unique karst landscape that characterizes the Karang Panganten we know today. Field observations show that the Karang Panganten area is heavily influenced by fault activities, such as tensile joints, fault breccias, and slickensides. One important finding in this observation is the slickenside, a smooth surface formed by friction between two rock blocks moving relative to each other. This slickenside provides clues to the relative movement direction between the two blocks and is an important indicator of tectonic activity in this region. This makes the Karang Panganten Area an educational facility object that showcases geological uniqueness in the West Bandung Regency area.

Molecular compositional variation of organic matter deposited on the East Tasman Plateau during the Paleocene–Eocene Thermal Maximum

Molecular compositions in sediments collected by Ocean Drilling Program Leg 189 at Site 1172 in the Tasmanian Gateway, Australia have been characterised by gas chromatography–mass spectrometry to assess the impact of the Paleocene–Eocene Thermal Maximum (PETM) on organic matter origins and evolution. Total organic carbon (TOC) and sulfur contents reach the lowest values immediately before the initiation of the negative carbon isotope excursion (CIE) in the shallow marine environment on the East Tasman Plateau. The TOC content increases slightly while the sulfur content increases more substantially during deposition of the CIE, suggesting the occurrence of low-oxygen environments during the PETM event. The studied section is thermally immature, as shown by the dominance of biological configuration biomarkers such as 17β(H),21β(H)-hopanes (ββ) and hopenes. Changes in relative abundance of compound classes and isomer ratios are largely caused by the variation of source inputs and depositional conditions. Very low abundance of marine steroids during the CIE, but very enriched hopanoids, indicate low marine productivity, in accord with substantial remineralisation of organic matter in the bottom waters. The ββ-hopanes are the most abundant hopanoid series, followed by the neohop-13(18)-ene and hop-17(21)-ene series, further verifying the immaturity of the organic constituents in the samples. Hopane ratios (ββ/(βα + αβ) and βα/(βα + αβ) with different carbon numbers are systematically higher in sediments deposited during the CIE than those formed pre- and post-CIE, suggest increased bacterial inputs. Higher C30/C29 and C30/C31 hopanoid ratios in the CIE sediments are consistent with a greater contribution from in situ bacterial organic matter, rather than continental soil erosion by flooding. This is supported by the higher C27–32 hopanoids/(C27 + C29 + C31n-alkanes) ratio and sulfur content during the CIE. A relatively lower TOC content in the sediments formed during the PETM is inferred to have been caused by dilution by both enhanced detrital input and intensified bacterial consumption. This study demonstrates that the biomarker approach can play an important role in the identification of organic matter origin and characterisation of depositional environment for PETM sequences.

Beyond boundaries: Depositional environment controls on erodibility, process, and form in rivers incising sedimentary bedrock

Bedrock rivers adjust to the properties of the rock into which they incise, imprinting the geologic past on Earth’s surface. We compared rock properties and channel form along the Dry Fork in the Allegheny Mountains, West Virginia, as it crosses between Mississippian sandstone and carbonate rock units, to investigate how the depositional history of channel-margin bedrock influences modern channel form. We used thin-section petrography to interpret site-specific depositional environments. We quantified rock strength with point-load testing, discontinuity spacing by measuring bed and fracture spacing, and channel form through cross-section surveys. Petrography indicates that the sandstone was likely deposited in an alluvial fan, while the carbonate formed in a shallow-marine environment. The sandstone has modestly higher point-load strength than the carbonate, but the units differ more dramatically in their discontinuity spacing. The sandstone is thinly (3–10 cm) bedded and densely (50–100 cm) fractured; the carbonate has thicker (45 cm) beds and sparser (180–300 cm) fractures. Sandstone channel cross sections are wider, shallower, and rougher, whereas carbonate cross sections are narrower, deeper, and smoother. Results suggest that a transition from plucking-dominated erosion in the discontinuity-rich sandstone to abrasion- and/or dissolution-dominated erosion in the discontinuity-poor carbonate, rather than differences in rock strength, drives observed morphologic differences. Differences in discontinuity spacing might arise from differential bed thickness between the two units, both because bed boundaries are discontinuities and because thinner beds lead to more densely spaced fractures. We hypothesize that depositional dynamics—the unsteady deposition of an alluvial fan resulting in thin beds versus steady, shallow-marine deposition that deposited thicker beds—explain the observed differences in bed thickness, discontinuity spacing, and modern erosion process dominance and channel form, emphasizing how modern Earth-surface processes are contingent on the geologic past.

Hotspots of human impact on the seafloor in the Southwestern Baltic Sea

The Southwestern Baltic Sea is a notable example of intense human impact on the seafloor in a confined shallow marine environment. Various marks left by dredging, dumping, fishing, anchoring, among others, reflect the different pressures on the seafloor. These activities represent cumulative stressors for marine ecosystems, potentially leading to habitat modification or loss. Characterizing and quantifying the extent of the different pressures is essential for understanding the system and evaluating the environmental status outlined by different legal frameworks. Here, the effects of different human activities on the seafloor in exemplary hotspots in the SW Baltic Sea are visualized and assessed. Actual anthropogenic marks are compared with assessments based on commonly accessible regional and local information from remote sensing data and institutional sources. About 36% of the seafloor of the investigated area is influenced, mainly by bottom trawling, propeller scouring, anchoring, and dumping. More than 91% of the human footprint corresponds to trawl marks, mainly affecting soft substrates. In addition, from 15% to 47% of the seafloor is disturbed in selected ‘detail areas' within the hotspots. Comparisons with indirect data used for regional pressure estimation demonstrate how hydroacoustic data can enhance assessments of seabed physical pressures. However, quantitative comparisons are challenging, especially when information on human activities is limited or when seafloor recovery rates in relation to the frequency of anthropogenic pressures are unknown.

Post-Marinoan paleoredox and paleoproductivity record in Puga cap carbonate: Implication for coastal life colonization at the Amazon Craton marginal Sea

The geochemical signatures in cap carbonate successions are critical records of paleoceanographic conditions following Snowball Earth events. These deposits offer insight into the shifts in redox conditions and the re-establishment of biogeochemical cycles during postglacial periods, providing a window into the evolving marine environments and potential drivers of early oxygenation. To track redox changes during this transition, we present improved high-resolution analyses of redox proxies across Puga cap carbonate (∼ 635 Ma) on the Southern Amazon Craton, Brazil, allowing for the identification of temporal redox transitions during the post-Marinoan transgression. The depletion of trace elements, particularly redox-sensitive elements (RSEs), such as Mo, U, and V in microbialites formed in basal cap dolostone, was deposited under oxic conditions. Following the initial melting of Marinoan glaciers, microbial mats flourished and grew in a semi-restricted shallow marine environment in the coastal paleoenvironment along the Amazon cratonic margin, where nutrient-rich surface waters fueled primary productivity. In contrast, the increase in RSEs in upper wave-dominated dolostone facies indicates predominantly dysoxic conditions in continuous sea level rise, resulting in the drowning of these early microbial environments and the precipitation of cap limestones. The sequential oxic-dysoxic redox marks the transition from shallow sea to deepening CaCO3-oversaturated platform conditions. These results demonstrate an unequivocal synchronous relationship between the initial oxygenation of the Amazon margin and the local microbial mat flourishment shortly after the Marinoan glaciation.

Persistence of a shallow-marine environment in the western Kunlun area (northwestern Tibet) until the early Maastrichtian: Evidence from radiolitid rudist bivalves

The closing of the Tethys Ocean during the Mesozoic and Cenozoic dramatically affected the palaeogeography, palaeoenvironment and biotic evolution of the Tibetan Plateau and surrounding areas. The timing of closure of the Tethys Ocean in different areas is recorded by the youngest marine deposits. In the western Kunlun area of northwestern Tibet, the Tielongtan Group represents the youngest marine deposits, and is rich in rudist bivalves; however, its depositional age, particularly the age of final deposition, is poorly constrained. Systematic and palaeobiogeographic analyses were conducted on rudists from the Tielongtan Group in the eastern Loqzung Mountains. Four genera and two species were identified: Biradiolites boldjuanensis, Gorjanovicia acuticostata, Durania sp. and Radiolites sp. The occurrence of the lower Maastrichtian index fossil, Biradiolites boldjuanensis, indicates that deposition of the Tielongtan Group continued until the early Maastrichtian. Therefore, the results of this and previous studies indicate that deposition of the Tielongtan Group spanned from at least the Turonian to the early Maastrichtian. Palaeobiogeographical analyses show that B. boldjuanensis was endemic in Central Asia, whereas G. acuticostata might have extended beyond the Mediterranean region. During the Late Cretaceous, the shallow ocean in the western Kunlun area contained both cosmopolitan and endemic rudists.

Provenance, environments, and tectonic signatures of Tanjong-Sandakan Formations, Northeast Sabah, Malaysia: Implications from sedimentology, palynology, and geochemistry

This study investigates marginal marine deposits found in the Tanjong and Sandakan formations from the Early to Late Miocene in Northeast Sabah. It examines sedimentology, trace elements (TE), rare earth elements (REE), hydrocarbon generation potential, and palynology to understand provenance, depositional environments, and paleoenvironmental conditions. Facies analysis identified four associations in the Tanjong and three in the Sandakan Formation, ranging from fluvial-deltaic to shallow marine environments. Mangrove-associated taxa, herbaceous and tree ferns typical of freshwater swamps, and coastal plants indicate a transition zone between terrestrial and marine environments. Siliciclastic deposits in the Northeast Sabah basin show varying redox conditions, ranging from dysoxic to oxic, as indicated by the Ni/Co, V/Cr, and U/Th ratios. These fluctuations may be linked to the tectonic evolution of the Sulu Sea and related sea-level lowstands. The low abundance of marine dinoflagellate cysts, along with high levels of rainforest and peat swamp pollen, suggests periods of subaerial exposure that contributed to the redox conditions. C-values and Sr/Cu ratios in the mudstone samples indicate semihumid to humid and warm conditions during the Miocene. Additionally, the distribution patterns of rare earth elements (REE) and the (La/Yb)N and Th/U ratios reveal consistent sedimentation rates in marginal marine environments. Palynofacies analysis indicates water column fluctuations, leading to oxidation during transport, resulting in low TOC values and kerogen types III and IV.Ternary diagrams of immobile TEs indicate that mudstone samples originate from active continental margins, linked to the rifting of the Sulu Sea during the Early to Middle Miocene. In contrast, sandstone samples exhibit characteristics of passive margins, likely due to recycled sediments from the early "Rajang Group Accretionary Complex." The plots for immobile TEs in the mudstones suggest intermediate and mafic sources, supporting the idea of uplift and erosion from deepwater sediments, as well as volcanic activity from the Cagayan and Sulu Arc systems. Sandstone samples may be sourced from acidic rocks associated with felsic intrusions in the Segama Valley, indicating a significant continental basement beneath the ophiolite. Keywords: Marginal marine, trace element, provenance, palynology, tectonic setting, Northeast Sabah.

Paleoclimatic and paleoenvironmental constraints on organic matter enrichment in the Paleocene strata in the Lishui Sag, East China Sea Shelf Basin

Using major and trace element analyses, this study investigated the impacts of paleoclimatic and paleoenvironmental variations on organic matter enrichment in the Paleocene Yueguifeng, Lingfeng, and Mingyuefeng formations in the Lishui Sag, East China Sea Shelf Basin. Multiple geochemical proxies suggest that during the deposition of the three formations, the paleoclimate evolved from a humid climate to an arid and then back to humid conditions, the paleosalinity conditions underwent brackish, saline, and fresh water sequentially, and the paleowater conditions shifted from relatively deep water to relatively shallow water and then to shallow water. Accordingly, the water column evolved from reducing to oxidizing and then to weakly oxidizing to oxidizing conditions. Organic matter productivity, as well as the preservation or degradation of organic matter, was controlled by covariation in the paleoclimatic and paleoenvironmental conditions. This can account for the difference in organic matter enrichment in the mudstones of the three formations. The mudstones in the Yueguifeng Formation were deposited in a semi-deep- to deep-water lacustrine environment with high primary productivity in a warm, humid climate. Numerous planktonic algae were efficiently preserved in stratified and dysoxic water columns, resulting in high organic matter enrichment in this formation. The mudstones in the Lingfeng Formation were formed in a shallow marine environment with low primary productivity in an arid climate. The combined effects of high salinity and oxygen-enriched conditions in the water bodies were unfavorable for the reproduction and preservation of planktonic algae, resulting in low organic matter enrichment. For the Mingyuefeng Formation, the slow tectonic subsidence and flat topography during the deposition of this formation led to the development of a swamp environment in a warm, humid climate. The swamp environment was characterized by an oxic water column, low aquatic organic matter input, and high terrigenous organic matter input. The Yueguifeng Formation has greater hydrocarbon-generating potential than the Lingfeng and Mingyuefeng formations. Constructing the developmental models of organic-rich mudstones based on the covariation in the paleoclimatic and paleoenvironmental conditions represents a valid method for understanding the hydrocarbon-generating potential of these source rocks.

Unveiling Preliminary Study of the Holocene Sedimentary Environments and Biofacies in Western of Al-Hammar Marsh, Southern Part of Iraq

Biofacies and sedimentary environment analyses were conducted across three sites west of Al-Hammar Marsh. Excavations were undertaken at different depths for a comprehensive study. The initial site was probed at 9 m depth, followed by the second site at 5 m, and the third site at 9 m. Subsequent examination of these samples aimed to unveil insights into grain size, fossil contents, and their respective ecological settings. The grain size analysis revealed three distinct sediment types: silt, sandy silt, and muddy sand. Additionally, fossil assemblages hinted at three primary biofacies. The first facies represented a fresh marsh-fluvial environment identified across all three sites at different depths. Specifically, this biofacies manifested from the surface to about 200 cm in site one, 50-150 cm in site two, and 50-250 cm in site three. The second biofacies indicated a shallow marine environment at depths ranging from 250 to 550 cm in site one, 200-300 cm in site two, and 300-650 cm in site three. Lastly, the third biofacies denoted a lagoon or tidal flat environment observed at 600-900 cm depths in site one, 300-500 cm in site two, and 700-900 cm in site three. Notably, the third biofacies in site three exhibited signs of influence from alkaline freshwater, particularly in the third location at a depth of 700-800 cm. This influence was attributed to a mixture of marine and freshwater species, including; Quinqueloculina candeiana, Quinqueloculina angulta, Cubicula fluminalis, and Melanoides tuberculate. Abundant occurrences of these species were noted in the silty clay lithology of this layer.

Benthic response to event deposition and environmental disturbance in a shoreface to subaqueous delta system: Ichnology of the Silurian-Devonian Furada Formation of Asturias, Spain

The Furada Formation of Asturias, Spain, represents a clastic shallow-marine unit deposited during the middle Silurian to the Early Devonian. This formation contains abundant evidence of event deposition and non-uniform distribution of bioturbation structures representing a benthic response to multiple stressors. The 170-m-thick succession was measured and described, and the ichnotaxa were recorded and associated with five sedimentary facies. Most shallow-marine environments are characterized by periodic events of environmental disturbance, mainly by episodic deposition, which may be recorded by a change in both the degree of bioturbation and ichnodiversity. The general depositional setting for this formation has been previously interpreted as a wave-dominated and storm-influenced shallow-marine environment. However, sedimentologic features described in this study, such as anomalous heterolithic and mudstone units, representing fluid mud layers, hyperpycnal flow deposits and plume collapse accumulations, suggest the influence of fluvial discharge, making it a more complex depositional setting. The proposed model comprises an inner sandy shoreface belt flanked seawards by a muddy subaqueous delta platform. The trace-fossil assemblages of this formation reflect environmental stress factors introduced by the interplay of storms and fluvial input (e.g., high sedimentation rate, fluctuating hydrodynamic energy, decreased substrate consolidation), resulting in reduced ichnodiversity and low abundance. From an ichnofacies perspective, the shoreface complex is characterized by the Cruziana Ichnofacies, whereas the subaqueous delta platform is represented by the Phycosiphon Ichnofacies. Integration of sedimentologic and ichnologic datasets allows for a refined depositional interpretation of the formation and greater understanding of the environmental diversity of wave-and river-influenced shallow-marine clastic systems, including the responses of the middle Paleozoic shallow-marine benthos to event sedimentation and environmental disturbance. This study is one of the first detailed documentations of the ichnology of subaqueous deltas.

The Baroch Nala section (NE Pakistan): A new PETM standard for the eastern Tethys

We present an integrated, high-resolution, biostratigraphical, mineralogical, and geochemical characterization of the well-exposed Upper Paleocene - Lower Eocene stratigraphic succession of the Surghar Range (Baroch Nala section, NE Pakistan). The faunal assemblages from the Baroch Nala section, dominated by hyaline benthic foraminifera and green calcareous algae, along with the significant terrigenous fraction and the presence of terrestrially derived organic matter, testify to the deposition in a low-energy shallow-marine environment. Such environmental conditions, coupled with weak diagenetic effects, allow us to integrate a continuous record of carbon stable isotopes with a detailed account of the biotic response by carbonate-producing assemblages, paleoclimatic information based on clay-minerals, and information on volcanic activity based on mercury concentrations. The environmental evolution from the Late Paleocene up to the Paleocene Eocene Thermal Maximum (PETM) is clearly documented, including the weaker warm excursion that precedes the PETM (i.e. the Pre-Onset Excursion “POE”), and the evolution of large benthic foraminiferal assemblages. The overall record perfectly shows how the turnover in benthic carbonate producers started with the onset of the PETM and was completed by the time the excursion ended, highlighting how (geologically) brief environmental oscillations can have long lasting effects on the biosphere.