The molecular-level differentiation characteristics and genetic mechanisms between expelled and retained oils in saline lacustrine shale remain poorly constrained, which restricts the accurate evaluation of in-situ shale oil accumulation potential. To fill this research gap, the objectives are to reveal the molecular geochemical differences between expelled and retained oils during thermal evolution and establish a valid discriminant system for saline lacustrine shale oil. Taking the Lower Ganchaigou Formation (E-3(2)) shale of the Qaidam Basin as the research object, we adopted semi-closed pyrolysis simulation combined with gas chromatography-mass spectrometry (GC-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to conduct systematic molecular geochemical analysis across a wide thermal maturity range (Ro = 0.54%-2.74%).Obvious molecular differentiation signatures between retained and expelled oils are identified. Retained oil is featured by a low Sigma nC(21)(-)/Sigma nC(22)(+) ratio, high C-29 regular sterane proportion, lagged sterane isomerization (C-29-20S/(20S + 20R) < 0.33; C-29-alpha beta beta/(alpha alpha alpha + alpha beta beta) < 0.28), bimodal double bond equivalent (DBE) distribution of N-1 heteroatomic compounds (peaks at DBE = 9 and 12), and a sharp increase in 4-MDBT/1-MDBT ratio (up to 19.73) at high maturity. In contrast, expelled oil is enriched in light saturated hydrocarbons, characterized by a high Sigma nC(21)(-)/Sigma nC(22)(+) ratio, dominant low-DBE (DBE = 1) O-2 compounds (accounting for up to 74.7%), and no abnormal elevation of 4-MDBT/1-MDBT ratio. Small-molecule, low-polarity components (light n-alkanes, low-DBE O-2 compounds) are preferentially expelled owing to high fluid mobility, whereas large-molecule, polar components (heavy hydrocarbons, high-DBE N-1 compounds) are trapped in shale reservoirs. For retained oil, the confined nanoscale pore environment restricts sterane conformational rotation (leading to maturity lag effect) and promotes selective methyl cleavage in dibenzothiophenes. Additionally, the favorable in-situ shale oil accumulation window of E-3(2) shale is determined as Ro = 0.7%-1.0%, with quantitative thresholds of retained oil content > 200 mg/g and N-1 class relative abundance of 25%-59%. This study establishes the first molecular discriminant system for expelled and retained oils in saline lacustrine sedimentary environments, clarifies the multi-factor controlled differential evolution mechanism, and provides key theoretical support and practical indicators for shale oil exploration and sweet spot evaluation in the Qaidam Basin and other similar saline lacustrine basins worldwide.

This study investigates the ichnological characteristics of deep-sea cores recovered from site U1580 on the southern Central Agulhas Plateau during International Ocean Discovery Program (IODP) Exp. 392, with a focus on the Paleocene-Eocene Thermal Maximum (PETM) event. By comparing pre-, syn-, and post-PETM intervals, this research applies trace fossil diversity, maximum trace diameter, and bioturbation patterns to assess benthic community responses to extreme climate changes including temperature changes, fluctuating bottom water oxygenation, nutrient availability, as well as changing deep sea circulation patterns. Trace fossil records such as ichnogenera diversity and maximum trace fossil diameters across 10 cm intervals (bins), were extracted from high-resolution photographs of cores U1580A and U1580B. Results reveal a reduction in maximum trace fossil diameters during the PETM, reflecting potential environmental stressors like elevated temperatures and lower oxygen (O2) levels, followed by a post-PETM recovery. Trace fossil diversity increased from the syn-to post-PETM interval, ecological reorganization and potential recolonization of newly available niches. A comparative analysis of the two cores highlights subtle differences, with core U1580B exhibiting larger average maximum trace fossil diameters possibly due to localized variations in seafloor topography, food availability and/or biological factors. The deep-tier trace fossil Zoophycos is both included and excluded from the analysis to explore how its burrow depth-which likely exceeds the 10 cm bin intervals used-impacts ichnological trends. Overall, the ichnological patterns presented here provide new insights into how deep-sea macrobenthic communities responded to PETM environmental stressors, complementing existing paleoenvironmental interpretations based primarily on microfossil data.

Accurate evaluation of adsorbed oil heterogeneity in laminated shales is critical for optimizing shale oil recovery and challenging assumptions of inherently low recovery potential in such reservoirs. This study integrates geochemical, petrophysical, and microscopic analyses to systematically investigate the compositional heterogeneity, storage mechanisms, and controlling factors of adsorbed oil within the Paleogene Shahejie Formation (Bohai Bay Basin), implementing T1-T2 NMR at tailored relaxation time thresholds for adsorbed oil characterization. Results reveal pronounced heterogeneity, with adsorbed oil concentrations significantly higher in organic- and clay-rich bright laminae than in massive or bioturbated facies, which act as preferential storage sites due to enhanced nanoporosity (10-50 nm mesopores), surface area (R2 = 0.77), and synergistic mineral-organic interactions (TOC: R2 = 0.75; clay content: R2 = 0.88). Adsorbed oil is enriched in C19+ n-alkanes, resins, and asphaltenes, retained via pi-pi stacking, hydrogen bonding, and van der Waals forces. Methodologically, multitemperature pyrolysis (S ' 2-1+S ' 2-2) yields movable oil of 0.06-8.82 mg/g (average 2.14 mg/g) but underestimates adsorbed oil by 40-50% (vs NMR), while solvent extraction also shows substantial deviations; T1-T2 NMR (0.013-0.022 mg/L, average 0.0165 mg/L) demonstrates superior sensitivity, primarily due to hydrocarbon volatilization (50-60% loss) during pyrolysis sample preparation. These findings refine sweet spot identification in laminated shale reservoirs, underscoring the need for method-specific calibration and correction factors to reconcile analytical discrepancies for improved movable oil estimation.

The unique sedimentary environments and subsequent diagenetic transformations in continental saline lake basins markedly shape the varied nature and characteristics of saline lacus-trine shales,thereby ultimately affecting how lacustrine organic matter(OM)accumulates.Howev-er,what chiefly governs OM enrichment in such settings is still not fully understood.This research focuses on the Damintun sag as a prime research example,utilizing an extensive array of methods like total organic carbon(TOC)analysis,X-ray diffraction,pyrolysis,trace element analysis,and iso-topic studies on shales from the Paleogene period.The objective was to shed light on the variability in OM concentration and its ties to the paleoenvironment.Findings reveal that the Es4 shale lithofa-cies largely consist of mixed and siliceous shales,exhibiting significant OM accumulation,where TOC content varies between 0.17％and 7.27％.Notably,TOC distribution reveals a significant verti-cal heterogeneity across different sequences.The level of OM enrichment within the saline lake ba-sin is primarily determined by paleoclimate,paleosalinity,paleooxidation,and paleoproductivity.Among these critical factors,the primary considerations with regard to influencers of organic materi-al enrichment are productivity and paleosalinity.Conditions conducive to organic matter enrichment include low salinity,anoxic environments,and suitable nutrient inputs.Furthermore,the deposition-al environment can have a strong impact on the determination of what type of organic matter accu-mulates.To illustrate,biomarker analysis tends to suggest that humid freshwater lakes are more welcoming to organic matter derived from higher terrestrial plants,whereas dry and saline lakes predominantly accumulate plankton,such as algae.Finally,this study establishes an OM enrich-ment model which effectively outlines the various stages of organic matter evolution and enrich-ment that occur within the saline lake basin.This model integrates the consideration of various pri-mary factors,including paleoclimate shifts,sedimentary dynamics,and organic matter preservation mechanisms,offering valuable insights into the complex processes governing OM distribution and enrichment within similarly structured geological settings.

Early marine carbonate cements generally form in CaCO3-supersaturated seawater at the seabed or shallow burial depths, resulting in syn-sedimentary cemented firmgrounds and hardgrounds. The processes controlling early marine diagenesis are complex, particularly in coastal environments where geochemistry is influenced by different water sources and local biogenic activity. Investigating the modern firmgrounds and hardgrounds in the intertidal zones of the U.A.E. reveals how physical, chemical and biological factors influence early marine precipitation. In these environments, early marine diagenesis is governed by interacting hydrogeochemical, microbial and physical processes, whilst bioturbation modifies solute transport dynamics. In situ porewater and sediment analyses show that the intensely bioturbated lower intertidal zone experiences enhanced sediment permeability, persistent seawater flushing and sediment reworking, producing geochemically uniform porewaters and fewer firmground features. In the middle intertidal zone, reduced seawater exchange, shallower bioturbation and longer porewater residence times promote geochemical conditions favourable for early marine cement precipitation. Additionally, mixing between upwelling continental brines and intertidal seawaters affects porewater redox, salinity and ion concentrations, leading to localised diagenesis. Spatial variations in porewater and sediment chemistry can develop over short distances (<1 km) because of complex hydrogeochemical interactions, in which bioturbation acts as an important modifier. This study highlights the importance of integrating ichnological, geochemical and hydrogeological approaches.

The Cambrian Period witnessed profound evolutionary, ecological, and geobiological transformations, including the vertical expansion of the colonization zone within marine sediments by burrowing animals-a key evolutionary step during the early Cambrian often referred to as the "Agronomic Revolution". Here, we document a well-preserved trace fossil assemblage from the lower Cambrian Mahto Formation (Cambrian Series 2) of the Kootenay Plains, Alberta, Canada. The ichnotaxa Diplocraterion isp., Rosselia isp., and Skolithos linearis occur as both epireliefs on bedding planes and in full relief from vertical cross-sections, offering valuable insights into early animal-sediment interactions in high-energy sandstone successions. Burrows penetrate up to 15-20 cm into cross-bedded quartzose sands, demonstrating localized but significant sediment reworking that influenced nutrient fluxes and oxygenation at the sediment-water interface. The mineralogy within the burrow fills reveals distinct behaviors: Rosselia shows clay depletion consistent with selective ingestion, whereas Skolithos displays mixed sand-clay infills, reflecting vertical transport and sediment mixing. These observations highlight the ecological impact of early Cambrian infauna on sedimentary fabrics, while underscoring a temporal decoupling between the evolution of complex behaviors (e.g., dwelling, sessile filter-feeding, suspension-feeding) and the delayed establishment of laterally continuous mixed layers. This suggests that the Mahto Formation records an important transitional stage in early Cambrian organism-sediment interactions, characterized by dense vertical burrowing within marginal-marine environments but lacking pervasive sediment homogenization. This research also highlights early behavioral and anatomical innovations, including the development of musculature and appendages that facilitated increasingly effective infaunal activity.

Characterizing the pore system of shale oil reservoirs is critical to elucidating petroleum accumulation mechanisms, enhancing oil recovery efficiency, and evaluating unconventional petroleum resources. However, research on lacustrine laminated shale pore systems remains limited and poorly understood, primarily constrained by the strong heterogeneity induced by differential lamina development. To address this gap, we collected 20 lacustrine shale samples from the fourth member of the Shahejie Formation in the Bohai Bay Basin and systematically investigated their nm-mu m scale pore structure using CO2 and N2 adsorption experiments. The results show that the laminated shales are composed of light-colored mineral-rich layers (quartz, feldspar, calcite, and dolomite) alternating with dark clay-organic matter layers. Their pore system is dominated by matrix intercrystalline, intergranular, dissolution pores, and microfractures, rather than organic-matter-associated pores, with pore diameters primarily ranging from 2 to 40 nm. Notably, mesopores account for over half of the total specific surface area and pore volume in all tested samples, and the abundance of clay and quartz minerals is identified as the key factor controlling micro-mesopore composition and complexity. These findings provide critical insights for understanding shale oil resource potential and delineating optimal exploitation targets in lacustrine basins.

The Paleocene-Eocene Thermal Maximum (PETM, similar to 56 Ma) marks a rapid, intense warming event at the Paleocene-Eocene boundary. However, the terrestrial record of the PETM is limited, and its paleoenvironmental impacts are debated. This study examines the effects of the PETM on terrestrial lake environments using mineralogical, inorganic and organic geochemical analyses of the Paleocene Kongdian Formation's organic-rich rocks from the Bohai Bay Basin. Findings show that global PETM warming drove regional aridification and evaporation, while carbonate isotopic signals (negative delta 13C, positive delta 18O) are consistent with enhanced hydrological cycling and salinity fluctuations, reflecting the interplay between global climate forcing and local hydrological responses. Nutrient influx during the PETM boosted paleoproductivity. Arid-adapted organisms like Podocarpidites and Ephedripites also became present. The PETM experienced heightened seasonal variance and climatic extremes, with elevated temperatures causing increased evaporation and salinity during dry seasons, indicating greater aridity. Seasonal precipitation likely intensified due to monsoonal rains or the tropical convergence zone's northward movement. Pollen from the Bohai Bay Basin indicates both significant episodic precipitation and increased aridity, reflecting complex climatic interactions. Increased detrital kaolinite content during the PETM suggests intensified physical weathering and erosion in kaolinite-bearing catchment areas, driven by episodic heavy rainfall. Our sedimentological observations (e.g., laminated shale cyclicity and detrital mineral assemblages) indicate sporadic heavy rainfall events, enhancing physical weathering and altering detrital sediment mineral content in the Bohai Bay Basin.

Lithium (Li) enrichment in the formational brines of deep sedimentary basins has emerged as a crucial component of global Li inventories. However, the processes driving the formation of Li brines remain poorly understood. Here we use lithofacies analysis and Li isotope geochemistry to investigate the sources and emplacement mechanisms within weathered subcropping units and overlying detrital sediments of the Peace River Arch (PRA) in the Western Canada Sedimentary Basin (WCSB). We analyze data from three drill cores that traverse Precambrian basement and five of its overlying siliciclastic and carbonate units. These cores reside both within and outside of the fault zone proposed as a migration pathway for hydrothermal emplacement. Lithofacies analysis revealed that these sediments were weathered directly from crystalline basement of the cratonic uplift and transported via a fluvial-deltaic system into the surrounding shallow marine basin. Like modern weathering regimes, we find Li concentrations are strongly lithofacies dependent, ranging from 0.4 ppm to 167.3 ppm, with δ7Li values ranging from 1.5‰ to 23.5‰. Our results show that superficially weathered, coarse-grained lithologies and carbonate facies are Li-depleted and δ7Li-enriched, whereas fine-grained facies characterized by the formation of secondary clay minerals are δ7Li-depleted and exhibit the highest Li concentrations. Contrary to the prevailing model of hydrothermal emplacement, we find no visual, mineralogical, or geochemical evidence of hydrothermal alteration. Instead, Li enrichment is attributed to weathering of the crystalline basement and syndepositional emplacement during basin evolution. Sedimentation continued throughout the overall transgression of the Devonian, resulting in the interfingering of these clastics with every onlapping unit until the PRA was buried at the end of the Devonian. This study is the first to directly trace Li from source to sink in an ancient sedimentary basin, and we show that the modern distribution of Li brine concentrations can be explained by their proximity and intercalation with weathered subcropping units. Moreover, our results provide a source and mechanism of transporting dissolved Li into the restricted basin, supporting previous suggestions that Li brines toward the southeastern portion of the WCSB are the result of basin scale evaporation-concentration of paleoseawater. Our results underscore the link between the nature and distribution of basin fill sediments and the formation of Li-enriched brines. As formational brines gain prominence as future Li resources, the methodology presented here establishes a framework for characterizing Li genesis, with applications for sedimentary basins worldwide.

Bedding planes hold significant value in ichnological analyses as they improve the recognition of ichnotaxa and yield important insights into the distribution and morphology of trace fossils. However, a significant limitation lies in the challenge of accurately estimating bioturbation intensity from bedding planes. This is in part because current approaches do not establish a connection between bioturbation intensity as seen on bedding planes (plan view) and in cross-section (elevation view). This disconnect complicates the integration of bedding plane assessments into more conventional datasets collected from elevation view. Seventy-seven million Monte Carlo simulations were performed on 11 non-palimpsest Skolithos assemblages, each with varying constraints on burrow length and diameter. These simulations were used to investigate the range and frequency of cross-sectional bioturbation intensities across a spectrum of bedding plane intensities (2–50%). The results show that elevation view bioturbation intensity can be reliably approximated by multiplying plan view bioturbation intensity by the average burrow length relative to the bed thickness, independent of burrow diameter. These findings improve the ichnological analysis of bedding planes for vertical trace fossil assemblages and offer a framework for future research into more complex assemblages.

Formation of microtubes, defined as small internal borings, in fossil and modern bone is a well-attested phenomenon. However, determining whether microtubes were created by microbial activity or abiotic processes is challenging, particularly in fossils. Here, we report abundant microtubes in compact bone from numerous specimens of the marine reptile Keichousaurus from the Middle Triassic of southwestern China. Light and scanning electron microscope imaging of osteological thin sections, and CT-based three-dimensional reconstruction of the microtubes, reveal geometric features typical of fungal hyphae, such as bifurcation and tight helical coiling. Some microtubes contain what may be the first known fossilized fungal vacuoles. The microtubes are thus likely to be of fungal origin, produced by saprobic marine fungi during decomposition. Furthermore, fluorine is abundant in the compact bone, and even more prevalent in the infillings that occur in many microtubes. The fungi evidently released calcium ions, took up fluorine from the reptiles’ bodies and promoted the formation of fluorite in the microtubes. The infillings represent the earliest known instance of fungal-induced biomineralization within fossil bone, demonstrating that some Middle Triassic fungi were capable of impacting global biogeochemical cycling by taking up substantial amounts of fluorine.

Conventionally, geologists have regarded mudstones as deposits formed through suspension settling in environments located at the terminus of sediment transport pathways, with the sediment sourced from a mix of detrital inputs into the basin and in situ production within the basin. However, mudstones are sedimentologically enigmatic as they are characterized by intricate small-scale features. Analysing mudstones with the typical techniques used for coarse grained siliciclastics does a disservice to the intricacies of these deposits. Grains, pores, and depositional fabrics within these rocks are not visible in hand sample, and often not even at the petrographic scale. Study of these features, at appropriate scales, can generate valuable insights into the physical and chemical conditions of their deposition. Along with analytical techniques, the conventionally held interpretations of these rocks are out of date. New insights into the origins and composition of grain components reveal significant variability, indicating these deposits are much more complex than traditionally understood. As a result, historical nomenclature and interpretation paradigms have undergone significant revision. However, there is still more research needed to fully address the challenges of mudstone description, classification and interpretation. This paper presents digestible discussions of changes in mudstone paradigms, the most effective practices consistent with modern understandings of mudstones, and considers areas that merit further consideration. Ideas presented herein are aimed at all those interested in mudstones, but is primarily meant for those new to the challenge of conducting mudstone analyses. Herein we recognize several preferred practices that have gained consensus in the literature, these include: (1) clearly defining common historical terms such as ‘clay’, ‘silt’, ‘bed’, and ‘shale’ depending on modern chosen usage; (2) outlining the transportational (i.e., functional) grain size of the deposit, as many constituents may be transported as amalgamated clasts; (3) clearly defining if reported mudstone composition is based on transported or apparent grain size (i.e., individual grain measurements); (4) thin section preparation methods and their integration with other complementary analytical techniques. As well, we discuss: (1) the use of both petrographic trace fossil analysis and microfacies analysis; (2) complex depositional mechanisms, beyond suspension settling, that lead to the accumulation of fine-grained deposits; and, (3) the interaction of several variables involved in accumulating organic-rich deposits. Ultimately, when embarking on mudstone analysis, one must first decide what question they are trying to answer. This will dictate the approach used, and if the focus is on the intricacies of grain size, composition, or depositional fabric.

Although bivalves can orient infaunal body position to current direction, trace fossils of bivalves have rarely been corroborated against paleocurrent directions determined from physical sedimentary structures. This study compares Lockeia (bivalve-generated trace fossil) orientation and length to the three-dimensional bedform cross-strata dip direction from fluvial deposits at two localities in the Late Jurassic Brushy Basin Member (Morrison Formation) of the western United States. Lockeia mean orientation at each site are comparable, but tangential, to physical sedimentary structure mean orientations. Comparing accuracy (within one standard deviation) and precision (within two standard deviations) in-context of five macroform surfaces, the Lockeia measurements are more accurate indicators of current direction than the physical sedimentary structures. Conversely, the physical sedimentary structures are more precise than the Lockeia measurements. This dissimilarity is partly a function of the variability of cross-stratum dip orientation produced by three-dimensional bedforms resultant from the tangential nature of the bedform, its preservation, and the method by which these are measured. Lockeia has greater paleocurrent representation accuracy than physical sedimentary structures since it is a linear measurement rather than a collection of measurements that can be tangential to paleoflow. Lockeia measurements show shifts vertically and laterally with macroform changes indicating potential use for identifying local changes in paleocurrent direction.

Characterizing the mobility of shale oil is crucial when attempting to understand petroleum accumulation, oil recovery enhancements, as well as petroleum resources assessments for the unconventional reservoirs. That study especially in the lacustrine environment remain, however, limited and are least understood due to laminae development heterogeneity. A total of 12 core samples from the third member of the Shahejie Formation of the Bohai Bay Basin were employed to study the shale oil mobility occurred in the lacustrine strata through nuclear magnetic resonance (NMR), Rock-eval pyrolysis, and multi-temperature pyrolysis experiments. Laminas consist of bright laminae that contain high contents of quartz, feldspar, calcite, and dolomite, which are frequently intercalated with dark laminae dominated by clay and organic matter. The movable oil contents estimated by NMR (3.96-7.05 mg/g) is higher than that defined by both Rock-eval pyrolysis (0.57-3.29 mg/g Rock) and multi-temperature pyrolysis methods (0.36-5.89 mg/g Rock). This divergence is likely due to the volatility of light hydrocarbons, resulting in the NMR estimations being considered the most reliable. The movable oil content that exists within bright laminae are typically higher than that to which resides within dark laminae due to the oils generated in dark beds migrating from the dark laminae segments to bright beds. This in turn leads to the increase of the heavy components, asphaltenes, in the kerogen of the dark laminae and that of light components in the bright laminae. Combination with the reservoirs characterizations results, it suggests that the pore sizes and structures may play a critical role in the aforementioned differences in movable oil content between dark and bright beds, where bright laminae is characterized by type H2 with the diameters of 100-500 nm, while dark laminae belong to type H3 with a smaller diameter of 20-200 nm. As a result, higher levels of movable oil were trapped within inorganic pores with a diameter of 100-500 nm in bright laminae, while heavier compositions with the characteristic of low mobility were absorbed in the kerogen. These findings have a significant impact on existing knowledge around the mechanisms of shale oil enrichment and the exploitation of sweet spots.

Analcime, a key mineral especially in organic matter-rich sediments, plays a critical role hydrocarbons generation from kerogen. However, its effect on hydrocarbon generation from type I kerogen remains unclear. In this study, semi-open thermal simulation experiments were conducted on lacustrine shale to investigate the relationship between analcime and hydrocarbon generation. Semi-open pyrolysis experiment was performed on type I kerogen in organic-rich shale containing of 15 %, 27 %, and 35 % analcime concentrations across a temperature range of 300 degrees C to 500 degrees C. The analcime collected from the study area is sedimentary and diagenetic, characterized as low-silica analcime formed by chemical reactions between clay minerals and sodium-rich alkaline water. Results demonstrate that increasing analcime contents significantly enhances hydrocarbon yields of oil and gas while reducing activation energy, indicating that analcime accelerates hydrocarbon generation from kerogen. However, the durations of hydrocarbon generation appear to decline with increasing analcime contents. Thus, analcime influences hydrocarbon generation by increasing the conversion rate and reducing the generation cycle primarily due to its catalytic effects. Specifically, analcime promotes organic matter decomposition through acidic catalysis and adsorption, establishing an efficient catalytic system.

Elevated lithium (Li) within the formational waters of deep sedimentary basins continues to garner attention as a widespread addition to global Li resources. However, the nature of Li emplacement remains understudied. Here we document elevated Li in Devonian evaporites of the Western Canada Sedimentary Basin and reconstruct the processes that led to their enrichment. Our results show bulk Li concentrations ranging from 49.4 ppm to 284 ppm. Contrary to previous speculation that Li is hosted within evaporitic minerals, our findings indicate that it is instead within aggregate grains of clay-sized particles composed of micas and clay minerals. The Li-bearing grains range from subangular to rounded, displaying a bimodal distribution with particle fractions of either medium- to coarse-grained silt or very fine sand. The individual particles average 304 ppm Li and attain concentrations as high as 394 ppm. Previous work has shown that Li was weathered from Precambrian basement and transported into the basin via fluvial discharge; however, no attempt has been made to characterize the distribution of these sediments by wind-borne processes. Thin sections reveal that these aggregate grains are widespread and that they dominantly occur in supratidal sediments, waning in abundance into lower intertidal deposits. Based on the particle distribution and several other lines of evidence, we suggest that these Li-rich detritals were deposited by wind-borne processes, and the results herein are the first to characterize the potential of wind-blown Li sediments. Given the extent of enrichment in these evaporites, we propose that aeolian processes play an important yet underappreciated role in transporting and accumulating Li-rich sediments. As alternative Li resources continue emerging, these findings highlight the potential of wind transport and provide a predictive framework for the paleogeographic distribution of Li-rich strata and their associations with Li-enriched brines.

Research on the ichnology of brackish-water environments began in the 1930s and has led to the identification of predictable infaunal patterns. Brackish-water deposits characteristically display low-diversity tracefossil assemblages consisting of both vertical and horizontal structures. These salinity-reduced ecosystems are dominated by opportunistic euryhaline-tolerant species. Osmoregulation-related selective pressures lead to decreased diversity and an abundance of infaunal organisms. In environments with fluctuating or low salinity, fauna adopt r-selected strategies and are characterized by rapid colonization dynamics, high population densities, elevated mortality rates and low-diversity assemblages. Tides in brackish-water settings contribute a plentiful food supply with tidal currents transporting marine-sourced and terrestrially sourced organic matter that settles on the sediment-water interface during slack-water periods. This increased food availability favours trophic generalists using various feeding strategies to exploit both intrastratal and surficial food resources. The ichnological characteristics of modern and ancient brackish-water strata are used to propose the Teichichnus Ichnofacies; they are temporally and spatially recurrent and reflect the biology of brackish-water settings. The Teichichnus Ichnofacies is recognized by reduced trace-fossil diversity, smaller trace sizes, dominance of structures reflecting trophic generalist behaviours, sporadic distributions of ichnofossils, locally high bioturbation intensities and opportunistic colonization. This ichnofacies is characterized by trace fossils interpreted to be associated with surface deposit feeding, intrastratal deposit feeding and subordinate filter feeding.

Wildfires play a crucial role in the carbon cycle. Their contribution to the global carbon cycle is expected to increase with climate change as fire activity, particularly in boreal forests, escalates. As 8-28% of annually produced pyrogenic carbon is transported through riverine systems, its impact on fluvial environmental conditions will likely increase in coming years. However, the impact of pyrogenic carbon on metal and nutrient transport remains poorly understood. Here, we compare the chemical composition of wildfire-derived pyrogenic carbon (F-PyC) with slow-pyrolysis biochar-derived pyrogenic carbon (B-PyC), both originating from the same mountainous boreal forest biomass, to determine if F-PyC shares physicochemical properties with artificial B-PyC. The results reveal notable differences in the physicochemical properties and bulk composition of F-PyC compared to B-PyC, even when both are produced under similarly high temperatures, due to the rapid heating and cooling during wildfires. These differences in pyrolysis conditions result in F-PyC having a smaller ash fraction (<2.7% vs. >5.0%), a more acidic pH (<7.0 vs. >7.8), and a less thermally mature mineral composition and surface functionality. Together these differences in properties result in markedly different leaching behaviors and suggest that F-PyC and slow pyrolysis B-PyC play different roles in elemental transport. Consequently, this work supports earlier claims that B-PyC is not a suitable proxy for the F-PyC, particularly with respect to elemental transport in fluvial environments. Our work highlights the necessity for research specifically focusing on F-PyC to accurately quantify the contribution of wildfires to global elemental cycling, presently and in the geologic past.

The Abu Dhabi coast, particularly the supratidal zone known as the " sabkha " , has been a subject of geological interest in recent decades due to its relevance as an analogue for subsurface petroleum reservoirs. The intertidal zone (Al Qantur lagoon) has received less attention, especially regarding neoichnological investigations. This study addresses this research gap by combining modern sedimentological and neoichnological observations. Three recurring depositional textures are identified in the sediments examined: the bioturbated peloidal grain- stone, microbially laminated bindstone, and bioclastic rudstone. Observed burrows are generally of two types; those attributed to worms ( Nereis polychaetes) and those to decapod crustaceans. Crustaceans homogenize sediments in distal areas by excavating dwelling structures, while worms act as mobile deposit feeders. The relatively low complexity and diversity of burrowing morphologies in Abu Dhabi are attributed to heightened environmental stressors, including salinity, heat, and subaerial exposure, as well as upward seepage of hypersaline continental brines. Porewater analyses indicate a stabilization of salinity within burrows, suggesting the infauna irrigate their burrows to cope with elevated salinity. Crustacean burrows enhance solute advection in the lower intertidal zone by increasing substrate permeability, facilitating the penetration of less-saline surface waters to greater depths. This study provides a unique neoichnological examination of Abu Dhabi's intertidal zones and assesses the impact of bioturbation on solute advection, an aspect often overlooked in contemporary carbonate sedimentological studies.

ABSTRACTSedimentological and ichnological descriptions of fluvio‐tidal translating point bars are rare, and complex physico‐chemical processes make highly detailed but concise facies descriptions challenging. Herein, mesofacies are defined to describe and interpret three ancient translating point bars from the Lower Cretaceous McMurray Formation, Alberta, Canada. Twenty‐three mesofacies are defined, based on their recurring sedimentological and ichnological characteristics. These mesofacies form the building blocks of beds and bedsets that make up three depositional facies. Facies 1 reflects sand dune migration at the channel base, which grades into inclined heterolithic stratification of Facies 2 and 3. Facies 2 occurs in the centre and seaward portions of the translating point bars and records tide‐dominated deposition of sand and muddy sand during periods of reduced river discharge. Ichnological suites and bioturbation intensities in these beds reflect persistent but variable brackish‐water conditions, fluctuating deposition rates and the deposition of mud. Mud beds are derived from flows with high suspended‐sediment concentrations. Tidally derived mud beds are typically bioturbated with trace fossil suites indicative of slow deposition rates and brackish‐water conditions. Mud deposited during elevated river discharge is burrowed after the dewatering of the bed. Facies 3 occurs at the landward apex of the translating point bar and is marked by sand‐rich and mud‐rich dune deposits with abundant soft‐sediment deformation, indicative of elevated flow velocities and deposition rates. Bioturbation is rare and sporadically distributed owing to unstable substrates. The distribution of the facies reflect the hydrodynamic variations that occurred vertically and laterally across the bar in response to temporal variations in fluvial and tidal flow interaction, as recorded by their mesofacies. The detailed facies analysis strongly suggests that deposition of the three McMurray Formation translating point bars occurred in proximity to the turbidity maximum zone of a fluvio‐tidal channel system.