Marine Sediments Research Articles

Paleo-climatic control on recharge and fresh-salt groundwater distribution in the Red River delta plain, Vietnam

Paleo-climatic induced sedimentation controls present-day recharge and the fresh-salt groundwater distribution in Quaternary delta systems. During sea-level highstands, marine clays with saline pore water were deposited and are interbedded with aquifers of coarse-grained sandy fluvial and shallow marine deposits, laid down during lowstands. The low-permeable marine layers may inhibit recent recharge to deeper aquifers, and thereby limit sustainable use of these freshwater resources. This phenomenon has been investigated in the Red River delta plain, using geophysical borehole logging, transient electromagnetic soundings, groundwater chemistry, stable isotope analysis and 3H and 14C dating of groundwater. Results reveal that marine saline pore water is still present in the Holocene marine clays, implying that fresh water has not entered the clays since their deposition. Therefore, recharge within the delta plain is not occurring and the deeper aquifers are hydraulically disconnected from the upper sandy layers. Today, recharge only occurs from the hinterland. Recharge during the last glacial period has flushed saline pore water from Pleistocene marine clays, but these clays were again affected by saline water during the Holocene transgression. The use of the groundwater resources in the delta plain must be adjusted to the present recharge to be sustainable.

Holocene hydroclimate synthesis of the Aegean: Diverging patterns, dry periods and implications for climate-society interactions

The Aegean region has a wealth of archeological data originating from a long and rich human history and is frequently used as a testbed for climate-society interactions at different time scales. Here, we summarize and synthesize 31 proxy records derived from lake and wetland sediments, marine sediments, and speleothems reflecting hydroclimatic conditions over the last 10,000 years in the Aegean. To enable comparison and numerical analyses, we convert each record into z-scores and average values into centurial and decadal bins. The long-term hydroclimatic trajectory is best described by individual trends in three sub-regions that periodically converge and diverge. The results from our analyses highlight the complex long- and short-term spatio-temporal patterns of the hydroclimate with periods of wetter and drier conditions. Statistical analyses of the last 3500 years, the most data-rich period, corroborate the complex climate picture. Three periods that appear dry in the regional averages, at 7250–6650 BP, 3350–2750 BP, and 1200–700 BP, highlight spatio-temporal variability and underpin the importance of local data when comparing hydroclimate data with archeological information. Considering the complexities and uncertainties in hydroclimate records, we advocate for careful consideration when utilizing these in studies of climate-society interactions, including transparency regarding their uncertainties and the relevance of each record to a respective archeological site. We have produced a freely available, simplified dataset that can be used by those interested in studying the region, as well as maps displaying climatic conditions during each century.

The Neogene of the Vienna Basin – a synthesis

We present a revision of geological and paleontological data of the Vienna Basin (VB). The deposits comprise Miocene terrestrial, lacustrine and marine sediments, corresponding the Ottnangian, Karpatian, Badenian, Sarmatian and Pannonian regional stages (= Burdigalian to Tortonian). New 3D seismics and the analyses of hundreds of core samples resulted in a wealth of information. Absolute ages were published for two tuffs and the lithostratigraphy was largely formalized. The evolution of the paleoenvironments in the VB strongly reflects the impact by global climatic events such as the Miocene Climatic Optimum, the Middle Miocene Climate Transition and the Tortonian Thermal Maximum. Global 3 rd order sea level cycles are reflected in the successions of marine depositional environments. Major drops of the relative sea level caused strong erosion along the basin margins, with up to 300 m paleorelief. The strongest phase of erosion was linked to tectonics. Around the Early/Middle Miocene boundary, Lower Miocene strata became tilted during the Styrian Tectonic Phase. Up to 600-m-deep subaerial canyons incised the VB at that time. A second phase of basin-wide erosion occurred during the Late Miocene when more than 200 m of upper Pannonian strata became removed from large parts of the VB after 9 Ma.

Stratigraphic overview of the Neogene Transylvanian Basin, Romania

Although the Transylvanian Basin is often referred as part of the Miocene Pannonian Basin System, we point out important tectonic and sedimentary differences reflected in the stratigraphy. The Neogene of the Transylvanian Basin can be split into two tectonic megasequences: Lower Miocene and Middle to Upper Miocene. The Early Miocene onset of the back arc extension in the Pannonian Basin was not observed in the Transylvanian Basin, where shallow to deep marine sediments were deposited in a flexural basin. Diverse types of facies developed in the continental (e.g., Sânmihai) and marine (e.g., Coruş, Chechiş, Hida) Lower Miocene formations. Although these are poorly constrained to the standard biostratigraphy, recent 87 Sr- 86 Sr data support their limited correlation with the Burdigalian. The Middle Miocene extension in the Transylvanian Basin is very weak compared to that the Pannonian Basin. As the high-resolution Middle Miocene regional biostratigraphy of the Badenian and Sarmatian was calibrated by magnetostratigraphy and radiometric dating of the volcanic tuffs up to the Serravallian/Tortonian boundary, the influence of the regional tectonics on the basin's evolution and stratigraphy can be better understood. The regional tectonics produced a progressive basin isolation starting with the late part of the Middle Miocene. The uplift of the Carpathians isolated the basin at the beginning of the Pannonian and initiated the fan delta, lacustrine, and fluvial sedimentation. The basin was rapidly uplifted and eroded, while post-extensional subsidence was still ongoing in the Pannonian Basin. Endemic fossil assemblages allow only regional-scale correlations for this interval. The uppermost part of the stratigraphic record is represented by the volcano-sedimentary formations generated by the late evolution of the Eastern Carpathians. The sedimentation and subsidence pattern of the Transylvanian Basin reflect the effect of retreating subduction zone in the Eastern Carpathians.

The Styrian Basin: an overview with new insights from seismic data

The Neogene Styrian Basin is the westernmost subbasin of the Pannonian Basin System. The last comprehensive studies on the basin were published in the last millennium. This overview of the current understanding of basin evolution is based on the re-interpretation of partly unpublished reflection seismic data and a wealth of sedimentological and stratigraphic studies performed during the last 25 years. Reflection seismic data indicate the presence of a major E to SE dipping detachment horizon within the pre-Neogene basement reflecting high-strain upper crustal extension during the early Miocene syn-rift stage of basin evolution. Fault block rotations caused subsidence in several subbasins, which developed often with marked asymmetric geometry. The maximum basin depth exceeds 4 km (Gnas Basin). Syn-rift deposits include thick alluvial fan and fan delta sediments overlain in the basin center by deeper marine pelitic rocks. Subduction-related magmatic activity commenced during the syn-rift stage and continued into the middle to late Miocene post-rift stage. Syn- and post-rift sediments are separated by the middle Miocene “Styrian Unconformity”. Shallow marine sedimentation, controlled by third- and fourth-order sea-level variations, prevailed during the early post-rift stage. The final stage of basin evolution was characterized by differential surface uplift, erosion, and Pliocene-Pleistocene basaltic magmatism.

Late Pleistocene charcoal-rich sediments in the Puerto Rico Trench, possible remnants of gigantic wildfires in North-Eastern South America

An 18,000 km2 area of the Guyana Shield of South America, known as the Gran Sabana, is characterized by savannah vegetation that contrasts strongly with surrounding rain forests. Its origin has been linked to multiple episodes of forest fires. In this paper, we report a deposit encountered in two piston cores sampled during the CASEIS marine cruise, at 6000 m-depth at the southern entrance of the Puerto Rico Trench. The existence of this deposit call into question our understanding of the evolution of the Gran Sabana. We sampled its upper ∼60 cm, which comprises leaves and wood fragments, seeds, and charcoal, intermixed with siliciclastic sediment of igneous-metamorphic continental provenance. Radiocarbon dates of the vegetal fragments and charcoal range between 30 and 23 kyr BP. We propose that these deep ocean charcoal-rich sediments, located 2500 km offshore from the Orinoco Delta, may be remnants of gigantic forest fires of the Guyana Shield. We infer that this material was eroded during an extreme regional rainfall event, transported down rivers during one or more episodes to the Orinoco delta, and then travelled offshore via a deep turbiditic submarine system flowing on the Atlantic seafloor. It finally reached the Puerto Rico Trench, forming what we term, the Baracuda Trench Debrite. While published paleoclimatic analyses of lacustrine sediments have suggested that the Gran Sabana originated during episodes of wildfire ∼12.5 kyr BP ago, radiocarbon dating of Baracuda Trench Debrite suggests the occurrence of earlier fires in this region, leading us to re-evaluate the age of the Gran Sabana. These fires occurred during the low glacial maximum (LGM) and were likely promoted by climate change.

Multivariate statistical “unmixing” of Indian and Pacific Ocean sediment provenance

AbstractThe geochemistry of marine sediment is a massive archive of (paleo)oceanographic information. Accessing that information requires “unmixing” the various influences on marine sediment geochemistry to understand individual sources and marine geochemical processes. Q‐mode factor analysis (QFA) and independent component analysis (ICA) are multivariate statistical techniques that have successfully been applied to large datasets of marine sediment element concentrations to identify the number and composition of marine sediment sources or end‐members. In this study, we apply both techniques to two datasets of marine sediment geochemistry, compare the output, and discuss the advantages of each approach. In both datasets, ICA identified a mixing trend between carbonates and dust, whereas QFA represented the end‐members as two separate factors. In the Pacific and Indian Oceans dataset, both techniques produced three factors or independent components involving rare earth elements, but two of the QFA factors explained a small, almost negligible, amount of the variability of the dataset. Also, QFA identified more aluminosilicate end‐members (dust or volcanic ash) than ICA. In the Indian Ocean Sites 738 and 752 dataset, ICA identified two processes affecting Sr and Ba concentrations as separate independent components, while QFA created a factor representing the covariation of Sr and Ba over intervals of the site's paleoceanographic history. The results of this study exemplify that QFA identifies covariances and finds discrete end‐members contributing to the bulk mass of sediment. ICA works best with non‐Gaussian element distributions and finds geochemical signals and mixing trends that constitute the characteristic structure of the multielemental data.

Assessment of physicochemical properties and radioactivity in groundwater at households living in bac Lieu province, vietnam.

This paper presents findings on groundwater physiochemical composition and radioactivity levels in households in Bac Lieu province, Vietnam. Through discriminant analysis, it was observed that groundwater quality exhibits spatial variations corresponding to saline intrusion zones. The paired-samples T-tests revealed significantly different ratios of Ra-224, Ra-226, and Ra-228 isotopes between Na-Cl and Ca-Na-HCO3 water types. All three water types had a ratio of Ra-226/Ra-228 of approximately one, indicating the presence of groundwater aquifers beneath the crust and fluvial marine sediment. Furthermore, strong associations between sulfate and calcium suggest that CO2 enrichment in groundwater aquifers indicates anoxic aquatic environments. Twenty-five of the thirty-three evaluated samples exceeded the national technical regulations for domestic water quality with parameters such as chloride, sulfate, sodium, gross alpha, or total dissolved solids. Fifteen samples exceeded gross alpha's allowable contamination threshold of 0.1Bq/L. The combination of Ra-226 and Ra-228 did not surpass the U.S. Environmental Protection Agency's recommended limit of 0.185Bq/L. However, nineteen samples exhibited annual committed effective doses of radium isotopes for infants that exceeded the WHO recommendation of 0.1mSv/year.

Response of Bathonian–Oxfordian transgressive-regressive cycles on foraminiferal morphogroups, and diversity: a case study from shallow marine deposits in north Gulf of Suez, Egypt

Response of Bathonian–Oxfordian transgressive-regressive cycles on foraminiferal morphogroups, and diversity: a case study from shallow marine deposits in north Gulf of Suez, Egypt

Enhanced deep-water circulation facilitated rare earth elements enrichment in pelagic sediments from the northwestern Pacific Ocean

The lack of knowledge about the enrichment mechanism of rare earth elements and yttrium (REY) in deep-sea sediments is impeding the development of theories and exploration strategies for pelagic REY-rich sediments. Ocean circulation variability seems to be crucial in enriching REY in pelagic sediments, which, however, has not been extensively studied. Here, we examined the Pb-Nd isotopic signals of bottom water recorded by the authigenic ferromanganese oxyhydroxide fractions, as well as the Mn/Al and Mn/Ti ratios of bulk samples from a well-dated sediment core in the northwestern Pacific Ocean. These proxies consistently indicate that enhanced deep-water circulation occurred in the study area at ∼11.5–9.5 Ma, which was most likely to be caused by changes in the flow path of bottom currents. The age of this distinct event consists with the forming age of highly REY-rich sediments. We propose that enhanced deep-water circulation in seamount areas could increase the flux of micronodules and fish debris into the pelagic sediments, facilitating the scavenging of REY from seawater. Our findings establish a connection between enhanced deep-water circulation and the enrichment of REY in pelagic sediments.

Use of a Glaciogene Marine Clay (Ilulissat, Greenland) in a Pilot Production of Red Bricks.

Uplifted occurrences of fine-grained glaciogene marine sediments are found throughout the northern hemisphere. These sediments could be used to produce local construction materials, to rely less on imported construction materials from southern regions. In this study, a representative occurrence from Ilulissat, West Greenland, was investigated as a potential resource for local brick production. The study comprised three parts: (1) raw material characterization based on grain size distribution, major element chemistry, including total carbon, sulfur, and chloride concentrations, mineralogy, morphology, and Atterberg limits; (2) the production of test bricks at a Danish brickwork; and (3) testing of the bricks based on total shrinkage, water absorption, hygroscopic adsorption, open porosity, bulk density, compression strength, and mineralogy. The bricks produced proved to have excellent compression strength, low open porosity, and low water absorption. The shrinkage could be reduced by adding 10% chamotte to the marine sediment. Based on the investigated properties, this indicates that this type of clay is highly suitable as a resource for bricks.

Endocranial anatomy and phylogenetic position of the crocodylian Eosuchus lerichei from the late Paleocene of northwestern Europe and potential adaptations for transoceanic dispersal in gavialoids.

Eosuchus lerichei is a gavialoid crocodylian from late Paleocene marine deposits of northwestern Europe, known from a skull and lower jaws, as well as postcrania. Its sister taxon relationship with the approximately contemporaneous species Eosuchus minor from the east coast of the USA has been explained through transoceanic dispersal, indicating a capability for salt excretion that is absent in extant gavialoids. However, there is currently no anatomical evidence to support marine adaptation in extinct gavialoids. Furthermore, the placement of Eosuchus within Gavialoidea is labile, with some analyses supporting affinities with the Late Cretaceous to early Paleogene "thoracosaurs." Here we present novel data on the internal and external anatomy of the skull of E. lerichei that enables a revised diagnosis, with 6 autapormorphies identified for the genus and 10 features that enable differentiation of the species from Eosuchus minor. Our phylogenetic analyses recover Eosuchus as an early diverging gavialid gavialoid that is not part of the "thoracosaur" group. In addition to thickened semi-circular canal walls of the endosseous labyrinth and paratympanic sinus reduction, we identify potential osteological correlates for salt glands in the internal surface of the prefrontal and lacrimal bones of E. lerichei. These salt glands potentially provide anatomical evidence for the capability of transoceanic dispersal within Eosuchus, and we also identify them in the Late Cretaceous "thoracosaur" Portugalosuchus. Given that the earliest diverging and stratigraphically oldest gavialoids either have evidence for a nasal salt gland and/or have been recovered from marine deposits, this suggests the capacity for salt excretion might be ancestral for Gavialoidea. Mapping osteological and geological evidence for marine adaptation onto a phylogeny indicates that there was probably more than one independent loss/reduction in the capacity for salt excretion in gavialoids.

Effect of Surface Charges in Polymer Coatings on Antifouling Performance in Marine Environments with Sediment.

The antifouling efficacy of hydrophilic polymer coatings is closely related to their surface charge. Many biological foulants such as mammalian cells and marine microalgae possess a negative surface charge, discouraging the use of positively charged polymer coatings for antifouling purposes. Instead, electrically neutral yet hydrophilic polymers have been widely employed, leveraging hydration layers to create a barrier against fouling. However, challenges arise in marine environments where both living marine organisms and sediments can adhere to solid surfaces, rendering previous findings less directly applicable. This study investigates the impact of a polymer coating surface charge on marine antifouling properties. Polymer brushes with various charges are applied to solid substrates, and the adhesion behavior of marine diatoms is assessed under both marine sediment-free and marine sediment conditions. The results underscore the effectiveness of negatively charged polymer brush coatings in marine antifouling, regardless of sediment presence.

Structural variability of protist assemblages in surface sediments across Italian Mediterranean marine subregions

Marine sediments host heterogeneous protist communities consisting of both living benthic microorganisms and planktonic resting stages. Despite their key functions in marine ecosystem processes and biogeochemical cycles, their structure and dynamics are largely unknown. In the present study, with a spatially intensive sampling design we investigated benthic protist diversity and function of surface sediment samples from three subregions of the Mediterranean Sea, through an environmental DNA metabarcoding approach targeting the 18S V4 region of rRNA gene. Protists were characterized at the taxonomic level and trophic function, both in terms of alpha diversity and community composition, testing for potential differences among marine subregions and bathymetric groups. Overall, Alveolata and Stramenopiles were the two divisions that dominated the communities. These dominant groups exhibited significant differences among the three Mediterranean subregions in the alpha diversity estimates based on the detected ASVs, for all computed indices (ASV richness, Shannon and Simpson indices). Protist communities were also found to be significantly different in terms of composition at the order rank in the three subregions p-value < 0.01). These differences were mainly driven by Anoecales, Peridiniales, Borokales, Paraliales and Gonyaulacales, which together contributed almost 80% of the average dissimilarity. Anoecales was the dominant order in the Ionian – Central Mediterranean and Adriatic Sea, but with considerably different relative abundances (52% and 36%, respectively), while Borokales was the dominant order in the Western Mediterranean Sea (33%). Similarly, significant differences among the three marine subregions were also highlighted when protist assemblages were examined in terms of trophic function, both in terms of alpha diversity (calculated on the ASVs for each trophic group) and community composition p-value < 0.01. In particular, the Adriatic Sea stood out for having the highest relative abundance of autotrophic/mixotrophic components in the surface sediments analyzed. Conversely, no significant differences in protist assemblages were found among depth groups. This study provided new insights into the taxonomic and trophic composition of benthic protist communities found in Mediterranean surface sediments, revealing geographical differences among regional seas. The results were discussed in relation to the Mediterranean environmental features that could generate the differences among benthic protist communities.

Evaluation of a Nanopore Sequencing Strategy on Bacterial Communities From Marine Sediments

ABSTRACTFollowing the development of high‐throughput DNA sequencers, environmental prokaryotic communities were usually described by metabarcoding on short markers of the 16S domain. Among third‐generation sequencers, that offered the possibility to sequence the full 16S domain, the portable MinION from Oxford Nanopore was undervalued for metabarcoding because of its relatively higher error rate per read. Here we illustrate the limits and benefits of Nanopore sequencing devices by comparing the prokaryotic community structure in a mock community and 52 sediment samples from mangrove sites, inferred from full‐length 16S long‐reads (16S‐FL, ca. 1.5 kbp) on a MinION device, with those inferred from partial 16S short‐reads (16S‐V4V5, ca. 0.4 kbp, 16S‐V4V5) on Illumina MiSeq. 16S‐V4V5 and 16S‐FL retrieved all the bacterial species from the mock, but Nanopore long‐reads overestimated their diversity (56 species vs. 15). Whether these supplementary OTUs were artefactual or not, they only accounted for ca. 10% of the reads. From the sediment samples, with a coverage‐based rarefaction of reads and after singletons filtering, Mantel and Procrustean tests of co‐inertia showed that bacterial community structures inferred from 16S‐V4V5 and 16S‐FL were significantly similar, showing both a comparable contrast between sites and a coherent sea‐land orientation within sites. In our dataset, 84.7% and 98.8% of the 16S‐V4V5 assigned reads were assigned strictly to the same species and genus, respectively, than those detected by 16S‐FL. 16S‐FL detected 92.2% of the 309 families and 87.7% of the 448 genera that were detected by the short 16S‐V4V5. 16S‐FL recorded 973 additional species and 392 genus not detected by 16S‐V4V5 (31.5% and 10.4% of the 16S‐FL reads, respectively, among which 67.8% and 79.3% were assigned), produced by both primer specificities and different error rates. Thus, our results concluded an overall similarity between 16S‐V4V5 and 16S‐FL sequencing strategies for this type of environmental samples.

Stable carbon isotope ratios of pristine carbohydrates preserved within nannofossil calcite

The geochemical characterization of phytoplankton-derived organic compounds found in marine sediments has been widely used to reconstruct atmospheric pCO2 throughout the Cenozoic. This is possible owing to a well-established relationship between the carbon isotope ratios of phytoplankton biomass and CO2 concentration in the ambient seawater. An ideal molecular target for such proxy reconstructions would be degradation resistant on geologic timescales and unambiguously associated with known, experimentally tractable, organisms, so that species-specific models can be developed, calibrated, and applied to appropriate material. However, existing organic matter targets do not meet these criteria, primarily owing to ambiguity in the source species of recalcitrant compounds in deep time. Here we explore the potential of a novel organic carbon target for isotopic analysis: acidic polysaccharides extracted from the calcite plates (coccoliths) that are produced by all calcifying haptophytes. Carbohydrates are usually rapidly remineralized in sediments, but coccolith-associated polysaccharides (CAPs) are mechanically protected from diagenesis within the coccolith calcite lattice. Coccoliths can be taxonomically separated by size and identified, often to species level, prior to CAP extraction, providing a species-specific record. Coccolith morphology and composition are important additional sources of information, which are then unambiguously associated with the extracted CAPs. We found that carbon isotope ratios of CAPs changed in response to the environmental changes associated with a glacial cycle, which we attribute to temperature-driven changes in average growth rate. Once the underlying biosynthetic processes and the associated isotope effects are better understood, this archive of pristine organic matter has the potential to provide insight into phytoplankton growth rates and atmospheric pCO2 far beyond the Cenozoic, to when the first coccolithophores inhabited the surface ocean over 200 million years ago.

Plane-wave and cylindrical-wave acoustic reflection from a marine sediment with layering representative of the New England Mud Patch.

An analysis is presented of reflection from a marine sediment consisting of a homogeneous mud layer overlying a sand-mud basement, the latter with an upward-refracting, inverse-square sound speed profile. Such layering is representative of the sediment at the New England Mud Patch (NEMP). By applying appropriate integral transforms and their inverses to the Helmholtz equations for the ocean and the two sediment layers, along with the boundary conditions, a Sommerfeld-Weyl type of wavenumber integral is obtained for the cylindrical-wave reflection coefficient of the sediment, R. A stationary phase evaluation of this integral yields a closed-form expression for the plane-wave reflection coefficient, R0. In the absence of attenuation, the plane-wave solution exhibits total reflection up to a critical grazing angle, ac, but when attenuation in the sediment is introduced, the region of total reflection in |R0| is replaced by a sequence of contiguous peaks. With realistic levels of sediment attenuation, the cylindrical-wave solution, |R|, exhibits a quasi-critical grazing angle, less than ac, which is strongly dependent on the source-plus-receiver height above the seabed, which is mildly dependent on the depth of the mud layer but is essentially independent of frequency. Such behavior is consistent with independent experimental observations at the NEMP.

Nursery Habitat Requirements for the Blue Swimming Crab: Implications for Larval Development

Overfishing causes a significant decline in blue swimming crab (Portunus pelagicus) populations, an essential marine resource for Thailand. This research aimed to identify suitable nursery areas for this species throughout the four distinct monsoon seasons. This is the first comprehensive study of habitat characteristics: water temperature, pH, salinity, dissolved oxygen, marine sediment, seagrass beds, and suitability assessment of nursery areas, using a combined approach of Analytic Hierarchy Process and Geographic Information Systems. Our findings reveal that highly suitable nursery habitats comprise a small percentage of the total study area, varying with the monsoon season: 1.66% in the Northeast Monsoon (NEMS), 1.00% in the NEMS transition (NEMST), 1.11% in the Southwest Monsoon (SWMS), and 1.97% in the SWMS transition (SWMST). These areas are concentrated along the coastlines of Sed Island, Phum Riang, Takrob, Tha Thong, and Donsak. Sed Island was designated as a fishery refuge zone in 2022. The identified nursery areas coincide with existing crab banks, highlighting the model's accuracy. Conversely, unsuitable areas were predominantly in shellfish farming zones and low-salinity estuaries. By identifying suitable nursery grounds for the blue swimming crab, this study offers valuable information that can support Thailand's sustainable management and conservation efforts for this species. Doi: 10.28991/HEF-2024-05-03-01 Full Text: PDF

A Spatially Restricted Distribution of Thermophilic Endospores in Laptev Sea Shelf Sediments Suggests a Limited Dispersal by Local Geofluids.

Thermospores, the dormant resting stages of thermophilic bacteria, have been shown to be frequent but enigmatic components of cold marine sediments around the world. Multiple hypotheses have been proposed to explain their distribution, emphasizing their potential as model organisms for studying microbial dispersal via ocean currents. In the Arctic Ocean, the abundance and diversity of thermospores have previously been assumed to be low. However, this assessment has been based on data mainly from the western fjords of Svalbard, thus leaving most of the Arctic unexplored. Here, we expand the knowledge about the distribution of thermospores in the Arctic Ocean by investigating the abundance and diversity of thermospores in heated shelf sediments from three sites in the outer Laptev Sea. Two of the sites are located in an area with methane-emitting cold seeps with a thermogenic source signature suggestive of an origin in a deep hydrocarbon reservoir, while the third site is a reference site not known to be impacted by seepage. We found that activity of viable thermospore populations was more prominent at one of the investigated seep sites. This finding is supported by both radiotracer growth experiments showing thermophilic, sulfate-reducing activity triggered by heating, as well as 16S gene sequence analyses showing significantly enriched ASVs affiliated to the phylum Firmicutes following high-temperature incubations. An enrichment of the sulfate-reducing, endospore-forming class Desulfotomaculia in heated samples compared to unheated samples was also observed. Furthermore, several ASVs identified at the seep site are closely related to thermospore-producing bacteria associated with the deep biosphere, including hydrocarbon and hydrothermal systems. Based on the combined information from induced activity, estimated abundance, and phylogenetic composition using 16S rRNA gene sequencing, we propose likely source environments and dispersal vectors for thermospores in the Arctic Ocean.

Heterolytic tide-dominated sedimentary facies and depositional environment: An Example from the Boka Bil formation, Sitapahar anticline, Bangladesh

The Baraichari Shale Formation, which is equivalent to the Boka Bil Formation, is well exposed within the Neogene sequence of the Sitapahar Anticline in the Chittagong-Tripura Fold Belt, Bengal Basin, Bangladesh. Regardless of its importance in hydrocarbon accumulation, a comprehensive facies analysis is essential to understand and explain the heterogeneity within different depositional architectural elements. The purpose of this work is to delineate the lithofacies characteristics, depositional environment heterogeneities and propose a generic depositional model for the Middle to Late Miocene shallow marine sediments of the formation. The sedimentary facies were investigated at three outcrops along the Kaptai–Chandraghona road cut sections of the Sitapahar anticline. The formation is composed of dark to bluish-gray shale, silty shale, yellowish brown siltstone, and gray to yellowish brown fine-to medium-grained sandstone. Eight distinct sedimentary facies have been identified and were categorized into three facies associations: subtidal or estuarine, mixed flats with tidal creeks, and tidal mud flats. The subtidal facies, predominant in the middle member, consists of fine to medium-grained ripple cross-stratified sandstone-siltstone, herringbone cross-stratified sandstone, and trough cross-stratified sandstone, indicating sub-tidal channel deposition. Mixed flats with tidal creeks exhibit heterolithic facies, suggesting energy level changes in intertidal to sub-tidal zones influenced by tidal currents. Tidal mud flats are predominantly laminated shale/mudstone and lenticular laminated sandstone-siltstone, reflecting deposition during tide transitions in the intertidal zone. Fining upward cycles within the formation indicate progressive progradation or changes in inner tidal flats conditions during regressive periods. These depositional settings serve as analogs for equivalent subsurface reservoirs and contribute to the construction of reservoir models with greater accuracy.