Marine Sedimentary Environments Research Articles

Transport and sedimentation of microplastics by turbidity currents: Dependence on suspended sediment concentration and grain size.

Using lock-exchange experiments, this study investigates the transport and sedimentation of microplastics (MPs) via turbidity currents. Two hypotheses were tested: MP sedimentation is influenced by suspended sediment concentration and grain size. Utilizing flows with different sediment concentrations and grain sizes in combination with three different MPs (PET fibers, melamine, and PVC fragments), the experiments revealed distinct sedimentation patterns: higher sediment concentrations enhance MP transport, and turbidity currents with finer sediments transported MPs over greater distances, highlighting the importance of sediment characteristics to predict MP distribution by such flows. Further, MP sedimentation patterns varied in dependence on MP-particle shape, size, and density, highlighting the crucial role of MP particle properties in determining MP distribution in turbidites. These findings enhance our understanding of the mechanisms controlling the spatial distribution of MPs in marine sedimentary-environments and underscores the importance of considering both hydrodynamic and particle-specific factors when addressing the complex behaviour of MPs.

Novel organophosphate esters and their transformation products in offshore sediment from Eastern China: Occurrence, temporal trend, and risk assessment.

Offshore sediment serves as an important sink for traditional organophosphate esters (TOPEs) originating from terrestrial sources. However, the contamination characteristics of novel OPEs (NOPEs) and their hydrolyzed and hydroxylated transformation products (Di- and OH-OPEs) in marine sediment are still unknown. In this study, 34 OPE-associated contaminants were measured in six offshore sediment cores (71 samples) collected from Eastern China. The total concentrations of Σ15TOPEs, Σ3NOPEs, Σ9Di-OPEs, and Σ7OH-OPEs in surface sediments were 3.16-73.4, n.d.-16.3, 4.48-21.4, and 0.14-0.42ngg-1, respectively. NOPE compounds, such as tris(2,4-di-tert-butylphenyl) phosphate and its diester product, exhibited high contamination levels, primarily due to their high hydrophobicity and extensive industrial applications. Additionally, atmospheric transportation, along with wet and dry deposition and ocean currents, plays a crucial role in their distribution in offshore sediment. The location conditions and historical usage also influenced the vertical distributions of OPE-associated contaminants in sediment cores. Notably, a concentration peak of bis(2,4-di-tert-butylphenyl) phosphate (B2,4DtBPP) was dating back to 1940s, indicating the early usage of antioxidant tris(2,4-di-tert-butylphenyl) phosphite. Furthermore, a risk quotient (RQ) model was employed to assess the ecological risks posed by OPEs. Generally, the acute toxicity-based predicted no-effect concentrations for studied compounds were 1 to 2 orders of magnitude lower than those based on chronic toxicity. NOPEs and B2,4DtBPP exhibited high ecological risks, with maximum RQ values of 1570-4877 based on acute toxicity and 93.4-197 based on chronic toxicity. Notably, ΣRQ values for NOPEs were significantly higher than those of TOPEs (Mann-Whitney U test, p<0.001), indicating their severe ecological risks in offshore sediment. Therefore, given the continuous input and considerable persistence of NOPEs in offshore sediment, their toxic effects and mechanisms warrant thorough investigation. This study provides the first evidence for the occurrence, temporal trends, and potential risks of NOPEs in marine sediment environment.

Vertical distribution of intracellular protoporphyrin IX in coastal sediment cores: Implications for sedimentology and microbial community composition

Protoporphyrin IX (PPIX), a basic porphyrin system found in nature, all “porphyrin-type” tetrapyrroles with a biological function are biosynthetically derived thereof. PPIX is a metalloprosthetic group of numerous proteins involved in diverse metabolic and respiratory processes across all domains of life, and is thus considered essential for respiring organisms. Determining the biotic and abiotic factors that influence marine microbial growth and community structure is critical for understanding global biogeochemical cycles. Here, we present vertical profiles of intracellular PPIX and four derivative products (Chlorophyll-a/b and Pheophytin-a/b) from two coastal sediment cores, alongside ancillary geochemical and 16S rRNA microbial community data. Our findings indicated that PPIX is present in the natural sediment environment and displays a decreasing trend with depth, revealing a significant positive correlation with both organic matter and microbial abundance. Co-occurrence networks revealed that the environmental distribution of PPIX was positively correlated with the microbial porphyrin producer (high genetic completeness), but negatively correlated with auxotrophs (absence or low genetic completeness). It emphasized the critical role of PPIX as a biological molecule involved in key physiological processes. These results suggest that PPIX is a prominent component of the shared extracellular metabolite pool, especially in anoxic marine sediments where it exists at physiologically relevant concentrations for microbial metabolism. This study highlighted the significance of PPIX in microbial ecology and its potential impact on biogeochemical cycles in marine sedimentary environments.

Insights from tensile fracture properties and full-field strain evolution of deep coral reef limestone under dynamic loads

Coral reef limestone (CRL) commonly undergoes dynamic tension when underground structures of island reefs encounter impacts, explosions, or seismic activities. Given the complexity of biological pores, the dynamic tensile fracture characteristics of CRL are poorly understood. Therefore, the dynamic tensile fracture behaviors of deep CRL were systematically observed by Split Hopkinson Pressure Bar tests and digital image techniques. Comparing to traditional rocks, the macro-pores near failure band would significantly change cracking path. The failure patterns are dominated by loading rate. The strongly dependence of dynamic tensile strength and dynamic crack initiation toughness on loading rate suggests the two indices overcome the effect of CRL macro-pores under dynamic impacts. At low loading rates, tensile fractures predominantly follow intergranular cracks, whereas transgranular cracks dominate at higher rates. The fractal dimension of fracture surface decreases with increasing crack propagation velocity, loading rate, and dynamic crack initiation toughness. Due to the unique marine sedimentary environment, the mechanical heterogeneity in multiple scales distinguishes CRL from terrestrial rock materials. The insights into underlying mechanisms of dynamic tension provide support to optimization of blasting scheme and stability assessments for island underground engineering.

Molecular organic geochemistry and origin of oil in the Potwar Basin, Pakistan

The Potwar Basin (PTB) is a prominent geological feature located in northern part of Pakistan, and is considered as one of the active and productive regions for petroleum and gas exploration in Pakistan. In this study, eight crude oil specimens originating from three distinct fields within the PTB were comprehensively examined to decipher the environmental conditions, source of organic matter (OM) and oil-oil correlations using gas chromatography coupled with flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC–MS). The molecular marker and hierarchical cluster analysis of PTB oils reveal two different crude oil families. Family-I showed relatively low values of Pr/Ph, C19TT/C23TT and C25TT/C24TeT, C27-C29 regular steranes, dibenzothiophene (DBT), fluorene (FL) and dibenzofuran (DBF), as well as C26/C28 TAS (20S) and C27/C28 TAS (20R). These results suggest that Family-I crude oils derived from marine environment of suboxic water bodies with higher contribution from green algae or planktonic microbes. However, Family II contains comparatively high values of the aforementioned molecular parameters, indicating that crude oils mainly originated from a lacustrine environment with a higher contribution of plant organisms under oxidizing conditions. Saturated hydrocarbon maturity parameters such as CPI and OEP, and C3122S/(C3122S + C3122R) and C3222S/(C3222S + C3222R) indicate PTB crude oils are thermally mature, while aromatic indices reveal that Family-II crude oils are high mature. The present research defines that PTB crude oils contributed from mixed organic matter sources of marine and lacustrine majorly from marine sedimentary environment with the bloom of algae and/or higher plants.

Spatiotemporal distribution of giant magnetofossils holds clues to their biological origin

Abstract Micrometer-size magnetite crystals with peculiar morphologies, such as spearhead, spindle, needle, and giant bullet, known as giant magnetofossils, were previously identified in marine sediments mainly during the Eocene epoch. The origin of these unusual magnetite crystals remains unclear because no known modern analogues have been found, and data about their spatiotemporal distribution are sparse. Here, using electron microscope observations, we performed a large-scale spatiotemporal search for these mysterious magnetite crystals. We report the occurrence of giant magnetofossils in variable marine sedimentary environments, including the first report in modern South Atlantic and Indian Ocean environments and the oldest occurrence at ca. 93 Ma in the North Atlantic Ocean. Grain-size data for the giant magnetofossils in the Southwest Pacific and North Atlantic Oceans suggest that the dimension of spearheads is sensitive to regional environments during similar warming periods but is insensitive to environmental conditions across the distinct geological periods at the same locality. The grain-size distributions of needles and giant bullets do not show significant changes in diverse environments. These observations greatly expand the known temporal and geographic distribution of giant magnetofossils, shedding new light on their likely biological origin.

An in-situ portable pore-water sampler for evaluating the vertical distribution in the sediment interface

The characteristics of chemical elements in marine pore-water are significant for investigating and evaluating the marine sediment environment (especially vertical distribution characteristics, etc.). Therefore, sampling high-quality pore-water is necessary for marine scientific research. This paper proposes an in-situ portable pore-water sampler that utilizes the compression spring structure, allowing the potential energy generated by the spring to be converted into kinetic energy for the sampling process. The sampler requires no other power and can be portable for marine pore-water sampling. We first described the sampler’s mechanical design, which can obtain one sediment-overlying water and three sediment pore-water samples at different depth profiles. Secondly, to judge the force state of the power spring, we designed laboratory experiments and simulation tests based on COMSOL Multiphysics to analyze the force during the working process of power springs. Finally, we deployed the sampler offshore in Zhoushan Islands for actual sampling, and we tested and compared the in-situ samples with the centrifugal samples to analyze the vertical distribution of chemical elements. The successful sea trials verified the reasonableness of the mechanical design, theoretical calculation and experimental analysis of the sampler. Furthermore, we will continue to optimize the sampler and apply it more widely.

МОРСКОЕ ОСАДКОНАКОПЛЕНИЕ НА ПОБЕРЕЖЬЕ ЮГО-ЗАПАДНОЙ ОКРАИНЫ ПРИМОРЬЯ В СРЕДНЕМ ГОЛОЦЕНЕ

A comprehensive study of marine sediments deposited at the southwestern margin of Primorye (Khasan settlement area) allowed us to consider in detail the palaeogeography of the coast in the second half of the Atlantic period of the Holocene, about 6 500–6 000 yr BP / 7 400–6 800 cal BP. Sedimentation in marine environments began with the development of postglacial oceanic transgression around 6 500 yr BP / 7 400 cal BP. A shallow marine bay formed on the coastal accumulation plain, into which the Tumannaya (Tumangan) River, the largest in the Sea of Japan basin, flowed. Avalanche sedimentation proceeded in the bay at an average rate of 16–24 mm/year within the confines of the estuary. The final phase of sedimentation after 6 200 yr BP / 7 100 cal BP occurred at a time when the transgression of the sea slowed down and sea level reached its maximum height of +1 m in the coastal area. Multi-species broad-leaved oak-dominated forests mixed with thermophilic hornbeam species clearly indicate optimum climatic conditions in the territory adjacent to the coast. The marine sedimentation stopped around 6 000 yr BP / 6 800 cal BP to resume in the middle of the Sub-Atlantic period of the Holocene.

Paleo-uplift forced regional sedimentary evolution: A case study of the Late Triassic in the southeastern Sichuan Basin, South China

The sedimentary environment of the Upper Triassic in the southeastern Sichuan Basin is obviously controlled by Luzhou paleo-uplift (LPU). However, the influence of paleo-uplift on the sedimentary patterns of the initial stages of this period in the southeastern Sichuan Basin has not yet been clear, which has plagued oil and gas exploration and development. This study shows that there is a marine sedimentary sequence, which is considered to be the first member of Xujiahe Formation (T3X1) in the southeastern Sichuan Basin. The development of LPU resulted in the sedimentary differences between the eastern and western Sichuan Basin recording T3X1 and controlled the regional sedimentary pattern. The western part is dominated by marine sediments, but the eastern paleo-uplift area is dominated by continental sedimentation in the early stage of T3X1, and it begins to transform into a marine sedimentary environment consistent with the whole basin in the late stage of the period recorded by the Xujiahe Formation. The evidences are as follows: (1) time series: based on the cyclostratigraphy analysis of Xindianzi section and Well D2, in the southeastern Sichuan Basin, the period of sedimentation of the Xujiahe Formation is about 5.9 Ma, which is basically consistent with the Qilixia section, eastern Sichuan basin, where the Xujiahe Formation is widely considered to be relatively complete; (2) distribution and evolution of palaeobiology: based on analysis of abundance evolution of major spore-pollen, many land plant fossils are preserved in the lower part of T3X1, indicates the sedimentary environment of continental facies. In the upper part of T3X1, the fossil of terrestrial plants decreased, while the fossil of marine and tidal environment appeared, this means that it was affected by the sea water in the late stages of T3X1; (3) geochemistry: calculate the salinity of water from element indicates that the uplift area is continental sedimentary environment in the early stage of T3X1, while the central and western areas of the basin are marine sedimentary environment. Until the late stage of T3X1, the southeast of the basin gradually turns into marine sedimentary environment, consisting with the whole basin; (4) types of kerogen: type Ⅲ kerogen representing continental facies was developed in the early stage of T3X1 in the uplift area, and type Ⅱ kerogen, representing marine facies, was developed in the late stage; while type Ⅱ kerogen was developed in the central and western regions of the basin as a whole in T3X1. This study is of great significance for understanding of both stratigraphic division and sedimentary evolution providing theoretical support for the exploration and development of oil and gas.

DMSOP-cleaving enzymes are diverse and widely distributed in marine microorganisms

Dimethylsulfoxonium propionate (DMSOP) is a recently identified and abundant marine organosulfur compound with roles in oxidative stress protection, global carbon and sulfur cycling and, as shown here, potentially in osmotolerance. Microbial DMSOP cleavage yields dimethyl sulfoxide, a ubiquitous marine metabolite, and acrylate, but the enzymes responsible, and their environmental importance, were unknown. Here we report DMSOP cleavage mechanisms in diverse heterotrophic bacteria, fungi and phototrophic algae not previously known to have this activity, and highlight the unappreciated importance of this process in marine sediment environments. These diverse organisms, including Roseobacter, SAR11 bacteria and Emiliania huxleyi, utilized their dimethylsulfoniopropionate lyase ‘Ddd’ or ‘Alma’ enzymes to cleave DMSOP via similar catalytic mechanisms to those for dimethylsulfoniopropionate. Given the annual teragram predictions for DMSOP production and its prevalence in marine sediments, our results highlight that DMSOP cleavage is likely a globally significant process influencing carbon and sulfur fluxes and ecological interactions.

Evolution of Cenozoic sedimentary architecture in Central and Southern South China Sea basins

The Central and Southern South China Sea (CSSCS) has a complex tectonic dynamic background and abundant oil and gas resources, which has always been a hot topic of academic and industrial attention. However, systematic analyses are still lacking regarding its sediment filling structure and evolution, mostly due to limited borehole penetration and poor quality of seismic reflection data for deeply buried sequences. No consensus has been reached yet on the sedimentary infilling processes, which impeded the reconstruction of the palaeogeography of Southeast Asia and the oil-and-gas exploration undertakings. Here, we illustrate the Cenozoic sedimentary evolution of the CSSCS region by synthesizing relevant data from previous literature and our own observations and displaying the evolution of depositional systems in sequential reconstructions. Besides, the controlling factors of preferred sedimentary scenarios in the CSSCS incorporate the latest interpretations of the spreading of South China Sea (SCS) as well as the demise of the hypothetical Proto-South China Sea (PSCS). The results show that there are three types of sedimentary basins in the CSSCS (foreland, strike-slip, and rift basins) with different sedimentary filling structures. The foreland basins formed a depositional pattern of ‘transition from deep water to shallow water environments’, dominated by deep-water depositional systems which were formed before the Early Oligocene with submarine fans developed. Later, the foreland basins were gradually dominated by shallow-water depositional systems with deltas and shallow marine facies. The strike-slip basins showed the depositional architecture of ‘transition from lake to marine environments’, i.e. the basins were dominated by lacustrine deposits during the Eocene and evolved into the marine depositional environment since Oligocene with delta developed in the western part of the basin. The depositional evolution of rift basins illustrated the characteristics of ‘transition from clastic to carbonate deposits’, i.e., the rift basins were dominated by Eocene–Oligocene shallow marine clastic depositional systems, while carbonate platforms started to develop since the Early Oligocene from east to west. The above-mentioned differences of depositional architecture in the CSSCS were controlled by the scissor-style closure of the PSCS and the progressive-style expansion of the SCS. Specifically, the early-period deep-water sedimentary environment of CSSCS basins was controlled by the distribution of PSCS in the Eocene. As the scissor-style closure of PSCS progressed from west to east during the Oligocene to Early Miocene, the northwest of Borneo continued to rise, providing a great number of clastic materials to the basins and gradually developing large-scale deltas from west to east. The distribution of early-period lacustrine sedimentation of strike-slip basins was affected by paleo uplift, and the basins transgressed from the northeast and gradually evolved into marine sedimentary environment due to the expansion of SCS. The expansion of SCS also controlled the sedimentary filling evolution of the rift basins, which broke away from the South China continent and drifted southward. Thus, the rift basins lacked the supply of terrigenous clastic sediments which hindered the development of large-scale deltas and formed a clear water environment conducive to the development of carbonate platforms from east to west.

Fibrous dolomite formation at a Miocene methane seep may reflect Neoproterozoic aragonite-dolomite sea conditions

Fibrous dolomite widely formed in Neoproterozoic marine sedimentary environments, but apparently disappeared in the Phanerozoic. Here, fibrous dolomite is recognised in a Miocene methane seep limestone (Marmorito, Italy) by synchrotron X-ray diffraction, length slow crystal optics and primary zonation under cathodoluminescence, which is unexpected. Low δ13C values and their negative correlation with MgCO3 contents indicate a formation driven by highly alkaline pore waters and catalysis of dissolved sulphide generated by sulphate-driven anaerobic oxidation of methane. Cementing cavities of reefal carbonate, Neoproterozoic fibrous dolomite might have formed under sulphate-reducing conditions like Quaternary reef microbialites. Since the cavities of Neoproterozoic reefs were restricted microenvironments, the formation of fibrous dolomite was possibly favoured by catalysis similar to its Miocene seep counterpart. Our findings reinforce the concept of penecontemporaneous dolomite formation by sulphide catalysis and contribute to our understanding of the environmental conditions of the Neoproterozoic.

Petrofabric and geochemical constraints on the origin of Liuyang chrysanthemum stone, South China

Chrysanthemum stone refers to a radial and chrysanthemum–like mineral aggregate. Liuyang chrysanthemum stone, distributed in the carbonate of the Permian Chihsian Formation in South China, has become a rare natural art treasure due to its unique radial shape. The lack of effective constraints on the petrography and geochemistry of the chrysanthemum stone in Liuyang restricts the understanding of its origin. Hence, petrography analysis and Raman microprobe spectroscopy were used to study the mineral compositions and textural characteristics of the Liuyang chrysanthemum. Element and isotope geochemistry studies were conducted to discuss the sedimentary environment, material source, and formation mechanism. The Liuyang chrysanthemum stone was formed in the period of aragonite sea, and developed in dark gray limestone as a white radial mineral aggregate. The primary mineral is celestite, a minor amount of which was filled with and metasomatized by calcite. Trace element characteristics (δCe = 0.46–0.70, V/Cr = 1.28–1.51, Ni/Co = 2.14–4.89, Sr/Ba = 14.42–45.17) and carbon and oxygen isotopic compositions (δ13CV–PDB = 3.0 ‰–3.8 ‰, δ18OV–PDB = 5.2 ‰–4.8 ‰) of the host rocks indicate an aerobic marine sedimentary environment. The significant difference in sulfur isotopic compositions between the chrysanthemum stone (δ34S = 29.4 to 28.1 ‰) and the host rocks (δ34S = –29.4 to –28.1 ‰) indicates that bacterial sulfate reduction (BSR) and anerobic oxidation of methane (AOM) has occurred. Petrography, trace element and C–O–S isotope geochemistry of the Liuyang chrysanthemum stone had revealed the formation process of the chrysanthemum stone. The organic matter was decomposed by O2 and produced CO2 in the aerobic marine sedimentary environment. With the continuous sedimentation and the oxygen consumption, the early sedimentary carbonate and bioclastic was gradually separated from the relatively aerobic environment. An anoxic sedimentary–diagenetic environment was formed and the BSR occurred, during which SO42– participated in the degradation of organic matter as an electron acceptor. The bacteria preferentially absorbed the light 32SO42– in pore water to produce 32S–rich FeS2 in the host rocks and the heavy SO42– was combined with the Sr2+ released by aragonite dissolved by the accumulated CO2 to precipitate the celestite. HCO3– accumulated during the AOM and the BSR resulted in the replacement of the celestite by the calcite.

Size effect of graphene oxide from quantum dot to nanoflake on the mobility of nanoplastics in seawater-saturated sand

Marine sedimentary environment serves as an important sink of terrigenous nanoplastics (NP) and graphene oxides (GO). In this study, we discovered that GO of varying sizes exhibited distinct binding modes with 200 nm NP in 35 practical salinity unit (PSU) seawater, resulting in varying impacts on the mobility of NP in porous media. GO-8, with a size of 8±2 nm, firmly adhered to the surface of NP and formed stable primary heterogeneous aggregates, which promoted NP mobility and increased the mass recovery of effluent (Meff) from 24.74% to 31.08%. GO-250 (246±10 nm) partly enveloped NP and only slightly increased the volume of heteroaggregates, which had minimal effect on NP transport. Conversely, GO-850 (855±55 nm) wrapped numerous NP particles to form large secondary heteroaggregates that clung to sand surfaces, providing additional attachment sites for NP, resulting in complete inhibition of NP mobility in porous media (Meff = 0%). In brackish water with 3.5 PSU, all GO-8, GO-250 and GO-850 achieved enhanced mobility of NP, with Meff increasing from 50.35% to 85.62%, 69.45% and 75.41%, respectively. The results indicate that GO size effects on NP mobility are also salinity-dependent.

A new biosurfactant-producing strain, Fictibacillus nanhaiensis ME46, isolated from an oil field in China

ABSTRACT The genus Fictibacillus contains twelve species significant in the synthesis of cellulose-degrading enzymes and phenylalanine dehydrogenase, isolated mainly from marine sedimentary environments. Here, we report a new biosurfactant-producing strain, Fictibacillus nanhaiensis ME46, isolated from Daqing oil field in China. The biosurfactant extracted from Strain ME46 was determined as surfactin, one of the representative families of lipopeptide biosurfactants. The yield of the surfactin produced by strain ME46 was 0.62 g·L−1 as determined by high-performance liquid chromatography, and the critical micelle concentration (CMC) of the surfactin was estimated to be about 68 mg·L−1 and the surface tension at CMC was 35.1 mN·m−1. This study extended our knowledge about the role of the species Fictibacillus nanhaiensis in the ecosystem of natural environments such as the oil field.

Biodegradation behavior of polybutylene succinate (PBS) fishing gear in marine sedimentary environments for ghost fishing prevention

This study evaluated the biodegradability of PBS fishing gear in marine sedimentary environments, which is a major cause of unintended catches caused by discarded fishing gear, known as “ghost fishing”. Based on the biodegradation analysis according to ISO 19679, the PBS fishing gear was converted into carbon dioxide by 27.3% for 180 days. After biodegradation, the remaining PBS exhibited a characteristic molecular weight decrease, indicating bulk erosion, but there was no change in crystallinity and thermal properties. Ultimately, degradation of the PBS proceeded primarily through surface abrasion with metabolic utilization of hydrolysis products by microorganisms. Biological studies showed that the Rhodococcus genus was the dominant microbe for PBS biodegradation. In an accelerated evaluation experiment using a lipase enzyme known to be produced by dominant bacteria, the PBS showed a high biodegradability of 48% in 10 days. From the perspective of biodegradation, biodegradable fishing gear can not only replace existing nondegradable fishing gear but also prevent ghost fishing through biodegradation in the marine sedimentary environment after use.

Kilometer-scale Δ13CH3D profiles distinguish end-member mixing from methane production in deep marine sediments

Methane stored in marine sediments can form by microbial and thermal decomposition of organic matter. Identifying the source of methane allows us to assess the potential of natural gas reservoirs and the limits of subsurface microbial life. However, such assessments are complicated by the burial and transport of methane, which can produce mixtures from multiple sources. We measured the abundances of stable isotopes (13C/12C and D/H), clumped isotopologue 13CH3D, and n-alkanes (C1/C2+3, methane over ethane plus propane) for gas samples collected by mud-logging to investigate how 13CH3D can be used to constrain sources of methane. Two kilometer-scale depth profiles representing the transition between microbial and thermal methanogenic zones were analyzed from the northeastern Gulf of Mexico and the western Black Sea. We found that Δ13CH3D values of methane do not follow conservative two-component mixing between shallow microbial methane and deep thermogenic methane transported by advection. Rather, methane isotopologues indicate re-equilibration along geothermal gradients following burial, which continues up to apparent temperatures of 100 ± 15 °C. The re-equilibration is likely microbially catalyzed, although this apparent temperature is ca. 20 °C higher than the putative upper-temperature limit of microbial methanogenesis in marine sediments. Above 150 °C, methane isotopologues are expected to equilibrate along geothermal gradients because the rate of abiotic D/H exchange becomes comparable to that of temperature increase with burial. This study provides novel kilometer-scale profiles of clumped methane isotopologues as a means to trace the upper-temperature limits of microbial activity in hydrocarbon-rich marine sedimentary environments.

Genome characterization of two novel deep-sea sediment fungi, Penicillium pacificagyrus sp. nov. and Penicillium pacificasedimenti sp. nov., from South Pacific Gyre subseafloor sediments, highlights survivability

BackgroundMarine deep subsurface sediments were once thought to be devoid of eukaryotic life, but advances in molecular technology have unlocked the presence and activity of well-known closely related terrestrial and marine fungi. Commonly detected fungi in deep marine sediment environments includes Penicillium, Aspergillus, Cladosporium, Fusarium, and Schizophyllum, which could have important implications in carbon and nitrogen cycling in this isolated environment. In order to determine the diversity and unknown metabolic capabilities of fungi in deep-sea sediments, their genomes need to be fully analyzed. In this study, two Penicillium species were isolated from South Pacific Gyre sediment enrichments during Integrated Ocean Drilling Program Expedition 329. The inner gyre has very limited productivity, organic carbon, and nutrients.ResultsHere, we present high-quality genomes of two proposed novel Penicillium species using Illumina HiSeq and PacBio sequencing technologies. Single-copy homologues within the genomes were compared to other closely related genomes using OrthoMCL and maximum-likelihood estimation, which showed that these genomes were novel species within the genus Penicillium. We propose to name isolate SPG-F1 as Penicillium pacificasedimenti sp. nov. and SPG-F15 as Penicillium pacificagyrus sp. nov. The resulting genome sizes were 32.6 Mbp and 36.4 Mbp, respectively, and both genomes were greater than 98% complete as determined by the presence of complete single-copy orthologs. The transposable elements for each genome were 4.87% for P. pacificasedimenti and 10.68% for P. pacificagyrus. A total of 12,271 genes were predicted in the P. pacificasedimenti genome and 12,568 genes in P. pacificagyrus. Both isolates contained genes known to be involved in the degradation of recalcitrant carbon, amino acids, and lignin-derived carbon.ConclusionsOur results provide the first constructed genomes of novel Penicillium isolates from deep marine sediments, which will be useful for future studies of marine subsurface fungal diversity and function. Furthermore, these genomes shed light on the potential impact fungi in marine sediments and the subseafloor could have on global carbon and nitrogen biogeochemical cycles and how they may be persisting in the most energy-limited sedimentary biosphere.

Cyclic threshold shear strain for pore water pressure generation and stiffness degradation in marine clays at Yangtze estuary

Cyclic threshold shear strain is a fundamental property of saturated soils under cyclic loading. To investigate the cyclic threshold shear strain for pore water pressure generation (γtp) and stiffness degradation (γtd), a series of strain-controlled multistage undrained cyclic triaxial tests were carried out on in-situ saturated marine clay in the Yangtze estuary with different plasticity index Ip. The test results show that both γtp and γtd increase with increasing Ip, and γtp is larger than γtd for the same marine clay tested under the same conditions, with γtp = 0.017 ~ 0.019%, γtd = 0.008 ~ 0.012% for Ip of 17, γtp = 0.033 ~ 0.039%, γtd = 0.020 ~ 0.025% for Ip of 32, and γtp = 0.040 ~ 0.048%, γtd = 0.031 ~ 0.036% for Ip of 40. Moreover, the development of stiffness degradation may not necessarily require the generation of pore water pressure but can be aggravated by it. Furthermore, the γtp and γtd of marine clay are compared with terrestrial soils and marine clays cited from the published literature, the results indicate that the special marine sedimentary environment and the combined action of flow and tidal wave system cause the γtp and γtd of marine clay in the Yangtze estuary to be smaller than that of the terrestrial clays and marine clays in other sea areas.

Origin of the Ultra-Deep Hydrocarbons from the Shunbei No. 1 Fracture Zone in the North of Shuntuoguole Low Uplift, Tarim Basin, North-Western China

In order to have a deeper insight into the accumulation mechanism of ultra-deep hydrocarbons, in this paper, the recently discovered ultra-deep Ordovician light oil and gas deposits (&gt;7200 m) in the Shunbei No. 1 fracture zone are studied intensively, including maturity, source kitchens, the extent of secondary alterations, and possible migration directions, based on an analysis of the molecular compositions and stable carbon isotopes of crude oils and natural gases. The average equivalent vitrinite reflectance (Rc) of these oils, estimated from light hydrocarbons (H versus I), MDI, DNR, and MDR, are about 1.50%, 1.58%, 1.48%, and 1.51%, respectively, which suggests that most of the oils are in the late stages of crossing the oil window. The two maturity grades (1.06–1.25% and 1.36–1.67%) of the oil samples calculated from the aromatic compounds indicate the presence of at least two stages of hydrocarbon charge. In addition, the positive correlation plot of DNR and MDR (y = 3.59x − 12.84; R2 = 0.96) indicates that oils in the southwestern region of the F1 (S1-11–S1-16) are slightly more mature than oils in the northeastern region of the F1 and the well at SL1, far from the No. 1 main fault zone. In addition, the study shows that these hydrocarbons belong to the same source kitchen of a reduced marine sedimentary environment with mixed organic matter comprising benthic and planktonic algae, based on biomarker parameters, light hydrocarbons, and carbon isotope compositions. The oil–oil correlation analyses suggest that the studied oil samples are probably derived from the in situ Lower Cambrian Yuertusi formation source rocks. Various geochemical parameters consistently show limited significant hydrocarbon alteration processes, indicating favorable preservation conditions in the study area. The integrated geochemical characteristics of the hydrocarbons allow us to infer that they mainly migrate vertically from the in situ Lower Cambrian Yuertusi formation source rocks toward the Ordovician reservoirs, followed by a certain degree of lateral migration from southwest to northeast.