Deciphering sedimentary provenance in the Okinawa Trough (OT) is vital for understanding the dispersal system from source to sink and the paleoenvironmental evolution in the East China Sea (ECS). Sources include the Huanghe, Changjiang, and Taiwan rivers, as well as the ECS shelf; however, there is controversy over which source has dominated sediment supply since the last deglaciation, and how the tidal currents, shelf circulation, and Kuroshio Current (KC) has controlled the sediment transport. Here, we present a high -resolution record of grain size and clay minerals over the last 14.3 kyrs in an AMS 14 C dated piston core from the middle OT. We use these data to reconstruct changes in the KC, identify the provenance of fine-grained sediment, and unravel the impact of paleoenvironmental factors on these provenance changes. A grain size component of 15.6 - 31.3 mu m was extracted to reconstruct the KC changes. These data show that the KC strengthened sharply until 10.2 ka, then kept strong and stable during the Holocene. Clay mineral assemblages indicate that the sediment was mainly derived from the ECS shelf between 14.3 and 8.6 ka, then from the Taiwan rivers after 8.6 ka. The shelf sediment was eroded and transported by intense tidal currents. Taiwan river sediment became the dominant source due to the development of Taiwan Warm Current rather than the strengthening of KC. The ratio of smectite and kaolinite to illite and chlorite content indicates that the sediment contribution from the Huanghe (old Huanghe delta) and Changjiang rivers increased from 7.6 to 5.0 ka and from 3.2 ka to the present. This increase is attributed to the strengthening of East Asian winter monsoon and the consequent intensification of cross -shelf circulation.

Dissolved carbon (dissolved organic carbon and dissolved inorganic carbon) is the major component of the ocean carbon cycle, representing one of the largest carbon pools on Earth. Cold seeps and hydrothermal systems serve as the two main windows for the material and energy recycling exchange between the lithosphere and outer spheres (biosphere, hydrosphere and atmosphere). However, recent studies have found that the dynamic activities of fluids in these two extreme systems are a crucial source of ‘new’ carbon in the deep ocean. These carbon sources may become vital contributors to carbon and energy in marine ecosystems, which affect the global deep-sea carbon budget, and the marine ecosystems as well. In this review, we summarize the sources and formation mechanisms of dissolved carbon in the seep fluids from the cold seeps and hydrothermal vents, the contribution of methane oxidation to dissolved carbon, and the characteristics of the carbon isotope composition in the fluid. Furthermore, we analyze and discuss the influence of carbon discharged from seabed on the seawater carbon cycle by comparing and contrasting these two extreme environments. The research may assist in promoting a deeper understanding of the carbon cycle and material interaction in the ocean, particularly further carbon cycle research in the back-arc basin where cold seeps and hydrothermal vents commonly prevail.

冷泉活动是现代深海极端环境系统之一,其在天然气水合物资源勘探、全球气候变化、极端环境生命活动等方面具有重要的科学研究意义.重建海底冷泉区氧化还原环境是研究其中生物地球化学过程、揭示甲烷渗漏活动特征的重要途径.近年来,大量矿物学及地球化学指标在冷泉系统氧化还原条件的恢复研究中获得了成功的应用.在前人研究的基础上,对自生矿物学标志、稀土元素、氧化还原敏感元素(Mo、U、Fe)和稳定同位素(钼同位素δ98Mo、铁同位素δ56Fe、硫同位素δ34S)等不同指标对氧化还原环境变化的响应机制进行了系统总结,从测试分析方法、后期成岩改造、单一指标的多解性等多个方面探讨了各指标的影响因素和当前仍存在的问题,并指出了未来该领域需进一步加强的关键研究方向.

Sediments on continental slopes, which are rich in hydrates and organic matters, may release methane into the overlying seawater and even into the atmosphere. To evaluate the impact of sediment emissions on oceanic methane cycling and greenhouse gas emissions, this study assessed the distribution of methane in surface sediments and water columns and calculated the sea-to-air methane flux in the Dongsha area of the northern South China Sea. Results show that the methane concentrations exhibited large spatio-temporal changes. In May 2019, the methane concentrations and sea-to-air methane flux (4.1 & PLUSMN; 3.7 & mu;mol m- 2 d-1) were close to the background values, indicating that in situ aerobic methane production was a weak atmospheric methane source. In contrast, in September 2020, abnormally high methane concentrations up to 26.6 nM were detected in the upper slope with water depths of 600-950 m and to the east of a seamount; the average sea-to-air methane flux increased to 11.3 & PLUSMN; 7.9 & mu;mol m- 2 d-1. The consistency of methane distribution throughout the water column and surface sediments, with a generally increasing trend with the increasing depth, indicates that in September 2020, sediment emissions were crucial methane sources in seawater and led to moderate emissions into the atmosphere. The heterogeneities of methane concentrations and sea-to-air methane fluxes were attributed to the uneven distribution of methane in the sediments. Besides, strong internal solitary waves in summer and autumn exacerbates methane release, especially around high terrain areas, such as in continental upper slopes and in the upstream side of seamounts. Our results demonstrate that methane released from the sediments, being perhaps affected by internal solitary waves induced sediments disturbance, substantially impacted the oceanic methane cycling in continental slopes. Thus, this study provides new insights into the methane budget of marginal basins.

海底水合物丘与泥火山均属于不同相态流体向上运移排出至地表过程中的产物,与这2种特殊地质体相关的浅表层天然气水合物具有独特的成藏过程和赋存规律,同时,它们也都是富碳流体排放的重要途径.然而,由于对这2种地质体缺少系统的调查,加之对浅表层天然气水合物资源和碳泄漏过程的研究程度不高,当前在海底水合物丘与泥火山特征刻画及准确甄别上还存在障碍,导致难以科学地评价与其伴生的水合物资源的聚集过程及环境效应.通过总结已有海底水合物丘与泥火山的阶段性研究工作,对该2种特殊地质体从地貌特征、内部结构、形成机制等方面开展比较研究,系统分析了二者的演化过程以及对与之相关的天然气水合物聚集过程的影响,并讨论了2种地质体的区别与联系.本研究可为理解全球海底富碳流体的排放及其对海洋碳循环的贡献以及海底浅表层天然气水合物资源量的评价提供参考.

Cycling and fates of iron (Fe) and sulfur (S) in marine sediments are influenced by depositional settings to differential extents. The information is crucial for addressing the responses of their benthic diagenesis to changing climates and environments and also for reconstructing paleo-depositional conditions, but has not been well constrained. Detailed chemical speciation was utilized to characterize geochemistry of Fe and S, and then to reveal the impacts of depositional settings on their diagenesis at three locations, representing contrasting depositional environments: (i) highly dynamic Yangtze River estuary (YRE), (ii) the depocenter of South Yellow Sea (SYS), which is only remotely impacted by large river, and (iii) the middle Okinawa trough (OT), a back-arc deep basin along the outer edge of the East China Sea (ECS) slope. Results show that the YRE sediments favor accumulation of total highly reactive Fe (FeHR), while the SYS sediments are poor in FeHR due to low FeHR in their source material and/or preferential trapping of FeHR during sediment transport through the semi-enclosed Bohai Sea. Ferruginous sediment regimes in the highly dynamic YRE system facilitate Fe(III) reduction and burial of unsulfidized Fe(II), while the SYS and OT sediments favor sulfate reduction and pyritization of Fe(II). Pyrite is always the main sink of reduced S that escapes reoxidation in the entire continental margin, regardless of depositional environments. Abundant reactive Fe(III) but low total reduced inorganic sulfide (TRIS) contents in the three sites suggest that TRIS burial is largely controlled by the availability of degradable OC and/or dynamic regimes of sediments. The applicability of two widely used Fe- and S-based proxies to distinguish bottom-water conditions, that is, OC/TRIS ratio and FeHR to total Fe (FeHR/FeT) ratio, were examined in the three contrasting environments, and caveats were given for future applications of the two proxies.

The diagenetic interplays of organic carbon (OC), sulfur (S), and iron (Fe) in marine sediments and their responses to changes in depositional and climatic conditions are poorly characterized. In this study, chemical speciation and isotopes were combined to characterize diagenesis of OC, S and Fe in sediments of the middle Okinawa Trough (OT), a back-arc deep basin along the edge of the East China Sea outer shelf, since the Last Glacial Maximum (LGM). Two key geochemical proxies, i.e., OC/pyrite-S ratios and the degrees of pyritization, indicate anoxic bottom-water conditions during the last Glacial/Deglacial, which promoted burial of OC and pyrite. However, a shift to oxic conditions during the Deglacial-Holocene transition facilitated aerobic respiration, resulting in lower burial of OC and pyrite. In contrast to previous studies, the environmental changes induced by large sea-level rises since the LGM have not triggered significant variations in pyrite-S isotopic compositions, probably due to persistently low sedimentation rates. Variable extents of Fe enrichment are identified in the sediments since the LGM, with lower enrichment during the Holocene probably due to increased distance of Fe shuttling and concomitant Fe ageing. Anoxic bottom water during the Glacial/Deglacial did not induce an expected intensification of OC sulfurization, probably because sedimentary Fe enrichment favored pyrite formation but competitively dampened OC sulfurization. Lines of geochemical evidence hint at a discontinuous deposition at similar to 200 cm depth probably caused by mass wasting.

海底冷泉-热液极端环境是岩石圈与外部圈层进行物质交换和能量流动的主要窗口,其独特的地质条件和营养模式孕育了繁茂的生物群落和生态系统.由于多种因素的叠加控制,海底极端环境的理化性质通常变化频繁且剧烈.大量研究表明,这种变化或波动又能不同程度地被环境中生存的生物记录下来,因此,生物所保留下来的某些地球化学信息具有恢复重建其生存环境变化的潜在能力,这对人类目前尚难自由出入的深海极端环境的探索尤为重要.本文从海底极端环境生物种类和空间分布、生物壳体的地球化学信息、生物元素和同位素地球化学指标以及生物有机生标等几方面出发,探讨当前科学家关注的典型地球化学指标对沉积环境的记录应用,并展望了未来需要进一步加强研究的几个方面,希望借此能引起广大研究者对该领域的兴趣和重视,以加深加快对海底极端环境内运行规律和影响的认识.

海洋沉积物中大部分甲烷会通过甲烷厌氧氧化作用(anaerobic oxidation of methane,AOM)而被消耗.早期研究表明,AOM可与硫酸盐、硝酸盐和亚硝酸盐的还原作用相耦合,从而有效减少甲烷向大气的排放.最近,金属依赖型AOM(metal-AOM,活性金属氧化物还原反应驱动的AOM)被证实存在于自然界沉积物和富集培养的样品中.但是,目前仍未从自然海洋环境中分离获得能够介导metal-AOM的微生物.对海洋沉积物中metal-AOM的研究大多聚焦于热液或冷泉等海洋特殊生境,一系列研究表明地质流体在这些海底化能自养生态系统的维持和演化方面起到了重要作用,并深刻影响全球地球化学循环,因此,该科学问题研究吸引了越来越多的注意力.本文讨论了可能参与海洋沉积物中metal-AOM的微生物类群及其地球化学证据,并在前人工作基础上,以冲绳海槽冷泉-热液共生区为例,提出一种新的metal-AOM作用机制.认为在全球冷泉-热液系统相互作用地区的调查有助于更好地探讨metal-AOM的发生机制及微生物在深海生境中分布的连通性问题.

海底通过泥火山释放的富甲烷流体是海洋甚至大气重要的碳源之一,对该系统内甲烷迁移与转化过程开展研究,有助于精确估算其碳排放总量.系统调研了国内外文献,认识到泥火山的碳排放具有强烈的时、空变化特征.在时间上,甲烷的排放主要发生在泥火山的喷发期和平静期,而在其消亡之后只出现微量的渗漏;在空间上,一个单独的泥火山中心、翼部和外缘分别发育强甲烷气泡泄漏、中等强度富甲烷和溶解无机碳(DIC)的流体泄漏以及大面积的DIC微渗漏;甲烷厌氧氧化和碳酸盐岩沉淀作用在翼部最强,对碳排放的拦截最有效,而在中心和外缘均较慢.全球陆坡和深水盆地沉积物通过泥火山向上释放的深部来源的甲烷通量为0.02 Pg C·a?1,这些碳可能引发海水缺氧、酸化和影响海-气交换通量,从而在千年尺度甚至更短时间内影响海洋吸收大气二氧化碳的能力.将来需要进一步对海底泥火山的发育数目和喷发周期进行统计,对不同类型的泥火山开展精细调查,以准确评估沉积物中自下而上的碳排放对海洋碳循环的影响,完善全球碳循环模式.

利用元素及同位素地球化学方法研究了冲绳海槽中部沉积物岩芯中有机碳及磷的地球化学特征及影响因素.结果表明,冲绳海槽沉积速率(16.5～32.5 cm/ka)变化小,不是沉积物中有机碳埋藏的重要影响因素.相对于全新世氧化性底水环境,末次盛冰期/冰消期冲绳海槽缺氧底水环境提高了沉积物对有机碳的埋藏效率.冲绳海槽沉积物中各形态磷的相对含量与其他边缘海沉积物中的相似.交换态磷(Ex-P)含量低、变化小.末次盛冰期/冰消期缺氧底水环境下铁氧化物的还原溶解导致铁结合磷(Fe-P)释放以及自生磷矿物(Au-P)的形成.全新世氧化性底水条件有利于铁氧化物的有效再生及对磷的再吸附,但不利于Au-P的保存.总有机碳(TOC)和有机磷(Org-P)之间良好的相关性表明TOC埋藏对Org-P含量的重要控制作用.冲绳海槽沉积物中碎屑磷(De-P)含量低于长江口及东海陆架沉积物中的含量,这与陆源碎屑向外海传输减弱有关.在约9.3 ka BP(岩芯200 cm深度),TOC、Fe-P、Org-P、De-P以及FeHR均出现的极小值可能由物质坡移造成.

碳酸盐晶格硫(CAS)是古环境恢复的重要手段之一,它系指在碳酸盐成岩过程中微量的硫酸盐离子取代碳酸盐离子并保存在晶格中的硫酸盐.CAS对矿物沉淀发生时的海水硫酸根的氧、硫同位素组成、硫酸盐浓度和当时古环境的氧化还原状态都有很好的保存和记录作用,因此引发了对其持续关注,并开展了一系列卓有成效的研究.本文综述了CAS当前的研究进展,主要从前处理方法、影响因素、同位素组成和古环境恢复等重点问题来探讨CAS的成因和CAS对不同沉积环境的恢复应用,并展望了需要进一步研究的几点研究方向,希望借此能引起广大研究者的兴趣和重视.

北极海域赋存丰富的油气和天然气水合物资源,也是全球环境变化的一个重要窗口,北极巴伦支海西南部陆架已发现大量天然气水合物赋存的识别标志,笔者综述了巴伦支海西南部海域陆架区水合物形成的条件和已发现的天然气水合物分布情况和泄漏特征,总结影响巴伦支海西南陆架区天然气水合物形成和分解的各项因素,评价北极巴伦支海西南部天然气水合物资源前景.掌握北极巴伦支海及其周边区域的水合物资源情况是提升中国在北极事务话语权的必要内容之一,北极海域水合物动态变化对于全球气候变化具有十分重要的指导意义;这类极地低温海域水合物流体聚集和运移特征十分特殊,对丰富水合物成藏研究有重要的理论意义.

Widespread seepage of methane from seafloor sediments on continental margins are released into seawater, a portion of which may escape to the atmosphere. To assess the water column distribution characteristics of methane and its input to the atmosphere, we investigated methane emissions from the shelf and west slope of the back-arc Okinawa Trough (OT), East China Sea. Our results showed a heterogeneity distribution of methane within the water column. The highest value, which was more than 10 times of the background concentration, occurred near a cold seep in the north of the study area which was discovered by a remotely operated underwater vehicle (ROV). Other sources of methane to the water column of the OT, besides cold seepage input, probably also include in situ aerobic methane production, advective transport from the continental shelf, and/or hydrothermal venting. Furthermore, the sea-to-air flux of methane throughout the study area was up to 116 μmol m–2d–1, noticeably higher than that in many other continental shelf waters and seep sites globally, indicating that this region is an active CH4 emission area. Our findings demonstrate that methane discharged from both cold seeps and hydrothermal vents have a significant influence on the methane cycle in the OT, providing a new insight for the methane budget of back-arc basins.

The methane-enriched fluids in cold seeps are likely to crystallize as gas hydrates and serve as crucial sources of carbon to seawater. In this research, we analyzed the pore-water composition in terms of CH4, dissolved inorganic carbon (DIC), Cl-, Br-, SO42-, Na+, Mg2+, Ca2+, Sr2+, and NH4+, and the delta C-13(DIC), delta C-13(CH4), and delta D-CH4 values of two gravity cores and six remotely operated vehicle (ROV) video-guided push cores retrieved from fault scarps and dome-like structures (DSs) on the western slope of the mid-Okinawa Trough. In addition, a reactiontransport model was applied to quantify the methane fluxes and related biogeochemical processes. Active seepage of biogenic (delta C-13(CH4) similar to -70 parts per thousand V-PDB) and thermogenic (delta C-13(CH4) = -40 parts per thousand to -56 parts per thousand V-PDB) methane was identified on fault scarps and dome structures, respectively. Methane seepage was controlled by the transport and dissolution of the ascending gas rather than by clay dehydration or gas hydrate dissociation-induced fluid advection. The high methane concentrations and shallow sulfate-methane transition zones (SMTZs; between 0.1 and 0.4 mbsf) at sites R3-C2, R4-C4, and R6-C1 suggest strong methane seepage at three of the four studied DS (the highest gas dissolution rates are 6450, 1475, and 515 mmol m(-2) yr(-1)). Site GC08, located along a fault scarp, exhibits a moderate methane seepage; the SMTZ is located at similar to 2.5 mbsf, and the rate of anaerobic oxidation of methane (AOM) is 130 mmol m(-2) yr(-1). The methane migrating from depth is mainly consumed by AOM. However, similar to 12%-66% of the methane released from the two most intensive seep sites escapes to the water column. The precipitation of high-Mg calcite (at all sites) and aragonite (only at site R3-C2) has fixed 27%-50% (average = 39%) of the DIC. Therefore, the carbon outputs to the water column have been reduced. In the study area, the area-weighted seafloor CH4 and DIC fluxes are similar to 30 and 20 mmol m(-2) yr(-1), respectively. Together, they correspond to similar to 7%-14% of the organic carbon burial rate, indicating that sediments could not be simply regarded as a stable carbon sink because they provide methane and a certain amount of DIC to the water column. Our findings contribute to the results of the ongoing efforts in understanding carbon cycling in submarine cold seep systems.

Marine sediments are the largest sink for organic carbon (OC) on Earth, and iron (Fe) oxides play an important role in stabilization of sedimentary OC. However, the roles of Fe oxides in OC stabilization during prolonged burial, for example, up to tens of thousands of years or more are still poorly constrained. In this study, we used traditional chemical extraction and near-edge X-ray absorption fine structure (NEXAFS) spectroscopic technique to characterize bulk OC and Fe-associated OC (Fe-OC) through depth in gravity cores collected from three sites near the Yangtze River Estuary (YRE), in the South Yellow Sea (SYS), and in the middle Okinawa Trough, which have contrasting depositional environments. Results show that depositional environments have exerted quite different influences on sources and burial of sedimentary OC, and thus on OC degradation during prolonged burial at the three sites. Reactive Fe (Fe-R) contents at the three sites are greatly influenced by sediment sources, the history of its transport, and its reworking intensity, with Fe-R contents near the highly dynamic YRE much higher than at the central SYS and the middle Okinawa Trough. The fractions of Fe-OC in total OC (f(Fe)(-OC)) displayed no clear or consistent trends with depth or by site, probably due to the dual roles of Fe redox cycling in OC protection versus its oxidation. As indicated by the f(Fe)(-OC), reactive Fe plays a limited role in OC preservation in margin sea sediments of East China. A combination of NEXAFS spectra and isotopic compositions of bulk OC and Fe-OC indicates that main OC functionalities have not experienced differential alterations and/or no specific OC moieties have been selectively stabilized/released during prolonged burial in the three contrasting depositional environments.

热液和冷泉活动是现代深海环境中两个重要的极端系统,它们均是岩石圈与外部圈层之间进行物质、能量转移和交换的重要途径,它们之间既有显著差异,但也存在很多相似点.一系列调查研究表明,在某些特殊构造单元,热液和冷泉活动可能并不是彼此孤立的,而是在构造地质、生物生态和元素循环上存在某种相互作用或耦合关系.冲绳海槽作为西太平洋一个典型的弧后盆地,发育了繁盛的热液和冷泉活动,是研究这两个海底极端系统相互影响机制的天然实验室.在大量文献调研和野外精细探测结果的基础上,分析了冲绳海槽内相互毗邻的冷泉和热液之间的物质扩散过程及生物地球化学作用,初步建立了两个极端系统内两种不同流体相互作用的概念模型,认识到未来如对两个深海极端环境共生区构造发育特征、地层流体演化、生物群落以及矿物元素组成进行系统分析,将有助于建立更加完善的冷泉-热液两个系统在物质和能量上的耦合关系模型,同时也有助于揭示它们在生物生态之间的沟通融合规律,最终可建立盆地尺度上热液-冷泉区相互作用模式,从而加深对西太平洋甚至全球范围内冷泉-热液两个极端环境系统甚至"流体-固体"耦合的规律性认识.

Research on the biomineralization in modern seafloor hydrothermal systems is conducive to unveiling the mysteries of the early Earth’s history, life evolution, subsurface biosphere and microbes in outer space.The hydrothermal biomineralization has become a focus of geo-biological research in the last decade,since the introduction of the microelectronic technology and molecular biology technology.Microorganisms play a critical role in the formations of oxide/hydroxides（e.g. Fe, Mn, S and Si oxide/hydroxides） and silicates on the seafloor hydrothermal systems globally. Furthermore, the biomineralization of modern chemolithoautotrophic microorganisms is regarded as a nexus between the geosphere and the biosphere, and as an essential complement of bioscience and geology. In this paper, we summarize the research progress of hydrothermal biomineralization, including the biogenic minerals, the microbial biodiversity, and also the interactions between minerals and microorganisms. In the foreseeable future, the research on hydrothermal biomineralization will inspire the development of geosciences and biosciences and thus enrich our knowledge of the Earth’s history, life evolution and even astrobiology.

Seafloor hydrothermal systems and cold seeps contribute considerable amounts of dissolved carbon to ocean water. To investigate the compositional characteristics and potential sources of the dissolved carbon in the Okinawa Trough (OT), East China Sea (ECS), we measured the concentrations and distributions of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and their C-13 stable isotopes in a full-depth water column in this area. Our results indicate that in the upper layer (water depth < 200 m), the dissolved carbon is mainly controlled by biological processes. In contrast, in the deeper layer, the concentration and isotopes are clearly influenced by seafloor hydrothermal and cold seep fluids in the OT. Based on our mass balance model estimation, cold seeps and hydrothermal fluids contribute up to 14.3% and 19.6%, respectively, of the seawater DIC. Our study shows that both of these extreme seafloor systems contribute considerable proportions of the local carbon budget. Moreover, they may also have an important impact on the extreme seafloor ecosystems therein.

Authigenic carbonates were recovered from the northern Okinawa Trough at 540-700 m water depth. Development of microbial communities and seepage dynamics driving the precipitation of authigenic carbonates remains poorly constrained, even though the source of methane-rich fluids, formation of Fe-rich carbonates, and the potential driving forces were previously reported. Here, petrologic observations, stable carbon and oxygen isotopic compositions, mineralogy, and lipid inventories of authigenic carbonates from the northern Okinawa Trough were analyzed. The carbonate minerals were comprised predominantly of aragonite, high-magnesium calcite, and siderite. The presence of molecular fossils diagnostic for anaerobic methane oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB) with pronounced C-13 depletions (as low as - 134 parts per thousand), together with highly negative delta C-13(carb) values (as low as - 55.8 parts per thousand), suggest that the carbonates precipitated from anaerobic oxidation of methane (AOM) with microbial methane as the predominant carbon source. The difference between measured and calculated delta O-18(carb) values (based on 0 parts per thousand of sea water delta O-18 vs V-SMOW) was higher than +3 parts per thousand in one of the carbonates (GGD16), reflecting an origin from gas hydrate dissociation. Most of the carbonates revealed delta O-18 offsets between measured and calculated values within + 3 parts per thousand, or a lower measured delta O-18 than calculated value, suggesting a mixture of methane-derived carbonates (low delta C-13 /high delta O-18) and detrital origin carbonates (high delta C-13/low delta O-18). Biomarker patterns varied significantly among samples. A suite of C-13-depleted biomarkers indicated the predominance of an ANME-1 assemblage for all samples, suggesting carbonates formed at low to medium methane flux. The predominance of ANME-1, abundant detrital minerals, and allochthonous biomarkers, as well as low carbonate contents indicate that most samples formed at greater depth within the sediment column. Only one carbonate sample in this study is interpreted to have precipitated at relatively shallower depth, as indicated by the occurrence of crocetane, dominance of aragonite, and higher overall carbonate content.