Marine Geology最新文献_第4页

Deep-water canyon-channel systems of the Queensland Plateau, Northeast Australia 澳大利亚东北部昆士兰高原的深水峡谷-水道系统

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-11-02 DOI: 10.1016/j.margeo.2025.107678

Sebastian Lindhorst , Linus Budke , Robin J. Beaman , Jan Oliver Eisermann , Christian Hübscher , Niko Lahajnar , Thomas Lüdmann , Jody M. Webster , Christian Betzler

Sediment conduits like erosive canyons and channels are common morphological elements of submarine landscapes down to abyssal depths. While canyon-channel systems connected to slopes and shallow water are well studied, detached sediment-routing systems emerging in deeper waters have received less attention, especially in carbonate settings. We study the sedimentary architecture and evolution of an extensive canyon-channel system in the ‘Willis Passage’, a marine strait between the Magdelaine and Willis carbonate banks (Queensland Plateau, northeast Australia). The canyon-channel system is detached from the slopes of the carbonate banks, emerges at depths of >500 m and runs over more than 100 km towards the slope break of the carbonate plateau. The canyon is several kilometres wide and several tens of metres deep. Morphological edges (knickpoints) occur along the canyon course; one with a plunge pool at its downstream foot wall. Current ripples and coarse-grained lag deposits at the floor of the canyon indicate bottom-current activity and possibly winnowing of fine-grained sediment. The seafloor outside the canyon is intersected by bundles of grooves (linear seafloor cuts), tens of kilometres long. Sedimentological and morphological characteristics indicate that canyon-channel system and grooves are shaped by eastward-flowing bottom currents, which is in a direction counter to the dominant westward-flowing oceanic current regime. We propose that eastward-flowing sediment-laden bottom currents originate from the channelization of oceanic currents by the carbonate edifices of the Queensland Plateau, paired with tidal pumping in the narrow passages between the banks. This mechanism is most efficient during episodes of lowered sea level, while bottom currents are much weaker during sea-level highstand. Our seismic data reveal the existence of buried individual canyon-channel systems and document that the Queensland Plateau underwent episodic changes in the local current regime since the upper Miocene. Based on new geophysical and oceanographic data, as well as video observations of the seafloor, we show that slope-detached deep-water canyon-channel systems act as a conveyor, routing sediment from carbonate platforms to the deep ocean. As a link between the neritic realm and abyssal depths, these systems are important agents of dismantling and degradation of carbonate platforms and underline the role of bottom currents in shaping these depositional environments.

侵蚀峡谷和沟渠等泥沙管道是深海海底景观的常见形态要素。虽然与斜坡和浅水相连的峡谷水道系统得到了很好的研究，但在较深水域出现的分离沉积物路径系统却很少受到关注，特别是在碳酸盐环境中。我们研究了“威利斯通道”中一个广泛的峡谷-水道系统的沉积结构和演化，威利斯通道是位于澳大利亚东北部昆士兰高原的麦格德雷恩和威利斯碳酸盐滩之间的一个海洋海峡。峡谷-水道系统与碳酸盐滩的斜坡分离，出现在500米深处，向碳酸盐高原的斜坡断裂延伸超过100公里。峡谷有几公里宽，几十米深。形态边缘（缺口点）沿着峡谷的走向出现；一个在下游的脚墙上有一个跳水池。峡谷底部的水流波纹和粗粒滞后沉积物表明底流活动，可能是细粒沉积物的筛选。峡谷外的海底被一捆捆的沟槽（线状海底切割）所交叉，这些沟槽长达数十公里。沉积学和地貌特征表明，峡谷-水道体系和沟槽是由东向流动的底流形成的，与主导的西向流动的海流形成的方向相反。我们提出，向东流动的含沙底流源于昆士兰高原碳酸盐构造对洋流的水道化，并与两岸之间狭窄通道的潮汐泵相结合。这一机制在海平面下降期间最为有效，而在海平面高水位期间，底流则要弱得多。我们的地震数据揭示了埋藏的单个峡谷-河道系统的存在，并证明了昆士兰高原自中新世上部以来在当地水流状态中经历了间歇性的变化。基于新的地球物理和海洋学数据，以及海底的视频观测，我们表明，斜坡分离的深水峡谷通道系统起着传送带的作用，将沉积物从碳酸盐台地输送到深海。作为连接浅海领域和深海的纽带，这些体系是碳酸盐岩台地解体和退化的重要因素，并强调了海底洋流在形成这些沉积环境中的作用。

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引用次数: 0

Impact of fluffy layer and bedform on turbulent intermittency in tidally induced bottom boundary layer 蓬松层和床型对潮致底边界层湍流间歇性的影响

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-29 DOI: 10.1016/j.margeo.2025.107677

Zhixin Cao, Chao Li, Zhenkun Lin, Yaokun Lin, Zhaohui Deng, Jiaxue Wu, Jie Ren

Bed roughness affects the turbulence structure within the bottom boundary layer (BBL), thus playing a significant role in sediment resuspension and transport. This study collected in-situ turbulence and sediment data within the BBL of the Pearl River Estuary (PRE) using a benthic quadrapod observation system. Based on quadrant analysis results, the presence of ripples leads to increased bed roughness, which enhances ejections and sweeps. We also find that sweep and ejection events possess stronger sediment mobilization capacity and higher transport efficiency, rather than simply having a larger time proportion. Additionally, under low bed shear stress, the presence of a fluffy layer makes the contribution of inward interactions to sediment flux during flood tide particularly significant. Consequently, we improved the method for determining the waiting time of the sediment flux intermittency index to identify the erosion of consolidated sediment layers.

河床粗糙度影响底边界层湍流结构，在泥沙再悬浮和输运中起重要作用。本研究利用底栖四足动物观测系统，收集了珠江口BBL内的湍流和泥沙资料。根据象限分析结果，波纹的存在导致床层粗糙度增加，从而增强喷射和扫射。我们还发现，横扫和喷射事件具有更强的泥沙动员能力和更高的输沙效率，而不是简单地具有更大的时间比例。此外，在低床层剪切应力下，松软层的存在使得向内相互作用对涨潮期间泥沙通量的贡献尤为显著。因此，我们改进了确定沙通量间歇指数等待时间的方法，以识别固结沉积层的侵蚀。

引用次数: 0

Vulnerability of blue carbon stocks to disturbance in sediments with low burial efficiency 低埋藏效率沉积物中蓝碳储量对扰动的脆弱性

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-28 DOI: 10.1016/j.margeo.2025.107676

Z.A. Roseby , T. Sengupta , S.L. Ward , D.F. Vosper , M. Blaauw , C.M. Roberts , J.D. Scourse

Continental shelf sediments – particularly soft, muddy habitats - serve as significant reservoirs of organic carbon over glacial-interglacial timescales and are subject to disturbance, notably from mobile bottom fishing gear. The quantity and quality of accumulated organic carbon varies across shelf environments, with muds storing more organic carbon than other substrate types. For effective marine management, it has been recommended that the reactivity, or ‘quality’, of organic matter should be considered when assessing the vulnerability of sedimentary carbon to disturbance. If management interventions are to be made to protect vulnerable organic carbon reservoirs on the seafloor, then it is also important to consider the burial efficiency of carbon. In areas of rapid sediment accumulation, carbon will be moved from surface to geological reservoirs more quickly, thus facilitating carbon sequestration. In this study, we assess the quantity, quality, and accumulation rate of organic carbon in the muddy depocenter of the Fladen Ground, northern North Sea - an area of low active sediment accumulation, with both historic and ongoing bottom trawling. All sediment cores analysed in this study display upwards coarsening of surface sediments, consistent with sediment disturbance and winnowing. Southern Fladen Ground sediments are especially well sorted, depleted in total organic carbon, and enriched in calcium carbonate - patterns that align with intensified trawling. Our results show very low modern organic carbon accumulation rates (∼0.7 g C m⁻² yr⁻¹), low organic matter reactivity (18.5 % labile), and that modern trawl events can potentially disturb sediments and carbon accumulated over the last ∼2300 years. These results indicate that sediment and organic carbon accumulation rates are an important consideration when assessing the vulnerability of sedimentary carbon.

大陆架沉积物——尤其是软质、泥泞的栖息地——在冰期-间冰期时间尺度上是有机碳的重要储存库，并容易受到干扰，尤其是来自移动式底部渔具的干扰。累积有机碳的数量和质量因陆架环境而异，淤泥比其他类型的基质储存更多的有机碳。为了有效地管理海洋，有人建议在评估沉积碳对干扰的脆弱性时应考虑有机物的反应性或“质量”。如果要采取管理干预措施来保护海底脆弱的有机碳储层，那么考虑碳的埋藏效率也很重要。在沉积物积聚迅速的地区，碳将更快地从地表转移到地质储层，从而促进碳的固存。在这项研究中，我们评估了北海北部弗拉登地泥质沉积中心有机碳的数量、质量和积累速率，这是一个低活跃沉积物堆积的地区，历史上和现在都有海底拖网捕捞。本研究分析的所有沉积物岩心均显示地表沉积物向上粗化，与泥沙扰动和筛分相一致。弗拉登南部的地面沉积物分选得特别好，总有机碳含量不足，碳酸钙含量丰富——这种模式与密集的拖网捕捞相一致。我们的研究结果表明，现代有机碳积累率非常低（~ 0.7 g C m−2 yr−1），有机质反应性很低（18.5%不稳定），现代拖网事件可能会干扰沉积物和过去~ 2300年积累的碳。这些结果表明，沉积物和有机碳积累速率是评估沉积碳脆弱性的重要考虑因素。

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引用次数: 0

Inorganic mineral flocculation within mid-to-high latitude deep coastal basins 中高纬度深海岸盆地内无机矿物絮凝作用

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-28 DOI: 10.1016/j.margeo.2025.107675

Jaia Syvitski , Ross Powell , Kumiko Azetsu-Scott , Ken Asprey , Eric Hutton , Gywn Lintern

Flocculation dynamics of inorganic mineral grains are quantified for ten mid-to-high latitude, deep coastal basins along the Atlantic, Pacific and Southern Oceans. Suspended floc populations are imaged in situ, capturing an undisturbed water column. The basins receive and accumulate low carbon sediment via delivery of inorganic mineral flocs that carry a reactive organic carbon component during transport. Suspended particles are distributed among four particle reservoirs each characterized by a settling velocity (w) and floc size (D): 1) microflocs and constituent grains (D < 50 μm, w < 4 m/day); 2) medium size flocs (D = 50 to 650 μm, w = 4 to 32 m/day; 3) large flocs (D = 650–5000 μm, w = 32 to 172 m/day); and 4) strings of flocs (5–100 mm in length, w = 200 to 400 m/day) sometimes forming “fabrics”. Stratified currents control flocculation by providing the necessary conditions to support bio-mediated inorganic flocculation. A multi-layer classification scheme based on vertical trends in floc concentration and diameter is used to identify hotspots of flocculation growth and decay within a suite of particle layers: 1) surface layers, 2) flocculation fronts, 3) dilution layers, 4) steady-state layers, 5) deep basin waters, 6) bottom boundary layers, and 7) shelf nepheloid layers. Flocculation fronts form along oceanographic sill depths carrying shear turbulence, and similarly along brackish to seawater mixing depths. Once flocs enter deep basin waters, their properties change little during sedimentation. Transit time for flocs to reach a basin's seafloor ranged from 1 to 14 days for basin depths 73 to 873 m. Evidence suggests multiple aggregation processes (e.g. doubling, onion skin, chaos) can act simultaneously within basin waters. Insights from this study can inform environmental management, such as mitigating the effects of sedimentation from human activities and understanding the implications of climate change on fjord ecosystems.

对大西洋、太平洋和南大洋沿岸10个中高纬度深海岸盆地的无机矿物颗粒絮凝动力学进行了定量研究。悬浮浮群在原地成像，捕捉未受干扰的水柱。盆地通过输送无机矿物絮凝体来接收和积累低碳沉积物，这些絮凝体在运输过程中携带活性有机碳成分。悬浮颗粒分布在4个颗粒库中，每个颗粒库的沉降速度（w)和粒径(D)分别为：1）微絮凝体和组成颗粒（D < 50 μm, w < 4 m/ D）；2)中型絮凝体（D = 50 ~ 650 μm, w = 4 ~ 32 m/ D）； 3)大型絮凝体（D = 650 ~ 5000 μm, w = 32 ~ 172 m/ D）；4)絮凝体串（长度5-100毫米，w = 200 - 400米/天）有时形成“织物”。分层电流通过为支持生物介导的无机絮凝提供必要的条件来控制絮凝。采用基于絮凝体浓度和粒径垂直趋势的多层分类方案，在一组颗粒层中识别絮凝生长和衰减热点：1)表层，2)絮凝锋，3)稀释层，4)稳态层，5)深盆地水域，6)底边界层，7)陆棚网状层。絮凝锋沿着带剪切湍流的海洋静止深度形成，类似地沿着咸淡水到海水混合深度形成。一旦絮凝体进入深盆地水域，它们的特性在沉积过程中几乎没有变化。在盆地深度为73 - 873 m的情况下，絮凝体到达盆地海底的运输时间为1 - 14天。有证据表明，多个聚集过程（如加倍、洋葱皮、混乱）可以同时在盆地水域内发生作用。这项研究的见解可以为环境管理提供信息，例如减轻人类活动造成的沉积影响，以及了解气候变化对峡湾生态系统的影响。

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引用次数: 0

Paleo-bathymetric Evolution of Prydz Bay since the Eocene-Oligocene Boundary, East Antarctica 东南极洲始新世-渐新世交界以来Prydz湾的古水深演化

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-27 DOI: 10.1016/j.margeo.2025.107674

Zijian Xiao , Xiaoxia Huang , Katharina Hochmuth

This study used backstripping analysis, combined with a multi-proxy dataset comprising borehole logs, multi-channel seismic surveys, high-resolution bathymetric data, and regional tectonic constraints to quantitatively reconstruct the paleobathymetric evolution of Prydz Bay. As the third largest bay in Antarctica, Prydz Bay is located in front of the Lambert Glacier-Amery Ice Shelf of the East Antarctic continental margin. Prydz Bay is covered by rich multi-channel seismic lines, and Ocean Drilling Program Leg 119 and 188 provided available lithology data of 8 boreholes, establishing it as an ideal area for basin analyses and paleobathymetric evolution. Core porosity data indicated that the sedimentary strata on the continental shelf are overcompacted due to grounded glacier loading, while the slope exhibits hemipelagic sedimentary characteristics. Considering the variability of deposition history and different crustal structure, the compaction was calculated separately between the continental shelf and slope. By comparison with previous studies, our new results quantitatively infer the thickness of sediment variations, and more detailed paleobathymetric grids were produced in different stages since Eocene-Oligocene boundary. The newly reconstructed paleobathymetry contributes to the understanding of the depositional response of ice sheet dynamics and ocean circulation changes, providing critical constraints on the coupled glacial-ocean-sediment system. Furthermore, spatially explicit gridded data could be used to establish more realistic regional ice sheet, ocean circulation, and climate models in the future.

本研究采用反采分析方法，结合钻孔测井、多通道地震调查、高分辨率测深数据和区域构造约束等多代理数据，定量重建了Prydz湾的古测深演化。普莱兹湾是南极洲第三大海湾，位于南极洲东部大陆边缘的兰伯特冰川-阿莫里冰架前。Prydz Bay被丰富的多通道地震线覆盖，Ocean Drilling Program Leg 119和Leg 188提供了8个钻孔的可用岩性数据，使其成为盆地分析和古测深演化的理想区域。岩心孔隙度数据表明，陆架上沉积地层受地面冰川负荷作用过度压实，坡面呈现半深海沉积特征。考虑到沉积历史的可变性和地壳结构的差异性，陆架和陆坡之间的压实度分别计算。通过与前人研究结果的比较，定量地推断了沉积物厚度的变化，并建立了始新世-渐新世界线以来不同阶段的更详细的古水深网格。新重建的古水深测量有助于了解冰盖动力学和海洋环流变化的沉积响应，为冰川-海洋-沉积物耦合系统提供关键约束。此外，空间明确的网格数据可用于未来建立更真实的区域冰盖、海洋环流和气候模式。

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引用次数: 0

Geyser and Zélée seamounts and adjacent basin as witnesses of SW Indian Ocean tectonic and carbonate-siliciclastic-volcanoclastic sediment interplay 间歇泉和zsamlsame海山及其邻近盆地是西南印度洋构造和碳酸盐-硅质-火山碎屑沉积相互作用的见证

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-26 DOI: 10.1016/j.margeo.2025.107673

Dhishna Buljore , Stéphan J. Jorry , Gwenael Jouet , Patrick Bachèlery , Fabien Paquet

This study examines the Late Quaternary sedimentary and volcanic history of Zélée and Geyser Seamounts, carbonate platforms in the Mozambique Channel (south-west Indian Ocean). These seamounts are in a region influenced by active tectonics, glacial-interglacial sea-level cycles, and persistent volcanic activity from both local (Mayotte and Comoros Archipelago) and regional (Madagascar) sources. As a result, they display complex sedimentary and geomorphic characteristics. The research uses sediment cores and seismic profiles to identify four glacial-interglacial stages. It traces shifts in sediment provenance and documents a transition from Madagascar-derived siliciclastic inputs to volcanic sediments associated with Mayotte volcanism around 150 ka.

The analysis also tests a model of platform formation in general on two independently formed edifices, Zélée and Geyser. Detailed geomorphological mapping reveals steep slopes, terraces, volcanic cones, and erosional features. Seismic profiles show stratified deposits including turbidites of different origins. These turbidites highlight episodic sediment transport. Volcanoclastic layers are linked to volcanic events, while siliciclastic layers trace back to Madagascar. Calciturbidites reflect carbonate shedding from Zélée and Geyser during sea-level changes.

The findings enhance our understanding of carbonate platform evolution in tectonically active marine environments, emphasizing the influence of volcanism, tectonics, and climatic fluctuations on sediment distribution and platform morphology. This study contributes a refined perspective on sedimentary processes and sediment provenance in carbonate platforms, with broader implications for reconstructing past oceanographic conditions in similar regions.

本研究考察了莫桑比克海峡（西南印度洋）碳酸盐台地zsamuelsame和Geyser海山的晚第四纪沉积和火山历史。这些海山所处的区域受到活动构造、冰期-间冰期海平面旋回以及来自当地（马约特群岛和科摩罗群岛）和区域（马达加斯加）的持续火山活动的影响。因此，它们表现出复杂的沉积和地貌特征。该研究利用沉积物岩心和地震剖面确定了四个冰期-间冰期。它追溯了沉积物来源的变化，并记录了从马达加斯加衍生的硅碎屑输入到150 ka左右与马约特火山活动相关的火山沉积物的转变。该分析还测试了两个独立形成的大厦，zsamusame和Geyser的平台形成模型。详细的地貌地图揭示了陡峭的斜坡、阶地、火山锥和侵蚀特征。地震剖面显示层状沉积，包括不同来源的浊积岩。这些浊积岩突出了幕式沉积物搬运。火山碎屑层与火山事件有关，而硅碎屑层可以追溯到马达加斯加。钙辉石反映了海平面变化过程中z薪金和间歇泉中碳酸盐的脱落。这些发现加强了我们对构造活跃海洋环境中碳酸盐岩台地演化的认识，强调了火山作用、构造作用和气候波动对沉积物分布和台地形态的影响。该研究为研究碳酸盐岩台地的沉积过程和沉积物物源提供了一个更精确的视角，对重建类似地区过去的海洋条件具有更广泛的意义。

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引用次数: 0

Post-glacial sandy contourite drifts in the Malta-Gozo Channel (Pelagian Platform, central Mediterranean Sea): Characteristics, bottom currents and implication for shallow-water contourite systems 马尔他-戈佐海峡（地中海中部伯拉吉海台地）冰川后砂质轮廓岩漂移：特征、底流及其对浅水轮廓岩体系的影响

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-24 DOI: 10.1016/j.margeo.2025.107672

Daniele Spatola , Aaron Micallef , Daniele Casalbore , Francesco Latino Chiocci , Eleonora Martorelli

An increasing number of studies have documented the occurrence of sandy contourites in modern systems. However, knowledge on their characteristics and links with oceanographic processes remains limited. In particular, the pattern of bottom current circulation on the Pelagian Platform (central Mediterranean Sea) and its driving mechanisms are poorly understood. To address these gaps, we analyse newly acquired very high-resolution geophysical and sedimentological data from offshore the Maltese Islands, which allow us to identify small-scale, sandy contourite drifts (named EM1–5), located in shallow water (depths between 50 and ∼ 100 m). Using a dense grid of high-resolution seismic profiles, multibeam bathymetry, and sedimentological analyses, we detail the internal and external geometry, morphology, and sedimentology of the deposits. Drifts EM1a, EM1b, EM1c, EM2, EM3, and EM5 appear as small elongated mounded deposits (separated and plastered drifts) cropping on the shelf seafloor, while EM4 is a buried mounded deposit located in the southern part of the study area. The spatial distribution of the studied drifts suggests that their formation is driven by a mesoscale anticyclonic gyre, tentatively ascribed to the Malta-Sicily Gyre, with currents enhanced by topographic interactions. Stratigraphic evidence suggests that this oceanographic dynamic has played a significant role in shaping the Maltese insular shelf since at least the Holocene, highlighting the potential of the Pelagian Platform to form carbonate sandy contourites. These findings advance the understanding of shallow-water (shelf-channelized) contourite systems and offer valuable insights to refine sedimentation models for carbonate-rich contourite deposits in temperate settings.

越来越多的研究记录了现代体系中砂质等高线的出现。然而，关于它们的特点及其与海洋学过程的联系的知识仍然有限。特别是对伯拉基平台（地中海中部）的底流环流模式及其驱动机制了解甚少。为了解决这些差距，我们分析了马耳他群岛近海新获得的高分辨率地球物理和沉积学数据，这些数据使我们能够识别位于浅水（深度在50至~ 100米之间）的小规模沙质轮廓岩漂移（命名为EM1-5）。利用高分辨率地震剖面的密集网格、多波束测深和沉积学分析，我们详细描述了矿床的内部和外部几何形状、形态和沉积学。EM1a、EM1b、EM1c、EM2、EM3和EM5漂流体在陆架海床上表现为小型细长的丘状沉积物（分离的灰泥漂流体），而EM4则为埋藏的丘状沉积物，位于研究区南部。所研究的漂移的空间分布表明，它们的形成是由一个中尺度反气旋环流驱动的，该环流初步归因于马耳他-西西里环流，地形相互作用增强了洋流。地层学证据表明，至少自全新世以来，这种海洋动力学在塑造马耳他岛陆架方面发挥了重要作用，突出了伯拉海地台形成碳酸盐砂质等高线岩的潜力。这些发现促进了对浅水（陆架河道化）廓长岩体系的理解，并为完善温带环境中富含碳酸盐的廓长岩沉积模式提供了有价值的见解。

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引用次数: 0

Multiple methane release events from Cascadia Margin sediments since 1 Ma inferred from pyrite multiproxy data 从黄铁矿多代理资料推断1 Ma以来卡斯卡迪亚边缘沉积物多次甲烷释放事件

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-23 DOI: 10.1016/j.margeo.2025.107670

Qiang Song , Jiasheng Wang , Thomas J. Algeo , Can Chen , Zhou Wang , Qin Yang , Kunlong Geng , Qing Li

Large-scale methane release events (MREs), which can trigger transient climatic hyperwarming, are associated with enhanced anaerobic oxidation of methane (AOM), generating diagnostic geochemical and petrographic signatures in authigenic pyrite. Previous studies of MREs have analyzed single proxies such as pyrite framboid size or the sulfur isotopic composition of bulk-sediment pyrite over short core intervals, providing insufficient data regarding the intensity and magnitude of such events. Here, we utilize multiple proxies (i.e., pyrite framboid content, size, and sulfur isotopic composition) to reconstruct a detailed history of paleo-MREs at Site U1329 (IODP Leg 311) on the Cascadia Margin since 1 Ma. The recovered pyrite consists mainly (>99%) of isolated framboids and framboid aggregates, some having late diagenetic overgrowths. The characteristics of these framboids reflect the intensity and magnitude of each MRE: strong events were associated with FeS₂ > 1.0 wt.%, mean framboid size >20 μm, and Δ³⁴S < 0‰ (where Δ³⁴S = δ³⁴S_CRS – δ³⁴S_SMTZ), whereas weak events were associated with FeS₂ = ∼0.5-1.0 wt.%, mean framboid size ∼10-20 μm, and Δ³⁴S > 0‰. The study core contains four MREs (one strong, three medium) with mean pyrite content of 1.27 wt.%, mean framboid diameter of 26±6 μm, and mean Δ³⁴S of 10.5‰ (cf. background interval values of 0.85 wt.% mean FeS₂ content; 12±2 μm mean framboid diameter; and 16.0‰ mean Δ³⁴S). Each MRE was associated with a glacio-eustatic lowstand, a relationship reflecting destabilization of gas hydrates through pressure release, leading to an upward flux of methane, shallowing of the sulfate-methane transition zone (SMTZ), and enhanced AOM activity. Our results indicate that the morphological and geochemical signatures of pyrite are important carriers of paleoclimate information that can be used to study the occurrence and intensity of paleo-methane events and further improve understanding of methane hydrate dynamics.

大规模甲烷释放事件（MREs）可引发短暂的气候过热，与甲烷厌氧氧化（AOM）增强有关，产生自生黄铁矿的诊断地球化学和岩石学特征。以前的MREs研究分析了单一的指标，如黄铁矿的草莓状大小或短岩心间隔内块状沉积物黄铁矿的硫同位素组成，提供的有关此类事件的强度和量级的数据不足。在这里，我们利用多种代理（即黄铁矿的含量、大小和硫同位素组成）重建了Cascadia边缘U1329遗址（IODP Leg 311）自1ma以来的古mres详细历史。回收的黄铁矿主要由（>99%）孤立的草莓状和草莓状团聚体组成，部分有晚成岩过度生长。这些frboids的特征反映了每个MRE的强度和大小：强事件与FeS2 >； 1.0 wt.%，平均frboid尺寸>；20 μm和Δ34S <； 0‰（其中Δ34S = δ34SCRS - δ34SSMTZ）相关，而弱事件与FeS2 = ~ 0.5-1.0 wt.%，平均frboid尺寸~ 10-20 μm和Δ34S >； 0‰相关。研究岩心包含4个MREs（1个强、3个中），平均黄铁矿含量为1.27 wt.%，平均树状直径为26±6 μm，平均Δ34S为10.5‰（cf.背景区间值为0.85 wt.%，平均FeS2含量为12±2 μm，平均Δ34S为16.0‰）。每个MRE都与一个冰川-上升低潮相关联，这种关系反映了通过压力释放导致天然气水合物不稳定，导致甲烷通量上升，硫酸盐-甲烷过渡带（SMTZ）变浅，AOM活动增强。结果表明，黄铁矿的形态和地球化学特征是古气候信息的重要载体，可用于研究古甲烷事件的产状和强度，进一步提高对甲烷水合物动力学的认识。

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引用次数: 0

Buried Middle Miocene cyclic steps on the northwestern slope of the Xisha carbonate platform, South China Sea 南海西沙碳酸盐岩台地西北坡中中新世隐伏旋回台阶

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-22 DOI: 10.1016/j.margeo.2025.107671

Biwen Wang , Jinfeng Ren , Zenggui Kuang , Guangfa Zhong

High-amplitude undulating seismic reflections within the Middle Miocene strata on the northwestern slope of the Xisha carbonate platform, located on the northwestern continental margin of the South China Sea, have drawn significant research interest over the past decade. Several conflicting genetic models have been proposed, including those suggesting carbonate reefs, turbidity-current or bottom-current channels, and fault-related features. This study examines the morphology, internal structures, and distribution of these undulations using 3D seismic data, combined with 2D seismic and drilling data. These undulations are characterized by long wavelength (0.5–2.3 km), low wave height (15–80 m), large aspect ratios (20–60), upslope-migrating waveforms, upslope-asymmetric cross-sectional morphology, typical stoss-side backset beddings and truncated lee sides, and are therefore identified as cyclic steps associated with supercritical flows. The slope-parallel crestlines of the cyclic steps further indicate their turbidity-current origin. Some coexisting downslope extending linear depressions are attributed to turbidity-current channels. Development of the cyclic steps is closely associated with the evolution of the Xisha carbonate platform. During the early Middle Miocene, when the carbonate platform productivity was high, abundant calcareous sediments were delivered from the platform margin to the study area, contributing to the formation of the cyclic steps in the lower slope off the platform. As the platform was drowning in the late Mid-Late Miocene, sediment supply from the platform was reduced, leading to the abandonment of the bedforms, with the bedform troughs being infilled by interbedded hemipelagites and turbidites. Our findings are significant for a better understanding of 3D morpho-sedimentary architecture of buried supercritical-flow bedforms that have been rarely reported, with implications for regional paleogeographic reconstructions and carbonate platform evolution.

近十年来，南海西北陆缘西沙碳酸盐岩台地西北坡中中新世地层的高振幅波动地震反射引起了人们的广泛关注。人们提出了几种相互矛盾的成因模式，包括碳酸盐岩礁、浊流或底流通道以及断层相关特征。本研究利用三维地震数据，结合二维地震和钻井数据，研究了这些波动的形态、内部结构和分布。这些波动具有波长长（0.5-2.3 km）、波高低（15-80 m）、宽高比大（20-60）、上坡迁移波形、上坡不对称横截面形态、典型的应力侧背向层序和背风侧截短等特征，因此被认为是与超临界流动相关的循环阶跃。旋回台阶的斜平行顶线进一步表明其浊流成因。一些同时存在的下坡扩展线性凹陷归因于浊流通道。旋回阶的发育与西沙碳酸盐岩台地的演化密切相关。中中新世早期，碳酸盐岩台地生产力较高，大量钙质沉积物从台地边缘向研究区输送，形成了台地下斜坡旋回台阶。中-晚中新世晚期台地淹水，台地输沙量减少，导致床型废弃，床型槽被互层半玄武岩和浊积岩填满。我们的发现对于更好地理解埋藏的超临界流层的三维形态-沉积结构具有重要意义，这对区域古地理重建和碳酸盐岩台地演化具有重要意义。

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引用次数: 0

Sedimentary dynamics in the subaqueous delta of the abandoned estuary: Effects of strong wave activity and riverine re-supply 废弃河口水下三角洲的沉积动力学：强波活动和河流补给的影响

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology

Pub Date : 2025-10-08 DOI: 10.1016/j.margeo.2025.107662

Chaoran Lin , Longhai Zhu , Yaping Wang , Rui Bao , Rijun Hu , Lingpeng Meng

Global climate change and the decline in riverine sediment supply are profoundly reshaping the fate and trajectory of numerous river deltas around the world. Notably, subaqueous deltas of abandoned estuaries (SDAEs) resulting from river diversion represent an extreme example of zero riverine sediment supply, yet studies of these environments remain scarce. Based on in-situ bottom boundary layer observations in both spring and summer in the SDAE of the Yellow River, we examined the variation patterns and controlling mechanisms of sediment dynamics —under the effect of strong wave activity and the new secondary distribution. Strong wave events exhibited a pronounced dual influence on SSC; alongshore wave substantially increase SSC (>21.28 g/L) by enhancing sediment resuspension and liquefaction, whereas onshore wave significantly reduce nearshore SSC through water mass replacement (with values rapidly dropping from 13.11 g/L to 1.14 g/L). Riverine re-supply due to the new secondary course of the Yellow River has altered sediment transport pathways, enabling SSC in the SDAE to reach as high as 22.34 g/L under calm weather conditions, and resulting in a net alongshore sediment flux of 117 kg/m². We identified and established three conceptual models of fluid mud formation mechanisms: wave-supported, wave-current coupled fluid mud (WCFM), and river advection. We identified and established three conceptual models of fluid mud formation: wave-supported, wave-current coupled fluid mud (WCFM), and river advection. Identification of the WCFM highlights the sustained impact of strong wave activity on sediment transport within the SDAE. These findings advance our understanding of sediment dynamics in the SDAEs and provide valuable theoretical references and comparative examples for the studying the global evolution of abandoned or sediment-starved delta.

全球气候变化和河流沉积物供应的减少正在深刻地重塑世界各地众多河流三角洲的命运和轨迹。值得注意的是，河流改道导致的废弃河口水下三角洲（SDAEs）是河流沉积物零供应的一个极端例子，但对这些环境的研究仍然很少。基于黄河南岸河段春夏两季底边界层观测资料，探讨了强波活动和新的二次分布作用下泥沙动力的变化规律和控制机制。强波事件对SSC具有明显的双重影响；近岸波通过加强沉积物再悬浮和液化作用显著增加SSC (21.28 g/L)，而近岸波通过水体质量替代作用显著减少SSC（从13.11 g/L迅速下降到1.14 g/L）。黄河新次河道的河道再补给改变了输沙路径，使SDAE的SSC在平静天气条件下高达22.34 g/L，导致净岸沙通量为117 kg/m2。我们确定并建立了三种流体泥浆形成机制的概念模型：波支撑、波流耦合流体泥浆（WCFM）和河流平流。我们确定并建立了三种流体泥浆形成的概念模型：波支撑、波流耦合流体泥浆（WCFM）和河流平流。WCFM的确定强调了强波活动对SDAE内沉积物输运的持续影响。这些发现促进了我们对SDAEs沉积动力学的认识，并为研究遗弃或缺沙三角洲的全球演化提供了有价值的理论参考和比较实例。

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引用次数: 0