The morphology and geochemistry of authigenic pyrite formed under methane seepage: Insights from the Laptev Sea

IF 2.6 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology Pub Date : 2025-04-09 DOI:10.1016/j.margeo.2025.107558

Alexey Ruban , Anastasia Nikolaeva , Vera Abramova , Alexander Ignatiev , Oleg Dudarev , Igor Semiletov , Maxim Rudmin

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引用次数: 0

Abstract

In cold seep environments, intense sulfate-driven anaerobic oxidation of methane (SD-AOM) generates significant amounts of hydrogen sulfide, facilitating pyrite precipitation in the sulfate-methane transition zone (SMTZ). To enhance the understanding of pyrite formation processes within the SMTZ, we analyzed the morphology, size distribution, trace element content, and sulfur isotopic composition of framboidal pyrite hosted in methane-derived authigenic carbonate crusts. These crusts were collected from two active cold seep sites in the Laptev Sea: the outer shelf and the continental slope. The main textural forms of authigenic pyrite were found to include spherical and polygonal framboids and their clusters, sunflowers, and rod-like aggregates. The diameter of most measured framboids does not exceed 20 μm, but some reach up to 74 μm. Despite the small size, their association with methane-derived authigenic carbonates indicates that SD-AOM plays a dominant role in pyrite precipitation. Specific pyrite textures, such as rod-like aggregates, and the large size of certain framboids further support that pyrite formation occurred within the SMTZ. Different textural relationships between pyrite aggregates and carbonate cement reflect both pre‑carbonate and post‑carbonate pyrite precipitation. Their coexistence within a single carbonate crust sample suggests multiple episodes of pyrite formation. The obtained δ³⁴S values for pyrite (ranging from −35.6 ‰ to −28.1 ‰ V-CDT) reveal a depletion of heavy sulfur isotopes at both sites, which is uncharacteristic of SD-AOM-associated pyrite. This phenomenon is likely attributed to the open-system conditions of pyrite formation, which result from the shallow SMTZ. The content of some trace elements in pyrite from the outer shelf is significantly lower than that in pyrite from the continental slope. This difference in trace element composition may reflect varying conditions under which pyrite precipitated, highlighting the influence of fluid migration regimes on mineral-forming processes. Lower Co/Ni ratios in pyrite from the continental slope indicate its formation under more sulfidic conditions. Our findings suggest that the depth of the SMTZ relative to the seawater-sediment interface is a critical factor controlling the morphological, isotopic, and trace element characteristics of pyrite, which should be taken into account when identifying paleo-seepage.

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甲烷渗流下形成的自生黄铁矿的形态和地球化学：来自拉普捷夫海的启示

在冷渗环境中，强烈的硫酸盐驱动甲烷厌氧氧化（SD-AOM）产生大量硫化氢，促进硫酸盐-甲烷过渡区（SMTZ）的黄铁矿沉淀。为了加深对SMTZ内黄铁矿形成过程的认识，我们分析了甲烷衍生自生碳酸盐岩地壳中草莓状黄铁矿的形态、粒度分布、微量元素含量和硫同位素组成。这些地壳来自拉普捷夫海两个活跃的冷渗漏点：外大陆架和大陆斜坡。自生黄铁矿的主要结构形式包括球形和多角形树状体及其簇状、向日葵状和棒状聚集体。大多数测量到的树状体直径不超过20 μm，但有些树状体直径可达74 μm。尽管体积小，但它们与甲烷衍生的自生碳酸盐的结合表明，SD-AOM在黄铁矿沉淀中起主导作用。特定的黄铁矿结构，如棒状聚集体，以及某些大尺寸的树状体进一步支持黄铁矿形成于SMTZ内。黄铁矿骨料与碳酸盐胶结物的不同结构关系反映了碳酸盐前和碳酸盐后黄铁矿的沉淀。它们在单一碳酸盐地壳样品中的共存表明黄铁矿形成的多个阶段。黄铁矿的δ34S值（V-CDT范围为−35.6‰~−28.1‰）表明两个地点的重硫同位素都存在损耗，这是非sd - aom伴生黄铁矿的特征。这种现象可能与浅层SMTZ形成黄铁矿的开体系条件有关。外陆架黄铁矿中某些微量元素的含量明显低于陆坡黄铁矿。微量元素组成的差异可能反映了黄铁矿沉淀的不同条件，突出了流体运移制度对矿物形成过程的影响。大陆斜坡黄铁矿Co/Ni比值较低，表明其形成条件较硫化物化。研究结果表明，相对于海水-沉积物界面的SMTZ深度是控制黄铁矿形态、同位素和微量元素特征的关键因素，在识别古渗流时应考虑这些因素。

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来源期刊

Marine Geology 地学-地球科学综合

CiteScore

6.10

自引率

6.90%

发文量

175

审稿时长

21.9 weeks

期刊介绍： Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.