Sulfur isotopic signatures of pyrite (δS) sensitively react to local environmental change. Here we elucidate mechanism of δS variation in the Holocene sedimentary strata of the Yangtze River Delta, through the analyses of multiple geochemical and physical indicators including total organic carbon, total nitrogen, stable isotopes of organic carbon, different iron solid phases, Sr/Ba ratios, and changes in sedimentation rates. Two heavy δS (∼30‰) layers that formed under contrasting redox conditions are preserved in the early Holocene transgressive tidal flat and late Holocene regressive mouth bar facies, respectively. Two hypotheses are proposed to explain these heavy δS layers: 1) in the transgression process, the heavy δS layers formed under stronger reducing conditions due to methane leakage; 2) in the regression process, the heavy δS layers formed under relatively weaker reducing conditions due to rapid deposition and low salinity. This study emphasizes the importance of physicochemical condition characterization in sediments, including redox conditions, in distinguishing the mechanisms that act to produce heavy δS signals.

中文翻译：

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长江三角洲全新世沉积物氧化还原条件对比记录的重硫同位素


黄铁矿的硫同位素特征 (δS) 对当地环境变化做出敏感反应。通过对总有机碳、总氮、有机碳稳定同位素、不同铁固相、Sr/Ba比值等多种地球化学和物理指标的分析，阐明长三角全新世沉积地层δS变化机制，以及沉降速率的变化。早全新世海侵潮坪和晚全新世海退河口坝相中分别保存了在对比氧化还原条件下形成的两层重δS（~30‰）层。提出了两种假设来解释这些重δS层：1）在海侵过程中，由于甲烷泄漏，在更强的还原条件下形成了重δS层； 2）在海退过程中，由于快速沉积和低盐度，在相对较弱的还原条件下形成了重δS层。这项研究强调了沉积物中物理化学条件表征（包括氧化还原条件）在区分产生重 δS 信号的机制方面的重要性。