Carbon and sulfur preserved in estuary and shelf sediments play a critical role in controlling sediment diagenesis related to the global biogeochemical cycle. Their ratio (C/S = 2.8) in mud sediments has been widely used to distinguish freshwater from marine environments; however, this ratio can be influenced by depositional evolution, physical reworking, and other sedimentological parameters. We present a new C/S ratio data set from surface sediments of five rivers (Aojiang, Feiyunjiang, Jiaojiang, Oujiang, and Qiantangjiang Rivers), as well as core sediments offshore of the Oujiang Estuary (core EC2005, 60 m), to discuss how the evolution of the depositional environment influenced carbon and sulfur preservation since the last deglaciation. To this aim, we measured the contents of total organic carbon (TOC), total sulfur (TS), and carbonate in the collected samples. Our results demonstrate that a C/S ratio of 2.8 can effectively separate freshwater environments (river sediments and core sediments deposited before 13.1 ka), suggesting the initial impact of sulfate-enriched seawater on carbon and sulfur perseveration at ~13.1 ka. However, the TS content is independent of the TOC content after 13.1 ka, implying that pyrite sulfur is derived not only from organoclastic sulfate reduction (OSR) but also from sulfate-driven anaerobic oxidation of methane (AOM) under anoxic diagenetic conditions. In the shallowest core section (shallower than 5 m; < 1.5 ka), the C/S ratios gradually increase from 1 to 2.8, which corresponds to an interval with sulfide reoxidation under suboxic conditions caused by strong physical reworking. When the sediment is buried to a certain depth (deeper than 5 m; > 1.5 ka), a high sedimentation rate is conducive to an AOM reaction, resulting in the generation of a large amount of pyrite and finally causing the minimum value of the C/S ratio to be approximately 1. However, during the transitional period of 13.1–11.0 ka, sediments deposited in the tidal environment show overlap with those deposited in the marine shelf environment, and C/S ratios decrease from >10 to ~1. In addition, we propose that C/S and C/N ratios could be combined to reveal the depositional evolution from terrestrial to marine environments, which is sensitive to sea level and climatic changes. Therefore, our new findings suggest that the sedimentation process can modulate the diagenetic path of mud sediments (e.g., OSR versus AOM), and geochemical indicators of environmental evolution should be carefully used in combination with sedimentological parameters in shallow depositional environments.

保存在河口和陆架沉积物中的碳和硫在控制与全球生物地球化学循环相关的沉积物成岩作用中起着关键作用。它们在泥沉积物中的比率 (C/S = 2.8) 已被广泛用于区分淡水和海洋环境；然而，这个比率会受到沉积演化、物理改造和其他沉积学参数的影响。我们提出了来自 5 条河流（鳌江、飞云江、椒江、瓯江和钱塘江）表层沉积物以及瓯江口近海核心沉积物（核心 EC2005，60 m）的新 C/S 比数据集，以讨论自上次冰消期以来，沉积环境的演变如何影响碳和硫的保存。为此，我们测量了总有机碳 (TOC)、总硫 (TS)、和收集的样品中的碳酸盐。我们的结果表明，2.8 的 C/S 比可以有效地分离淡水环境（13.1 ka 之前沉积的河流沉积物和核心沉积物），这表明富含硫酸盐的海水对约 13.1 ka 的碳和硫持续存在的初始影响。然而，TS 含量在 13.1 ka 后与 TOC 含量无关，这意味着黄铁矿硫不仅来自有机碎屑硫酸盐还原（OSR），还来自缺氧成岩条件下硫酸盐驱动的甲烷厌氧氧化（AOM）。在最浅的岩心段（小于 5 m；< 1.5 ka），C/S 比从 1 逐渐增加到 2.8，这对应于强物理再加工导致的低氧条件下硫化物再氧化的区间。当沉积物埋藏到一定深度（大于 5 m；> 1.5 ka）时，较高的沉积速率有利于 AOM 反应，导致大量黄铁矿的生成，最终导致 C 的最小值/S 比值约为 1。然而，在 13.1-11.0 ka 的过渡期，潮汐环境中沉积的沉积物与海洋陆架环境中沉积的沉积物表现出重叠，C/S 比从 >10 下降到~1。此外，我们建议可以结合 C/S 和 C/N 比来揭示从陆地到海洋环境的沉积演化，这对海平面和气候变化很敏感。因此，我们的新发现表明，沉积过程可以调节泥质沉积物的成岩路径（例如，OSR 与 AOM），