To better understand the depositional constraints on the sulfate reduction process, we present a set of sulfur isotope data for hand-picked pyrites (δ³⁴S_pyr) from the coarse fraction (63–250 μm) of bulk sediments, coupled with the contents of carbonate, total organic carbon (TOC) and nitrogen (TN), as well as δ¹³C values of the TOC, from sediments of core EC2005 on the inner shelf of the East China Sea (ECS) since 16.4 ka. Our results show that core sediments were deposited in a terrestrial environment before 13.1 ka (stage I) when pyrite rarely occurred. During stages II (13.1–12.3 ka) and III (12.3–12.1 ka) seawater began to influence the core location, forming a tidal flat environment where abundant pyrites are well preserved. Then the inner shelf of the ECS was fully flooded, and two intervals with high (stage IV:12.1–6.0 ka; stage VI: 5.2–1.5 ka) and low sedimentation rate (stage V: 6.0–5.2; stage VII: 1.5 ka-present) are identified respectively. When compared with previous δ³⁴S values of chromium-reducible sulfur (δ³⁴S_CRS) derived from the bulk sediments, δ³⁴S_pyr values are usually higher, indicating the macroscopic pyrites form in the later stages of sedimentary diagenesis when ongoing sulfate reduction has distilled porewater sulfate to a high degree. Considering the wide occurrence of biogenic shallow gas (dominated by CH₄) in these sediments, sulfate-driven anaerobic oxidation of methane (SO₄-AOM) and organoclastic sulfate reduction (OSR) are expected to be two competitive pathways for sulfate reduction. We propose that the changes in sedimentation rate controls the pace of migration of the sulfate methane transition zone (SMTZ). When sedimentation rate is low, the SMTZ may be fixed in a certain depth (e.g., sediments deposited in stage III and V), where H₂S is produced by SO₄-AOM. In contrast, when sedimentation rate is very high (> 1 cm/yr), the SMTZ would be deep, and H₂S is mostly produced by OSR. Further, our results imply that sulfur diagenesis in recent (since 1.5 ka) ECS mud sediments might be influenced by physical reworking (e.g., typhoon) and/or biological activity (bioturbation), resulting in partial reoxidation of pyrite crystals in fluid mud. Our findings therefore demonstrate that pyrite sulfur isotope compositions (bulk δ³⁴S_CRS & hand-picked δ³⁴S_pyr) are sensitive to local environmental evolution and the combined use of these two indicators can provide new insights into pathway of sulfate reduction in unsteady environments.

为了更好地理解对硫酸盐还原过程沉积的限制，我们提出了一组手工采摘黄铁矿硫同位素数据（δ ³⁴小号_PYR）从大容量沉积物的粗级分（63-250微米），再加上的内容碳酸酯，总有机碳（TOC）和氮（TN），以及δ ¹³TOC的C值，来自16.4 ka以来东海内陆架EC2005核心的沉积物。我们的结果表明，核心沉积物在13.1 ka（第一阶段）之前沉积在陆地环境中，而黄铁矿很少发生。在第二阶段（13.1–12.3 ka）和第三阶段（12.3–12.1 ka）期间，海水开始影响岩心的位置，形成了一个潮汐平坦的环境，其中大量的黄铁矿得到了很好的保存。然后，ECS的内层被完全淹没，两个间隔高（阶段IV：12.1–6.0 ka；阶段VI：5.2–1.5 ka）和低沉积速率（阶段V：6.0–5.2；阶段VII：1.5 ka） -）分别被识别。当与以前相比δ ³⁴铬还原性硫的价值观（δ ³⁴小号_CRS）从散装沉积物，δ衍生³⁴ S _pyr值通常较高，这表明当持续进行的硫酸盐还原作用已将蒸馏的孔隙水硫酸盐高度蒸馏时，在沉积成岩作用的后期形成了宏观的黄铁矿。考虑到这些沉积物中生物浅层气体（CH ₄占主导）的广泛存在，预计硫酸盐驱动的甲烷厌氧氧化（SO ₄ -AOM）和有机碎屑硫酸盐还原（OSR）是硫酸盐还原的两个竞争途径。我们建议，沉积速率的变化控制着硫酸盐甲烷过渡带（SMTZ）的迁移速度。当沉积速率较低时，SMTZ可能会固定在一定深度（例如，阶段III和阶段V中沉积的沉积物），其中H ₂S由SO ₄ -AOM产生。相反，当沉积速率非常高（> 1 cm / yr）时，SMTZ会很深，而H ₂ S主要由OSR产生。此外，我们的结果表明，最近（自1.5 ka起）ECS泥浆沉积物中的硫成岩作用可能受到物理改造（例如台风）和/或生物活性（生物扰动）的影响，从而导致流体泥浆中黄铁矿晶体的部分再氧化。因此，我们的研究结果表明，黄铁矿硫同位素组合物（δ散装³⁴小号_CRS＆手工采摘δ ³⁴小号_吡）对当地环境的演变很敏感，并且这两个指标的结合使用可以为不稳定环境中硫酸盐还原的途径提供新的见解。