Cold seep carbonates are commonly used to record the nature of seepage, including fluid sources, diagenetic environments, and variations in seepage activity. However, the relationship between diagenetic environments and trace element enrichment in dynamic environments is poorly understood. Pipe-morphology cold seep carbonates form from outside to inside in methane seeps and record variations in elements and isotopes over time, which can be used to reconstruct diagenetic environments and fluid dynamics. In this work, we analysed the mineral compositions, carbon and oxygen (CO) isotopes and major and trace element contents in different areas of pipe-morphology cold seep carbonate collected from the Qiongdongnan Basin in different growth directions. The cold seep carbonate exhibits changes from high-magnesian calcite (HMC) to aragonite and then to HMC, indicating that it has undergone changes in the sedimentary environment inside the fluid migration pathway. On the basis of these findings, the formation of this pipe-morphology cold seep carbonate is divided into three stages. The low δ13C values (from −36.13 ‰ to −32.18 ‰) indicate anaerobic oxidation of methane during carbonate formation. The response of δ13C to changes in the methane flux is not obvious. The gradual increase in δ18O from the outer to the inner portions suggests that the methane flux affected δ18O. The samples have relatively high enrichment factors (EFs) of molybdenum (Mo) and high molybdenum/uranium (Mo/U) ratios. The UEF values show an increasing trend from the outer to the inner portions, whereas the changes in MoEF, CdEF and VEF are not obvious. However, MoEF, CdEF, and VEF all have good correlations with Mn/Al and Fe/Al, indicating that the particulate shuttle process significantly impacts the enrichment of Mo, Cd, and V. We concluded that the enrichment of U is influenced by the methane flux, whereas the enrichment of Mo, Cd and V is unrelated to methane dynamics. This study provides insights into the behaviour of the methane flux and seawater, redox-sensitive trace element contents and changes in the sedimentary environment and plays an essential role in understanding the activities of cold seeps in dynamic environments.

中文翻译：

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南海北部琼东南盆地管状-形貌冷泉碳酸盐岩多阶段形成及地球化学响应


冷渗碳酸盐通常用于记录渗流的性质，包括流体来源、成岩环境和渗流活动的变化。然而，成岩环境与动态环境中微量元素富集之间的关系知之甚少。管道形态冷渗碳酸盐在甲烷渗漏中从外到内形成，并记录元素和同位素随时间的变化，可用于重建成岩环境和流体动力学。本工作分析了琼东南盆地不同生长方向采集的管状形态冷泉碳酸盐岩不同区域的矿物组成、碳氧 （CO） 同位素和主微量元素含量。冷渗碳酸盐表现出从高镁方解石 （HMC） 到文石再到 HMC 的变化，表明它在流体迁移途径内的沉积环境中发生了变化。根据这些发现，这种管道形态冷泉碳酸盐的形成分为三个阶段。低 δ13C 值（从 -36.13 ‰ 到 -32.18 ‰）表明碳酸盐形成过程中甲烷的厌氧氧化。δ13C 对甲烷通量变化的响应并不明显。δ18O 从外部到内部逐渐增加表明甲烷通量影响了 δ18O。样品具有相对较高的钼 （Mo） 富集因子 （EF） 和高钼/铀 （Mo/U） 比率。UEF 值呈从外部到内部增加的趋势，而 MoEF 、 CdEF 和 VEF 的变化并不明显。 然而，MoEF、CdEF 和 VEF 都与 Mn/Al 和 Fe/Al 具有良好的相关性，表明颗粒穿梭过程显着影响 Mo、Cd 和 V 的富集。我们得出结论，U 的富集受甲烷通量的影响，而 Mo、Cd 和 V 的富集与甲烷动力学无关。这项研究提供了对甲烷通量和海水的行为、氧化还原敏感微量元素含量和沉积环境变化的见解，并在了解动态环境中冷泉的活动方面发挥着重要作用。