Diagenetic Processes and Authigenic Mineral Formation in Amazon Shelf Sediments

这项研究是amasds项目（多学科亚马孙大陆架沉积物研究）的一部分，该项目旨在了解影响或受亚马孙大陆架颗粒通量影响的物理、化学和地质过程。由于亚马逊河的大量沉积物排放和潮汐过程对细粒陆架沉积物的广泛再悬浮，亚马逊陆架上出现了高颗粒通量。该研究的这一组成部分检查了亚马逊内陆陆架泥中发生的铁和锰还原反应。Fe和Mn反应明显优于SO4反应，这可能是由于低有机C、中等富铁颗粒与海底大量非稳态沉积和物理改造之间的良好平衡。这些性质促进了低SO4矿床中典型的非硫化自生矿物（铁碳酸盐、铁、铝硅酸盐）的形成，强烈影响了铁载体相成岩再活化/沉淀过程中微量元素的输出和储存，抑制了底栖生物群落和含壳动物。并对保存下来的沉积记录的性质产生重大影响。这些特征表明，亚马逊陆架可能类似于古代的铁石或绿地形成环境。影响这些过程的变量之间的关系将在亚马逊陆架和三角洲陆架地区进行研究。通过了解沉积物的化学相在这个河口沉积的过程，可以更好地表征其他河流/海洋系统。特别是，亚马逊陆架内泥中发生的铁和锰还原反应依赖于低有机C之间的平衡，陆架内泥依赖于低有机C、中等富铁颗粒、大量非稳态沉积和海底物理改造之间的平衡。在亚马逊陆架和三角洲陆架地区，将研究原位沉积进入历史地质记录的过程。

This research is part of the AmasSeds Project (A Multi- disciplinary Amazon Shelf Sediment Study), which seeks to understand the physical, chemical and geological processes that affect, or are affected by, particle fluxes on the Amazon shelf. High particulate fluxes occur on the Amazon shelf as a result of the enormous sediment discharge from the Amazon River and the extensive resuspension of fine-grained shelf sediment by tidal processes. This component of the research examines Fe and Mn reduction reactions occurring in Amazon inner shelf muds. The dominance of Fe and Mn reactions over SO4 reactions apparently results from a favorable balance between low organic C, moderately Fe-rich particles, and massive nonsteady-state deposition and physical reworking of the seabed. These properties promote the formation of nonsulfidic authigenic minerals (Fe-carbonates, Fe, Al-silicates) more typical of low SO4 deposits, strongly influence export and storage of minor/trace elements during diagenetic remobilization/ precipitation of Fe carrier phases, inhibit benthic communities and shell-bearing fauna, and have major consequences for the nature of the preserved sedimentary record. These characteristics suggest the Amazon shelf may be an analogue to ancient environments of ironstone or greensand formation. Relationships between the variables affecting these processes will be investigated in the Amazon shelf and delta-shelf region. By understanding the processes by which chemical phases of sediment are deposited in this estuary, other river/ocean systems can be better characterized. In particular, Fe and Mn reduction reactions occurring in Amazon inner shelf muds depend upon a balance between low organic C, inner shelf muds depend upon a balance between low organic C, moderately Fe-rich particles, massive nonsteady-state deposition and physical reworking of the seabed. The processes by which in situ precipitates enter the historical geological record will be investigated in the Amazon shelf and delta-shelf region.