Diagenetic Processes and Authigenic Mineral Formation in Amazon Shelf Sediments

这项研究是AmasSeds项目(亚马逊大陆架沉积物多学科研究)的一部分，该项目试图了解影响亚马逊大陆架颗粒通量或受其影响的物理、化学和地质过程。由于亚马逊河的巨大泥沙排放和潮汐过程对细粒陆架沉积物的广泛再悬浮，亚马孙大陆架上出现了高颗粒物通量。该研究的这一部分考察了亚马逊内陆架泥浆中发生的铁和锰还原反应。铁和锰反应对SO4反应的优势显然是低有机碳、中等富铁颗粒和海床大量非稳态沉积和物理改造之间的有利平衡的结果。这些性质促进了更典型的低SO4矿床的非硫化物自生矿物(Fe-碳酸盐、Fe、Al-硅酸盐)的形成，强烈影响了铁载体相成岩再动员/沉淀过程中微量/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铁岩或绿砂形成的环境。将在亚马逊陆架和三角洲陆架区域调查影响这些过程的变量之间的关系。通过了解该河口沉积物的化学相沉积过程，可以更好地描述其他河流/海洋系统的特征。特别是，亚马逊内陆架泥浆中发生的铁和锰还原反应取决于低有机碳之间的平衡，内陆架泥浆取决于低有机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。将在亚马逊陆架和三角洲陆架地区调查原地降水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.