Carbonate-Associated Sulfate in Modern Sediments of South Florida: Diagenetic Relationships

南佛罗里达现代沉积物中碳酸盐伴生硫酸盐：成岩关系地球上和地球附近硫的生物地球化学循环。S的表面是紧密相连的。通过一系列复杂的反馈。环境氧化还原条件，包括大气中氧气的可用性。我们描述和量化这些循环以及相关生物圈影响的能力取决于细菌硫酸盐还原过程中32S相对于34S的强烈优先利用。从历史上看，通过监测海洋的34S，可以估计出关键氧化还原途径相对量级的时间趋势，这在有限的石膏沉积记录中得到了体现。因此，模型只能和数据一样好，而这些数据甚至不能为大多数前寒武纪提供最小的约束。在地球上。在早期历史中，石膏沉积较少，风化脆弱，保存较差。鉴于这些并发症，碳酸盐相关硫酸盐或CAS作为一种有前景的新重晶石方法的补充，但通常不会与之重叠，已成为一种可行的替代方案。CAS通常以百万分之几百到几千的浓度出现，是大多数石灰石和白云岩的组成部分，对古代海水硫酸盐的连续、高分辨率记录显示出很大的希望。对该方法的兴趣正在达到顶峰，但应用远远超过了跟踪CAS基本系统和通过成岩作用潜在的海水信号损失的研究。尽管CAS在古代沉积物中取得了令人鼓舞的初步结果，但在现代环境中，控制因素更容易受到独立约束，因此没有系统地尝试在现代环境中测试该方法。此外，现代校准的任何尝试都忽略了地质记录中最丰富的碳酸盐成分的前兆——碳酸盐岩泥。以及成岩作用的影响。拟议研究的主要目的是了解CAS如何在南佛罗里达的现代碳酸盐沉积物中被合并、分布和保存。具体来说，我们将在佛罗里达湾和礁岛向海的泻湖地点仔细选择一组特征鲜明的沉积环境，观察同位素和浓度趋势。由此产生的多样性转化为控制硫循环的参数的时空梯度，如易失性有机化合物的有效性、盐度以及沉积物的物理和生物特性。在一个演化的孔隙水硫酸盐储层范围内，在早期成岩时间尺度上，在经历碳酸盐溶解、沉淀和矿物转化的大量泥浆样品中记录的海水同位素信号的整体保真度如何？尽管我们认识到现代和古代环境之间存在着深刻的差异，但正是这些大块的泥浆样本将阐明在哪些条件下原始信号可能被保存下来，也可能被不保存下来。各种较粗的骨骼成分也将被追踪，从生命到埋葬，一直到几米深。里昂促成了这些目标。在包括南佛罗里达在内的现代环境中工作的经验，尽管所提出的许多问题将源于测试古环境代理的稳健性的最终目标。尤其是里昂。过去在沉积成岩作用、碳酸盐沉积学/地球化学和硫地球化学方面的工作将是最有帮助的。这项研究的重点。根据小组在审查本提案的早期版本后的要求，将允许我们在严格的有机和无机地球化学背景下跟踪CAS。多组分方法，包括速率测量、浓度和同位素测定，用于广泛的相关物种，旨在提供生物地球化学硫质量平衡，以了解活性碳酸盐颗粒中硫酸盐的ppm水平。最后，CAS可以帮助填补许多空白。Claypool曲线。通过使用从最古老的岩石中提取的浅水碳酸盐岩的连续剖面。但就像所有的碳酸盐代用物一样，我们的解释只能与我们对多种成岩途径的理解一样好。

Carbonate-Associated Sulfate in Modern Sediments of South Florida: Diagenetic Relationships Biogeochemical cycling of sulfur at and near the earth.s surface is intimately linked.through a complex set of feedbacks.to ambient redox conditions, including the availability of atmospheric oxygen. Our ability to delineate and quantify these cycles and the associated biospheric impacts hinges on the strong preferential utilization of 32S relative to 34S during bacterial sulfate reduction. Historically, temporal trends in the relative magnitudes of critical redox pathways have been estimated by monitoring the 34S of the ocean as manifested in a limited sedimentary record of gypsum. Consequently, the models are only as good as the data, which fail to provide even minimal constraints for most of the Precambrian. During the earth.s early history, gypsum deposition was less abundant, and preservation is poor due to its vulnerability during weathering. In light of these complications, carbonate-associated sulfate or CAS, which is complementary to but generally not overlapping with a promising new barite approach, has emerged as a viable alternative. CAS, which often occurs at concentrations of hundreds to thousands of ppm, is a component of most limestones and dolostones and shows great promise for continuous, high-resolution records of ancient seawater sulfate. Interest in the method is peaking, yet applications greatly outnumber studies tracking even the basic systematics of CAS and the potential loss of seawater signals through diagenesis. Despite encouraging initial results for CAS in ancient sediments, no systematic attempt has been made to test the method in a modern setting where the controlling factors are more easily and independently constrained. Furthermore, any attempts at modern calibration have neglected the precursor of the most abundant carbonate component of the geologic record.carbonate mud.and the effects of diagenesis. The primary objective of the proposed study is to understand how CAS is incorporated, distributed and preserved in modern carbonate sediments in south Florida. Specifically, we will observe isotopic and concentration trends across a carefully chosen set of well-characterized depositional settings in Florida Bay and at lagoonal sites seaward of the Keys. The resulting diversity translates into spatial and temporal gradients in the parameters that control sulfur cycling, such as the availability of labile organic compounds, salinity and the physical and biological properties of the sediment. What is the overall fidelity of the seawater isotopic signal recorded in bulk mud samples that are undergoing carbonate dissolution, precipitation and mineral transformations on early diagenetic time scales within the confines of an evolving pore-water sulfate reservoir? Although we recognize the profound differences between modern and ancient settings, it is these bulk mud samples that will illuminate the conditions under which primary signals may or may not be preserved. Various coarser sketetal components will also be tracked from life through burial to depths up to several meters. These goals are facilitated by Lyons. experience working in modern settings, including south Florida, although many of the questions asked will stem from the ultimate goal of testing the robustness of a paleoenvironmental proxy. In particular, Lyons. past work with sediment diagenesis, carbonate sedimentology/geochemistry and sulfur geochemistry will be most helpful. The tight focus of this study.as requested by the panel following review of an earlier version of this proposalwill allow us to track CAS within a rigorous organic and inorganic geochemical context. The multi-component approach, including rate measurements and concentration and isotopic determinations for a wide range of relevant species, is designed to provide the biogeochemical sulfur mass balance necessary for understanding ppm levels of sulfate within reactive carbonate grains. In the end, CAS may help fill the many gaps in the .Claypool curve. through use of continuous sections of shallow-water carbonates from even the oldest rocks. But as with all carbonate proxies for ancient seawater, our interpretations are only as good as our understanding of the multiple diagenetic pathways.