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

南佛罗里达州现代沉积物中与碳酸盐相关的硫酸盐：成岩关系

• 批准号: 0207565
• 负责人: Timothy Lyons
• 金额: $ 12.32万
• 依托单位: University of Missouri-Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0207565&HistoricalAwards=false
• 关键词: Carbonate; Associated; Sulfate; Modern; Sediments

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.

南佛罗里达现代沉积物中的碳酸盐伴生硫酸盐：成岩关系地球表面和附近的硫的生物地球化学循环通过一套复杂的环境氧化还原条件（包括大气氧的可用性）密切相关。feedbacks.to 我们能够描绘和量化这些周期和相关的生物圈影响取决于细菌硫酸盐还原过程中32 S相对于34 S的强烈优先利用。 从历史上看，关键氧化还原途径的相对大小的时间趋势已经通过监测海洋的34 S来估计，这表现在石膏的有限沉积记录中。 因此，模型只能和数据一样好，而数据甚至不能为前寒武纪的大部分地区提供最小的限制。 在地球的早期历史中，石膏沉积物并不丰富，并且由于其在风化过程中的脆弱性而保存不佳。 鉴于这些复杂性，碳酸盐相关硫酸盐或CAS，这是一个有前途的新的重晶石方法的补充，但通常不重叠，已成为一个可行的替代方案。 CAS通常以数百至数千ppm的浓度存在，是大多数石灰岩和白云岩的组成部分，并显示出对古海水硫酸盐的连续，高分辨率记录的巨大希望。 人们对该方法的兴趣正在达到顶峰，但应用的数量远远超过了跟踪CAS的基本系统学和海水信号在成岩作用中的潜在损失的研究。 尽管令人鼓舞的CAS在古代沉积物中的初步结果，没有系统的尝试，以测试在现代环境中的控制因素更容易和独立的约束的方法。 此外，任何现代校准的尝试都忽略了地质记录中最丰富的碳酸盐成分的前体-碳酸盐泥和成岩作用的影响。 该研究的主要目的是了解CAS是如何在南佛罗里达现代碳酸盐沉积物中被整合、分布和保存的。 具体来说，我们将观察同位素和浓度的趋势，在一个精心选择的一套良好的特点沉积设置在佛罗里达湾和泻湖网站海的钥匙。 由此产生的多样性转化为控制硫循环的参数的空间和时间梯度，如不稳定有机化合物的可用性、盐度以及沉积物的物理和生物特性。 在不断变化的孔隙水硫酸盐储层的范围内，在早期成岩时间尺度上经历碳酸盐溶解、沉淀和矿物转化的散装泥浆样品中记录的海水同位素信号的总体保真度是多少？ 虽然我们认识到现代和古代环境之间的深刻差异，但正是这些大量的泥浆样本将阐明原始信号可能或可能不被保存的条件。 还将对各种较粗的碎屑组分进行跟踪，从生活到埋藏，深度可达数米。 这些目标是由里昂推动的。在现代环境中工作的经验，包括南佛罗里达，虽然所问的许多问题将源于测试古环境代理的鲁棒性的最终目标。 尤其是里昂。过去在沉积物成岩作用、碳酸盐沉积学/地球化学和硫地球化学方面的工作将非常有帮助。 专家组在审查了该提案的早期版本后要求的study.as的紧密关注将使我们能够在严格的有机和无机地球化学背景下跟踪CAS。 多组分方法，包括速率测量和浓度和同位素测定范围广泛的相关物种，旨在提供必要的地球化学硫质量平衡，了解ppm水平的硫酸盐在活性碳酸盐颗粒。 最后，CAS可能有助于填补克莱普尔曲线中的许多空白。即使是最古老的岩石，也能通过使用连续的浅水碳酸盐岩切片。但是，正如所有的碳酸盐替代物的古代海水，我们的解释是一样好，我们的理解的多成岩途径。