Collaborative Research: Tropical Taphonomy and Porewater Geochemistry: Comparative Analysis of Molluscan Preservation in Siliciclastic and Carbonate Sediments, Western Carribean

小行星9628369 软体动物碳酸盐的死后命运受到生物和地球化学循环过程的影响，但对热带地区这些过程的速率和选择性知之甚少，也不知道它们对幸存的化石记录的净影响可能是什么。 了解这些现象是先决条件，无论是在使用埋藏破坏重建古环境条件（如taphophophaphiases标准），并在控制的偏见，古生态，古地理和进化分析。 这些问题也具有地球化学意义，因为壳材料的Sr同位素组成可能会受到有机质呼吸作用和孔隙沃茨中碳酸盐和硅酸盐矿物溶解所驱动的组成变化的影响。 这一拟议的西加勒比热带硅质和碳质沉积物的合作实地研究将主要集中在巴拿马的圣布拉斯群岛，其次是洪都拉斯的洛斯科奇诺斯大陆架;它建立在巴拿马博卡斯德尔托罗地区成功的埋藏学试点研究和佛罗里达湾碳酸盐沉积物中广泛的孔隙水工作的基础上。 这项研究将产生有关热带硅质碎屑的埋藏模式和过程的第一批资料，这些碎屑约占低纬度现代大陆架地区的一半，并将首次对单一区域内富铁（硅质碎屑）和贫铁沉积物（碳酸盐）的碳酸盐反应性和孔隙水演化进行测试。 该研究将量化：1。作为物理环境的函数的死亡双壳类壳的死后损伤（例如，水深、粒度、沉积速率（由Pb-210测定），包括钻孔、结壳、圆化、表面退化和破碎的频率; 2.死后损害作为孔隙水化学的函数，特别是控制碳酸盐溶解和重结晶速率的碳酸、主元素和次元素以及硫系统参数;样品还将允许测定孔隙水中的稳定同位素（C S）和87 Sr/86 Sr成分，以评估孔隙水化学如何影响有和没有微结构改变的壳材料的同位素特征;& 3.埋藏破坏的选择性作为双壳类分类学、生活习性、矿物学和显微结构的函数，以及这些因素相对于环境力量在确定死亡组合条件和偏差的地理变异中的重要性; 4.时间平均尺度的环境变化，地层无序，以及贝壳损坏和贝壳死亡后年龄之间的关系（即，（a）对埋藏钟的测试），特别是作为沉积速率、溶解速率、局部壳输入的组成和其他环境排列变量的函数;以及 5.在特定条件下的贝壳降解速率和途径，使用长达3年的贝壳实验阵列;这是测试贝壳破坏的选择性和控制的确证手段，对化石组合的成分保真度有影响。

9628369 Walter The post-mortem fate of molluscan carbonate is influenced by processes of biological and geochemical recycling, but little is known about the rates and selectivities of these processes in the tropics, nor what their net effect on the surviving fossil record might be. Understanding these phenomena is pre-requisite both in using taphonomic damage to reconstruct paleoenvironmental conditions (e.g. taphofacies criteria) and in controlling for bias in paleoecologic, biogeographic, and evolutionary analyses. These issues also have geochemical significance, because Sr isotope compositions of shell material may be affected by compositional changes driven by organic matter respiration and by carbonate and silicate mineral dissolution in pore waters. This proposed collaborative field study of tropical siliciiclastic and carbon sediments of the western Caribbean will focus primarily on the San Blas Archipelago of Panama, and secondarily on the Los Cochinos shelf of Honduras; it builds on a successful taphonomic pilot study in the Bocas del Toro area of Panama, and extensive pore-water work in carbonate sediments of Florida Bay. This research will produce the first information on taphonomic patterns and processes in tropical siliciclastics, which constitute about half of modern shelf areas in low latitudes, and will permit the first test of carbonate reactivies and pore-water evolution in both Fe-rich (siliciclastic) and Fe-poor sediments (carbonates) within a single region. The research will quantify: 1. post-mortem damage on dead bivalve shells as a function of physical environment (e.g., water depth, grain size, sedimentation rate as determined by Pb-210), including frequency of boring, encrustation, rounding, surface degradation, and fragmentation; 2. post-mortem damage as a function of pore-water chemistry, particularly carbonic acid, major and minor element, and sulfur system parameters that govern rates of carbonate dissolution and recrystallization; samples will also permit determination of stable isotope (C & S) and 87Sr/86Sr compositions in pore-waters to assess how pore-water chemistry influences the isotopic signatures of shell material with and without microstructural alteration; 3. selectivity in taphonomic destruction as a function of taxonomy, life habit, mineralogy and microstructure of bivalves, and the importance of these factors relative to environmental forces in determining geographic variation in death assemblage condition and bias; 4. environmental variation in scales of time-averaging, stratigraphic disordering, and relationships between shell damage and shell age-since-death (i.e., test for a taphonomic clock), especially as a function of sedimentation rate, dissolution rate, composition of local shell input, and other environmentally arrayed variables; and 5. rates and pathways of shell degradation under specific conditions, using experimental arrays of shells deployed over periods up to 3 years; this a corroborative means of testing for selecitivities in and controls on shell destruction, with implications for compositional fidelity of fossil assemblages.