Taphonomic Tiering: Preservational Constraints on Micro- and Macrofauna

海洋碳酸盐系统的保存和破坏（如硬地层、贝壳、珊瑚礁、有孔虫试验）在古生物学和沉积学文献中占有重要地位，从贝壳硬体的保存到各种物理和生物过程的破坏。碳酸盐的产生和破坏这一研究领域在生态和环境领域获得了更大的动力，并与古生物学家一起，将提供关于现代环境和过去环境中全球碳预算的信息。通过对两种重要的碳酸盐生产生物（软体动物和有孔虫）的底栖海洋系统实验领域埋藏学相关文献的回顾，发现大多数关于这些重要生物的埋藏学工作主要关注影响沉积物/水界面保存的过程，而很少研究发生在沉积物-水界面以下和沉积物内部的过程。在这个界面和沉积物中，骨骼硬体可能被降解、再循环或保存。人们对居住在这些沉积物中的微生物和微生物的降解速度知之甚少。该建议直接解决了对实验工作的需求，并重新评估了先前估计的浅层硅塑性环境中骨骼硬部件的碳酸盐保留率。本研究提供了解决软体动物外壳、钙质和凝集有孔虫以及甲壳类外骨骼在沉积物中不同深度的保留率的方法。此外，人们对这些硬物是如何在不同的地球化学环境中保存或降解的知之甚少。强调实验现场工作和孔隙水地球化学，这项为期3年的研究将评估软体动物外壳和甲壳类外骨骼的骨骼保留率和保存特征，并在佐治亚州沿海选定的沉积环境中对“埋藏活化带”（TAZ）内的钙质和凝集有孔虫进行测试。埋藏梯度将与从沉积物表面到一米深的孔隙水分析一起进行检查，以评估保存分层或“埋藏分层”。本研究的目标是：1)在沿海和河口不同的硅质碎屑环境中，记录骨骼保存的埋藏深度随沉积物埋深的增加而呈现的埋藏梯度。重要的是，我们将研究沉积物中不同的地质微生物区（使用孔隙水化学分析）如何影响骨骼硬部件的保存；2)评估沉积物中不同位置和深度的不同盐度梯度的埋藏学特征；3)评估有孔虫和软体动物在体积上对降解或保存速度的依赖；4)确定不同埋藏深度下壳/试壳微观结构和矿物学对保存的影响；5)用亚化石沉积物检验我们的现代发现，根据现代研究，确定亚化石和化石河口环境中的贝壳或有孔虫是否保留了地质微生物特征。无脊椎动物和原生生物保留率的实验数据将大大加强岩石记录中保存的可比环境的古生态学研究。

Walker 9628221 Preservation and destruction of marine carbonate systems (e.g., hardgrounds, shells, reefs, foraminiferan tests) has figured prominently in the paleontological and sedimentological literature from the preservation of shelly hardparts thorough time to destruction by various physical and biological processes. This area of research , carbonate production and destruction, is gaining more momentum in ecological and environmental fields, and in conjunction with paleontologists, will provide information on global carbon budgets both in modern environments and for the past. A review of the pertinent literature in experimental field taphonomy from benthic marine systems focusing on two important carbonate producers (mollusca and foraminifera), revealed that most taphonomic work on these important organisms primarily concerns the processes that affect preservation at the sediment/water interface, and rarely are processes examined which happen below the sediment-water interface and deeper, within the sediments. At this interface and within the sediments, skeletal hardparts are presumably degraded and recycled or preserved. Little is known about the rate of degradation on micro- and macroorganisms that inhabit these sediments. This proposal directly addresses the need for experimental work and a reevaluation of the previously estimated carbonate retention rates of skeletal hardparts in shallow, siliciclastic settings. This proposed research provides methods to address retention rates at varying depths within the sediments for molluscan shells, calcareous and agglutinated foraminifera and crustacean exoskeletons. Additionally, little is known about how these hardparts are preserved or degraded in varying geochemical milieus. Emphasizing experimental field work and porewater geochemistry, this proposed 3-year study will evaluate skeletal retention rates and preservational signatures of molluscan shells, crustacean exoskeletons, and tests of both calcareous and agglutinated foramin ifera within the "taphonomically active zone" or TAZ, of selected depositional settings of coastal Georgia. Taphonomic gradients will be examined in conjunction with porewater analyses from the sediment surface to a depth of one meter to assess preservation stratification or "taphonomic tiering." Goals of this proposed research are 1) document taphonomic gradients of skeletal preservation with increasing burial depths in the sediments, across different siliciclastic environments within coastal and estuarine settings. Importantly, we will study how the different geomicrobial zones (using porewater chemistry analyses) within the sediments affect preservation of skeletal hardparts; 2) assess taphonomic characteristics across salinity gradients at different localities and depths within the sediments; 3) assess scale dependency, with regard to size, of taphonomic rates of degradation or preservation between foraminiferans and molluscs; 4) determine the effects of shell/test microstructure and mineralogy on preservation at different burial depths in these depositional settings; and 5) test our modern findings with a subfossil deposit to determine if geomicrobial signatures are retained on shells or forams in subfossil and fossil estuarine environments in light of the modern studies. Experimental data on invertebrate and protist retention rates would greatly enhance paleoecological studies on associations from comparable settings preserved in the rock record.