Taphonomic Tiering: Preservational Constraints on Micro- and Macrofauna

沃克9628221保存和破坏海洋碳酸盐系统(例如，硬地、贝壳、生物礁、有孔虫测试)在古生物学和沉积学文献中占有重要地位，从保存贝壳硬质部分到通过各种物理和生物过程进行破坏。碳酸盐生产和销毁这一研究领域在生态和环境领域获得了更多的动力，并将与古生物学家一起提供关于现代环境和过去的全球碳收支的信息。回顾了海底海洋系统中两个重要的碳酸盐生产者(软体动物和有孔虫)的试验场埋藏学方面的相关文献，发现这些重要生物的大部分埋藏学工作主要涉及影响沉积物/水界面保存的过程，很少有人研究发生在沉积物-水界面以下和沉积物内部更深的过程。在这个界面和沉积物中，骨骼的硬质部分可能会被降解，并被回收或保存。人们对栖息在这些沉积物中的微生物和大型生物的降解速度知之甚少。这一建议直接解决了实验工作的需要，并重新评估了在浅层硅质碎屑环境中骨骼硬质部分先前估计的碳酸盐保留率。这项拟议的研究提供了解决软体动物贝壳、钙质和凝集的有孔虫和甲壳类外骨骼在不同深度的沉积物保留率的方法。此外，人们对这些坚硬部分如何在不同的地球化学环境中保存或降解知之甚少。这项为期3年的研究侧重于实验野外工作和孔隙水地球化学，将评估软体动物贝壳、甲壳类外骨骼的骨骼保留率和保存特征，以及在佐治亚州沿海选定的沉积环境的“挖掘学活动区”(TAZ)内对钙质和凝集性有孔虫的测试。将结合从沉积物表面到一米深的孔隙水分析来检查地块的坡度，以评估保存分层或“地块的分层”。这项拟议研究的目标是：1)通过海岸和河口环境中不同的硅质碎屑环境，记录骨骼保存随沉积物中埋藏深度的增加而变化的岩屑梯度。重要的是，我们将研究沉积物中不同的地球微生物带(利用孔隙水化学分析)如何影响骨骼部分的保存；2)评估沉积物中不同地点和深度的跨盐度梯度的地质特征；3)评估有孔虫和软体动物之间的生物降解或保存速度对规模的依赖程度；4)确定贝壳/测试微结构和矿物学对这些沉积环境中不同埋藏深度的保存的影响；以及5)利用亚化石沉积物对我们的现代发现进行测试，以根据现代研究确定是否在亚化石和化石河口环境中的贝壳或孔洞上保留地质微生物特征。关于无脊椎动物和原生生物保留率的实验数据将极大地加强对保存在岩石记录中的可比环境中的联系的古生态研究。

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.