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.
