EXPERIMENTAL TAPHONOMY WITH WET-CHEMISTRY MICROSENSORS AND GENETIC ANALYSES CRACKS A TAPHONOMIC WINDOW AJAR

There are many pathways which soft-bodied organisms can take to enter the fossil record, leading to different taphonomic expressions such as kerogenization, phosphatization, and pyritization, to name a few. These expressions assist in capturing paleontological information crucial to taxonomy, paleobiology, and the anchoring of dates and character states for genetic clocks and phylogenies. Burgess Shale-type preservation is one of the best known and most-celebrated soft-bodied preservation modes, with many hypotheses as to its formation. Among the more compelling hypotheses is that of Gaines et al. (2012), wherein fauna are deposited in turbidity currents, becoming entrapped in clays and subsequently entombed by a calcite seal that forms because of heightened calcium and alkalinity levels in the Cambrian ocean.

Experimental decay helps to groundtruth the feasibility of taphonomic hypotheses describing the soft-bodied fossil record, and here we conduct experiments to test the calcite-seal generation hypothesis. Our experiments buried individual peppermint shrimp, Lysmata wurdemanni, in jars with kaolinite and submerged in seawater of varying composition (specifically, levels of calcium) in both anoxic and aerobic settings to observe (1) whether calcite seals would form in the fine clay, and (2) how the microchemistry and microbiology of the water and sediments varied with differing treatment parameters.

Results have been intriguing and, at times, counterintuitive. For example, replicates in calcium-amended seawater have slightly lower pH than their seawater counterparts, and some of the highest sulfide levels have been found in aerobic shrimp-bearing jars. Principal coordinate analysis shows strong differentiation between the microbial communities in seawater and calcium-amended seawater in shrimp-bearing replicates. Microchemically, the strongest differentiations are between the water column and the sediment, with subtle variations in the sediment and a nearly homogeneous water column. In no case have calcite layers been observed to form in the upper layers of the kaolinite. These experiments serve to highlight the varied and unexpected insights experimental taphonomy can provide, and that it is a critical aspect of hypothesis evaluation in soft-bodied preservation.