Assessing soft tissue preservation in a variety of saline Environments through actualistic decay experiments and an isotopic assessment of pyritized plant fossils from the Mazon Creek, IL

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Most taphonomic pathways for soft-tissue preservation require minerals either forming on the surface of or replacing tissues. Among various other factors, the rates at which these reactions occur impact the quality of fossil preservation. Generally, rapid mineral precipitation has the potential to retain finer morphological features, whereas slower reactions allow for significant information loss through decay. In aqueous settings, such reaction rates can be affected by the abundance of dissolved ions (ionic strength). To determine the influence of salinity within preservation pathways, two research projects were conducted. ... The second project focused on Mazon Creek deposits which are well known for containing fossils from two distinct environments: the Essex fauna from a marine setting, and the Braidwood flora and fauna from brackish water. As a result, the collection of Mazon Creek deposits show a transition from lower salinities to a fully marine environment. Before the effect of differing salinity on the overall quality of Mazon Creek fossils can be determined, a solid understanding of the nodule formation needs to be obtained. To investigate the concretion formation, the pyrite in three woody plant Mazon Creek fossils where analyzed for the 34S isotopic ratios through Secondary Ion Mass Spectrometry (SIMS). Vertical and horizontal transects (relative to the fossil surface) were collected on each pyrite section. Area images were also collected on sample 102B and isotopic data was collected on the areas with high 34S counts. In addition, the species distribution of an undescribed Mazon Creek deposit, the Sun Spot Mine, is shown and determined to be similar to the Essex fauna.