FACTORS INFLUENCING FOSSIL PRESERVATION IN THE PENNSYLVANIAN KEECHIE CREEK SHALE OF MINERAL WELLS, TEXAS

A goal of community paleoecology is to investigate the distribution of organisms through geologic time. By studying high-resolution changes in fossil communities, we can understand what structured past ecosystems, and predict how modern ecosystems will respond to human influence. To determine the efficacy of the fossil record for evaluating paleocommunity distributions and changes through time, paleontologists need to test for potential taphonomic effects on how these paleocommunities are perceived. Here, we compare the total amount of fossil material through five stratigraphic beds in the Late Pennsylvanian Keechie Creek Shale of Texas to evaluate potential taphonomic and environmental controls on fossil preservation potential. We collected five 4 L bulk sediment samples every 0.4m stratigraphically at Mineral Wells Fossil Park. We sorted the material, identified to genus, and counted all specimens of the abundant brachiopods Crurithyrus, Rhipidomella, and Neochonetes >2mm, as a proxy for total fossil material.

There is a marked increase in fossil material upsection. Sample 0.0m had 110 total specimens, 0.4m had 380, 0.8m had 663, 1.2m had 1203, and 1.6m had 935. The increase was greatest in Crurithyrus, which might indicate real ecological change. The chemical compositions of five sediment samples were measured via handheld x-ray fluorescence spectroscopy. While samples were generally similar, the horizon showing the greatest fossil abundance (sample 1.2m) also contained less total calcium than surrounding samples. This suggests that slightly more siliciclastic facies, which may represent rapid depositional events or minor transgressive lags, are more favorable for fossil preservation than more calcareous shales. To further evaluate which of the three factors (taphonomic, ecological, environmental) is driving the variation we see through the samples, we will include additional samples upsection and incorporate other proxies for fossil abundance and community composition.