PALEOECOLOGY OF THE PENNSYLVANIAN KEECHIE CREEK SHALE OF MINERAL WELLS, TEXAS

Community paleoecology investigates the distribution of organisms through ecological 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. The Pennsylvanian of Texas is characterized by cyclical deposition of sandstone, coal, black shale, limestone, and gray shale, in repeated successions known as cyclothems. The gray shale lithofacies often contain well-preserved and abundant benthic fauna. The consistency and repetition of the grey shales allow us to test richness, evenness, and relative abundances of taxa. The richness, evenness, and relative abundance of taxa will enable us to learn more about the environment it was taken from and help us understand what was happening.

We collected four 4 liter bulk sediment samples (every 0.5m vertically) from the Keechie Creek Shale at Mineral Wells Park (MWP) in north Texas to compare with other grey shale assemblages from previous studies of the Midland Basin. We sorted, identified to genus, and counted all specimens >2mm. In the MWP section, we found uniform richness (17, 15, 16, and 16) from bottom to top of the section. Evenness was 0.43, 0.23, 0.35, and 0.39 up section. Brachiopods dominated all samples; Relative abundance (RA) of brachiopods was 84%, 95%, 97%, and 97% upsection. Bivalves had their highest RA in the lowest stratigraphic (6%). The decrease in the RA of bivalves upsection is the opposite of a prior study of the Finis Shale, a slightly younger member of the Midland Basin. The brachiopod Crurithyris increased in RA upsection: 5%, 3%, 46%, 58%. This parallels a decrease in the brachiopod Neochonetes upsecton: 73%, 88%, 50%, 33%. Both trends also contrast with prior research on the Finis Shale. This suggests that the changes through time in the grey shale depositional environments were driven by different mechanisms at various times in the Midland Basin. We will be further exploring if these changes are driven by ecological, environmental, or taphonomic processes.