LOCAL BRACHIOPOD DIVERSITY IN THE PINERY AND RADER MEMBERS OF THE BELL CANYON FORMATION, GUADALUPE MOUNTAINS NATIONAL PARK, WEST TEXAS

Diversity patterns in the fossil record reflect ecological dynamics that govern the distribution and relationship of species through geologic time. Understanding the structure of local communities will gain insight into the dynamics responsible for producing local, regional, and global diversity patterns. This study compares the diversity and taxonomic composition of brachiopods between the Pinery and Rader Members of the Bell Canyon Formation (Guadalupian, Middle Permian) in the Delaware Basin of West Texas. The Bell Canyon Formation records deposition on the slope by sediment-gravity flows seaward of the Permian Reef complex. The Pinery is the basinal equivalent of the Seven Rivers Formation on the shelf, and the Rader is the basinal equivalent of the Yates Formation. Bulk samples of fossilized local communities (2–6 kg of limestone each) were collected from the Pinery and Rader at four geographic locations within Guadalupe Mountains National Park. Silicified fossils were extracted from limestone by immersion in 10% HCl in a basin lined with ~850µ mesh. Whole and fragmented brachiopods were identified to the generic level; for fragmented material, only brachiopods hinges were used for taxonomic identification. Brachiopod diversity was measured as species richness and rank abundance, and ordination techniques were employed to assess changes in taxonomic composition. Additionally, size-frequency distributions were generated to determine the effect of size sorting. Preliminary results indicate that brachiopod communities within the Pinery changed from communities dominated by Hustedia and several genera of punctate spirifers to communities where chonetids, rhynchonellids, and Composita are common. These results imply a change in environment on the slope, or, that different areas of brachiopod communities are being sampled by debris flows on the slope. This analysis will provide fundamental information on the diversity of communities in the Pinery and Rader Members during progradation of the platform through this interval.