PERMIAN BRACHIOPOD COMMUNITIES OF WEST TEXAS I: COMMUNITY PALEOECOLOGY

The Permian Basin of West Texas is geologically well explored and contains exceptionally well-preserved silicified faunas. The brachiopods were thoroughly and consistently described by G. Arthur Cooper and Richard Grant, yet they have not been studied paleoecologically, nor have they been studied in the context of the available sequence stratigraphic framework. We have analyzed the distributions of 731 brachiopod species within the Glass Mountains in the southern part of the basin (264 Wolfcampian; 172 Leonardian; 312 Guadalupian). Despite claims that the brachiopods were over-split taxonomically, the number of single occurrences is not statistically different from modern benthic foraminifera or from late Cretaceous mollusks. The Chao2 estimator of total species richness suggests that 87% of all Wolfcampian species were sampled, but only 64% of the Leonardian and 61% of the Guadalupian. None of the analyses suggest that sampling, silicification, or taxonomic analysis has biased the overall fauna to preclude paleoecological analysis. Rarefaction based on the number of occurrences of genera confirms that high-diversity assemblages occurred throughout the study interval, and in both the Glass and Guadalupe Mountains. However, the species-level rarefactions based on occurrences reveal that 4 of the 5 most diverse assemblages are from the Glass Mountains suggesting the presence of a species richness gradient in the brachiopod faunas of the Delaware Basin. A subset of 191 localities (including 512 species and 142 genera) from the Leonardian and lower Guadalupian of the Glass Mountains samples four third-order depositional sequences. Ordination of these brachiopod data indicates that each third-order sequence has a distinctive suite of brachiopod species even though a similar range of carbonate ramp habitats was sampled. Overall, these data and similar analyses of other taxonomic groups provide an exceptional opportunity to reconstruct the paleoecology of a complex marine ecological landscape and how it changed over evolutionary timescales.