Environmental disruptions influence taxonomic composition of brachiopod paleocommunities in the Middle Permian Bell Canyon Formation (Delaware Basin, West Texas)

Paleontologists have identified patterns of stability in the diversity and composition of communities over millions to tens of millions of years within the fossil record. It is unclear, however, what processes are responsible for controlling the stability observed in these communities--for example, local species interactions within communities, local species-environment relationships, immigration of species from the regional biota. This study tests whether the taxonomic composition of local brachiopod paleocommunities occupying a slope environment across a approximately 40 km (super 2) region remains temporally uniform over a 5.4 myr interval of time recorded by the Pinery, Rader, Lamar, and Reef Trail Members of the middle Permian (Capitanian) Bell Canyon Formation (BCF). Two third-order sequence boundaries have been previously recognized in this formation, indicating episodes of environmental disruptions related to sea-level fall within the basin that can induce habitat tracking or immigration events from other basins. Presence-absence data analyzed by cluster analysis, ordination techniques, and rank-occurrence plots demonstrate that compositional turnover occurs within the BCF. Change in composition of the Lamar Member paleocommunities documents the replacement of established brachiopods with new taxa, including the immigration of two new brachiopod genera from outside North America, indicating the influence of regional-scale effects on community assembly. The results based on metacommunity models suggest that dispersal plays an important role in the assembly of brachiopod paleocommunities in the Delaware Basin. Results also indicate that fossil communities provide useful information for interpreting placement of sequence boundaries and the magnitude of disruption.