HABITABLE ZONE DISTRIBUTION OF EARLY TRIASSIC RHYNCHONELLIFORM BRACHIOPODS IN THE DINWOODY BASIN OF THE WESTERN UNITED STATES

The deleterious environmental conditions that culminated with the end-Permian mass extinction event, such as marine anoxia and hydrogen sulfide poisoning, persisted globally through the Early Triassic (Isozaki, 1997; Grice et al., 2005). This continuation of marine environmental stress was a contributor to the near extinction and delayed recovery of rhynchonelliform brachiopod populations through the Early Triassic (Bottjer et al., 2008). The presence of near shore habitable zones provided temporary places of refuge from otherwise hostile open marine conditions (Beatty et al., 2008). These habitable zones would have varied in size and location relative to eustatic sea level fluctuations. We hypothesize that habitable zone variability ultimately determined paleoecological patterns (colonization, distribution, and extinction) of rhynchonelliform brachiopods in the Early Triassic Dinwoody Basin. For this study brachiopods were collected by bulk shell bed sampling from five localities dispersed throughout the Early Triassic Dinwoody Basin. Paleoenvironmental interpretations such as facies analysis and depositional trends were recorded from field observations and correlated with previous publications (Paull et al., 1989; Schock, 1981). Combining these data sets provided evidence necessary to interpret the paleoecological trends of rhynchonelliform brachiopods, from their initial appearance through to their extinction, which can be explained by the variable habitable zone hypothesis. Global brachiopod populations in the Early Triassic are poorly understood due to a lack of research, especially for the Western U.S. (Chen et al., 2005). The proper interpretation of the paleoecology of these brachiopods on a regional scale within the Dinwoody Basin will provide insight as to how brachiopods survived through the Early Triassic on a global scale. In times of environmental crisis like the end-Permian mass extinction, paleoecology and study of extinction survivability may serve as useful proxies for the current global warming and extinction stresses occurring in our oceans today.