TRACING THE PERMIAN-TRIASSIC EXTINCTION: PALEOENVIRONMENTAL PATTERNS ACROSS THE WESTERN UNITED STATES DURING THE LATE PALEOZOIC AND EARLY MESOZOIC

The Permian-Triassic boundary (PTB) marks Earth's most profound mass extinction event, with an estimated 87% to 95% of marine and terrestrial species extinct. Despite extensive global studies, the biostratigraphic and chronostratigraphic details of the PTB in the western United States remains less well explored than other regions. This study investigates the biostratigraphic framework, depositional environments, and temporal correlations of key stratigraphic units across the western U.S., elucidating the paleogeography from the late Guadalupian (260 Ma) to the end of the early Triassic Olenekian (246.7 Ma). This interval witnessed significant regression linked to peak global warming at the PTB (252 Ma) and extensive terrestrial denudation post-extinction. Our findings suggest that this regression, represented by the transition from regional limestones of the Kaibab, Park City, Phosphoria and other formations to red shales in the regional Moenkopi and Chugwater formations, was driven by a massive and abrupt influx of sediments, effectively closing the former ocean seaway that extended into Kansas and Nebraska during the Permian. This event created large scale sabkha depositional environments along the now arid coastal plains. A notable exception is the persistent seaway into central Utah, which provides a unique continuous nearshore and marine record, offering critical insights into the ecological repercussions of the PTB extinction. This study aims to clarify the paleontological impacts obscured by rapid, climate-driven environmental shifts in the region, and how these paleogeographic insights integrate with contemporary interpretations of the mass extinction's severity in the American West.