FAUNAL AND GEOCHEMICAL CHANGES ACROSS THE NORIAN-RHAETIAN BOUNDARY IN EASTERN PANTHALASSA: RAMPING UP TO THE END-TRIASSIC MASS EXTINCTION

The Triassic Period ends with one of the most severe mass extinctions of the Phanerozoic, but increasing evidence indicates that elevated biotic turnover and paleoecological restructuring occurred throughout the short Rhaetian Stage and possibly in the latest Norian (Late Triassic). However, the fossil record of the Norian-Rhaetian boundary interval is poorly understood in the benthic realm. Here, we present bulk sample data collected from the upper Nun Mine and lower Mount Hyatt members of the Gabbs Formation in western Nevada, representing the late Norian through the early Rhaetian in eastern Panthalassa. The faunal succession from this shallow marine depositional sequence suggests that the environmental perturbations that caused a significant turnover in the pelagic realm had a minimal effect on the diversity of the benthic systems, but paleoecological shifts across the boundary interval include the rapid decline of important middle and late Norian eco-groups, including the cementing bivalves. These changes correspond with a strontium isotope excursion indicating a major shift in weathering products which continued into the Early Jurassic. A clear understanding of the faunal succession leading into the End-Triassic mass extinction interval is imperative for accurately defining biotic effects of the environmental perturbations on marine ecosystems and the duration of the recovery.