Ocean Acidification and Prolonged Anoxia during the End-Triassic Mass Extinction: Insights from the Qiangtang Basin, Eastern Tethys

Abstract: The End-Triassic Mass Extinction (ETE) exerted a profound impact on marine ecosystems. It is widely accepted that the primary trigger was the massive volcanic eruptions of the Central Atlantic Magmatic Province (CAMP). While environmental perturbations during this event have been extensively documented in the Western Tethys, high-resolution studies in the Eastern Tethys remain limited. This study presents a continuous Triassic-Jurassic marine succession from the Qiangtang Basin in Tibet, China. A high-precision geochronological framework was established by integrating U-Pb zircon dating with cyclostratigraphic tuning. Based on boron isotope  analysis of brachiopod fossils, we reconstructed the seawater pH, which revealed a prominent negative excursion synchronous with the carbon isotope  shift, providing robust evidence for ocean acidification during the ETE. Furthermore, uranium isotope data exhibit a negative excursion with a longer duration than that of boron isotopes, suggesting that marine anoxia persisted far beyond the interval of acidification. Our findings indicate that both ocean acidification and anoxia were direct drivers of the mass extinction; however, they played distinct roles: acidification primarily triggered the initial biotic crisis, whereas prolonged anoxia hindered the subsequent biotic recovery. The recurrence of coupled ocean acidification and anoxia, linked to global carbon cycle perturbations, represents a recurring mechanism for catastrophic ecological impacts throughout Earth's history.