Geochemical studies of marine sediments indicate that most Oceanic Anoxic Events (OAEs) appear coincident with Large Igneous Province (LIP) volcanism. OAE 1d records peculiar paleoceanographic changes and global carbon cycle perturbations, however, its association with volcanism has not yet been supported by robust geochemical evidence. To examine the potential role of volcanism we investigated the mercury (Hg) concentration and isotopic record of OAE 1d interval at the Youxia section, southern Tibet. The interval prior to OAE 1d is marked by a combined positive Delta Hg-199 and Hg content shift, which suggests a volcanic Hg source. These findings are consistence with a prominent increase in sea surface temperatures and atmospheric CO2 before OAE 1d. We suggest that eruption of the central portion of the Kerguelen LIP may have been the main source of the Hg anomaly and resulted in global environment perturbations that drove the onset of the anoxia event.

Plain Language Summary The mid-Cretaceous is characterized by globally high temperature, sea-level, and atmospheric CO2. Recurrent volcanism considered to be the main driver of the Cretaceous hothouse, led also to frequent ocean anoxia events and global carbon cycle perturbations. One such perturbation is oceanic anoxic event (OAE) 1d; however, unlike other OAEs its association with volcanism has not yet been proven. Mercury (Hg) is mainly sourced from volcanism, and enhanced volcanic activity is recorded as spikes in Hg concentration in marine sediments. We used multiple geochemical proxies, especially Hg chemical analyses, to examine the potential role of volcanism in the OAE 1d event. Based on the data, we find a volcanic derived Hg anomaly occurred just prior to the onset of the OAE. These findings are in agreement with a prominent increase in sea surface temperatures and atmospheric CO2 at the same period. We suggest then that the eruption of the central portion of Kerguelen LIP resulted in global environment perturbations that drove the onset of the OAE 1d.