The terrestrial sedimentological response of the Toarcian oceanic anoxic event in the Sichuan Basin, SW China

The Toarcian oceanic anoxic event (T-OAE, ～183 Ma) was a typical hyperthermal in the Mesozoic, marked by a significant negative carbon isotope excursion, large-scale organic matter burial, and enhanced hydrological cycling. The geochemical characteristics, sedimentological response, and duration of the T-OAE have been well investigated in marine successions but are poorly known in the continental environment. Here, we conducted a systematic geochemical and sedimentological investigation on the Da'anzhai Member corresponding to the T-OAE in the eastern Sichuan Basin, SW China. Geochemical data indicate a prominent negative excursion in organic carbon isotope (δ¹³C_org) and enrichment of total organic carbon (TOC), most likely associated with the T-OAE. Sedimentological investigations found a large number of shell concentrations and storm beds occurring in the T-OAE interval, and these shell concentrations can be attributed to three genetic factors: wave, storm, and biological productivity, with the storms being the main controlling factor. Statistical analyses of the storm beds demonstrated that the frequency and intensity of storm activities in the Sichuan Basin increased significantly during that period. The increased abundance of storm beds and shell concentrations was a typical sedimentological response to the T-OAE in coastal terrestrial systems.