Carbon sequestration in an expanding lake system during the Toarcian Oceanic Anoxic Event

Abstract

The Early Jurassic Toarcian Oceanic Anoxic Event (~183 Ma) was marked by marine anoxia–euxinia and globally significant organic-matter burial, accompanied by a major global carbon-cycle perturbation probably linked to Karoo-Ferrar volcanism. Although the Toarcian Oceanic Anoxic Event is well studied in the marine realm, accompanying climatic and environmental change on the continents is poorly understood. Here, utilizing radiometric, palynological and geochemical data from lacustrine black shales, we demonstrate that a major lake system developed contemporaneously with the Toarcian Oceanic Anoxic Event in the Sichuan Basin, China, likely due to enhanced hydrological cycling under elevated atmospheric pCO2. Coeval accelerated organic-carbon burial in both marine and lacustrine basins suggests nutrient delivery as the prime cause for global carbon-cycle recovery during the Toarcian Oceanic Anoxic Event. Increased lacustrine organic productivity from elevated fluvial nutrient supply resulted in the burial of ~460 Gt of organic carbon in the Sichuan Basin alone, creating an important negative feedback in the global exogenic carbon cycle, which significantly shortened the global δ13C recovery