Carbon sequestration in an expanded lake system during the Toarcian oceanic anoxic event

The Early Jurassic Toarcian oceanic anoxic event (∼183 Ma) was marked by marineanoxia–euxinia and globally significant organic-matter burial, accompanied by amajor global carbon-cycle perturbation probably linked to Karoo–Ferrarvolcanism. Although the Toarcian oceanic anoxic event is well studied in themarine realm, accompanying climatic and environmental change on the continentsis poorly understood. Here, utilizing radioisotopic, palynological and geochemicaldata from lacustrine black shales, we demonstrate that a large lake systemdeveloped contemporaneously with the Toarcian oceanic anoxic event in theSichuan Basin, China, probably due to enhanced hydrological cycling underelevated atmospheric pCO2 . We attribute increased lacustrine organicproductivity to elevated fluvial nutrient supply, which resulted in the burialof ∼460 Gt of organic carbon in the Sichuan Basin alone, creating an importantnegative feedback in the global exogenic carbon cycle. We suggest that enhancednutrient delivery to marine and large lacustrine systems was a key component inthe global carbon cycle recovery during the Toarcian oceanic anoxic event andacted to shorten the duration of the recovery of global δ 13C values.