The deposition environment during the Da'anzhai Member in the lower Toarcian is thought to have been that of a giant freshwater lake encompassing the whole of the Sichuan basin, around 3 times larger than Lake Superior, coeval with the Toarcian Oceanic Anoxic Event around 183 Ma.
During the Da'anzhai Member in the lower Toarcian, sediments were deposited in an extensive freshwater lake that covered the Sichuan basin, approximately three times larger than Lake Superior, occurring at the same time as the Toarcian Oceanic Anoxic Event around 183 Ma.