In 1972, after frequent investigations on lithology, sedimentology and palaeontology (especially on palaeobotany), the Upper Triassic coal series (formerly the "Lalaqing Coal Series") in the Baoding area, southwestern Sichuan was previously divided by No. 1 Regional Geological Survey Team of Yunnan Province into two formations in ascending order as the Daqiaodi Formation, and the Daqing Formation (consisting of the Lower and Upper Members).