Sedimentary facies and palaeogeographic evolution of the Lanping Basin in Yunnan

Seven types of sedimentary facies have been distinguished for the Triassic strata in the Lanping Basin,Yunnan according to rock types,sediment supply,genetic mechanism and depositional sequences,including the continental volcanic debris flow facies,fluvial facies,delta facies,tidal-flat facies,shallow-marine shelf facies,carbonate platform facies and deep-water basin facies.The detailed studies of the above-mentioned sedimentary facies integrated with the reconstruction of the palaeogeographic frameworks indicate that the basin recorded the depositional evolution of two phases of transgressive-regressive cycles from the continental environment through the siliciclastic marine basin to the carbonate marine basin and finally to the siliciclastic marine basin again throughout the Triassic.In general,the sea area in the basin was relatively smaller during the early stage,while during the late stage,the increasing sea area led to the formation of the whole marine basin.