The alluvial fan-delta depositional systems in the Lower Triassic Qingtianbao Formation, Junmachang, Eryuan, western Yunnan

The present paper gives a detailed description of macroscopic features, compositions, textures and structures and organic fossils in main rock types from the Lower Triassic Qingtianbao Formation, Junmachang, Eryuan, western Yunnan. The facies classification is involved in three sedimentary facies including alluvial fan, fluvial and delta facies, three sedimentary subfacies including channel filling, delta front and prodelta subfacies, and six sedimentary microfacies including braided channel, flood plain, subaqueous distributary channel, interdistributary bay, channel mouth bar and sheet sand microfacies. The vertical retrogradational sequences of the alluvial fan, fluvial and delta deposits in the Lower Triassic Qingtianbao Formation in the Junmachang region shows that the widespread transgressions once took place in the Yanyuan-Lijiang basin during the Qingtianbaoan of the Early Triassic, resulting in the sedimentary evolution from the continental facies to the marine facies in the Junmachang region.