An approach to the sedimentary facies in the Upper Triassic Xujiahe Formation in the Hebaochang region at the boundary of the Sichuan-Chongqing zone

The Upper Triassic Xujiahe Formation in the Hebaochang region at the boundary of the Sichuan-Chongqing zone is developed as the coal measures dominantly composed of sandstones and mudstones interbedded with thin coal beds,and overlain pseudoconformably upon the erosional surface of the marine carbonate rocks from the Middle Triassic Leikoupo Formation and underlain disconformably or conformably below the Jurassic red beds.The authors in the present paper interprete the sedimentary facies in the study area as the lacustrine facies including the shallow lake subfacies and littoral swamp subfacies on the basis of a careful description of the distribution,lithology and structures of the sandstones in the study area.