The genetic types of the reservoir sandstones from the Xujiahe Formation in the central-southern Sichuan transitional zone

The clastic reservoir sandstones are developed in the central-southern Sichuan transitional zone, especially in the second, fourth and sixth members of the Late Triassic Xujiahe Formation. The genetic types of the reservoir sandstones consist of delta-plain distributary channel sandstones, delta front subaqueous distributary channel sandstones, river mouth bar sandstones, littoral lake beach and shallow lake bar sandstones. The distribution, textures and structures, and physical properties are examined in detail for the reservoir sandstones of varying origins.