Sequence stratigraphy and reef beach distribution of Feixianguan Formation in western Hubei-eastern Chongqing area: a case study of the third member of Feixianguan Formation in Jiannan and adjacent area

The sequence boundary identification, sequence unit division, isochronous stratigraphic framework establishment and sedimentary system of bioreef-beach bodies in the third member of the Lower Triassic Feixianguan Formation in and around Jiannan town in the western Hubei and eastern Chongqing area were studied based on drilling, logging, core, outcrop, seismic and testing data. The Feixianguan Formation consists of two third-order sequences, SQ1 and SQ2. The SQ1 was composed of the first and second members of Feixianguan Formation, while the SQ2 was made up of the third and fourth members of Feixianguan Formation. The third member of Feixianguan Formation can be further refined into three fourth-order sequences, which are sq1, sq2, and sq3 from bottom to top. The third member of Feixianguan Formation can be divided into inner, central and outer gentle slope facies, and further divided into 9 beach subfacies, including oolitic, granulated, bean, biodetritus, sandy clastic and inter beaches, and lower slope, upper slope and platform depression. During the deposition of the third member of Feixianguan Formation, the terrain of the study area was high in the west and low in the east. The high-energy shoal was distributed in the central area,while the granulated beach and main reservoirs were mainly distributed in the north and south of the study area.