Sequence stratigraphy and sedimentary evolution of the 3rd and 2nd members of the Palaeogene Shahejie Formation in the Xiliu-10 fault block, Raoyang depression, central Hebei

Sequence stratigraphic division, sedimentary characteristics, and sedimentary facies distribution and evolution are examined in detail on the basis of high-resolution sequence stratigraphic theory, cores and well logs for the 3rd and 2nd members of the Palaeogene Shahejie Formation in the Xiliu-10 fault block, Raoyang depression, central Hebei. The 3rd and 2nd members of the Palaeogene Shahejie Formation may be divided into 4 third-order cycles, 11 fourth-order cycles and 32 fifth-order cycles. Lithologically, the rock types dominantly contain fine-grained sandstone, siltstone and mudstone. The sedimentary environments consist of the braided delta plain and delta front subfacies, which may be subdivided into 7 sedimentary microfacies, including the channel bar, channel filling, overbank, channel margin, subaqueous distributary channel, subaqueous interdistributary bay and channel mouth bar microfacies. Combined with the regional tectonic evolution and sedimentary background, it is believed that the 3rd and 2nd members of the Palaeogene Shahejie Formation mainly experienced the evolutionary processes from the regression to the transgression during their deposition.