Sequence stratigraphic and sedimentary facies analysis of the 1st and 2nd members of the Shahejie Formation in A district, northwestern Liaodong Bay

The 1st and 2nd members of the Shahejie Formation in A district, northwestern Liaodong Bay may be divided, on the core examination and sequence stratigraphic and sedimentary facies analysis, into two third-order sequences SQs2 and SQs1, each of which may be composed of the transgressive (TST) and high-stand (HST) systems tracts, three sequence bounding surfaces, and two maximum flooding surfaces including mfss2 and mfss1 in an ascending order. The sandstones, gravelly sandstones and coarse-grained clastic rocks appear in the second member, and mudstones and dolostones occur in the first member of the Shahejie Formation. Sedimentary facies are assembled by lake, littoral-shallow lake subfacies, and mud flat, mixed beach, sandy beach and calcareous beach microfacies. In the sequence SQs2, there occur the mixed beach and sandy beach deposits in which the sandstones serve as the excellent reservoir rocks. In the sequence SQs1, there occur the mud flat deposits in which the biogenic dolostones act as the excellent reservoir rocks.