High-precision sequence stratigraphic framework and sedimentary system evolution in the middle submember of the 3rd member of the Shahejie Formation in the Laizhouwan depression

The sequence stratigraphic framework and sedimentary system evolution are discussed on the basis of three-demensional seismic data,core examination and well logs for the middle submember of the 3rd member of the Shahejie Formation in the Laizhouwan depression. Collectively,the middle submember of the 3rd member of the Shahejie Formation may be involved in one third-order sequence,and subdivided into six 4th-order sequences. Three systems tracts including the lowstand,transgressive and highstand systems tracts are based on the first and maximum flooding surfaces and the bounding surface of the enveloping surface defined by the delta phases within the highstand systems tract. The fan delta and nearshore subaqueous fan deposits appear in the lowstand systems tract in the western and northern parts. The braided delta deposits and the slope turbidite fan deposits occur in the transgressive and highstand systems tracts,where the favourable lithologic traps may be recognized as preferred targets in the future exploration.