GENETIC SEQUENCE STRATIGRAPHIC FRAMEWORK, DEPOSITIONAL STYLE, AND HYDROCARBON OCCURRENCE OF THE UPPER CRETACEOUS QYN FORMATIONS IN THE SONGLIAO LACUSTRINE BASIN, NORTHEASTERN CHINA

The Qingshankou, Yaojia, and Nenjiang (QYN) formations in the Songliao basin of northeastern China can be used to illustrate the application of sequence stratigraphic analysis in a lacustrine setting and to provide a good example of hydrocarbon occurrence in a lacustrine stratigraphic framework. The QYN genetic stratigraphic sequence, bounded by maximum flooding surfaces or beds, is a low-frequency second-order sequence or supercycle in a lacustrine basin with a ramp margin. Use of subaerial unconformity and transgressive surfaces allows further subdivision of the QYN sequence into a progradational systems tract, lowstand prograding complex, and retrogradational systems tract. Delta-system styles are dominated by the physiography and relative intensity of fluvial and wive processes. Ql and N1 maximum-flooding-related deposits used to identify the QYN genetic stratigraphic sequence boundaries are the main petroleum source rocks and regional seals, and play an important role in determining hydrocarbon distribution in the Songliao basin. The Y1 lowstand prograding complex and Y2 & 3 retrogradational systems tract in the northern part of the basin are the most important reservoir and producing intervals within the QYN sequence.