Sequence Stratigraphic Features of Nonmarine Cretaceous Sediments in Songliao Basin, Northeast China

Abstract

Abundant fossils indicate that Cretaceous siliciclastics of the Songliao basin were deposited in nonmarine environments. However, a relative lake-level curve constructed by the author is somewhat like the eustatic sea-level curve for this period published by Haq et al., 1987. Based on stratigraphic work, a revised definition of a supersequence is proposed. The composition of the lowstand system tract in the nonmarine sequence is different from its marine counterpart, such as the lowstand-prograding complex being absent in some sequences and the basin floor fan often replaced by the alluvial fan or evaporate. A sequence that juts across the reflection event, signified T{sub 2}, which separates the Aptian (Quantou Formation) and Albian (Qingshankou Formation) units, has been studied in detail. Numerous small symmetrical stair-like grabens, containing erosional and leveed channels, developed on top of the Quantou Formation. A number of oil reservoirs are related to channel sands, overbank sediments, and turbidite lobes that form a complex network over a large area east of the Daqing oil field. No shelf edge is present in the nonmarine facies tract, and the transgressive system tract is only developed on the western flank of the basin. Cores, well logs, high-resolution and three-dimensional seismic data, andmore » seismic modeling have been studied from this area.« less