Architecture and facies model in a non-marine to shallow-marine setting with continuous base-level rise: An example from the Cretaceous Denglouku Formation in the Changling Depression, Songliao Basin, China

Abstract

The analysis of 2D and 3D seismic data, drilled cores and well log data has resulted in a sequence stratigraphic framework of the Cretaceous Denglouku Formation in the Changling Depression in the underfilled Songliao Basin. The Cretaceous Denglouku Formation can be divided into four third-order sequences. Each sequence consists of two systems tracts: a transgressive systems tract and a highstand systems tract. A braided river delta is the main sedimentary facies in the study interval. These sequences were deposited in a back-arc rift basin during a transitional period from fault-dominant subsidence to downwarp subsidence. A sequence stratigraphic model is discussed based on the above interpretations. Typical unconformities are absent due to the absence of base level fall. Instead, maximum regressive surfaces, which are generally reworked by transgressive ravinement, act as the sequence boundaries. Each sequence bounded by these surfaces can be divided into two depositional units: a transgressive unit (TST) and normal regressive unit (HST). On land, a TST is characterized by a decreasing channel/floodplain ratio, and an HST is characterized by an increasing channel/floodplain ratio. Lakes are analogs to marine settings in which the shoreline moves forwards and backwards, and their strata show alternating retrogradation and progradation patterns. The results of this study may encourage the application of similar approaches to the correlation of successions within and beyond the Songliao Basin.