Late syn-rift sequence architecture and sedimentary evolution of a continental rift basin: A case study from Fulongquan Depression of the Songliao Basin, northeast China

Abstract

Abstract As an important stage in continental rift basin evolution, late syn-rift stage is characterized by the combination of broad crustal subsidence and episodic pulses of extension. Sequence architecture and sedimentary filling process during this period present a certain particularity due to distinctive tectonic subsidence and variable influencing factors. This paper analyzes sequence stratigraphy and sedimentary facies development and their evolution in the Fulongquan Depression, a continental rift basin of the Songliao Basin, and discusses the determinants influencing the sequence architecture and depositional systems evolution. During late syn-rift stage, a major transition in the depositional systems, from predominantly lacustrine and correlated depositional systems to fluvial-floodplain settings, was recorded in the evolution of basin fill. This gradual and slow peneplanation is the final response to the decrease of differential subsidence. The spatial and temporal variability of sedimentary evolution are mainly associated with specific growth history of the major boundary faults. Sequence stratigraphic units recognized in the Fulongquan Depression are likely corresponded to different episodic pulses of extension respectively. Each sequence can be further divided into a lowstand systems tract (LST), transgressive systems tract (TST) and highstand systems tract (HST). Maximum differential subsidence and water deepening mainly occur in the LST. The expanded TST and HST of each sequence tend to be developed in a broader thermal subsidence regime. The depositional systems transition and detrital provenance changes usually occur in the HST. Throughout the late syn-rift stage, in addition to major changes of provenance systems, tectonic movement is likely to be the main factor in controlling the variations of sediment supply. With the decrease of tectonic activity, the impact of climate changes and lake level fluctuations on basin filling tends to be increased.