The subsurface structure and stratigraphic architecture of rift-related units in the Lishu Depression of the Songliao Basin, China

• Classic rift stages can be further subdivided into discrete phases on the basis of the variation of sedimentary conditions.
• Lishu Depression has unique sequence stratigraphy architecture and sediment stacking patterns in each rifting sub-stage.
• A critical and high-resolution tectonostratigraphic perspective on the evolution of a continental rift basin was provided.

This contribution reports the basin configuration feature, stratigraphy and sedimentary architecture of the Lishu Depression in the Songliao Basin, China. The activity rate, distribution and style of local faulting demonstrate the timing and extent of regional rifting. Distinct episodes of compressional tectonic activity caused uplift and exposure of strata evident as the traditional syn- and post-rift stages of basin evolution. These episodes led to the sequential denudation of the Upper Jurassic Huoshiling Formation, Lower Cretaceous Yingcheng and Denglouku Formations, and corresponding regional unconformities. Acting in tandem with regional compression, activity along the major boundary faults influenced the evolving basin configuration, as well as seismic sequences and sedimentary patterns. Seismic, well log and drill core data described here show subdivision sections of the Lishu Depression strata according to discrete phases of the traditional syn-rift stage of deposition. We refer to these sub-stages as the initial rifting, the intensive rifting and the recession phases. The basin configuration shifted from a graben/half-graben configuration during the initial rifting phase, to a dustpan-shaped half-graben pattern during the subsequent phase of intensive rifting, and finally into a gentle sedimentary basin during the final recession phase. The early seismic sequence divides into a lowstand systems tract (LST), transgressive systems tract (TST) and highstand systems tract (HST). Evidence of the LST within the seismic sequence becomes less apparent with the intensive rifting phase, while the HST occupied an increasing proportion of the section. The shallow water depositional fill formed during the final recession phase consists only of TST and HST components. Depositional environment then shifts from alluvial fan and shallow lacustrine systems to fan delta, braided delta – lake, and finally to a braided fluvial setting. The vertical stacking pattern shifts from retrogradational, to progradational, to aggradational. Identification of sub-structural units and interpretation of their genetic relationships helps clarify basin evolution, and thus serves larger-scale continental basin analysis.