Sequence stratigraphic framework of the Hekou Group and evolution of the Lanzhou-Minhe Basin

The Hekou Group in the Lanzhou-Minhe Basin formed during the Early Cretaceous consists primarily of the tremendous terrigenous clastics composed of alluvial fan, fan-delta and lacustrine depositional systems. The stratigraphic sequences in the basin are involved in the retrogradational, aggradational and progradational cycles that represent the tectonic cyclic episodic products. The sequence stratigraphic framework of the Hekou Group is made up, on the basis of sequence features and lithofacies changes, of the lake transgressive (LTST), lake flooding (LFST) and lake regressive (LRST) systems tracts. The basin went, by and large, through the initial rifting and subsiding during the Jurassic, spreading and expansion during the middle Early Cretaceous, and collapse during the late Early Cretaceous.