Characteristics of Early Cretaceous prototype basin of Liupanshan Group in Liupanshan Basin

Liupanshan Basin is a Mesozoic-Cesozoic rift sedimentary basin which is located in the southern North China Plate and the east extension part of Hexi Corridor and lies along Qinling-Qilian Caledonian fold belt. In this paper, the authors analyzed con-glomerate gravel characteristics and palaeocurrent of Liupanshan Basinand explored provenance characteristics of Lower Cretaceous strata. Outcrop observations show that separation and grinding roundness of conglomerate and sandstone of Sanqiao Group are poor, reflecting middle-low structure maturity and nearby source. At the beginning of the Early Cretaceous, basin boundary was affected by strong compressive tectonic background of Late Jurassic, a series of highland internal basins and peripheral mountains suffered from weathering denudation, and the southwestern margin was mainly characterized by coarse clastic sedimentary piedmont pluvial fan ac-cumulation and deposited piedmont pluvial fan of predominantly coarse fragments, which was gradually transitional to braided river towards the interior of the basin. In late Early Cretaceous, the basin boundary was expanded towards the west. Accompanied by alternate drought-humid climate, there developed alluvial fan, braided river, delta, shallow lake and saline lake facies.