Evolution of the lower Cretaceous Chifeng half-graben basins, inner Mongolia, China

As a result of complex extensional tectonics in northeast China and southern portions of Mongolia, some workers have interpreted the Cretaceous Maanshan Uplift and associated Chifeng basins as metamorphic core complex. Previous work has relied solely upon kinematic indicators to determine the structural origin of these basins. To fully understand the creation of these basins, the sedimentiological record was analyzed in this study. The early Cretaceous sedimentary fill of these basins was analyzed to determine if it is synextensional in nature, and if so what manner of extension was in progress during that deposition.The Chifeng basins are filled with four distinct facies associations and are floored by Late Jurassic and Early Cretaceous volcanics of intermediate and felsic composition. The facies associations observed are interpreted as lacustrine/fluvial deposits, alluvial fan conglomerates, distal fan deposits with fluvial deposits, and hanging wall derived fluvial deposits. These facies are composed of sediment shed from the footwall and hanging wall of the master faults and volcanic deposits. Paleocurrent indicators, primarily in the form of imbrication, along with clast count data show provenance directly off the structure separating the two basins and from the eastern margin of the southeast basin. The distribution of facies, as well as paleocurrent data, provenance data, and structural geometry, implies that these basins are of half-graben origin and that no sedimentological evidence exists of an Early Cretaceous metamorphic core complex near Chifeng.