Ordos basin was separated from the adjacent Liupanshan and Hetao basins in Cretaceous

thus it was a separated non-equilibrium downwarped basin.The basin has a north-south axis with west-dipping axial plane and the basin-margin slope being gentle in the east and steep in the west.The center of subsidence is located in the western side of the basin

where the sedimentary thickness is obviously larger than the surrounding uplifted zone.The asymmetrical structure and evolution of sedimentary environment have not only controlled the lithology

sedimentary facies and distribution of strata in the basin

but also resulted in the basin margin to be dominated by glutinites and sandstones of alluvial fan

fluvial

delta plain and distributary channel facies

while the inner part of the basin to be dominated by sandstones and mudstones of eolian desert

delta front and lake facies.Elevation and subsidence

denudation and relief would have influenced the plane distribution of Lower Cretaceous.The thickness of residual sediment is thin in the eastern part and margin of the basin

while it is thick and completely preserved in the downwarping regions in central and western parts of the basin.The Luohe Formation is the most widely distributed

followed by Huanhehuachi Formation

while Luohandong and Jingchuan Formations have only been partially preserved in the downwarping regions in the west and in the north.