TILLOID AT THE BOTTOM OF THE SEDIMENTARY COVERS ON THE MARGINS OF THE ORDOS BASIN

This paper describes in detail the geological characteristics of tilloid conglomerate in the eastern and western parts of the Ordos basin. The thickness of the conglomerate varies greatly from O to 50m. The gravels are complex in composition, highly varied in size. mostly angular to subrouned in shape and arranged chaotically without bedding. Ice-scoured polished surfaces and striations are pesent on some of them. Conglomerate is persistent stratigraphieally and shows an unconformable contact with the underlying Archean-Middle Proterozoie strata and a disconformable relation with most of the overlying Cambrian. Its age should be Sinian and its stratigraphie horizon is largely equivalent to that of the Luoquan Formation. An analysis of regional paleogeograpby and paleotectonic environments shows that the conglomerate was produced when the continental ice sheet on the North China platform reteated gradually towards the Ordos plateau at the end of the Sinian. As it was reworked by subsequent geological cxogenic forces, its original genetic characteristics have become not very distinct.