OVERLAPPING OF THE LOWER CAMBRIAN HOUJIASHAN FORMATION OVER THE PRE-CRYOGENIAN SEQUENCES IN THE NORTHERN JIANGSU AND ANHUI PROVINCES

The northern Jiangsu and Anhui provinces is at the south-eastern margin of the North China Plate and its Neoproterozoic sequences are up to about 5000 m thick, resting unconformably on the Fengyang Group schists and Wuhe Group gneiss (where the radiometric age 2650 Ma, zircon U-Pb technique) and unconformably covered by the Lower Cambrian Houjiashan Formation. The Neoproterozoic-Cambrian boundary is represented by the regional unconformity between the different horizontal formations in different locations and the overlapping Lower Cambrian Houjiashan Formation. According to the biostratigraphic correlations based on predominant assemblages of Charaia-Tawuia type macrofossils, Leiosphaeridia-Trachysphaeridium type microfossils and Conophyton-Acaciella-Baicalia-Jurusania type stromatolites, the Neoproterozoic sequence in this region can be correlated with that of the Jixian and eastern Liaoning regions, and suggest that the formations is Pre-Cryogenian. The biota in this region is considerably primary and simple, compared with the Sinian Doushantuo’s (post-Nantuo Glaciation) or Lantian’s (post-Leigongwu Glaciation). Reasonably. This assemblage was possibly deposited preceding these Cryogenian Glaciations, and it is a Pre-Ediacaran biota. On the basis of integrated lithologic, biostratigraphic and structural data, we could reveal the geologic history of northern Jiangsu and Anhui provinces from Neoproterozoic to early Cambrian. During Qingbaikou period, Huainan district in southern part of the region was transgressed in the first instance, and then this region was wholly merged by warmly shallow sea, with the transgression expanded. The folds and uplifts by structural movements caused Huainan district emerged firstly, and sea water withdrew from Huanbei district in northern part of the region finally. This region was weathered until an early Cambrian transgression, and the sediments of Houjiashan Formation overlapped different horizontal Neoproterozoic formations in different locations.