Tectonic evolution of Qingyang and Wushenqi paleo-uplifts during the Early Paleozoic and its control on Cambrian lithofacies paleogeography in the Ordos Basin

The tectonic evolution process of Paleozoic paleo-uplifts in the north and south of the Ordos Basin is still not quite clear and this restricts the oil and gas exploration and the study on sedimentary filling evolution process in the basin. Based on the latest drilling, outcrop and seismic data, the study characterizes and defines the Qingyang and Wushenqi paleo-uplifts by means of seismic identification of reflector contact relationship and shore facies. The results show that the two paleo uplifts have experienced six major stages of evolution, namely the gradual submersion in the Cambrian, uplifting and denudation from the Cambrian to the Ordovician, stabilization of the Qingyang paleo-uplift and rapid subsidence of the Wushenqi paleo-uplift after the Yeli-Liangjiashan period, the compression, denudation and finalization of the paleo-uplifts during the Late Caledonian, the extinction of the paleo-uplifts in Carboniferous-Permian, and the tectonic tilting and finalization after the Permian. The two paleo-uplifts were similar during the early stages and differentiated during late stages with the south uplift rising and north uplift subsiding. The two paleo-uplifts together formed an alternative rising-subsiding framework that had obviously controlled the sedimentary reservoirs of the Cambrian system. The paleo uplifts are gentle in the east and steep in the west. The east is more favorable for the large scale development of dolomite reservoirs. During the process of Cambrian lithofacies paleogeography evolution, both paleouplifts controlled the lithofacies paleogeography framework but with the Qingyang paleouplift working more continuously on the uplift-depression pattern and sedimentation. The Huaiyuan tectonic movement in the late Cambrian led to the uplift and denudation of the Ordos Basin, resulting in a widespread development of karstification at the top of the Cambrian.