DISCUSSION ON THE GEOLOGICAL AGE OF THE XIANGSHAN GROUP IN THE ORDOS BASIN

A pile of continental slope gravity flow sediments with olistostrom developed in the west and the southwest margins of the Ordos Basin within the middle and upper Ordvician systems. The middle Ordovician is generally referred to as the Pingliang Group while it is remained as the Xiangshan Group in Ningxia Hui Autonomous Region due to the discovery of the Cambrian fossils in the sequences. However,the author believes that the geological age of the group should be attributed to the Ordovician Period since the Cambrian fossils discovered in foreign rock fragments. Consequently,the contradiction between the strati-graphic sequence and the discovered fossils can be settlled.