Abstract:

 Based on the investigation results of outcrop, especially considering the  universal existence of Pingliang Formation shale in western and southern Ordos Basin, combined with the outcrop and well information, this paper systemically studies the sedimentary environment of Qilian Sea of Ordos Basin in Early Paleozoic Ordovician, and lithofacies palaeogeography of every sedimentary period is reconstructed. Affected by the formation of the central paleo up-lift and Qilian Sea's invading gradually toward east, the lithofacies paleogeographic framework of Ordos Basin totally showed that open-sea platform, limited sea platform and evaporating platforms were successively distributed during Majiagou age 1, Majiagou age 2 and Majiagou age 3. During Majiagou age 4 and Majiagou age 5, shallow-water carbonate facies, especially edge slope facies and shoal reef facies, were developed and they will be the potential reservoirs. During Majiagou age 6 and Pingliang age, the maximum regression occurred, and open-sea facies and deep-sea basin facies were developed. The graptolite shale of Pingliang Formation is good source rock. The study of the lithofacies paleogeography of Ordovician in Ordos Basin has important significances in both geological theory and production.

Key words: Ordos Basin, lithofacies palaeogeography, Qilian Sea, Ordovician period, slope facies