Abstract:

The main type of the west part of the Ordos Basin is the thrust nappe tectonics. The sedimentary characteristics, basement styles, tectonic framworks,evolution and their mechanism are different on each side of Qingtongxia-Guyuan Fault. The east and west parts of the fault are known as SN trending tectonic belt and Liupanshan arcuate tectonic belt respectively. The thrust nappe tectonics consist of four parts:nappe system, front zone,outer front zone and autochthon. They consist of a series of imbracate faults thrusting eastward and northwestward. Most of the thrusts appear to be steep in the upper parts and gentle in the lower with decollements. The fronts of the thrust sheets are most likely uplifts or anticlines, but the tail of them depressions or synclines. In the Middle Proterozoic-Early Palaeozoic, the north and south parts of the area were aulacogen and passive continental margin of Qinling-Qilian Geo-syncline respectively. In the Late Paleozoic, the south part was a foredeep and the north part was a impactogen. The SN trending tectonic belt formed and developed mainly in Indo-China and Yanshan movements. Liupanshan arcuate thrust belt and Yinchuan Graben formed in the Cenozoic. This part of the basin is one of the most favourable region for oil prospecting. There are thick sediments, better sources and reservoirs, more types and a large amount of traps. So the preservation condition has become the key point for oil prospecting. Generally speaking, the autochthons and front zones have superiority over the nappe systems, the tails of thrust sheet are superior to its front. The east of SN trending tectonic belt is better than the west of it, and the outer front zone is superior to the nappe system and the front zone. The autochthons of Weizhou-Majiatan district and the north part of the outer front zone of SN trending tectonic belt are the most favourable for oil and gas.