Abstract:

Owing to complicated geological evolution and the following reformation caused by the succeeding strong multiphase tectonic movement, the multiperiod prototype basin of the Mesoproterozoic southwestern Ordos Basin was vertically stacked, and the original appearance of each prototype basin was no longer in existence, which restricted the indepth understanding of the original appearance of each prototype basin, of the stacking process of multiphase basin prototype, of its dynamic environment, and of the reasonable exploration of oil and gas. Combined with the tectonic background research of North China Craton at the same time, the prototype basin and its genetic mechanism of Huangqikou and Wangquankou in Daijian Period, Southwest Ordos Basin have been analyzed through the seismic interpretation, drilling data interpretation, and test data analysis. The research findings show that in the early stage of Huangqikou Period, under the background of the clockwise rotation of the North China Craton, the research area, the southwestern Ordos Basin, was rifting under the strikeslip extensional dynamic environment, and filled with a large number of alluvial fan systems and delta systems and a small lake system. In the late stage of Huangqikou Period, the research area began to enter into the postrift depression stage, mainly was filled with lakedelta system covered the lower lacunae sequence of lower Huangqikou Formation. In Wangquankou Period, with the increase in regional extrusion, owing to the subduction of oceanic crust, the “S” type of monzonitic granite of Xiazhai System derived from volcanic arc or syncollision orogeny intruded in Maxianshan group; the southwestern Ordos Basin was under the backarc compressive depression dynamic environment, which developed a set of carbonate rocks of tidal flat depositional system, mainly stromatolite dolostone. Then, because of compressive uplifting, the Daijian System (Huangqikou Formation and Wangquankou Formation), underwent erosion in Qingbaikou Period and Nanhua Period.

Key words: Daijian System, Huangqikou stage, Wangquankou stage, prototype basin, genetic mechanism, Southwest Ordos Basin