The Weibei uplift, located in the southern Ordos Basin, is an important strategic area for oil and gas exploration with multiple sets of source rocks. However, due to the lack of effective thermal indicator data, the thermal maturity distribution and thermal history of different source rocks remains poorly constrained. In this paper, based on the large number of measured vitrinite reflectance data and fission track analysis data, we have determined thermal evolution degree of different source rocks and reconstructed tectonic-thermal history in the Weibei uplift. The results show that the thermal evolution degree of different source rocks in the Weibei uplift is generally characterized by high values in the north and west, low in the south and east. The source rocks of the Late Triassic Yanchang Formation are in the stage of maturate oil-generating, while the Carboniferous-Permian and Ordovician source rocks are in the stage of gas-generating. In addition, there is a positive correlation between the vitrinite reflectance and depth of the different layers. The apatite fission track data indicates that the Weibei uplift has undergone large-scale uplift and cooling since the end of Early Cretaceous（ca.110 Ma）, and it is also associated with characteristic of early uplift in the south and late uplift in the north. After ca.40 Ma, the whole Weibei uplift has been rapidly uplifted. The study results of thermal evolution history show that the highest thermal evolution degree in different layers was reached in the Early Cretaceous period. From the Cambrian to the Jurassic, the paleogeothermal gradient was generally lower, and the maximum paleogeothermal gradient was up to 46 ℃/km in the Early Cretaceous, which was influenced by tectonic thermal events. Since the Late Cretaceous, paleogeothermal gradient was obviously reduced. The Early Cretaceous was the main oil-gas generation period of the Ordovician, Carboniferous-Permian and Triassic source rocks, which was controlled by high geothermal gradient and tectonic-thermal events of the Early Cretaceous. Since the Cenozoic, the Weibei uplift experienced a large uplift-cooling event, as a result, the formation temperature decreased and the hydrocarbon generating process cease.
Ren Zhanli Qi Kai. Thermal maturity distribution characteristics and thermal history reconstruction of hydrocarbon source rocks in the Weibei uplift, Ordos Basin[J]. Chinese Journal of Geology, 2018, 53(3): 959-971.