Mesozoic and Cenozoic Tectono-Thermal Reconstruction of the Southern Ordos Basin: Revealed by Apatite Fission Track and (U-Th)/He Dating

Abstract

The Ordos Basin is rich in oil and gas resources in the Paleozoic strata. The southern part of the basin boasts a thick Paleozoic sedimentary sequence, enriched organic matter, favorable sedimentary facies, and hydrocarbon source rocks with an over-mature thermal evolution stage. However, the lack of in-depth study of the tectono-thermal evolution in the southern basin limits regional oil and gas exploration. In this study, drill core and outcrop samples were collected from the Shanbei Slope and the Weibei Uplift, respectively. These samples were subjected to apatite fission track (AFT) and (U-Th)/He dating (AHe). The results were used to reconstruct the thermal history of the southern basin, calculate exhumation rates, and analyze the tectonic evolution of the basin. The seven annealed AFT data values from the Shanbei Slope range from 21.4 to 52.8 Ma, with mean track lengths of 13.24 μm, and the twelve unannealed AFT data values from the Weibei Uplift range from 111.9 to 204.6 Ma. The seven AHe data values from the Shanbei Slope range from 17.0 to 31.8 Ma, and the eight AHe data values from the Weibei Uplift range from 31.7 to 47.5 Ma. The thermal history is characterized by a prolonged phase of burial and heating from the Triassic to the Late Early Cretaceous, followed by a phase of uplift and cooling that continued into the Cenozoic. This cooling phase exhibits three distinct stages with varying rates of uplift and cooling. According to the dating results, the cooling timing of the southern basin was earlier than that of the central part, and the southern basin experienced higher uplift rates during the Paleogene than in other periods of the Cenozoic. This may be attributed to the far-field effects of the collision between the Indian Plate and the Eurasian Plate during the Paleogene.