Distribution of radioactive elements (U, Th) in the upper Paleozoic coal-bearing strata of the eastern Ordos basin

The presence of radioactive elements are detected by more 50 well loggings and plotted spatially and vertically to image their distribution, in the eastern Ordos basin. The radioactive element is investigated through quantitative methods, such as inductively coupled plasma mass spectrometry and X-ray diffraction. Results show the presence of three significantly high radioactivity of natural gamma-ray (GR) layers: (1) Kf with GR content ranging from 120.5 to 738.1 API, 2.93-39.97 ppm of U, and 8.4-97.93 ppm of Th, (2) Kd with GR content ranging from 121.2 to 475 API, 3.17-40.03 ppm of U, and 4.26-42.63 ppm of Th, and (3) Kb with GR content ranging from 117.4 to 453.4 API, 1.26-47.47 ppm of U, and 2.37-84.11 ppm of Th. The high concentrations of U and Th in coal-bearing deposits are spatially related to the rock blocks in the vicinity of the folded margins, which are rich in elements and are related to syndepositional volcanism before coal formation. The layers with significantly high radioactive content of U and Th might play a role in promoting and catalysing the hydrocarbon generation of coal-bearing hydrocarbon source rocks, which are also the reliable precise chronostratigraphic markers in continental strata for lacking of reliable marine markers.