Paleoclimatic reconstruction during the North China Craton drifting: Evidence from hydrogen and oxygen isotope composition of kaolinite in coal-bearing strata claystone

Abstract

In order to reconstruct the paleoclimatic conditions of the Late Carboniferous-Early Permian coal-accumulation period in the Datong Basin, this paper analyzes the mineralogical characteristics of coal-bearing strata claystone in the Dongzhouyao mine of the Datong Basin and the stable isotope data of the kaolinite minerals isolated after clay separation. The δD (−80 to −105‰) and δ18O (13.9 to 16.3‰) values of the Late Carboniferous-Early Permian kaolinite are close to the kaolinite line, suggesting that these kaolinites formed by surface weathering before sedimentation. The calculated paleotemperatures during kaolinite formation in the upper Benxi Formation (Fm.), Taiyuan Fm., and the lower Shanxi Fm. are about 29.1 °C, 26.8 °C, and 25.7 °C, respectively. These temperatures suggest that kaolinites formed under warm-temperate to tropical conditions. In addition, according to the trend of gradually decreasing paleotemperature during kaolinization from the upper Benxi Fm. to the lower Shanxi Fm. and combined with previous studies, we inferred that the change of temperature in the study area was caused by the gradual northward movement of the North China Craton (NCC) during the Late Paleozoic Ice Age (LPIA). Meanwhile, as the plate drifts to higher latitudes, the water interacted with kaolinite gradually changes from heavy water (D218O) to light water (H216O), leading to differences in the H and O isotopic compositions of kaolinite in different periods.