Carbon and oxygen isotope characteristics of carbonate rocks in the Mesoproterozoic Jixian System of the Ordos Basin and their implications

Abstract The paleoenvironment of Jixian carbonate rocks in the Mesoproterozoic Ordos Basin is studied by carbon and oxygen isotope analysis, diagenetic environment analysis, and restoration of paleosalinity and paleotemperature. The results indicate that the carbonate rocks of the Jixian System have always been in a near surface environment and have not been deeply buried, the variation range of d 13CPDB and d18OPDB is relatively narrow, ranging from -5.75 ‰ to 1.41 ‰ and -8.88 ‰ to -4.01 ‰, respectively, which is consistent with the stable tidal flat sedimentary environment during the Mesoproterozoic in the study area. The paleosalinity (Z) ranges from 111.7 to 127.1, and the paleotemperature (T) ranges from 32.71℃ to 57.33 ℃, indicating a relatively warm paleoclimatic environment during the Mesoproterozoic period in the study area. Analysis shows that in a warm paleoclimatic environment, although carbon and oxygen isotopes, Z, and T have certain fluctuations, their range is relatively small, reflecting to some extent the stable tectonic environment of the study area during the Mesoproterozoic period. Comprehensive research shows that the Ordos Basin had a warm climate and a stable tectonic environment in the Mesoproterozoic, which may be a good response to the North China Block's position near the equator and continuous thermal subsidence in the Mesoproterozoic.