Kungurian sedimentary environments in the slope facies of the Xuyong area, South China, and a comparative analysis of low-latitude palaeogeography

The Kungurian period in the late Palaeozoic was characterized by a climatic transition from icehouse to greenhouse conditions, during which organisms flourished. Thick carbonate rocks developed in shallow water in most of the low-latitude palaeogeographic areas of the globe in this period. The sedimentary environments have long been considered steady and unidirectional. However, studying the Xuyong section in South China and comparing it with other regions may change this view. In this study, we obtained the lithological and geochemical data for slope facies carbonate rocks, including eight sedimentary microfacies from MF1 to MF8. The results showed transgressions in the Xuyong section characterized by an increase in palaeosalinity, a decrease in seawater temperature, and an increase in reduction. By comparing 13 sections from the same low palaeolatitude, we found that there may be four changes in the carbon isotope and strontium isotope chemical strata. These changes might provide support for a potential global palaeoenvironment event, the Kungurian Carbon Isotopic Excursion. Moreover, although the geochemical characteristics in different regions include good comparability, nonetheless seawater circulation and the palaeoclimate were found to be the main factors influencing the carbon cycle after excluding the influence of tectonic factors and volcanic eruptions. Additionally, we inferred that although thick carbonate rocks were produced in different low-latitude oceans, these carbonate rocks did not necessarily form in the same environment. During periods of tectonic stability, the influence of palaeoclimatic conditions on sedimentary environments cannot be ignored.