Carbon and oxygen isotopic studies of the horizon of Kueichousaurus Fauna

Kueichousaurus fauna is the typical representative of the biological radiation in the latest Triassic marine ecosystem, In order to study the palaeoenvironment of the Kueichousaurus fauna, the authors measured the fine sections in Dingxiao and its adjacent areas of Xingyi, Guizhou Province, and tested the whole rock carbon and oxygen isotope compositions by using the carbonate rock. According to the analytical results, the δ¹³C values in Nimaigu section range from -6.3 ‰ to 2.6 ‰, and δ¹⁸O values are between -5.7‰ and -1.2‰; the δ¹³C values in Xiemi section range from-4.5‰ to 2.5‰, and δ¹⁸O values are in the range of -5.7‰——1.2‰; the δ¹³C values of Bawei section range from 0.5 ‰ to 2 ‰, and δ¹⁸O values are between -6.4‰ and 0.1‰; the δ¹³C values in Dingxiao section range from-4.3‰-2.1‰, and δ¹⁸O values are between-7.3‰ and 2.5‰. According to the correlation analysis of carbon and oxygen isotope data, the isotopic values of Nimaigu, Xiemi and Dingxiao sections were less affected by diagenesis. There are obvious negative δ¹³C anomalies in the lower part of the horizon of Kueichousaurus fauna in Nimaigu, Xiemi and Dingxiao, closely related to the rapid death of marine organisms in low-water-level periods and the volcanism. Due to the influence of late diagenesis on the Dingxiao section, the seawater paleotemperature in Xingyi area was recovered by using δ¹⁸O data of Nimaigu, Xiemi and Dingxiao sections. It is shown that the temperature was between 19 and 27℃, with an average about 23℃, which indicates a warm climate during that period.