PALAEOENVIRONMENTAL CHANGES RECORDED BY THE CALCRETES AT MIAOHE, YICHANG

Two types of calcrete at Miaohe, Yichan, i.e., pedogenic calcrete and groundwater calcrete were studied in this paper. Calcite cements were separated from the pedogenic calcrete for ESR dating and δ¹³C and δ¹⁸O analysis. δ¹³C values of calcite cements are obviously lighter than the host sediments, and δ¹⁸O values of calcite cements slightly heavier than those of the host sediments. It's inferred that the palaeotemperature was 8~12℃, the mean annual rainfall was 760~770 mm and C₄ plants accounted for~84% when these calcretes were formed in the glacial stages.