Carbon and oxygen isotope characteristics and palaeoenvironmentalimplication of the Cenozoic lacustrine carbonate rocks in northern QinghaiTibetan Plateau
Yi Haisheng Lin Jinhui Zhou Kenken Li Junpeng
1 Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu610059,Sichuan
2 College of Materials and Chemistry Chemical Engineering, Chengdu University of Technology, Chengdu610059,Sichuan
Through systematic sampling and analyses of the lacustrine carbonate rocks in the Cenozoic continental strata in the northern QinghaiTibetan Plateau, by using the carbon and oxygen isotopes as proxies, the environmental evolution of the Early Cenozoic is revealed according to the palaeolacustrine evolu￣tion. The results indicate that the δ18O and δ13C in the bioclastic limestone samples have the lowest values in all the samples in this area, reflecting that they were deposited in an open freshwater lacustrine environment with a short period of water residence. There is a positive relation between the δ18O and δ13C in the micritic limestone samples, reflecting that they were deposited in an obvious closed saline water laustrine environment. The obviously enriching of δ13C in stromatolitic limestones may be related to the microbial activities. The δ18O value of the lacustrine carbonate rocks gradually increased from Eocene to Oligocene and then to Miocene. The δ13C changed from a negative value in the Paleogene to a positive value in the Neogene, which reflects that the lacustrine system in this area evolved from an open system to a closed one. Thus the prediction can be made that the palaeoclimate changed greatly throughout the PaleogeneNeogene period.
. Carbon and oxygen isotope characteristics and palaeoenvironmentalimplication of the Cenozoic lacustrine carbonate rocks in northern QinghaiTibetan Plateau[J]. JOPC, 2007, 9(3): 303-312.
