Determination of the geologic age of the bottom interface of Quaternary of Caidamu Basin

Up to now there are different viewpoints on the geologic age the bottom interface of Quaternary. The determination of the geologic age of the bottom interface of Quaternary of Caidamu Basin is not only favorable to the theoretical study of Quaternary but also of importance to the observation of biogas reservoirs. The geologic age is determined as 2.5 Ma B.P. based on the variation of sporopollen assemblages, the evolution of palaeoclimate, the unconformity formed by intense tectonic movement, the contact state of sediment and the variation of archaeomagnetism. The bottom interface is identical with that of Quaternary loess in the northwest of China determined by Liu Tun-sheng of our country and that of Quaternary glacial age beginning determined by Shakleto N. T. based on the profile of DSDP site 552A hole in North Atlantic Ocean. It is a unconformity surface in which the basin graduates into conformity contact. The palaeoclimate becomes cold suddenly across it. A lot of strong first appears here.