柴达木盆地第四纪底界时代及识别标志

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

目前,人们对第四纪的底界地质年代尚存在不同的看法.明确柴达木盆地第四纪底界的地质年代不仅有利于第四级地层的理论研究,而且对于有效的寻找第四纪生物气藏具有重要的实际.依据孢粉组合变化及古气候演化、强烈的构造运动形成的不整合、沉积物接触关系以及古地磁的变化作为确定第四纪底界的主要依据,综合研究确定柴达木盆地第四纪底界为2.5MaB.P.,这一界面同我国学者所确定的西北地区第四纪黄土的下限以及N.J.Shackleton等依据北大西洋DSDPsite552A钻孔剖面所确定的第四纪大规模冰期开始一致.该界面为向盆地逐渐变为整合接触的不整合面,穿过该界面气候突然变冷,并首次大量出现强壮青星介.

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.