柴达木盆地大浪滩梁-ZK02孔的磁性地层及其古环境研究

摘要

对柴达木盆地西部大浪滩盐湖梁-ZK02孔岩芯进行详细的磁性地层研究,确定钻孔岩芯的B-M界线位于315m,Jaramillo位于405～430m,Olduvai位于772 ～ 816m.在磁性年代学框架基础上,以蒸发岩沉积序列作为主要依据,结合碎屑岩变化以及孢粉分析,认为该地区在第四纪发生过三次较大的沉积环境变化,分别发生在2.5～2.2Ma,1.2～0.7Ma与0.4Ma.青藏高原第四纪的隆升是造成上述三次变化的主要原因,其中早更新世末—中更新世早期的隆升对柴达木盆地的气候影响较大,导致柴达术盆地的气候由温凉湿润转换为寒冷干旱.高原隆升引起的气候干旱并非简单的逐渐加剧,而是早更新世末期以来,气候湿润期表现得更为湿润,这种现象可能由高原隆升增加了夏季风的强度导致,冰川和积雪面积的增大也起到了叠加效应.%A detailed magnetostratigraphic investigation has been carried out on a 1000-m-thick sequence of Liang-ZK02 Borehole in Dalangtan, northwest of the Qaidam Basin. Magnetostratigraphic results show that the B-M boundary of borehole is located in 315m, Jaramillo subchron and Olduvai subchron are located in 405 ~430m and 772 ~816m, respectively. Three large environmental changes in Quaternary, occurred around 2.5 ~ 2. 2Ma, 1. 2 ~0. 7Ma and 0.4Ma, are identified based on integrated analysis of evaporites, clastic rock and sporo-pollen record. The uplift of Xizang ( Tibetan) Plateau was probably the main reason for these environmental changes, paleoclimate of Qaidam Basin transferred from cool, wet climate to cold, dry climate in the end of Early Pleistocene to early Middle Pleistocene because of the uplift of the Xizang( Tibetan) Plateau. The trend of aridification caused by uplift is not intensified gradually, the climate became wetter in humid period since the end of Early Pleistocene, which might result from intensified strength of summer monsoon caused through uplift of Xizang(Tibetan) Plateau, where the glacier and snow covered areas increased.