【作者】 秦永鹏；

【导师】 杨振宇；

【作者基本信息】 南京大学 ， 构造地质学， 2012， 硕士

【摘要】 上世纪末,众多学者利用磁性地层建立了柴达木盆地第四系的年代框架,但由于采样密度与古地磁仪器精度的限制,上述年代框架已不能满足现今高精度环境变化的要求,需要新的测年数据对其进行修订与补充。本文选取柴达木盆地大浪滩地区梁ZK02孔与梁ZK06孔岩芯进行岩石磁学与磁性地层研究,探讨大浪滩地区与柴达木盆地第四纪的环境演化。岩石磁学与扫描电镜结果表明钻孔沉积物中的主要载磁矿物为胶黄铁矿、磁铁矿与赤铁矿。其中胶黄铁矿为湖泊的自生矿物,在沉积后不久形成,其携带的剩磁方向与磁铁矿、赤铁矿携带的碎屑剩磁可进行对比。磁性地层的研究结果表明梁ZK02孔岩芯的B/M界线位于315m,Jaramillo位于405-430m,Olduvai立于772-816m,布容期内记录了Norwegian-Greenland Sea事件,松山期内记录了Cobb Mountain事件,Bjorn事件,Gardar事件,Gilsa事件,Reunion Ⅱ与Reunion Ⅰ事件。梁ZK06孔岩芯的B/M界线位于326m,Jaramillo位于427-457m,Olduvai位于904-952m,并记录了松山期内的Cobb Mountain与Gardar事件。在建立年代框架的基础上,结合梁ZK02孔与梁ZK06孔的岩性与孢粉变化,认为大浪滩地区分别在2.5-2.2Ma,1.2-0.7Ma与0.4Ma发生了三次沉积环境变化。通过与前人工作的对比,认为这三次沉积环境变化在整个柴达木盆地均有记录,前两次记录了高原在第四纪的隆升,最后一次：0.4Ma的沉积环境变化是高原隆升或者其它事件所引起,还需更多的研究。上述变化中,1.2-0.7Ma的高原隆升导致柴达木盆地的气候由温凉湿润转换为寒冷干旱,并且根据岩芯中芒硝的出现,认为0.9Ma之后,柴达木盆地西部至少出现6次强冷颤动。梁ZK02孔与梁ZK06孔岩芯从底部到顶部蒸发岩含量以及种类逐渐增多,暗示了高原隆升引起的气候干旱化过程,然而高原隆升造成的气候干旱化趋势并非简单的逐渐加剧,而是在早更新世末期以来气候湿润期表现得更为湿润,这种现象的出现可能是高原隆升增加了夏季风的强度所导致,冰川和积雪面积的增大也起到了叠加作用。更多还原

【Abstract】 The chronological framework of Quarternary strata based on magnetostratigraphy in the Qaidam Basin has been carried out by many researchers during the last century. This framework, however, cannot be suitable for the high resolution study of paleo-environmental change because of lower sampling density and precision of instruments, which need to be revised by the new careful study.In order to discuss the paleo-environmental change of Dalantan area and Qaidam basin, we carried out rock magnetic and magnetostratigraphic investigations on Liang-ZK02and Liang-ZK06borehole in the Dalangtan area of the northwestern part of the Qaidam Basin. Rock magnetic and scanning electron microscope results suggest that greigite, magnetite and hematite are the main magnetic carriers in the sediments of two boreholes. Greigite is very probably authigenic origin that was formed during the deposition, which carried both normal and reversal magnetic polarities, and showed mostly consistent with the polarities defined by magnetite/hematite. Magnetostratigraphic results show that the B/M boundary of Liang-ZK02borehole is located at315m, and the Jaramillo subchron and Olduvai subchron are located in405~430and772-816m, respectively. The excursion event of Norwegian-Greenland Sea in the Brunhes Chron, and Cobb Mountain event, Bjorn event, Gardar event, Gilsa event, Reunion Ⅰ and Reunion Ⅱ events in the Matuyama Chron are also discovered. The B/M boundary of Liang-ZK06borehole is located at a depth of326m, and the Jaramillo subchron and Olduvai subchron are located in427-457and904-952m, respectively. The Cobb Mountain and Gardar events are found in the lower part of the borehole.Three large environmental changes occurred around2.5-2.2Ma,1.2-0.7Ma and0.4Ma, are identified based on integrated analysis of evaporate rock, clastic rock and pollen records in the Liang-ZK02and Liang-ZK06boreholes. These three events can be traced through entire Qaidam basin. The former two environmental changes may be related to the uplift of Tibetan Plateau, and the later need to be confirmed weather its relation with the uplift of Tibetan Plateau. Paleo-climate in the Qaidam Basin changed from cool, wet climate to cold, dry climate in1.2-0.7Ma because of the uplift of the Tibetan Plateau. It can also be inferred that at least6extreme cold weather conditions revealed after0.9Ma based on the appearance of the mirabilites in the boreholes.Gradual increasing composition and variety of evaporate rock indicate the tendency of aridification. However, this trend induced through the uplift is not intensified gradually, the climate became wetter in the humid period since the end of Early Pleistocene, which might result from intensified strength of summer monsoon caused through the uplift of Tibetan Plateau, where the glacier and snow covered areas increased.更多还原