【作者】 武力超；

【导师】 岳乐平；

【作者基本信息】 西北大学 ， 第四纪地质学， 2005， 硕士

【摘要】 青海西宁盆地地处我国东部湿润季风区、西北内陆干旱区及青藏高原高寒区的交汇地带,内部发育良好的早中新世地层,其中含著名的谢家地方哺乳动物群,动物群所在剖面是我国谢家阶的层型剖面。通过对谢家剖面的磁性地层学研究,较精确地确定谢家地方哺乳动物群年龄及其所在谢家阶的地层年代对我国北方尤其西部哺乳动物演化进程和新近系建阶,以及对青藏高原隆升过程的研究都具有重要的科学意义。 谢家剖面古地磁测量结果显示,谢家剖面记录了18个正极性段与17个负极性段,可以与标准极性柱C5ACn—C6Cn.1n之间的极性很好的对比。运用内插法得出剖面顶部的磁性地层年龄约为14.05Ma;底界年龄约为23.41Ma;整个剖面的年龄跨度约9.31Ma。 著名的谢家哺乳动物群年龄大约为18Ma左右,为早中新世中晚期,相当于MN4最早期。 测得谢家剖面中谢家组的年龄为15.68—22.93Ma,时代为中中新世晚期至早中新世晚期。因此原先认为是早中新世的谢家组上部地层实为中中新世的沉积,马哈拉沟组顶部地层为早中新世沉积。 西宁盆地、兰州盆地、临夏盆地的磁性地层、生物地层、岩石地层的对比表明位于青藏高原东北部的周缘盆地在青藏高原的第二次隆升时被迫的进行了相应的应力调整和变形,并在刚成形的亚洲季风共同作用下,导致自身古环境发生重大变迁。同时鉴于青藏高原东北部各盆地新生代地层具有较强的区域对比性,建议在以后的中国新生代地层区划中分划出青藏高原东北地层区。更多还原

【Abstract】 The early Miocene sediments deposited very well in Xining basin that located in junction zone among eastern humid monsoon areas、 northwestern inland arid areas、 alpine cold regions of Tibet plateau. It remained famous Xiejia mammal fauna. Xiejia profile that mammalian fossils were collected is also the Xiejia Stage stratotype profile. We can get the accurate age of Xiejia mammal fauna and Xiejia Stage by the magnetostratigraphy study on xiejia profile. And it was very important to the study of mammal evolution process in northern china especially in western china, Neogene Stage establishment, study of the uplift process of Tibet plateau.Paleomagnetic measurements demonstrate that Xiejia profile records 18 normal and 17 reversed polarity zones. These polarity zones corresponded very well with polarity zones between C5ACn and C6Cn.1n in Cande 95 Time scale. We use inter— interposition method to calculate the age of profile. The age of the upper stratigraphy was 14.05 Ma, the age of the lower stratigraphy was 23.41 Ma, the span of the whole profile was 9.31 Ma.The paleomagnetism age of the xiejia mammal fauna is about 18Ma. It dates as late early Miocene and is approximately equivalent to early MN4.The geological age of the Xiejia Formation is 15.68—22.93Ma. It was dated between late time of middle Miocene and late time of lower Miocene. So, the upper sediments of the Xiejia Formation deposited in middle Miocene. The upper sediments of the Mahalagou Formation deposited in lower Miocene.Great paleoenvironment change of the basins that located in northeast region of Tibet plateau is closely related to the second uplift of Tibet plateau and the formation of Asia monsoon. This conclusion was found by the analysis and correlation of magnetstratigraphy、 biostratigraphy、lithohorizon in xining basin、 lanzhou basin and linxia basin. Owning to the depositing features in these basins, the Tibet plateau northeastern stratium area should be classified by stratigraphy classification work in the future.更多还原