赤平投影方法在古地磁要素倾斜校正中的应用

针对在利用古地磁要素定量确定板块运动中,实测的古地磁要素需进行倾斜校正,古地磁学家所用的数学方法进行校正等问题,采用赤平投影方法,从古地磁的基本原理入手,重点介绍了赤平投影方法在古地磁要素倾斜校正中如何应用。得出赤平投影方法可以应用于古地磁要素的倾斜校正中,并且具有操作简单、直观的特点。     

Terrace dating as an archive of the run-through of the Sanmen Gorges

Analysis of morphological properties in the Sanmen Gorges region of the Yellow River shows that four river terraces have been developed at the entrance to the gorges. Commonly, thick aeolian loess-paleosol sequence was deposited on the terraces, which makes it easy to date the terraces. The dating of paleomagnetic, loess-paleosol sequence matching and thermoluminescence show that terraces T₂, T₃ and T₄ were formed 0.129 Ma, 0.625 Ma and 0.865 Ma ago, respectively. The formation of these terraces in this region indicates that the Yellow River has experienced four intensive downcutting events during the last 0.9 Ma. The Yellow River cut through the Sanmen Gorges and inpoured into the East China Sea no later than 0.865 Ma.     

Magnetostratigraphy and pavleo-environmental record of Tertiary deposits of Lanzhou Basin

The Tertiary deposits of the Yongdeng section, the Lanzhou Basin were studied by means of magnetostrati-graphy. The magnetostratigraphic sequences from Paleocene to Miocene were established, and the time scale for the corresponding stratigraphy and mammalian faunas was also established by referring to their correlation to the GPTS of BKSA95 (The geomagnetic polarity time scale which was thoroughly revised and updated by Berggreen et al. in 1995). In the end the paleoenvironmental records and their relationship with the uplifting of the Tibetan Plateau were discussed. The results are as follows. The top boundary of the Xiliugou Formation is dated to be 51 Ma, i.e. Eocene. TheYehucheng Formation covers the time span of 51-31.5 Ma, i.e. from late Early Eocene to early Early Oligocene. The Xianshuihe Formation covers the time span of 31.5-15 Ma, i.e. from Early Oligocene to Middle Miocene. The lower member of the Xianshuihe Formation spans from 31.5 to 20.0 Ma, i.e. from Early Oligocene to early Early Miocene. The middle member is from 20.0 to 16.5 Ma, i.e. in the middle Early Miocene.     

北京平谷马坊Zk09钻孔新生代地层格架及其地质意义

本文基于北京平谷马坊地区Zk09钻孔新生代地层岩性岩相分析和沉积物古地磁等测试,建立了北京平原泃河水系中下游冲洪积区完整新生代地层格架。其中,0m～180m为中更新世-全新世陆相辫状河和曲流河沉积,180m～240.5m为中新世-上新世残坡积、湖积和三角洲前缘沉积。Zk09钻孔新生代不连续地层揭示了北京平原区两次重要的抬升构造事件：第一期构造事件发生于中新世,而不是前人研究认定的早更新世或上新世末,其最终结束了大渤海湾盆地古近纪盆-岭构造系统演化;第二次构造事件发生于中更新世早期,其可能是目前以走滑运动为主的最新构造变动形式起始时间。