Magnetostratigraphy and paleoenvironmental record of Tertiary deposits of Lanzhou Basin

The Tertiary deposits of the Yongdeng section, the Lanzhou Basin were studi ed by means of magnetostratigraphy. The magnetostratigraphic sequences from Paleocene to Miocene mere established, and the time scale for the correspo nding stratigraphy and mammalian faunas was also established by referring t o their correlation to the GPTS of BKSA95 (The geomagnetic polarity time sc ale which was thoroughly revised and updated by Berggreen et al, in 1995). In the end the paleoenvironmental records and their relationship with the u plifting of the Tibetan Plateau were dis cussed. The results are as follows . The top boundary of the Xiliugou Formation is dated to be 51 Ma, i.e. Eoc ene. The Yehucheng 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 Xianshnihe Formation spans from 31.5 to 20.0 Ma, i. e. from Early Oligocene to early Early Miocene. The middle member is from 2 0.0 to 16.5 Ma, i.e. in the middle Early Miocene.