| 摘 要： |
The Liupan Mountain area, a north-trending mountain range, located in the northeastern-most active structural margin of the Tibetan Plateau and the convergence zone of the East Asian monsoon region, provides an ideal geological setting for investigating the tectonic events in the northeastern Tibetan Plateau and the Cenozoic evolution of the Asian aridification. We provide magnetostratigraphic and paleoenvironmental records for a Late Cenozoic sedimentary core drilled in the Guyuan in the Liupan Mountain. The lithology of the core can be roughly divided into two parts. The lower part (depths of 795-40 m) is composed of lacustrine sediments and the upper part (depths of 40-0 m) is composed of fluvial deposits. Magnetostratigraphy of the 795 m deep core dates the magnetic polarity sequence between similar to 8.2 and 0.03 Ma. The Brunhes/Matuyama, Matuyama/G, and Gauss/ Gilbert boundaries are located at depths of 53.55 m, 161.50 m, and 264.75 m, respectively. Four intervals with relatively higher accumulation rates were identified at ca. 7.64-6.03, 5.24-4.18, 3.60-2.58, and 1.07-0.78 Ma. All of this evidence is probably related to the pulses of tectonic uplift of the northeastern (NE) Tibetan Plateau. The frequency-dependent susceptibility values have exhibited obvious decreasing trends since similar to 8.2 Ma, indicating obvious aridification in the Guyuan Basin since the Late Miocene, but relatively high values occurred between 4.6 and 3.5 Ma. The enhancement of the aridity in the Liupan Mountain since similar to 8.2 Ma was due to the combined effect of global climate cooling and the uplift of the Northern Tibetan Plateau since the Late Miocene. |
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