HR: 0830h
AN: GP11C-0275    [PDF]
TI: Neogene Magnetostratigraphy of the Guide Basin and its Implications for Pliocene Evolution of the NE Tibetan Plateau
AU: * Yan, M
EM: maoduyan@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Fang, X
EM: fangxm@loess.llqg.ac.cn
AF: Chinese Academy of Science, State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Xi'an, Shanxi, 710075 China
AU: Pares, J M
EM: jmpares@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Rea, D K
EM: davidrea@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Van der Voo, R
EM: voo@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Song, C
AF: Lanzhou University, National Laboratory of Environmental Systems in Western China, Ministry of Education of China and College of Resources and Environmen, Lanzhou, Gansu, 730000 China
AU: Li, J
AF: Lanzhou University, National Laboratory of Environmental Systems in Western China, Ministry of Education of China and College of Resources and Environmen, Lanzhou, Gansu, 730000 China
AB: In order to provide age constraints to the Cenozoic clastic sedimentary rocks in the intramontane Gonghe and Guide Basins, we carried out a lithostratigraphic and magnetostratigraphic investigation of two sections north of the town of Guide. The resulting correlation of the magnetic stratigraphy with the geomagnetic polarity time scale and the lithological changes along the sections, allow us to propose new unit divisions of the sedimentary infilling of the Guide Basin. The strata are divided into two groups: the Oligocene Xining Group and the Miocene to Pliocene Guide Group. The Guide Group can now be further divided into five informal formations (with ages shown in parentheses): the Amigang (1.8 to 2.6 Ma), Ganjia (2.6 to 3.6 Ma), Herjia (3.6 to 7.8 Ma), Ashigong (7.8 to $>$12 Ma), Garang ($<$16 to 18.4 Ma) and the Guidemen Formation (18.4 to 20.5 Ma). Three episodes of rapid ($>$20 cm/ka) sediment accumulation are observed in our section during the late Miocene to latest Pliocene, with ages of about 6 Ma, 3 Ma and 1.9 Ma. Massive conglomerates of the Ganjia Formation characterize the 3.6 to 2.6 Ma interval. Massive gravels of similar ages appear to be widespread in the nearby basins of Linxia, Jiuquan (northern Qilian Shan), Hexi and Qaidam, documenting enhanced Pliocene tectonic activity and erosion in the NE Tibetan Plateau. Five S-vergent thrust faults, affecting the Miocene and Pliocene molasse sediments, caused shortening of the basin section estimated at about 25 km since 8 Ma.
DE: 1520 Magnetostratigraphy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting