HR: 08:00h
AN: T11G-01    [Abstracts]
TI: Stable Isotopic Constraints on Climatic and Topographic Development Along the Northern Margin of the Tibetan Plateau
AU: * Kent-Corson, M L
EM: malkc@stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305, United States
AU: Ritts, B D
EM: britts@indiana.edu
AF: Indiana University, Department of Geological Sciences, Bloomington, IN 47405, United States
AU: Graham, S A
EM: graham@pangea.stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305, United States
AU: Chamberlain, C P
EM: chamb@stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305, United States
AB: One of the salient features of the greater Himalayan/Tibetan orogen is the large sedimentary basins that sit along the northern margin of the Tibetan Plateau. These basins record the surface uplift of adjacent ranges and the attendant reorganization of climatic patterns. As such, we present a record of oxygen and carbon isotope values of Cenozoic sedimentary units along the northern margin of the Tibetan Plateau. The 15 sedimentary sections that this study encompasses have been measured and sampled at the meter scale, and include strata of fluvial, lacustrine, floodplain, and alluvial fan origin, as well as deposits of one brief marine transgression. Localities studied include sections in the Qaidam Basin (Xiao Qaidam, Lake Mahai, Lao Mangnai, Ganchaigou, Lenghu, and Lulehe), Tarim Basin (Puska, Aertashi, Miran River, and Jianggalsay), Hexi Corridor (Shiyougou, Jiuquan, and Baiyanghe), and the Altun Shan (Subei and Xorkol). These sections were chosen because they are the most temporally complete nonmarine Cenozoic sections in the region and have the most robust age constraints, which include biostratigraphy, magnetostratigraphy, and thermochronology. Many of the same sections have also been previously used to decipher the structural history of nearby ranges. An initial subset of the >3,000 samples collected agrees with the previous findings of Graham et al., 2005, but our increased spatial and temporal resolution reveals how isotopic stratigraphic records locally reflect development of topography and subsequent reorganization of atmospheric circulation. For example, in the Qaidam Basin, two stratigraphic sections in the northern part of the basin show that oxygen isotope values increase steadily by 5-6 permil from the middle Eocene to Pliocene, despite several changes between fluvial and lacustrine depositional environments. This contrasts with the isotope stratigraphies from western Qaidam presented in Graham et al. (2005) and this study, that show a steady oxygen isotope profile between the Oligocene and Miocene, followed by a decrease in oxygen isotope values between the Miocene and Pliocene. The variation in isotopic records shows that the isotopic expression of the development of topography may vary widely within a basin depending on study locale. Isotopic analysis of modern waters that we and others have collected in this region is consistent with this interpretation, with rivers recording distinct values locally depending on their drainage area. The importance of local bounding ranges controlling the isotopic evolution of these sections is confirmed by our paleocurrent and provenance work.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 8100 TECTONOPHYSICS
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8169 Sedimentary basin processes
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: 2007 Fall Meeting