科研之友
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摘要
In northwestern China, carbonate delta O-18 variation has been closely associated with evaporation and precipitation, whereas the variation of carbonate delta C-13 generally reflects patterns of palaeovegetation. Located within the transitional zone between the Chinese Loess Plateau and the Tibetan Plateau, the Lanzhou Basin has developed a continuous sequence of Cenozoic sediments which have been subjected to detailed sedimentological and high-resolution magnetostratigraphic analyses. In the present study, pedogenic carbonate O and C isotopic analyses were obtained throughout the entire Cenozoic sequence. The delta O-18 record exhibits a general positive trend with several abrupt changes. A dramatic positive shift in the delta O-18 record at similar to 33 Ma indicates the initiation of the aridification process within the basin, which was likely associated with the late Eocene westward retreat of the Tethys Sea and global cooling. Two significant positive shifts in the delta O-18 record at similar to 22 Ma and similar to 3.5 Ma are synchronous with major increases in aeolian dust deposition-on-the Chinese Loess Plateau and in the North Pacific Ocean, suggesting the intensified aridity of the Asian interior, which is likely related to the stepwise uplift Of-the Tibetan Plateau via the blocking of water vapour pathways. The delta C-13 values exhibit a weak positive trend with a remarkable shift at similar to 3.5 Ma. This trend is likely related to a decrease in vegetation density in response to the ongoing Cenozoic aridification, whereas the shift at similar to 3.5 Ma may reflect the large-scale expansion of C-4 plants.
- 出版日期2016-8-1
- 单位兰州大学
