The Xining Basin on the northeastern Tibetan Plateau holds the longest continuous Cenozoic stratigraphic record in China.The sequence record contains considerable information on the history of Tibetan uplift and assoc...The Xining Basin on the northeastern Tibetan Plateau holds the longest continuous Cenozoic stratigraphic record in China.The sequence record contains considerable information on the history of Tibetan uplift and associated climatic change.In particular,high resolution n-alkane biomarker proxy and pollen records have been obtained from the Paleogene sediments of the Xiejia section of the basin.A combination of the n-alkane and palynological records reveals that the paleoclimate in the Xining Basin experienced a long-term cooling trend from 50.2 to 28.2 Ma with a distinctive ecological event spanning 37.5 to 32.7 Ma.Since this ecological event,a vertical zonation of vegetation from lowland arid grasses,to middle-elevation subtropical broad-leaf plants,to high-elevation coniferous trees was established.We interpret that these changes in climate and vegetation were probably responses to a combination of long term global cooling since the Eocene climatic optimum and uplift of the surrounding mountains on the northern Tibetan Plateau in the early Cenozoic.展开更多
The Eocene was marked by significant cooling during which the global climate was transformed from greenhouse to icehouse conditions. Notable coeval events were the India-Asia collision and the retreat of the Paratethy...The Eocene was marked by significant cooling during which the global climate was transformed from greenhouse to icehouse conditions. Notable coeval events were the India-Asia collision and the retreat of the Paratethys Sea in Asia. The Eocene section of the long and continuous sedimentary succession of the Xining Basin in Northwest China is characterized by red mudstones with intercalated gypsum and muddy-gypsiferous layers. In this study, we conducted a semi-quantitative analysis of the mineralogy of bulk samples and the clay fraction using X-ray diffraction, with the aim of characterizing the Eocene climatic evolution of the northeastern margin of the Tibetan Plateau and inland Asia. We used a new pretreatment method to address the problem of extracting sufficient clay particles from the gypsum and gypsiferous layers. The bulk mineralogy is dominated by quartz, feldspar, calcite, gypsum and dolomite; and the clay mineralogy is dominated by illite, chlorite, and smectite(including irregular mixed-layer illite-smectite(I/S)). The variations of the clay mineral assemblages indicate the occurrence of alternations between warm humid conditions and hot dry conditions, with relatively high humidity during ～52–50,～41.5–39 and ～35–34 Ma. Comparison of the results with the timing of Tibetan Plateau uplift, transgressions and regressions of the Paratethys Sea, and the marine oxygen isotope record suggest that the Eocene climatic evolution of the study region was driven fundamentally by global climate change.展开更多
基金supported by the National Natural Science Foundation of China (41021001,40920114001 and 40501079)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-Q09-04)
文摘The Xining Basin on the northeastern Tibetan Plateau holds the longest continuous Cenozoic stratigraphic record in China.The sequence record contains considerable information on the history of Tibetan uplift and associated climatic change.In particular,high resolution n-alkane biomarker proxy and pollen records have been obtained from the Paleogene sediments of the Xiejia section of the basin.A combination of the n-alkane and palynological records reveals that the paleoclimate in the Xining Basin experienced a long-term cooling trend from 50.2 to 28.2 Ma with a distinctive ecological event spanning 37.5 to 32.7 Ma.Since this ecological event,a vertical zonation of vegetation from lowland arid grasses,to middle-elevation subtropical broad-leaf plants,to high-elevation coniferous trees was established.We interpret that these changes in climate and vegetation were probably responses to a combination of long term global cooling since the Eocene climatic optimum and uplift of the surrounding mountains on the northern Tibetan Plateau in the early Cenozoic.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41722206, 41430531, 41690114 & 41374072)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB26000000)the International Cooperation Program of the Chinese Academy of Sciences (Grant No. 131C11KYSB20160061)
文摘The Eocene was marked by significant cooling during which the global climate was transformed from greenhouse to icehouse conditions. Notable coeval events were the India-Asia collision and the retreat of the Paratethys Sea in Asia. The Eocene section of the long and continuous sedimentary succession of the Xining Basin in Northwest China is characterized by red mudstones with intercalated gypsum and muddy-gypsiferous layers. In this study, we conducted a semi-quantitative analysis of the mineralogy of bulk samples and the clay fraction using X-ray diffraction, with the aim of characterizing the Eocene climatic evolution of the northeastern margin of the Tibetan Plateau and inland Asia. We used a new pretreatment method to address the problem of extracting sufficient clay particles from the gypsum and gypsiferous layers. The bulk mineralogy is dominated by quartz, feldspar, calcite, gypsum and dolomite; and the clay mineralogy is dominated by illite, chlorite, and smectite(including irregular mixed-layer illite-smectite(I/S)). The variations of the clay mineral assemblages indicate the occurrence of alternations between warm humid conditions and hot dry conditions, with relatively high humidity during ～52–50,～41.5–39 and ～35–34 Ma. Comparison of the results with the timing of Tibetan Plateau uplift, transgressions and regressions of the Paratethys Sea, and the marine oxygen isotope record suggest that the Eocene climatic evolution of the study region was driven fundamentally by global climate change.
