| The change of the Cenozoic climate, the uplift weathering and erosion of the Tibetan Plateau and its effect on climate and environment are the main scientific problems of international front science at present, meanwhile, the Tibetan Plateau is a typical example to explore the interaction between the deep process and the surface process of the earth. The conceptual model holds that the uplift of the Tibetan Plateau can accelerate the weathering of the continental silicate rocks and the burial of the organic carbon, decrease the atmospheric carbon dioxide concentration, cause the Cenozoic global cooling, while the global cooling reacts to the climate change through forming the bipolar icecaps, enlarging the temperature gradient between low latitude and high latitude, lowering the sea level et al. However, duing to lacking evidence and big differences among the uplift processes of the Tibetan Plateau, the change of the Cenozoic climate, the history of the weathering and erosion and its controlling factors, which is limited our understanding on the change of the Cenozoic climate, the uplift weathering and erosion of the Tibetan Plateau and its effect on climate. At present, getting more long sequences of the tectonic and climatic records in and around the Tibetan Plateau is the key to solve these problems.Qaidam basin is the largest basin in northern Tibetan Plateau, well-developed Cenozoic stratigraphic in western Qaidam Basin is a detailed record of the deformation and uplift of the surrounding mountain, the weathering and erosion history of the provenance and the processes of the climate change. Based on "basin-mountain coupling" theory and precise Paleomagnetic age, we carried out detailed analyses of color, carbonate, chloride ion, Sulfate radical and TOC contents from the Neocene sediments in Honggouzi area, we reconstructed the Miocene climate change of this area. Through analysis of the sedimentary facies, paleocurrent direction, provenance, unconformity et al, and their responses to the tectonic activities, we reconstructed the Miocene tectonic activities of the area. We compared the erosion rate with the tectonic activities and the climate change, in order to find out the controlling factor of the Miocene erosion in this area. Through comparison with the uplift of the Tibetan Plateau, the history of the tectonic activities and erosion, the records of the local and global climate change to explore the controlling factors of the Asian climate change and the interaction among the processes of the tectonic activities, climate and erosion in northern Tibetan Plateau. Through this research, we obtained the following conclusions:1. Through high-resolution magnetostraitigraphy studies combining with the macroscopically age control of the Ostracode fossils, we established a detailed chronology sequence of the Neocene stratigraphic since17.25Ma. In addition, the widely used stratigraphic units of the Xia Youshashan, Shang Youshashan, Shizigou and Qigequan Formations were formed at>16.5Ma,16.5-10Ma,8.9-5.23Ma and<5.23Ma, respectively.2. Based on the measurement and analysis of the Carbonate contents, Chloride ion contents, Sulfate radical contents, color and TOC of the Miocene sediments in the Honggouzi section of western Qaidam Basin, the climate changes in this area can be divided into the following five stages:there is a dry climate between17.25and16.7Ma; there is a semiarid-semi humid climate between16.7and11.OMa, but is characterized by Continuous drought (the drought intensified in14.8and12.6Ma respectively); there is a relatively arid climate with fluctuations between11.0and7.8Ma; there is a semiarid climate with large fluctuations between7.8and5.6Ma (6.8-6.4Ma is a dry climate); there is a dry climate between5.6and5.23Ma.3. Through analyses the changes of the unconformity, sedimentary grain-size, sedimentary facies, the components of the conglomerates,paleocurrent direction et al, there are four intense tectonic uplift events happened in this region since17.25Ma. They happened respectively at>17.25,12.6-12.2,10-8.9and <5.23Ma.4.17.25-16.5Ma the erosion rate is the high;16.5-10Ma the erosion rate is relatively low (but12.6-12.2Ma the erosion rate is high),8.9-6.4Ma the erosion rate is high and the erosion rate increases after5.6Ma. The erosion rate of this area shows no obvious connection with climate, but is well consistent with tectonic activities, namely, the tectonic active period corresponds with the stages of the high erosion rate or the erosion rate increases dramatically. Thus, in Honggouzi area the regional tectonic activity is the main factor to control the erosion rate.5. We found the uplift of the Tibetan Plateau and the global cooling are the factors for the aridity of the Honggouzi region since middle Miocene. However, the global cooling is the main factor for the aridity.The drought events of17.25-16.7Ma and12.6Ma are mainly controlled by the uplift of the Tibetan Plateau, while the drought events of14.8,11.0and6.8Ma, and the humid events of16.7-14.8,7.8-6.8and6.4-5.6Ma are mainly controlled by the global climate change.The drought events of5.6Ma maybe controlled by the uplift of the Tibetan Plateau and the global climate change.6. The global cooling is caused by the decreasing of the carbon dioxide concentration, while the decrease of carbon dioxide concentration is caused by the silicate weathering and organic carbon burial. Through comparison with the history of the Tibetan Plateau uplift, the history of erosion around Asia, the history of the global erosion and the processes of the global cooling, we support the theory that the uplift of the Tibetan Plateau drives the global cooling.The uplift of the Tibetan Plateau and the global cooling are the factors for the late Neocene climate changes in the Honggouzi region of the western Qaidam Basin, however, the global cooling is caused by the uplift of the Tibetan Plateau. Thus, the uplift of the Tibetan Plateau is likely to be the controlling factor of the Asian inland drought. |
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