The widely distributed thick gravel deposits along the rim of the Tibetan Plateau have been long thought to be the product of rapid tectonic uplift of the plateau. However, this has been challenged by recent works tha...The widely distributed thick gravel deposits along the rim of the Tibetan Plateau have been long thought to be the product of rapid tectonic uplift of the plateau. However, this has been challenged by recent works that suggest these thick gravels may be the result of climate change. In this paper we carried out a detailed field measurement of gravel grain sizes from the Jiuquan and Gobi Gravel Beds in the top of the Laojunmiao section in the Jiuxi Basin in the northern margin of Qilian Mts. (northern Tibetan Plateau). The results suggest that the grain sizes of the Jiuquan and Gobi Gravel Beds over the last 0.8 Ma are characterized by nine coarse-fine cycles having strong 100-ka and 41-ka periodicities that correlate well with the loess-paleosol monsoon record and isotopic global climatic record from deep sea sediments as well as by a long trend of coarsening in gravel grain size. The coarse gravel layers were formed during the warm-humid interglaciations while the fine layers correspond to the cold-dry glaciations. Because the paleoclimate in NW China began to get dramatically drier after the mid-Pleistocene, we think the persistent coarsening of gravel grain size was most probably caused by the rapid uplift of the northern Tibetan Plateau, and that the orbital scale cyclic variations in gravel grain size were driven by orbital forcing factors that were superimposed on the tectonically-forced long-term coarsening trend in gravel size. These findings also shed new light on the interaction results of climate and tectonics in relation to the uplift of the Tibetan Plateau.展开更多
基金Supported by NSFC (Grant Nos. 40334038 and 40421001)the National Basic Research Program of China (Grant No. 2005CB422000)the President Fund Program of Chinese Academy of Sciences
文摘The widely distributed thick gravel deposits along the rim of the Tibetan Plateau have been long thought to be the product of rapid tectonic uplift of the plateau. However, this has been challenged by recent works that suggest these thick gravels may be the result of climate change. In this paper we carried out a detailed field measurement of gravel grain sizes from the Jiuquan and Gobi Gravel Beds in the top of the Laojunmiao section in the Jiuxi Basin in the northern margin of Qilian Mts. (northern Tibetan Plateau). The results suggest that the grain sizes of the Jiuquan and Gobi Gravel Beds over the last 0.8 Ma are characterized by nine coarse-fine cycles having strong 100-ka and 41-ka periodicities that correlate well with the loess-paleosol monsoon record and isotopic global climatic record from deep sea sediments as well as by a long trend of coarsening in gravel grain size. The coarse gravel layers were formed during the warm-humid interglaciations while the fine layers correspond to the cold-dry glaciations. Because the paleoclimate in NW China began to get dramatically drier after the mid-Pleistocene, we think the persistent coarsening of gravel grain size was most probably caused by the rapid uplift of the northern Tibetan Plateau, and that the orbital scale cyclic variations in gravel grain size were driven by orbital forcing factors that were superimposed on the tectonically-forced long-term coarsening trend in gravel size. These findings also shed new light on the interaction results of climate and tectonics in relation to the uplift of the Tibetan Plateau.
