Another Discussion about the time and Mechanism of the Connection of “Chuan and Xia Rivers” in the Upper Reaches of the Changjiang River

The connection of Chuan and Xia Rivers in the upper reaches of the Changjiang River is a major geological event for the establishment of the Changjiang River system with the time of the cross of early and middle Pleistocene, equivalent to the bed age of reticulated red clay of the Shanxiyao Formation, which overlying the early Pleistocene Yichang gravel bed. The early Pleistocene gravel layers, named Yichang gravel bed, Baishajing gravel bed and Yanglou gravel bed on the periphery of Jianghan-Dongting basin, have angular unconformable contact with the lower strata and parallel unconformable contact with the overlying reticulated red clay. The connection contributed to the formation of the middle Pleistocene Palaeo-lake of Jianghan-Dongting and the extensive development of the reticulated red clay deposit, which is not only the performance of hot and humid climate, abundant rainfall in the middle Pleistocene, but also the sedimentary record and environmental response of the obtained upstream water source through the connection. It may not be simply due to river traceability erosion, but has a significant relationship with the Pleistocene tectonic movement, or the movement may aggravate the erosion. The unconformable interference recorded by Pleistocene stratigraphy and the paleo-seismic wedge structure in the gravel layer are important manifestationof the tectonic movement in the middle reaches of the Changjiang River. The time of this tectonic movement is 1.2-0.75 Ma, consistent with the time of kunhuang movement or Yuanmao movement. It was the action of regional tectonic movement that triggered the connection of Chuan and Xia Rivers, and even the evolution of the Jinsha river system and the formation of the Changjiang River, as well as the major adjustment of China's river system.