也谈长江上游“川峡二江”续接贯通的时限和机制  

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

作　　者：陈立德 CHEN Li-De(Wuhan Center of China Geological Survey(Central South China Innovation Center for Geosciences),Wuhan 430205,Hubei,China)

机构地区：[1]中国地质调查局武汉地质调查中心(中南地质科技创新中心),湖北武汉430205

出　　处：《华南地质》2022年第2期250-264,共15页South China Geology

基　　金：中国地质调查局项目(1212011140035,1212010013500150005)。

摘　　要：长江上游“川峡二江”续接贯通是长江水系建立的重大地质事件,其时限为早/中更新世之交,相当于“宜昌砾石层”上覆善溪窑组网纹红土底界年龄。早更新世“宜昌砾石层”“白沙井砾石层”“阳逻砾石层”等江汉-洞庭盆地周缘的“长江砾石层”与下伏地层之间呈角度不整合接触,与上覆网纹红土之间为平行不整合接触关系。“川峡二江”续接贯通促成了江汉-洞庭“中更新世古湖”的形成和广泛发育的网纹红土层沉积,这既是中更新世气候湿热、雨量充沛的表现,也是长江上游“川峡二江”续接贯通、攫取上游水源的沉积记录和环境响应。长江上游“川峡二江”续接贯通可能并非简单的河流溯源侵蚀,而是与更新世的构造运动有重大关系,或者是更新世构造运动加剧了河流的溯源侵蚀。更新世地层记录的不整合界面和砾石层中的古地震楔构造是这一构造运动在长江中游地区的重要表现形式,这一构造运动的时限为1.2~0.75 Ma,与“昆黄运动”或“元谋运动”的时限一致。正是在区域构造作用下,触发了“川峡二江”的续接贯通,甚至包括金沙江水系的演化和长江的形成,乃至中国水系的重大调整。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 manifestation of 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.

关 键 词：“长江砾石层” “宜昌砾石层” 网纹红土 古地震楔 川峡二江 

分 类 号：P534.63[天文地球—第四纪地质学]