宜昌砾石层石英Ti-Li心ESR年龄及其对三峡贯通时限的指示  

CHRONOLOGY OF YICHANG GRAVEL LAYER BASED ON QUARTZ TI-LI CENTER ESR DATING AND ITS IMPLICATIONS FOR THE INCISION TIMING OF THE THREE GORGES VALLEY

作　　者：魏传义[1,2] 刘春茹[2] 李长安[1,3] 尹功明 韩非[2] 张岱[1] 李亚伟 张玉芬 WEI Chuan-yi;LIU Chun-ru;LI Chang-an;YIN Gong-ming;HAN Fei;ZHANG Dai;LI Ya-wei;ZHANG Yu-fen(School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;Institute of Geology,China Earthquake Administration,Beijing 100029,China;State Key Laboratory of Biogeology and Environmental Geology,Wuhan 430074,China;Institute of Geophysics and Geomatics,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学(武汉),地球科学学院,武汉430074 [2]中国地震局地质研究所,北京100029 [3]生物地质与环境地质国家重点实验室,武汉430074 [4]中国地质大学(武汉),地球物理与空间信息学院,武汉430074

出　　处：《地震地质》2020年第1期65-78,共14页Seismology and Geology

基　　金：国家自然科学基金(41671011)资助。

摘　　要：江汉盆地是长江贯通三峡后的第一个卸载盆地。前人的研究表明堆积于江汉盆地西缘的宜昌砾石层是三峡贯通后的直接沉积地层,因此,宜昌砾石层堆积的下限年龄可为长江贯通三峡提供重要的年代约束。但传统的相对年代学方法研究在宜昌砾石层中难以取得较好的成果。因此,直接对快速堆积的宜昌砾石层的形成年代和时间跨度开展年代学研究就需要寻找一种更可靠的绝对测年方法,同时这也是现有研究中的一个重点和难点。据此,文中在宜昌砾石层最具代表性的3个连续的沉积剖面上自上而下系统地采集了8个厚层砂质透镜体样品,采用石英Ti-Li心ESR测年方法对其堆积年代和地层时代跨度进行研究。结果显示:宜昌砾石层堆积的年代下限约1.12Ma BP,上限约0.73Ma BP,为早更新世晚期到中更新早期约0.4Ma的沉积层。结合前人的物源示踪结果,分析认为至少在1.12Ma BP之前长江就已经贯通三峡。Uplift of Tibet Plateau and formation of Asian Monsoon greatly affect East Asian geomorphological evolution,climate change and environment systems.Thus,those phenomena also control the origin,size and direction of river systems.The Yangtze River,as the most important linkage between Tibet Plateau and the East Asian marginal seas,delivers large volumes of water,sediment,and associated chemicals from its headwater regions and tributaries to the East China Sea,significantly influencing sedimentary system evolution in its drainage basin.Therefore,the formation of the modern Yangtze River and its geological-time evolution history have been paid more and more attention to since the beginning of the last century.After debated for more than a century,the First Bend in Shigu area and the Three Gorges have been known as the key capture point of the Yangtze River’s evolution history.In particularly,the Three Gorges incision period remains greatly controversial,which mainly focuses on Cretaceous period-Neogene period,early Pleistocene period,and late Quaternary period.The Yichang Gravel,just located downstream and outlet of the Three Gorges with an inverted triangle shape,is mainly distributed in western Jianghan Basin with over 1000 km^2.Because of its wide distribution and key geographical location,many typical profiles of Yichang Gravel have been the critical materials for studies on stratigraphic division,geomorphic evolution,and paleoenvironment change in middle Yangtze River Basin,especially on the Three Gorges incision history.Based on the previous field investigation,the Yichang gravel unconformably overlies the Cretaceous bedrocks and underlies the mid-Pleistocene vermicular red earth.In addition,studies on heavy mineral assemblages,Pb isotopic compositions of detrital K-feldspar grains,magnetic characteristics as well as pollen assemblage characteristics have showed that sediments in Yichang Gravel are mainly derived from upper Yangtze River Basin,such as Jinshangjiang drainage,Minjiang drainage,Jialingjiang drai

关 键 词：江汉盆地 宜昌砾石层 石英 Ti-Li心 ESR法测年 三峡贯通 

分 类 号：P597[天文地球—地球化学]