地震地质 ›› 2020, Vol. 42 ›› Issue (1): 65-78.DOI: 10.3969/j.issn.0253-4967.2020.01.005

• 研究论文 • 上一篇    下一篇

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

魏传义1,2)(), 刘春茹2), 李长安1,3,)*(), 尹功明2), 韩非2), 张岱1), 李亚伟1), 张玉芬4)   

  1. 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
  • 收稿日期:2019-03-06 出版日期:2020-02-20 发布日期:2020-02-20
  • 通讯作者: 李长安
  • 作者简介:

    〔作者简介〕 魏传义, 男, 1990生, 2019年于中国地质大学(武汉)获第四纪地质学专业博士学位, 中国地震局地质研究所博士后, 现主要从事新构造年代学与物源示踪研究工作, E-mail: chuanyiwei@ies.ac.cn

  • 基金资助:
    国家自然科学基金(41671011)资助

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

WEI Chuan-yi1,2)(), LIU Chun-ru2), LI Chang-an1,3)(), YIN Gong-ming2), HAN Fei2), ZHANG Dai1), LI Ya-wei1), ZHANG Yu-fen4)   

  1. 1) School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
    2) Institute of Geology, China Earthquake Administration, Beijing 100029, China
    3) State Key Laboratory of Biogeology and Environmental Geology, Wuhan 430074, China
    4) Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China
  • Received:2019-03-06 Online:2020-02-20 Published:2020-02-20

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。

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

Abstract:

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 1 000km2. 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 drainage and Wujiang drainage. Based on the above comprehensive analysis, researchers demonstrated that the depositing time of Yichang Gravel can best constrain the Three Gorges incising time.
The absolute altitude of Yichang Gravel exceeds 110m, and many thick sand lens are developed from top to bottom of the profiles. In this study, we applied the quartz Ti-Li center ESR dating method in Yichang Gravel to determine its absolute formation age, and then to constrain the minimum cutting-through time of Three Gorges. Eight samples(SXY-1, SXY-2, YC-1—4, LJY-1, LJY-2)were collected from the sand lens at depths of 4m, 19m, 40m, 51m, 63m, 75m, 83m and 99m respectively from the top of the profile. At the same time, in order to evaluate the residual dose of Ti-Li center after sunlight bleaching, we also sampled four modern surface Yangtze River sediments near Yichang Gravel for ESR measurement.
The result shows that the quartz Ti-Li center ESR signal intensity of the 4 modern fluvial sediments samples are zero, which implies that the Ti-Li center ESR signal intensity of quartz in Yichang Gravel sand lens could be bleached to zero before the last burial. Thus, the above results indicate that the ESR dating results of this paper are reliable. The ESR absolute age from top to bottom of the profile is 0.73Ma BP,0.87Ma BP,0.98Ma BP,1.04Ma BP,1.05Ma BP,1.10Ma BP, 1.11Ma BP, 1.12Ma BP, respectively. The ESR dating results show that the Yichang Gravel began to deposit at about 1.12Ma BP until 0.73Ma BP, and the Ti-Li center ESR age indicates that the Yangtze River cut through Three Gorges area no later than 1.12Ma BP.

Key words: Jianghan Basin, Yichang Gravel Layer, quartz, Ti-Li center, ESR dating, Three Gorges valley incision

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