乌东德库区古堰塞湖沉积物特征及形成年代研究

Sediment characteristics and formation age of ancient dammed lakes in Wudongde Reservoir Area

摘要

古堰塞湖湖相沉积物中含有反映地质环境演化的重要信息，通过对湖相沉积物的研究能够进一步揭示乌东德库区古堰塞湖的形成及消亡过程。以金沙江下游乌东德库区内的湖相沉积物为研究对象，通过现场调查、粒度试验和光释光测年，探讨该区湖相沉积物的空间分布、粒度层序特征和形成年代。研究结果表明：(1)乌东德库区内湖相沉积物连续分布于攀枝花市上游金沙水电站坝址下游至金坪子滑坡前缘的金沙江两岸，可见最大连续沉积厚度≥50 m,分布高程从962 m到10 38 m;(2)C-M图解显示沉积结束时水动力条件变化剧烈水力搬运能力变强，且多处“顶层”湖相沉积物与河流相砂卵石层的叠置关系反映沉积过程的结束很可能对应了一次较大程度的水动力环境突变事件；(3)根据测年结果推算的湖相沉积物开始形成时间(堵江时间)为距今53~45 ka,湖相沉积物沉积结束时间(溃坝时间)为距今20 ka左右。

Abstract

The lacustrine sediments of the ancient dammed lakes contain important information reflecting the evolution of the geological environment. Through the study of lacustrine sediments, the formation and extinction process of the ancient barrier lake in the Wudongde Reservoir Area can be further revealed. The lacustrine sediments in the Wudongde Reservoir Area in the lower reaches of the Jinsha River are taken as the research object, and the spatial distribution, grain size sequence characteristics and formation age of lacustrine sediments in this area are discussed through field investigation, grain size test and OSL dating. The results show that:(1)The elevation of lacustrine sediments visible in the Wudongde Reservoir Area ranges from 908 m to 1 038 m, mainly exposed in the broad valley and convex bank area;(2)The C-M diagram shows that at the end of deposition, the hydrodynamic conditions changed dramatically and the hydraulic transport capacity became stronger, and the superposition relationship between the “top layer” lacustrine sediments and fluvial sand and pebble beds in many places can reflect that the end of deposition process corresponded to a large-scale disastrous flood event;(3)The results of OSL dating indicated that formation time of sediments(the time to block the river) is 34 ka BP, and the end time of lacustrine sediment deposition(the time to break the dam) is about 20 ka BP.

关键词

古堰塞湖 / 湖相沉积物 / 沉积特征 / 溃决洪水 / OSL测年

Key words

ancient dammed lake / lacustrine sediments / sedimentary characteristics / outburst flood / OSL dating

Author summay

王团乐(1971—), 男, 高级工程师, 学士, 主要从事水利水电工程地质勘察方面生产与研究。E-mail: [e-mail]

基金资助

中国三峡建工(集团)有限公司科研项目(WDD/0569)

国家自然科学基金项目(U22A20601)