摘要:
青藏高原在末次冰期晚期(30—40 ka B.P.,相当于MIS3a阶段)出现的暖湿气候事件强烈地影响了川西高原东缘河流地质生态环境.表现在深切河谷中普遍发育大型滑坡、泥石流、冲洪积扇体等灾变事件和古堰塞湖沉积.本文重点剖析了岷江上游、大渡河中游大型堵江事件的地形地貌特点、沉积物发育特征、沉积年代学、新构造背景等,同时分析了黄河上游玛曲段大型冲-洪积扇体的沉积特征与时代.结果表明在川西高原东缘深切河谷普遍存在距今30—40 ka时期的堵江事件,而这一时期在黄河上游发生大型冲-洪积事件和黄河袭夺若尔盖古湖事件,二者均与青藏高原末次冰期暖湿事件同步.研究认为这期急剧气温变化增强了河谷侵蚀和卸载能力,而东缘强烈的地震断层活动又触发了突发事件的发生,暖湿气候事件与新构造运动在时空上的耦合共同塑造了晚更新世晚期川西高原东缘深切河谷系统特殊的地质生态环境及其演变.
Abstract:
The 30–40 ka B.P. warm-humid climate event (corresponding to the epoch of MIS3a) that occurred during the last glacial period in Tibet greatly influenced the geoenvironment in west Sichuan, characterized by development of large-scale catastrophic landslides, mudflow, alluvial and colluvial fans, dammed lakes and river capture, etc.. In this paper, the authors present morphological and depositional features, geochronology and neotectonic settings of some typical, large-scale river damming events documented along the upstream Minjiang and Dadu Rivers, and along the Maqu valley of the Yellow River. The results show that large-scale river damming in the deeply incised river valley in west Sichuan plateau and alluvial and fluvial fans deposition along the Maqu Valley of the Yellow River as well as the capture of the Zoig Lake by the Yellow River consistently occurred during the time span of 30–40 ka B.P., which was synchronous with the warm-humid climate event in Tibet. It is considered that rapid increase in temperature enhanced the capability of river erosion and deposition, while large earthquakes on active faults in east Tibet might have triggered catastrophic events in the river valleys, thus the warm-humid climate event was coupled tempo-spatially with neotectonics, which jointly shaped the geo-ecosystem of the deep-incised valleys in western Sichuan.
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