滇西北丽江地区石鼓古湖的发现及其在现代金沙江河谷发育中的意义  

Discovery of Shigu Paleolake in the Lijiang area, northwestern Yunnan, China and its significance for the development of the modern Jinsha River valley

作　　者：赵希涛[1] 曲永新[1] 张永双[2] 胡道功[2] 郭长宝[2] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《地质通报》2007年第8期960-969,共10页Geological Bulletin of China

基　　金：中国地质调查局国土资源大调查项目<滇藏铁路沿线地壳稳定性调查评价>(编号:1212010541404)资助。

摘　　要：在云南石鼓"长江第一湾"附近河段两岸发现了10多处典型的第四纪湖相沉积物露头,它们构成了金沙江第二、三、四级阶地的基座。热释光(TL)和U系法年龄测定及磁性地层学研究结果表明,该套湖相沉积物中上部的时代属于243.3～88.0kaBP的中更新世晚期至晚更新世早期,上覆的第四级阶地沉积物的年龄为88.0～80.9kaBP。湖相沉积物的粒度、地球化学和粘土矿物分析结果表明,其沉积环境有由温湿向湿热转化的趋势。根据对玉龙雪山更新世冰川作用的研究,石鼓古湖最初应是玉龙雪山西麓中更新世早期玉龙冰期冰碛物堰塞金沙江河谷而成的,中更新世晚期丽江冰期的冰水沉积物进一步加以堰塞,直至8万多年前被金沙江侵蚀而再次贯通。The authors found more than a dozen outcrops of typical Quaternary lacustrine deposits on both banks of the Jinsha River near the ＂First Bend of the Yangtze River＂, Shigu, Yunnan, which constitute the bases of terraces Ⅱ, Ⅲ and Ⅳ of the Jinsha River. The results of the thermoluminescent and U-series dating and magnetostratigraphic research show that the ages of the middle and upper parts of the lacustrine deposits range from 243.3 to 88.0 ka BP, being equivalent to late Middle Pleistocene to early Late Pleistocene, while the ages of the deposits of overlying terrace Ⅳ range from 88.0 to 80.9 ka BP. The grain size, geochemical and clay mineral analyses of the lacustrine deposits show that their sedimentary environment had a trend of changing from warm-humid to hot-humid. According to a study of the Pleistocene glaciation of the Yulong Snow Mountains, ＂Paleolake Shigu＂ was an ice-dammed paleolake formed by damming of the Jinsha River valley by moraines of the early Middle Pleistocene Yulong glaciation and later further damming by glaciofluvial deposits of the late Middle Pleistocene Lijiang glaciation at the western foot of the Yulong Snow Mountains. It opened and overflowed owing to erosion of the modern Jinsha River more than 88,000 years ago.

关 键 词：滇西北 石鼓“长江第一湾” 同位素年龄测定 中-晚更新世 古湖 金沙江河谷发育 

分 类 号：P941.78[天文地球—自然地理学] P941.77