ISSN 1002-1027　　CN 11-2952/G2

### The Discovery and Its Significance of Late Quaternary Involution in the Area of Lower Reach of Qingshuihe River, Ningxia, China

ZHANG Ke, LIU Kaiyu, YANG Jingchun

1. Department of Urban and Environmental Sciences, Peking University, Beijing, 100871
• Received:1999-09-27 Online:2000-09-20 Published:2000-09-20

Abstract: In the lake-face strata located in the lower reach of the Qingshuihe River, Ningxia with the latitude of 37.4° N and the elevation about 1230m, involution dated in late period of late Quaternary was discovered, which indicates that the south limit of permafrost had once expanded approximately to the latitude of 37.4° N in that time in Ningxia and that the annual mean temperature was 8～9℃ lower than today. Because the intensive tectonic uplift in the northeast margin of Tibetan Plateau and cold and dry weather in the last glacial maximum, the Qingshuihe River was so blocked that along the margin of the blocked-lake the involution was developed.