摘要
根据已发现的若干古冰缘现象,北京西山可以划分为6次更新世冰缘期。在冰缘期期间,地表气温比现今低12—15℃;冬季固体降水量比现今大;多年冻土深度达-3—20m以上;自然环境为稀树草原或冻原。中国东部冰缘区南界达38°N。
Periglacial phenomena are widely distributed in Western Mountain of Beijing, China. This paper is the first report on the studies of some fossil periglacial phenomena in that region. Four kinds of fossil periglacial phenomena were found: ice wedges, periglacial involution, congelifolds and congelisolifluctive deposits. According to stratigraphical and chronological data, the periglacial periods have been divided as following:
1. Guanting periglacial period, characterized by the congelisolifluctive deposits developed in Shizhuang formation, with an age of 2.43 Ma B.P. from paleomagnetic dating;
2. Yanchi periglacial period, characterized by the congelifold developed in Yanchi formation, with an age of 0.5 Ma B.P. from pleomagnetic dating;
3. Zhaitang periglacial period(Ⅱ), characterized by the periglacial involution developed in Zhaitang formation, with an age of 0.3 Ma B.P. from paleomagnetic dating;
4. Zhaitang periglacial period( Ⅰ ), characterized by the ice (soil) wedge developed in Zhaitang formation, with an age of 0.2 M a B.P. from paleomagnetic dating;
5. Qiansangyu periglacial period(Ⅱ), characterized by the ice (sand) wedges developed in Qiansangyu formation, with an age of 0.13 Ma B.P. from paleomagnetic dating;
6. Qiansangyu periglacial period( Ⅰ), characterized by the ice (soil) wedge developed in Qiansangyu formation, with an age of 0.018 Ma B.P. from thermolunscent dating.
These fossil ice wedges, periglacial involutions and congelifolds indicated a rather arid and windy periglacial environment with a mean annual temperature estimated to be some 12 -15℃colder than that at the present. During about 0.5-0.018 Ma B.P., the southern boundary of Pleistocene permafrost extended to the latitude 38°N. The depth of permafrost is about -3 m to -20 m, during Pleistocene periglacial periods.
Finally, the problems on vegetations, precipitation etc. were discussed.
出处
《冰川冻土》
CSCD
北大核心
1991年第2期159-167,共9页
Journal of Glaciology and Geocryology
基金
中国科学院地质研究所科学基金
关键词
冰缘
更新世
自然环境
Pleistocene, periglacial phenomena, periglacial periods, natural environment
