天山北坡黄土记录的中更新世以来干旱化过程

对天山北坡沙湾县东湾镇厚71 m的风成黄土剖面气候代用指标的研究表明,中更新世以来北疆地区气候环境演化经历了0.80~0.60 Ma气候相对湿润时期、0.60~0.25 Ma干旱化时期和0.25~0 Ma干旱气候3个时期,气候总的变化趋势是越来越干旱。在0.60和0.25 Ma左右发生了重要的干旱化气候事件,这些事件加速了该区的干旱化进程。黄土的形成年代说明,北疆的古尔班通古特沙漠早在0.8 Ma前就已经有相当规模了,现在的干旱气候格局是0.25 Ma左右形成延续至今。天山北坡0.8 Ma开始堆积黄土、准噶尔盆地沙漠大规模扩张主要是1.2 Ma左右青藏高原及亚洲山地强烈隆升造成大气环流发生巨大调整的结果。

LOESS SEDIMENTS IN THE NORTH SLOPE OF TIANSHAN MOUNTAINS AND ITS INDICATION OF DESERTIFICATION SINCE MIDDLE PLEISTOCENE

Loess sediments in Xinjiang in the interior of Asia possess important environment information such as the formation and development of deserts,air-circulation,and the uplift of Tibetan Plateau.In this study,detailed climatic proxies of a 71 m-thick eolian loess section at Dongwanzhen in Shawan County,located at the north slope of Tianshan,are measured and analyzed.Environment history of North Xinjiang area since middle Pleistocene has been reconstructed.The environment history with a gradual drying trend can be divided into three periods.The first period from 0.80 to 0.60 Ma is a relative wet stage,the second period from 0.60 to 0.25 Ma is an accelerated drying stage,and the third period from 0.25 Ma to now is the formation of modern dry climate stage.Two significant climatic events that happened around 0.60 and 0.25 Ma promoted the process of drying.These evidences indicate the deserts existed in North Xinjiang area as early as 0.8 Ma,and the modern dry climatic pattern formed during 0.25 Ma.