青藏高原东北缘循化-官亭地区2.6万年以来气候变化研究

STUDY ON THE LOESS RECORDS OF THE CLIMATE CHANGE SINCE 26k aB .P . FROM XUNHUA TO GUANTING BASIN IN THE NORTHEASTERN BOUNDARY OF THE TIBETAN PLATEAU

根据粉尘搬运的动力学原理,利用温湿度组合、风力强度变化和粉尘源区收扩演变特点,分析了青藏高原东北缘循化-官亭地区黄土的粒度、磁化率特征及其反映2.6万年以来的气候波动、区域环境变化以及冬夏季风关系等,划分了主要气候演化阶段,取得了以下重要认识:1)山脉阻挡是造成循化-官亭盆地黄土剖面记录气候波动差异的主要影响因素,拉脊山东南段是亚洲冬季风和高原冬季风系统的重要分割线;2)循化盆地和官亭盆地约26kaB.P.气候变化主要分为2个阶段,每个阶段又可分为若干个亚阶段;3)青藏高原东北缘官亭-循化地区全新世适宜期时间可能为6.0~3.7kaB.P.,官亭盆地和循化盆地黄土粒度磁化率明显差异的原因可能主要受风场的控制。

According to the dynamic principle of dust transportation and combining the characteristics on constitution of temperature and humidity, wind intensity change and the evolution of dust source area, two typical loess profiles in the Xunhuan-Guanting areas on the northeastern margin of the Qinghai-Xizang Plateau are studied. They are JC and XK loess-paleosol profiles, and the length of Baizhuang JC profile (35°41'21"N, 102°33'29" E) in Xunhua Basin is 2.3 m in thickness and a total of 47 samples were taken at a interval of 5 cm in this section (including the surface soil and 614C age samples). The length of Minhe XK profile (35°59'51"N, 102°44'42" E) in Guanting Basin is 6 m in thickness and a total of 61 samples were taken at a interval of 10 cm (also including 614C age samples), in this profile, 0~1.6 m is the paleosol layer and 1.6~6.0 m is the loess layer. We also find that the ages are 26.1 ka B. P. and 23.4 ka B. P. in bottom of JC profile and XK profile by dating methods. Then the grain size and magnetic susceptibility of the loess are analyzed and reflected that the climate volatility, regional environmental changes and the relationship between winter and summer monsoons since 26 ka B. P., based on the above analysis, the main climate evolution stages have been divided. In this paper, the following important understandings have been made:(1) the mountain block is the main influencing factor for the difference in the record of the loess profiles in the Xunhua-Ganting Basin. The southeastern part of the Laji Mountain is an important dividing line for the Asian winter monsoon and the Plateau winter monsoon system.(2) The climate change of the Xunhua Basin and the Guanting Basin is mainly divided into two stages since 26 ka B. P., and each of them can be divided into several sub-stages.(3) The Holocene Optimum period of the Guanting-Xunhua area in the northeastern margin of the Tibetan Plateau may be 6.0~3.7 ka B. P. And the reason for the significant difference in the grain size and magnetic susceptibility of the loess in the Guanting Basin and the Xunhua Basin may be mainly controlled by the wind field.