摘要
位于现代季风区边缘的沙漠－黄土边界带，具有高度不稳定性。末次间冰期以来历经多次北进南退移动和暖湿、冷干变化。依据古风成砂－黄土－古土壤叠覆更替的沉积序列和磁化率等气候代用指标分析，对末次间冰期以来，尤其是特征时期边界带的位置进行了讨论。其中，盛冰期时移动幅度最大，南界可能达３０°Ｎ左右；末次间冰期和全新世气候鼎盛期最靠西北，南界在古长城以北。全球冰期－间冰期波动导致的气候变化以及东亚冬夏季风强弱变化是控制边界带移动和气候变化的根本因素。
The desert-loess boundary belt is a transitional zone between the desert and loess area,where aeolian sand and loess deposition are intercalated with each other.This belt is distributed extensively in China,but this study is confined to area to the east of Yinshan Mountains→Helanshan Mounains,in the transitional zone from semi humid forest to arid desert under contemporary monsoon climate. Based on the changes in sedimentary facies,magnetic susceptibility,and geochemistry indices,the climatic varioation since Last Interglacial is divided into three periods and several phases:(1)the latest warm-wet period in Last Interglacial stage which was characterized by warm wet climate in general with comparatively cold dry intervals;(2)the cold dry period in Last Glaciation(70 000～10 000 a B.P.),when the climate was cold and dry especially during 21 000～10 000 a B.P.There were two warmer (cooler) wetter stages at 56 000￣45 000 a B.P. and 35 000￣21 000 a B.P.;(3)the frequent climatic variation period in Holocene(10 000a B.P.——present).The climate retained some characteristics of the Last Glacial Period and was cold and dry in Early Holocene(10 000￣7 500 a B.P.),but warm and wet in Middle Holocene,and then fluctuating cold dry in Late Holocene. The above warm(wet) cold(dry)climatic change may be compared with the global climatic variation indicated by the oxygen isotope record in the deep sea sediments and the loess paleosol series of the adjacent Loess Plateau.The warmest (wettest)period appeared in the Last Interglacial stage and Middle Holocene;the extreme cold(dry)period occurred in the Last Glacial Maximum Period. The frequent climatic change in the desert loess boundary belt since the Last Interglacial stage reflected the multiple spatial shifts in bio climate zone and shifts in the position of the boundary belt. (1)The location of desert loess boundary belt during the Last Interglacial stage.At that time,its southern border was situated to the north of its recent position and nearly at the today's 200mm annual precipitation isoline;the northern border was close to Ulan Bator in Mongolia→Mazongshan Mountain→Anxi in China;and its width was smaller than that of today. (2)The position of desert loess boundary belt during the Last Glaical Period.At the beginning of the cold period,the boundary belt took the place of desert and desert steppe position,with its southern border located near the 450mm isohyet and its northern border similar to that of today.During the interstadial phases,the southern border was shifted 225 km northwards from today's position,approximately along the line of east side of Da Hinggan Ling→north of Hunshandake→Hohhot→Baotou→Yinchuan.During the Last Glacial Maximum,the desert loess boundary belt was shifted to the far south,with its southern border probably along situated the line of Hangzhou→Nanchang→Changsha and northwardsto Chengdu,ending at Gongga Mountain near the southern border of modern seasonally frozen ground;the northern border was close to the 400mm isohyet of today,its middle part being at the zone of the ancient Great Wall ruins. (3)The site of desert loess boundary belt during the warm period in Holocene.Its southern border went to the line of Dalad qi→Otog qi→Lingwu,which followed the present 200mm isohyet.The northern border was located in the zone of Shandan→Alxa Youqi→Yabreishan Mountain→Mongolia. The shift of desert loess boundary belt is an inevitable outcome of the global glacial interglacial climatic variation and is related to the variations of the East Asian monsoon which was strengthened by the dynamic and thermodynamic processes along with the uplift of the Qinghai Xizang Plateau.
出处
《第四纪研究》
CAS
CSCD
北大核心
1997年第2期158-167,共10页
Quaternary Sciences
基金
国家自然科学基金
中国科学院西安黄土与第四纪地质国家重点实验室基金
关键词
沙漠
黄土
边界带
气候变化
晚更新世
the Last Interglacial Period,desert loess boundary belt,climatic change
