摘要
青海湖湖东地区广泛分布着风成沉积物,区域内典型风成沉积剖面的年代数据和环境代用指标准确记录了区域古环境变化。沉积物粒度端元分析方法能够将复杂的粒度数据分离出多个具有特定指示意义的粒度端元组分,广泛应用于古环境的重建研究。基于多次野外综合考察,选取青海湖湖东沙地厚度为500 cm的全新世典型风成砂-古土壤剖面,采用粒度端元分析方法对粒度数据进行分离,筛选出3个代表不同沉积动力特征的端元组分。通过分析各端元的粒度分布特征,并结合色度、磁化率和有机质指标进行对比分析发现,端元1与区域暖湿气候条件下的风化成壤作用有关,可以间接指示区域的水分条件;端元2和端元3代表了近地面风力的强弱,共同指示区域风沙活动的强弱。结合剖面年代和其他代用指标以及已有研究结果,可将研究区全新世以来的气候变化大致分为4个阶段:9.5 ka B.P.以前,气候整体以冷干为主;9.5~3.5 ka B.P.,气候温暖湿润,成壤作用明显增强;3.5~1.5 ka B.P.,气候经历暖湿-冷干的转变;1.5 ka B.P.以来,气候总体冷干。
The Qinghai Lake Basin,located in the northeast of Qinghai-Tibet Plateau,is an ideal region for studying palaeoenvironmental changes due to its special geographical location and sensitive response to climate change.In this paper,we obtained a typical aeolian sand-paleosoil profile on the eastern edge of the east sandy land of Qinghai Lake,named DST3(36°46'12.07"N,100°53'3.86"E;3549 m a.s.l.;ca.500 cm in thickness).Using AMS14C and Optically Stimulated Luminescence(OSL)chronometry to determine the age of the profile,the ages of the profile is 0~10.6 ka B.P.At the same time,the climatic proxies such as the grain-size,chromaticity,magnetic susceptibility and organic matter of the sediment of the profile were measured,and using the End-Member unmixing method to decompose the grain-size data into 3 End-Members.Among them,the End-Member 1(peak value is 11.2μm)consists of a silt-sized(2~63μm)main component,which is a near-surface suspended component,and its content is the highest in the palaeosol layer(48.7%).Combined with the support of other climate proxies,we think that the End-Member 1 is related with the pedogenesis of aeolian deposits,and indirectly indicates the dry and wet changes in the area.End-Member 3(peak value is 126.7μm)is the coarsest component in the profile,and the main component of the grain size is fine sand(125~250μm),which belongs to the near-surface jump component,and its content is the highest in the aeolian sand layer(55.1%),combined with the support of other climate proxies,we think that End-Member 3 can indicate the strength of the regional aeolian activity.End-Member 2(peak value is 111.5μm)is dominated by very fine sand(63~125μm)and fine sand,and contains a small amount of silt,which is a near-surface suspension and jump component.Its content is the highest in sandy loess layer(65.2%).End-Member 2 and the chromaticity parameter a*have a similar change trend in the vertical direction of the profile,indicating that the End-Member 2 is controlled by the strength of the wind,but it is not completely consistent with the environment indicated by End-Member 3.Therefore,we think that End-Member 2 may be a near-source deposition under the action of lower-intensity near-surface winds,which together with End-Member 3 indicates the strength of regional aeolian activity.In order to explore the characteristics of the Holocene climate change in the study area,we combined the existing records of paleoenvironmental proxy records,such as summer insolation,content of total organic carbon in sediments and pollen concentration of trees in Qinghai Lake,etc.The Holocene climate and environmental changes in the study area is roughly divided into four phases:(1)Before 9.5 ka B.P.,the climate was generally cold and dry,with a tendency toward warm and humid.The wind force was weakened,and the effect of pedogenesis was improved.(2)In the period of 9.5~3.5 ka B.P.,the conditions of hydrothermal combination were better.The climate was warm and humid,and the pedogenesis effect was relatively strong.(3)The climate tended to be cold and dry during the period of 3.5~1.5 ka B.P.,regional aeolian activity began to increase,and the intensity of pedogenesis weakened.(4)Since 1.5 ka B.P.,the climate has further deteriorated and the aeolian activity has intensified.
作者
白敏
鲁瑞洁
丁之勇
王琳栋
Bai Min;Lu Ruijie;Ding Zhiyong;Wang Lindong(MOE Engineering Research Center of Desertification and Blown-Sand Control,Faculty of Geographical Science,Beijing Normal University,Beijing 100875;State Key Laboratory of Earth Surface Processes and Resource Ecology,Faculty of Geographical Science,Beijing Normal University,Beijing 100875)
出处
《第四纪研究》
CAS
CSCD
北大核心
2020年第5期1203-1215,共13页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41571184)资助。
关键词
青海湖
粒度端元
全新世
环境变化
Qinghai Lake
End-Member analysis
Holocene
environmental change
