在西风带、东亚季风和印度季风的共同影响下,青藏高原不同区域全新世气候变化过程存在显著差异,加强不同区域古气候变化研究对重建青藏高原全新世气候变化过程及理解其变化机制具有重要意义.以青藏高原东部川西高原理塘县毛垭坝盆地全新世地层为研究对象,在14C测年的基础上,通过沉积环境和多个古气候代用指标的分析,重建了全新世气候变化过程.毛垭坝盆地早-中全新世冰水湖沉积物覆盖在末次冰期冰碛物之上,晚全新世为冲洪积物.全新世沉积物在筛除砾石(粒径＞2 mm)后的粒度组成以中粉砂以下粒级(粒径＜32μm)为主,占比多＞80％,是冰川磨蚀作用的产物.磁化率在古土壤层明显增大,结合粒径＜1 μm粒度组分的出现,可能说明成壤作用生成的强磁性矿物是磁化率值增大的原因.在冰水湖还原环境中磁化率值显著减小,可能与磁性矿物溶解有关.结合总有机碳(TOC)和色度参数的综合分析表明,毛垭坝盆地早全新世气候温干,中全新世暖湿,晚全新世温干,这一变化过程与青藏高原东部全新世气候变化总的趋势相符.在晚全新世气候温干的趋势下,毛垭坝盆地在2 700 a BP古土壤发育,气候温湿.
Abstract
[Objective]The Holocene climate of the Tibetan Plateau(TP)is mainly controlled by midlatitude westerlies,the East Asian monsoon,and the Indian monsoon.Previous studies have identified different patterns of Holocene climate change in different regions of the TP.Holocene climate reconstructions for the entire TP help us comprehensively understand the internal linkages of different factors influencing the climate change in the TP.[Methods]In this paper,we study the Holocene climate in the eastern TP based on 14C dating,lithology and vari-ous proxies from the glaciolacustrine strata in the Maoyaba Basin in Litang County,western Sichuan Plateau.[Re-sults]The Early-Middle Holocene glaciolacustrine sediments covered the last glacial moraines,and then the alluvi-al-proluvial fans were common during the Late Holocene in the Maoyaba Basin.The grain size of all samples mainly shows a bimodal size distribution after sieving out＞2 mm particles.The content of the grain size below medium silt(＜32 μm)is more than 80％,which may be produced by glacial abrasion.The magnetic susceptibility increases obviously in the paleosol,and the appearance of＜1 μm particle size components may indicate that the strong mag-netic minerals were generated by pedogenesis.However,the magnetic susceptibility decreased significantly in the glaciolacustrine sediments,which may be related to the dissolution of magnetic minerals in the reducing environ-ment.[Conclusion]Comprehensive analysis of the sedimentary environment,grain size,magnetic susceptibility,total organic carbon(TOC)and color parameters indicates that the Maoyaba Basin was temperate and dry in the Early Holocene,warm and wet in the Middle Holocene,and temperate and dry in the Late Holocene.This pattern is consistent with the general trend of the Holocene climate in the eastern TP.The paleosol dated to～2 700 cal.yr.B.P.in the Maoyaba Basin indicates a relatively wet period against the background of cooling and a dry climate in the Late Holocene.
维普
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