末次间冰期以来临夏地区气候变化的黏土矿物学及地球化学记录

摘要

Clay mineralogical and chemical elements analyses of the loess-paloesol deposit of Tawan Profile in Linxia Basin indicated that the climate of Linxia experienced a four-phase alteration, I. E. Relatively warm/humid (92.4 ~78. 8 ka) -cold/arid (78.8 ~59.8 ka) -relatively warm/humid (59.8 ~47.7 ka) -cold/arid (47. 7 ka to present) since the last interglacial period. The loess-paleosol deposit of the profile was dominated with illite, chlorite, mixed layer illite-smectite and minor palygorskite. Palygorskite was ubiquitous in the sediment, suggesting that on the whole the region was relatively arid throughout the period. W( TiO2 )/w( A12O3 ) ratio of the loess-paleosol deposits indicated of the same origin. The loess-paleosol alternation was attributed to different weathering intensities, which were closely related to rainfall and temperature conditions in the period. Relative proportions of clay minerals, CIA values, w ( A12O3 )/w ( Fe2O3 ) , w( SiO2 )/w( A12O3) , w( SiO2 )/w( Fe2O3 ) and w( MgO)/w( A12O3 ) varied quite sharply during the warm and humid period , but rather stable during the cold and arid period. The variation of the clay mineralogical features and major elements indicated significant cooling events occurred at the period of 92. 4 ~ 78. 8 ka and 47. 7 ka ~ present, suggesting unstability of the climate environment in Linxia since the last interglacial period, which was probably related to the winter and summer monsoons in the plateau.%临夏盆地塔湾剖面黄土-古土壤沉积物的黏土矿物学及常量元素特征分析表明,末次间冰期以来临夏地区气候变化经历了从相对温暖湿润(Ⅰ阶段:92.4-78.8 ka)-寒冷干燥(Ⅱ阶段:78.8 -59.8ka)—相对温暖湿润(Ⅲ阶段:59.8 ～47.7 ka)—寒冷干燥(Ⅳ阶段:47.7 ka以来)等4个阶段的演化.黄土-古土壤中黏土矿物以伊利石、绿泥石、伊/蒙混层及坡缕石等为主,并且坡缕石在沉积物中广泛发育,表明末次间冰期以来临夏地区总体上以相对干燥为主.w( TiO2)/w( Al2O3)比值表明沉积物剖面中黄土-古土壤层可能具有相同的物源,黄土-古土壤交替的发育特征应该为不同时期风化程度差别所致,与当时的大气降水量及温度密切相关.在相对温暖湿润的时期,黏土矿物相对含量、化学蚀变指数CIA值及w(Al2O3)/w( Fe2O3)、w(SiO2)/w(Al2O3)、w( SiO2)/w( Fe2O3)和w(MgO)/w(Al2O3)等氧化物比率变化波动较大；在寒冷干燥的时期,黏土矿物相对含量、CIA值及各氧化物比率较为稳定.黏土矿物学及常量元素变化特征共同揭示92.4-78.8 ka期间和47.7 ka以来出现明显的降温事件,说明临夏地区末次间冰期以来气候环境的不稳定性,可能与高原冬、夏季风的此消彼长密切相关.