常量元素氧化物含量及其比值揭示的中晚全新世以来玛曲高原的环境演变

Environmental Evolution since the Middle-Late Holocene in the Maqu Plateau Reflected by Constant Element Oxides Content and Ratios

对玛曲高原具有代表性的黄土-古土壤-风成砂剖面(OL剖面)常量元素氧化物含量及其比值的地球化学特征分析表明:(1)常量元素氧化物总含量为91.93%且SiO2(67.93%)】Al2O3(11.2%)】Fe2O3(3.97%)】CaO(3.76%)】K2O(2.16%)】Na2O(1.81%)】MgO(1.1%);(2)玛曲高原处于较弱的脱Ca、Na初级风化阶段,并伴有碳酸盐的淋失;(3)玛曲高原的气候经历了冷干-凉润-温湿-凉干的冷暖旋回。依据常量元素氧化物含量及其比值揭示的环境特征并结合14 C测年将玛曲高原中晚全新世以来的环境演变划分为4.6ka BP以前的风沙活动强烈期、4.6~4.3ka BP的风沙活动较弱期、4.3~0.3ka BP的固结成壤期和0.3ka BP至今的风沙活动增强期4个阶段。

Based on the concentration of constant element oxides of a middle-late Holocene loess-paleosoil-aeolian profile in the Maqu Plateau,we have found the total concentration of constant element oxides is up to91.93%,and is followed by SiO2(67.93%)>Al2O3(11.2%)>Fe2O3(3.97%)>CaO(3.76%)>K2O(2.16%)>Na2O(1.81%)>MgO(1.1%).Accompanied by carbonate leaching and the depletion of mobile element Na and Ca,the profile had experienced an incipient stage of chemical weathering.The ratio of the constant element oxides indicated that the climate of the Maqu Plateau had changed in temperature cycle from cold-dry-cool-humid-warm-humid to cool-dry since middle-late Holocene.Based on the environmental characteristics revealed by concentration of constant element oxides and ratiosand combined with 14 C dating,the environmental evolution in the Maqu Plateau since the middle-late Holocene can be divided into four stages.Before 4.6 ka BP,cold-dry climate with strong winds prompted intense aeolian activities so the Plateau had experienced a strong sandstorm activity period.From4.6to 4.3 ka BP,sand activity weakened with the climate transit from cold-dry to cool-humid.During 4.3-0.3 ka BP,under the background of increasing temperature and humidity,sand dunes getting fixed and consolidated into soil.Since then sand activity increased with the climate became cool and dry.