基于端元法的银川盆地MIS6—MIS5气候变化探究

MIS6-MIS5 Climate Change of Yinchuan Basin Based on End-member Method

银川盆地位于东亚季风与西风带的交界带,地层沉积物记录着气候环境的演变信息。通过对银川盆地LS01钻孔沉积物进行光释光定年、粒度分析以及端元分析重建了该地区MIS6—MIS5时期的气候演变序列。结果表明,端元分析得到4个有具体环境指示意义的端元Em1—Em4:Em1代表了水动力较弱的弱流水或湖沼相沉积;Em2代表了水动力较强的河流沉积;Em3和Em4可指代区域构造抬升事件。气候演变分为6个阶段:150~137 ka(MIS6),银川盆地气候冷干,出现两次构造抬升事件;137~110 ka(MIS5),气候整体较为暖湿,期间有3次暖事件a1(137~129 ka)、a2(124~120 ka)和a3(118~111 ka);110~107 ka(MIS5),气候转向冷干;107~102 ka(MIS5),气候由冷转暖,出现冷事件b1(106~104 ka),整体偏暖湿;102~87 ka(MIS5),气候较冷干;87~75 ka(MIS5),出现冷事件b2(87~84 ka),但整体偏暖湿。该区域MIS6—MIS5阶段气候变化主要受夏季太阳辐射和岁差驱动。

The Yinchuan Basin is located in the junction of the East Asian monsoon and the west wind strip.Sediments in the basin records the climatic environment evolution.In this study,the climatic evolution sequence(MIS6-MIS5 period)in the basin was reconstructed with photoluminescence dating,grain-size analysis,and end-element analysis on sediments from borehole LS01.Four end-members(Em1 to Em4)with specific environmental indications were obtained from the end-element analysis.Em1:weak flow or lacustrine-facies deposits with weak hydrodynamics;Em2:fluvial deposits with strong hydrodynamics;Em3 and Em4:regional tectonic uplift.The climate evolution comprises six stages(1-6):(1)Yinchuan Basin had cold-arid climate with two tectonic uplift events in 150-137 ka(MIS6);(2)The climate was warm and humid as a whole,and there were three warm events at a1(137-129 ka),a2(124-120 ka),and a3(118-111 ka)in 137-110 ka(MIS5);(3)the climate turned to cold and arid in 110-107 ka(MIS5);(4)107-102 ka(MIS5),cold events b1(106-104 ka)and b1(106-104 ka)occurred and the climate was cold and dry in general;(5)102-87 ka(MIS5),the climate was cold and arid;(6)in 84-75 ka(MIS5),there was a cold event L2(87-84 ka)but the climate was warm and humid as a whole.The climate change in MIS6-MIS5 phase was mainly driven by solar radiation and precession in summer.