腾格里沙漠南缘地处中国西北沙漠与黄土交错带,也是东亚冬季风与夏季风交替控制的过渡地带,其对全球气候变化十分敏感,是研究古气候与古生态的理想地点。选择该区域一典型剖面即土门剖面(TMS)为代表,通过野外考察、采样和室内采用X-射线荧光光谱仪进行主量元素测试,探讨了以该剖面主元素氧化物为气候代用指标指示的腾格里沙漠沙漠南缘末次间冰期5e (MIS5e)的古气候变化。年代相当于MIS5e的土门剖面末次间冰期5e层段(TMS5e)由16层风成砂、11层湖积黄土和5层湖相构成,记录了14.5个风成砂与湖相或和湖积黄土构成的沉积旋回与元素旋回。分析结果显示,该层段8种主量元素的含量高低依次为:SiO_2>Al_2O_3>CaO>TOFE(FeO+ Fe_2O_3)>K_2O>MgO>Na_2O>TiO_2,平均值依次为64.11%、11.31%、5.15%、4.08%、2.37%、2.26%、2.01%、 0.41%。这些主量元素在TMS5e层段的垂直方向上呈两组镜像对称变化:一组为SiO_2,其含量在风成砂层位显峰态,而在湖相和湖积黄土层位显谷态;另一组为Al_2O_3、TOFE、CaO、MgO、Na_2O、K_2O、 TiO_2,它们在风成砂层位呈谷态,在湖相和湖积黄土层位显谷态。土门剖面TMS5e层段的主元素氧化物指示的MIS5e腾格里沙漠南缘的气候是不稳定的,经历了14.5次暖湿与冷干交替的气候波动,且可划分为TMS5e5(139~129.30 ka BP)、TMS5e4(129.30~124 ka BP)、TMS5e3(124~ 119.50 ka BP)、TMS5e2(119.5~116.5 ka BP)和TMS5e1(116.5~113.70 ka BP)等5个亚段,其在时代上与末次间冰期5eGRIP冰芯delta~(18)O记录的5个阶段具有遥相关关系。该研究深化了对我国西北季风边缘区MIS5e古气候状况的了解,也为国际上仍有争议的MIS5e气候是不稳定的理论观点提供了有力的地质证据。
英文摘要:
Situated in the interlaced belt between the desert and loess under control of the East Asia winter and summer monsoons,the Tumen section on the southern edge of the Tenger Desert is very sensitive to the global climate changes,and it is the ideal place to study paleoclimate and paleoecology. Through the field investigation, collecting samples and experiment of x-ray fluorescence spectroscopy,we chose the TMS5e segment in the Tumen section to discuss the paleo-climate changes during the MIS5e of the Last Interglacial. The TMS5e consists of 16 layers of aeolian dune sands,11 layers of loess and 5 layers of lacustrine facies. Based on the analysis of the major elements and ages of the TMS5e segmemt,we found 14.5 major elememt cycles that are similar to the sedimentary cycles. The contents of 8 major elements in the TMS5e display as SiO_2>Al_2O_3>CaO>TOFE>K_2O>MgO> Na_2O>TiO_2,ranging from 53.63 to 74.14%,8.32 to 12.98%,2.70 to 6.99%,2.5 to 5.80%,2.07 to 2.81%,1.22 to 3.47%,1.60 to 2.41%,and 0.24 to 0.60%,respectively,with the average of 64.11%,11.31%,5.15%,4.08%, 2.37%,2.26%,2.01%,and 0.41%,respectively. The curves of major elements within the TMS5e sequence vertically present symmetric changes:SiO_2 shows high peaks in the dune sands,but low values in the lacustrine and loess. the other element Al_2O_3,CaO,TOFE,K_2O,MgO,Na_2O and TiO_2 show the opposite trend,with low values in the dune sands and high peaks in the lacustrine and loess. It suggests that the climate is instable in the TMS5e in southern Tengger Desert during the MIS5e period,and it has experienced at least 14.5 warm-cold climate fluctuations. The TMS5e could be divided into five sub-stages:TMS5e5(139-129.3 ka BP),TMS5e4(129.3-124 ka BP),TMS5e3(124-119.5 ka BP),TMS5e2(119.5-116.5 ka BP),and TMS5e1(116.5-113.7 ka BP),which correspond to the MIS5e5-MIS5e1 in the GRIP ice core. This study helps us to further understand the paleo-climate variations on the marginal areas in the Northwest of China during the MIS5e,and provide geological evidence to support the climate instability in the MIS5e.