Located at the northeastern margin of the Qinghai-Tibet Plateau(QTP) in the Asian interior, the Lake Qinghai is sensitive to environmental change and thus an outstanding site for studying paleoenvironmental changes. Thick deposits in the Lake Qinghai provide important geological archives for obtaining high-resolution records of continental environmental history. The longest drilling core obtained from the Lake Qinghai, named Erlangjian(ELJ), reached about 1109 m and was investigated to determine its clay mineral assemblage and grain size distributions. Clay mineralogical proxies, including type, composition, and their ratios, as well as the illite crystallinity(KI) and chemical index(CI), in combination with grain size data, were used for reconstructing the history of paleoenvironmental evolution since the late Miocene in the Lake Qinghai Basin. The clay mineral records indicate that the clay mainly comprise detritus originating from peripheral material and has experienced little or no diagenesis. The proportion of authigenic origin was minor. Illite was the most abundant clay mineral, followed by chlorite, kaolinite, and smectite. Variations of clay mineral indexes reflect the cooling and drying trends in the Lake Qinghai region, and the grain size distribution is coincided with the clay minerals indexes. The paleoclimatic evolution of the Lake Qinghai Basin since the late Miocene can be divided into five intervals. The climate was relatively warm and wet in the early of late Miocene, then long-term trends in climate change character display cooling and drying; later in the late Miocene until early Pliocene the climate was in a short relatively warm and humid period; since then the climate was relatively colder and drier. These results also suggest multiple tectonic uplift events in the northeastern QTP.
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：SiO2〉Al2O3〉CaO〉TOFE（Fe O＋Fe2O3）〉K2O〉MgO〉Na2O〉TiO2,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SiO2,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Al2O3、TOFE、CaO、Mg O、Na2O、K2O、TiO2,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5e GRIP冰芯δ18O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。
腾格里沙漠南缘土门剖面末次冰消期层段由3层沙丘砂、2层湖相沉积、2层古土壤和5层黄土构成。主元素氧化物中，Si02含量在沙丘砂层呈现峰态，而在黄土、湖相沉积及古土壤呈现谷态；A1203、TFe（Fe203＋FeO）、CaO、MgO、Na20、K20和TiO2则在沙丘砂层呈现为谷，在黄土、湖相沉积及古土壤中呈现为峰，Si02分别与A1203等氧化物在垂直方向上呈镜像对称。结合研究区地形，对元素氧化物特征分析后，认为可用硅铝比高低变化指示本区东亚冬夏季风变化。划分出了9个冷暖波动事件，按时间先后依次为：C5（14930-14847 a BP）、W4（14847-13810 a BP）、C4（13810-13620 a BP）、W3（13620-13340 a BP）、C3（13340-13010 a BP）、W2（13010-12650 a BP）、C2（12650-12050 a BP）、W1（12050-11860 a BP）和C1（11860-11600 a BP）。本研究层段与格陵兰GRIP冰芯及南京葫芦洞石笋记录的末次冰消期冷暖变化有较高的相似性，可能本区末次冰消期季风气候变化受北半球高纬驱动。
