腾格里沙漠腹地第四纪古湖泊演化过程研究

In the arid Tengger desert, more than one humid large river or lake period were existed during the geological history, especially a megalake in late Quaternary. According to this, the paleoenvironmental research of deserts is not only in aridification and desert formation, but also in the evolution of alternation between desert and lake. The first drill core in the central Tengger Desert, revealed that the lake already formed before the desert formation at 0.9Ma; and deserts alternated with lakes after the desert formation. But the definite processes of the paleolake evolution were still not clear, also the climatic condition controlling the alternation between desert and lake. Therefore, we want to place another drill core at Bayankehu Lake, the largest lake in the central desert. The chronological frame of the core will be established after systemic paleomagnetism and OSL dating; and the sedimentary environment will be determined after grain-size and color analysis combining with the first drill core. Based in these, the processes of paleolake during Quaternary will be confirmed; the desert formation and desert developmental pattern will be perfected; and the mechanism controlling the alternation between desert and lake will be understood. Meanwhile, some valuable hydrographic geological data will be provided for ecological and agricultural developing.

现今干旱的腾格里沙漠在地质历史时期存在不止一次水分充裕的河湖期，甚至在晚第四纪有古大湖发育。腾格里沙漠的古环境研究不仅仅局限于干旱化与沙漠形成这一科学问题，更为重要的是开展沙漠与河湖耦合演化的综合研究。我们在沙漠腹地首个钻孔的研究表明，在0.9Ma沙漠出现之前湖泊已经存在，之后存在多次沙漠和湖泊的交替；但是对于古湖泊的具体期次和控制沙漠和湖泊交替演化的气候条件至今仍不清楚，因此申请在沙漠腹地大湖区中心的巴彦克湖进行岩心钻探。通过系统的古地磁和光释光年代学研究建立该钻孔的年代框架；结合已有的首个钻孔记录，通过粒度和色度分析确定沉积环境。以确定腾格里沙漠第四纪古湖泊的演化阶段，完善沙漠形成历史和沙漠发育模式研究，探寻干旱化趋势下沙漠形成过程中控制沙漠与湖泊消长发育的构造和气候因素，并为现代水文水资源应用提供基础地质资料。

为了了解位于西风-季风交汇区的腾格里沙漠第四纪古湖泊的演化历史，项目在腾格里沙漠腹地图兰太盐湖进行岩心钻探，孔深122.63 m，平均取心率75%，遗失地层主要为含水丰富的中、细砂层。整个钻孔从底到顶可分为四个岩性段：122.63-110.86 m，黄色细/中砂层夹薄层灰白色碳酸盐层；110.83-87.3 m，灰白色碳酸盐层夹薄层灰黄色灰黑色细/中砂层；87.3-45.47 m，灰黑灰黄色细/中砂层与灰褐灰黄色粉砂/粘土层互层；45.47-0 m，灰黄灰黑色细/中砂层，夹薄层灰绿色粉/细砂层。. 通过系统的古地磁测量和分析，M/B界线位于93.9 m，底部并未出现正极性段，经过与相邻查汗池盐湖WEDP01钻孔对比，认为未超过0.9 Ma。13.1 m处样品钾长石光释光IRSL200和 pIRIR290信号测年结果分别为104.48±5.33 ka和196.77±19.63 ka，40.8 m和62.7 m处两个样品已经饱和，且最小年龄已经超过200ka。我们利用代表粉尘粒级的5-125 μm粒级含量，通过轨道调谐，获得了比较精细的年代，获得钻孔底部年龄为0.893 Ma。. 通过岩性观察以及粒度、色度、磁化率、碳酸盐、可溶盐离子等代用指标分析，图兰太地区从0.893Ma以来，在0.726和0.457Ma干旱化加剧，湖泊从碳酸盐、硫酸盐型咸水湖逐渐变为现在的卤盐湖；在0.885、0.86-0.84、0.78-0.76、0.7、0.66、0.62、0.54、0.507、0.4、0.24、0.22-0.2、0.123、0.1 Ma，发育了较大的湖泊或发生湖泊扩张。湖泊的出现或扩张具有比较明显的冰期间冰期旋回，且大部分湖泊期出现在冰消期。而在2.6-0.9 Ma，WED01钻孔记录的腾格里沙漠腹地的湖泊格局在2.6 Ma形成之后，一直是淡水或微咸水湖，并且湖泊的周期性变化并不突出。0.9 Ma之后湖泊类型的改变和周期性出现，与青藏高原隆升和北半球冰量变化有关。