钻孔记录揭示的乌兰布和沙漠南部晚第四纪环境演化

发布时间：2018-03-04 16:30

本文选题：乌兰布和沙漠　切入点：钻孔岩芯　出处：《兰州大学》2015年硕士论文　论文类型：学位论文

【摘要】：位于内蒙古高原的西南部的乌兰布和沙漠,是中国北方主要的沙漠之一,也是北半球重要的粉尘源区。该沙漠北部主要为固定沙丘和沙垄为主,南部主要为高大沙丘及金字塔形沙丘组成。对于乌兰布和沙漠南部高大沙丘区的环境变化,由于缺乏可靠的沉积记录和足够的年龄数据支持,沙漠环境变化及沙漠形成演化过程目前还不清楚。本研究通过在乌兰布和南部高大沙丘核心区开展沙漠钻探,获得一根120.5 m长的沙漠钻孔岩芯(WL12ZK-1岩芯)。对岩芯开展了详细的沉积地层描述。使用石英光释光测年和钾长石多步法红外后红外释光测年方法,建立钻孔岩芯的年龄框架。使用古环境代用指标(粒度、烧失量、孢粉、介形虫)对WL12ZK-1钻孔记录的环境变化进行了分析,以便重建该地区的环境变化。石英光释光性质(包括剂量恢复实验,释光信号特征)检验,结果表明对小于6万年的年轻样品石英光释光测年方法是可靠的。钾长石释光测年的结果可靠性通过内部信号检验和钾长石年龄—激发温度坪区实验检验。钾长石和石英测年结果的对比也进一步指示了年龄框架的可靠性。结合之前沙漠北部已有的WL10ZK-1和WL10ZK-2钻孔岩芯沉积记录,乌兰布和沙漠南部钻孔岩芯WL12ZK-1古环境代用指标和年龄结果表明乌兰布和沙漠地区干旱环境在中晚更新世就已经形成,沙漠沙丘沙环境至少在~230 ka以前就已经形成,该地区植被自此以来主要是沙漠植被和草甸植被。在约155 ka前开始在该地区形成了由黄河作为主要补给水源的古大湖,古湖泊环境可能一直持续到~87 ka前后,古湖泊可能经历了多次湖面进退波动,孢粉分析表明古湖泊周围主要生长着草甸植物。在~87 ka之后,乌兰布和沙漠地区古湖泊消失,沙漠环境再次形成,在末次冰期该地区很可能没有任何稳定的古大湖发育。乌兰布和沙漠南部末次冰期至全新世早期沙漠环境稳定存在,干旱环境持续至今。内蒙古高原南部的沙漠在末次间冰期、全新世早期和距今约2 ka以来发生了进一步扩张。研究结果表明构造活动和气候变化是更新世中期以来内蒙古南部沙漠形成的主要原因,此外晚全新世的人类活动可能促进了沙漠的进一步扩张。
[Abstract]:The Wu Lan Buhe Desert, located in the southwest of Inner Mongolia Plateau, is one of the major deserts in northern China and an important dust source in the Northern Hemisphere. The northern part of the desert is dominated by fixed sand dunes and ridges. The south is mainly composed of tall sand dunes and pyramidal dunes. For the environmental changes in the high sand dunes in the southern part of the Wu Lan Buhe Desert, due to the lack of reliable sedimentary records and sufficient age data, It is not clear how the desert environment changes and the desert formation and evolvement. This study carried out desert drilling in the core area of Wu Lan Buhe and high sand dunes in the south. A 120.5 m long desert drilled core WL12ZK-1 core has been obtained. Detailed sedimentary strata description has been carried out on the core. The methods of quartz photoluminescence dating and potassium feldspar multistep infrared post-infrared luminescence dating have been used. The age frame of borehole core was established. The environmental changes of WL12ZK-1 borehole records were analyzed by using paleoenvironment substitute indexes (granularity, loss of fire, sporopollen, ostracoda). In order to reconstruct the environmental changes in the area. Quartz photoluminescence properties (including dose recovery experiments, luminescent signal characteristics) tests, The results show that the method of quartz photoluminescence dating for younger samples of less than 60,000 years is reliable. The reliability of potassium feldspar dating results is verified by internal signal test and potassium feldspar age-excitation temperature plateau test. The comparison of stone and quartz dating results also further indicates the reliability of the age framework. Combined with previous WL10ZK-1 and WL10ZK-2 drilled core sediment records in the northern part of the desert, The substitution index and age of WL12ZK-1 in the core of the southern Wu Lan Bohe Desert indicate that the arid environment in the area of Wu Lan Buhe has been formed in the middle and late Pleistocene, and the sand environment in the desert dunes was formed at least 230ka ago. Since then, the vegetation in this area has been mainly desert vegetation and meadow vegetation. About 155 ka ago, the ancient Great Lakes were formed in the region, where the Yellow River is the main source of water supply, and the ancient lake environment may last until about 87 ka. The ancient lakes may have experienced many fluctuations in the lake surface, and pollen analysis showed that there were mainly meadow plants around the ancient lakes. After 87 ka, the ancient lakes of Wu Lan Buhe desert area disappeared and the desert environment was formed again. During the last glacial period, there was probably no stable paleolake development in this area. The desert environment in the southern part of Wu Lan Buhe Desert remained stable from the last glacial period to the early Holocene, and the arid environment continued to this day. The desert in the southern Inner Mongolia Plateau was in the last interglacial period. The results show that tectonic activity and climate change are the main causes of desert formation in southern Inner Mongolia since the middle Pleistocene. In addition, human activities in the late Holocene may have contributed to the further expansion of the desert.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.63

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