达里湖17.8-6.8ka BP期间的水位演化及古气候环境

发布时间：2018-05-14 11:23

  本文选题：末次冰消期 + 湖泊水位　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：本研究选取达里湖西北岸一个典型湖相沉积剖面(DLB),测试了13个样品的光释光(OSL)年代,建立了该剖面的年代序列(17.8-6.8 ka BP);同时,还分析了该剖面沉积物的粒度、烧失量、色度、元素、孢粉及介形类等环境代用指标,并对各指标的环境意义进行了分析和讨论,重建了末次冰消期-中全新世早期达里湖的水位演化及古气候环境。结果表明:在17.8 ka BP前后,该沉积剖面由以砾石为主的冲洪相沉积转变为以砂组分为主的湖相沉积,指示着达里湖进入了相对高水位时期。在17.8-13.5 ka BP和13.1-12.2 ka BP期间,剖面沉积物以细砂组分为主,易溶元素的含量相对较高,暗示着这两阶段相对较高的湖泊水位。这两个阶段沉积物中的孢粉含量以草本植物为主,有机质和碳酸盐的含量和色度a*值相对较高,暗示着该地区气候的转暖。这表明17.8 ka BP以来的湖泊水位升高很可能是由于自末次盛冰期进入末次冰消期后气温升高使得流域山地冰雪的大量消融所造成的。但是,在末次冰消期的13.5-13.1 ka BP和12.2-11.8 ka BP期间,该剖面沉积物的中值粒径显著增大,难溶元素SiO2的含量显著升高,布氏土星介的丰度相对较高,指示着达里湖的水位显著降低。这两阶段沉积物中的孢粉、有机质、碳酸盐的含量显著降低,色度L*值相对较高,暗示着显著冷干的气候环境。与全球气候变化记录相比,可发现这两个时期大致对应着两次仙女木时期事件。因此,这两个时期显著降低的湖泊水位很可能是仙女木时期较低的气温使大量的区域水储存在了流域山地冰雪中所引起的。从11.8 ka BP开始,该剖面沉积物的中值粒径再次显著减小,易溶元素的含量明显升高,指示达里湖水位的再次升高。在11.8-7.6 ka BP期间沉积物中有机质和碳酸盐的含量值明显升高,孢粉的含量亦显著增加,这暗示这一时期的湖泊水位升高是由于进入全新世后区域气候转暖、有效降水增多所造成的。进入中全新世后(7.6-6.8 ka BP),该剖面沉积物中值粒径降低到了整个剖面的最小值、而粘土含量达到了最高值,这指示着达里湖水位达到了本研究时段的最高值。该阶段沉积物中木本植物的孢粉含量占绝对优势,有机质和碳酸盐的含量均显著升高,这表明该时段的气候更为温暖、有效降水快速增加,从而使达里湖水位达到了最高。与附近区域典型湖泊及全球气候变化记录对比发现,17.8-6.8 ka BP期间达里湖的水文演化记录与其他湖泊有一定的可比性。在末次冰消期的两次仙女木事件,达里湖水位表现出快速而显著的降低变化,这反映了气温变化对湖泊水位的显著影响,也暗示着末次冰消期期间(17.8-11.8 ka BP)达里湖水位的升降主要与气温控制的山地冰雪消融有关;而进入全新世后,尤其是7.6-6.8 ka BP期间由于该地区的冰雪已基本融化,这一时期达里湖水位的变化则主要受季风影响的降水变化的控制。
[Abstract]:In this study, a typical lacustrine sedimentary profile on the northwestern shore of Lake Daly was selected, and the OSL dating of 13 samples was tested, and the dating sequence of this section was established, which was 17.8-6.8 ka BPN, and the grain size, loss of fire, chromaticity of the sediment in this section were also analyzed. Elements, sporopollen and ostracods, and so on. The environmental significance of each index was analyzed and discussed. The water level evolution and paleoclimate environment of Dali Lake during the last ice extinction period and early Middle Holocene were reconstructed. The results show that before and after 17.8 ka BP, the sedimentary profile changed from gravel-dominated alluvial facies to lacustrine facies dominated by sand composition, indicating that Dali Lake has entered a relatively high water level period. During the periods of 17.8-13.5 ka BP and 13.1-12.2 ka BP, the sediment in the profile is mainly composed of fine sand and the content of soluble elements is relatively high, which implies that the lake water level is relatively high in these two stages. The sporopollen content in the sediments of these two stages is dominated by herbaceous plants, and the content of organic matter and carbonate and the value of chromaticity a * are relatively high, indicating the warming of climate in this area. It is suggested that the elevation of lake water level since 17.8 ka BP may be due to the melting of snow and ice in mountainous regions of the basin due to the rise of air temperature since the last ice peak period entered the last ice extinction period. However, during 13.5-13.1 ka BP and 12.2-11.8 ka BP in the last ice depletion period, the median particle size of sediment in this section increased significantly, the content of insoluble element SiO2 increased significantly, and the abundance of Blindahl Saturn medium was relatively high, indicating that the water level of Lake Daly was significantly decreased. The contents of sporopollen, organic matter and carbonate in the sediments of these two stages were significantly decreased, and the values of chrominance L * were relatively high, suggesting a significant cold and dry climate environment. Compared with the global record of climate change, it is found that these two periods correspond roughly to two Andromeda events. Therefore, the lake water level decreased significantly in these two periods is probably caused by the lower temperature in the Andromeda period, which caused a large amount of regional water to be stored in mountain snow and ice in the basin. Starting from 11.8 ka BP, the median particle size of sediment in this section decreases significantly again, and the content of soluble elements increases obviously, indicating that the water level of Lake Daly is rising again. During the period of 11.8-7.6 ka BP, the content of organic matter and carbonate in sediments increased obviously, and the content of sporopollen also increased significantly, which suggested that the elevation of lake water level in this period was due to the regional climate warming after Holocene. An increase in effective precipitation. After entering the middle Holocene, the mean grain size of sediment in this section decreased to the minimum value of the whole section, and the clay content reached the highest value, indicating that the water level of Lake Daly reached the highest value in this study period. In this stage, the sporopollen content of woody plants occupies the absolute predominance, and the contents of organic matter and carbonate increase significantly, which indicates that the climate is warmer and the effective precipitation increases rapidly in this period, which makes the water level of Dali Lake reach the highest level. Comparing with the records of regional typical lakes and global climate change, it is found that the hydrological evolution records of Dali Lake during the period of 17.8-6.8 ka BP are comparable to those of other lakes. During the last two Andromeda events, the water level of Lake Daly showed a rapid and significant decrease, which reflected the significant influence of temperature change on the water level of the lake. It also suggests that the rise and fall of Lake Dali water level during the last ice depletion period (17.8-11.8 ka) is mainly related to the melting of ice-snow in the mountainous regions controlled by air temperature, but after entering the Holocene, especially during the period of 7.6-6.8 ka BP, the ice and snow in the region have basically melted, In this period, the water level of Dali Lake is mainly controlled by the monsoon precipitation.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P532;P343.3
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本文编号：1887662