發(fā)布時(shí)間：2018-05-14 11:23

  本文選題：末次冰消期 + 湖泊水位�。� 參考：《中國地質(zhì)大學(xué)(北京)》2017年碩士論文

【摘要】：本研究選取達(dá)里湖西北岸一個(gè)典型湖相沉積剖面(DLB),測(cè)試了13個(gè)樣品的光釋光(OSL)年代,建立了該剖面的年代序列(17.8-6.8 ka BP);同時(shí),還分析了該剖面沉積物的粒度、燒失量、色度、元素、孢粉及介形類等環(huán)境代用指標(biāo),并對(duì)各指標(biāo)的環(huán)境意義進(jìn)行了分析和討論,重建了末次冰消期-中全新世早期達(dá)里湖的水位演化及古氣候環(huán)境。結(jié)果表明:在17.8 ka BP前后,該沉積剖面由以礫石為主的沖洪相沉積轉(zhuǎn)變?yōu)橐陨敖M分為主的湖相沉積,指示著達(dá)里湖進(jìn)入了相對(duì)高水位時(shí)期。在17.8-13.5 ka BP和13.1-12.2 ka BP期間,剖面沉積物以細(xì)砂組分為主,易溶元素的含量相對(duì)較高,暗示著這兩階段相對(duì)較高的湖泊水位。這兩個(gè)階段沉積物中的孢粉含量以草本植物為主,有機(jī)質(zhì)和碳酸鹽的含量和色度a*值相對(duì)較高,暗示著該地區(qū)氣候的轉(zhuǎn)暖。這表明17.8 ka BP以來的湖泊水位升高很可能是由于自末次盛冰期進(jìn)入末次冰消期后氣溫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期間,該剖面沉積物的中值粒徑顯著增大,難溶元素SiO2的含量顯著升高,布氏土星介的豐度相對(duì)較高,指示著達(dá)里湖的水位顯著降低。這兩階段沉積物中的孢粉、有機(jī)質(zhì)、碳酸鹽的含量顯著降低,色度L*值相對(duì)較高,暗示著顯著冷干的氣候環(huán)境。與全球氣候變化記錄相比,可發(fā)現(xiàn)這兩個(gè)時(shí)期大致對(duì)應(yīng)著兩次仙女木時(shí)期事件。因此,這兩個(gè)時(shí)期顯著降低的湖泊水位很可能是仙女木時(shí)期較低的氣溫使大量的區(qū)域水儲(chǔ)存在了流域山地冰雪中所引起的。從11.8 ka BP開始,該剖面沉積物的中值粒徑再次顯著減小,易溶元素的含量明顯升高,指示達(dá)里湖水位的再次升高。在11.8-7.6 ka BP期間沉積物中有機(jī)質(zhì)和碳酸鹽的含量值明顯升高,孢粉的含量亦顯著增加,這暗示這一時(shí)期的湖泊水位升高是由于進(jìn)入全新世后區(qū)域氣候轉(zhuǎn)暖、有效降水增多所造成的。進(jìn)入中全新世后(7.6-6.8 ka BP),該剖面沉積物中值粒徑降低到了整個(gè)剖面的最小值、而粘土含量達(dá)到了最高值,這指示著達(dá)里湖水位達(dá)到了本研究時(shí)段的最高值。該階段沉積物中木本植物的孢粉含量占絕對(duì)優(yōu)勢(shì),有機(jī)質(zhì)和碳酸鹽的含量均顯著升高,這表明該時(shí)段的氣候更為溫暖、有效降水快速增加,從而使達(dá)里湖水位達(dá)到了最高。與附近區(qū)域典型湖泊及全球氣候變化記錄對(duì)比發(fā)現(xiàn),17.8-6.8 ka BP期間達(dá)里湖的水文演化記錄與其他湖泊有一定的可比性。在末次冰消期的兩次仙女木事件,達(dá)里湖水位表現(xiàn)出快速而顯著的降低變化,這反映了氣溫變化對(duì)湖泊水位的顯著影響,也暗示著末次冰消期期間(17.8-11.8 ka BP)達(dá)里湖水位的升降主要與氣溫控制的山地冰雪消融有關(guān);而進(jìn)入全新世后,尤其是7.6-6.8 ka BP期間由于該地區(qū)的冰雪已基本融化,這一時(shí)期達(dá)里湖水位的變化則主要受季風(fēng)影響的降水變化的控制。
[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.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P532;P343.3
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本文編號(hào)：1887662