吉兰泰盆地MIS 3阶段沉积环境及生态环境研究

发布时间：2019-05-24 10:56

【摘要】：中国西部地区存在着大量湖泊,这些分布于干旱-半干旱区的湖泊能够敏感地记录区域内干湿变化、流域生态演化等丰富的气候与环境信息。因此,通过研究不同时期的湖岸堤、湖积阶地和高位湖相沉积物等地层地貌证据,可以重建湖面波动历史和湖泊演化过程,为恢复和理解区域古环境提供确切的证据。而近年来,中国西部地区部分古湖岸的OSL测年结果似乎在否定该区基于14C测年的深海氧同位素3阶段(下文简称"3阶段"或"MIS 3时段")高湖岸特征,部分古湖岸的测年结果却又试图强化西部地区3阶段气候环境不同于全球的区域特殊性。可见对于我国西部地区3阶段时期是否曾普遍发育古湖泊,在学术界尚存在争议。前人研究显示,至少在早于距今60～50 ka之前的某个时段曾经存在一个几乎覆盖整个吉兰泰盆地、河套盆地及周边乌兰布和沙漠、库布齐沙漠的"吉兰泰-河套"古大湖。该古大湖的发现对深入理解河套地区晚第四纪黄河演化、区域气候特征、乌兰布和沙漠及库布齐沙漠的形成演化都具有重要意义。假如该古大湖确实存在,那么本文所研究的吉兰泰地区则正处于其西部湖盆之中。虽然前期14C测年结果支持该区MIS 3阶段时期发育高湖岸,且最高湖岸线形成于早于距今6万年之前的某个时段,距今5-6万年之后至全新世期间形成了海拔高程分别为1060-1050、1044-1035 m的一系列湖岸线。但是,在位于现今吉兰泰盐湖东岸的乌兰布和沙漠中的钻孔中却未发现MIS 3阶段的沉积物,有研究据此推断现今乌兰布和沙漠覆盖的地区于MIS 3时段可能处于风沙环境。可见,吉兰泰盆地在MIS 3时段的自然环境状况尚有待进一步研究。因此,本文在前人研究基础上,对吉兰泰盐湖西岸早先认为可能形成于MIS 3阶段的湖岸(海拔高程为1050-1060 m)重新开挖剖面并测定石英OSL年代,并在吉兰泰盆地边缘的磴口次级隆起区钻取了 81 m深的岩芯,结合磴口次级隆起区的钻孔地层序列与OSL测年,试图揭示吉兰泰盆地在MIS 3时段是否存在积水环境,并通过孢粉记录分析,探讨了 MIS 3时段吉兰泰盆地的生态环境。本文得到以下初步认识:(1)早于距今76 ka之前的某个时段,吉兰泰盆地应当处于深湖环境,但更可能是距今90 ka之前就存在一个湖水覆盖吉兰泰盆地和河套盆地大面积地区的"吉兰泰-河套"大湖;在距今76～52 ka时段,吉兰泰盆地湖水较之前有所降低,盆地的边缘出现风沙堆积;吉兰泰盆地的浅湖环境可能由距今52 ka一直持续至距今39 ka,其间湖水上涨,但该时段湖面的升高更多的是在青藏高原快速隆升的影响下吉兰泰湖盆中心自南向北调整的结果;距今39～13 ka时段,吉兰泰盆地虽然仍处于湖泊状态,且湖水在距今23 ka左右再次蔓延至磴口次级隆起区,但此时段湖水主要局限于吉兰泰盆地内部,高湖岸一直处于1060-1050m左右,并且不断波动,而磴口次级隆起区可能为出露水面的湖滨环境,而现今的乌兰布和沙漠的大面积地区为风沙环境;而在13～8 ka时段,黄河从现今乌兰布和沙漠的东南部注入形成面积较大的古屠申泽。(2)本文贺兰山前古河道剖面的沉积序列及OSL测年结果表明,在距今57～32ka之间,贺兰山西麓曾出现大规模的地表径流,并为吉兰泰盆地提供大量的水源,可见此时段,贺兰山西麓大量降水成因的地表径流,对于盆地内湖面上升也有重要贡献。(3)MIS 3阶段,磴口次级隆起区钻孔地层中的孢粉分析结果显示,该区沉积的孢粉以藜科、蒿属、禾本科、香蒲属、莎草科占优势,且其建群种主要是藜科植物,考虑到这些孢粉的传输距离较短,因此认为这种孢粉组合可能暗示MIS 3时段磴口次级隆起区处于湖泊与荒漠草原共存的状态,周边山地可能发育有云杉林与松林;而吉兰泰盆地1060 m湖岸线剖面地层序列及孢粉分析结果显示,此时段最大可能是盆地内部发育浅水湖泊,盆地周边以荒漠环境为主,植被发育可能较差。
[Abstract]:There are a large number of lakes in the western part of China. These lakes, which are distributed in arid and semi-arid areas, can be sensitive to the rich climate and environmental information in the area, such as the change of dry and dry, and the ecological evolution of the river basin. Therefore, by studying the formation and geomorphological evidence such as the lake bank, the lake-area terrace and the high-order lake-phase sediment in different times, the lake wave history and the lake evolution process can be reconstructed, and the exact evidence is provided for the restoration and understanding of the regional paleo-environment. In recent years, the annual results of the OSL in part of the ancient lake in the western part of China appear to have negative characteristics of the high lake shore of the deep-sea oxygen isotope 3 (hereinafter referred to as" "Phase 3" or "MIS 3 period" "), which is based on the 14C dating in the region, The results of the survey in part of the ancient lake have also tried to strengthen the regional particularities of the three-stage climate in the western region. It can be seen whether the ancient lake has been developed in the three-stage period in the western region of China, and there is still a dispute in the academic circles. Previous studies have shown that at least one period before the current of 60-50 ka, there existed a "Glantey-Hetao"-old Great Lakes covering the whole of the Grangtai basin, the Hetao basin and the surrounding Ulana and the desert and the Kubuqi Desert. The discovery of the Great Lakes is of great significance to the deep understanding of the evolution of the Yellow River in the late Quaternary of the Hetao area, the regional climate characteristics, the Ulan Buh and the formation and evolution of the desert and the Kubuqi Desert. If the Great Lakes do exist, the area of the Gillertai area studied in this paper is in the lake basin of the west. Although the early 14C dating results support the development of the high lake shore in the MIS 3 stage of this area, and the highest lake shore line is formed earlier than 60,000 years ago, a series of lake shore lines with elevation elevation of 1060-1050 and 1044-1035m are formed in the period from 5 to 60,000 years from now to the Holocene. However, in the drilling of the Ulaanb and the desert located in the east coast of the current Glantey Salt Lake, there are no deposits in the MIS stage, and it is concluded that the area covered by the Ulaanb and the desert may be in a sandstorm environment during the period of MIS 3. It can be seen that the natural environment in the period of MIS 3 is still to be studied. Therefore, on the basis of the previous research, this paper re-excavated the cross-section of the lake shore (1050-1060m with the elevation of 1050-1060m) in the MIS 3 stage and the quartz-OSL's in the west bank of the Gillantai Salt Lake, and drilled the 81-m-deep core in the secondary uplift area at the edge of the Gillantai basin. Based on the drilling formation sequence and the OSL dating of the secondary raised area of the MIS, an attempt was made to reveal the existence of the accumulated water environment in the MIS 3 period in the Grangtai basin, and through the analysis of the spore-pollen records, the ecological environment of the Jilin-Lantai basin in the 3-time period of the MIS was discussed. The following preliminary recognition is made in this paper: (1) The Gillantai basin should be in the deep lake environment before the 76 ka, but it is more likely that there is a large "Glantey-Hetao" of the lake in the area of the Jilantai basin and the Hetao basin before the 90ka. in that period from 76 to 52 ka, the lake water in the Gillantai basin is lower, and the edge of the basin is sand-laden; the shallow lake environment in the Gillantai basin may last from 52 ka to 39 ka this year, with the lake water rising, But the increase of the surface of the lake is the result of the rapid uplift of the Qinghai-Tibet Plateau and the result of the adjustment from the south to the north of the center of the Grangtai lake basin. The Gillantai basin is still in the lake state for the period from 39 to 13 ka, and the lake water again spread to the secondary raised area of the lake at about 23 ka. But at this time, the lake water is mainly confined to the interior of the Gillantai basin, and the high lake shore is at about 1060-1050m and is constantly fluctuating, while the secondary uplift area of the basin is likely to be the lakeside environment of the exposed water surface, and the large area of the current Ulaanbu and the desert is a sand and sand environment; and in the period of 13 to 8 ka, The Yellow River is injected from the southeast of Ulaan and the desert to form a large area of ancient Tu-Sze. (2) The sedimentary sequence of the section of the ancient river channel of Helan Mountain in this paper and the results of the measurement of the OSL show that a large-scale surface runoff has occurred at the western foot of the Helan Mountain, and a large amount of water source is provided for the Gillantai basin, and the surface runoff of a large number of precipitation causes at the western foot of the Helan Mountain is visible at this time. There is also an important contribution to the rise of the lake in the basin. (3) The results of the pollen and pollen analysis in the drilling formation at the stage of MIS 3 and in the secondary uplift area of the reservoir show that the sporo-pollen in this area is dominant in the family, the genus Artemisia, the Gramineae, the Typha, and the Cyperaceae, and the group of them is mainly the Cycophytes, taking into account that the transmission distance of these sporopollen is short, Therefore, it is considered that this sporo-pollen assemblages may imply that the secondary uplift of MIS 3 is in the state of the coexistence of the lake and the desert steppe, and the surrounding mountains may be developed with the spruce forest and the pine forest, while the stratigraphic sequence and the sporo-pollen analysis results of the 1060m lake line in the Gillantai basin show that, At this time, the largest potential of the section is the development of shallow lake in the basin, and the surrounding of the basin is dominated by the desert environment, and the development of the vegetation may be poor.
【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】：P512.2

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