【作者】 杨丽萍；

【导师】 陈发虎；

【作者基本信息】 兰州大学 ， 自然地理， 2008， 博士

【摘要】 吉兰泰盐湖位于内蒙古自治区阿拉善左旗吉兰泰镇(39°36′～39°42′N,105°35′～105°45′E),多年平均降水量108.89 mm,多年平均蒸发量2954.00 mm,气候干旱,植被稀少,沙漠化严重。河套盆地位于内蒙古西部(39°20′～41°20′N,106°～112°E),北至阴山脚下,南临鄂尔多斯高原北面的库布齐沙漠边缘,西接乌兰布和沙漠,东及东南与蛮汗山山前丘陵及和林格尔丘陵相接。年降水量大部地区介于150～400 mm之间,年蒸发量介于2000～2800 mm之间。从构造上看,吉兰泰断陷盆地隶属于河套断陷盆地的一部分,河套断陷盆地是介于南部的鄂尔多斯隆起和北部的阴山隆起之间的新生代断陷盆地,盆地中心沉积了巨厚的第四系湖相沉积,现代黄河自西而东穿过河套盆地。位于季风与西风过渡带的吉兰泰-河套地区,生态环境极其脆弱,对气候变化反映敏感,第四纪地层中记录着丰富的环境变化信息。前人根据吉兰泰-河套地区若干地点发现的湖岸堤、湖相地层提出可能存在“吉兰泰古湖”、“河套古湖”。但是,吉兰泰和河套地区是否存在统一的巨大古湖是一个值得深入研究的、重大的区域环境问题,目前尚缺乏系统的研究。本研究充分利用现代遥感技术的特点与优势,以多源遥感影像数据作为切入点,结合野外地质、地貌考察和差分GPS测高,系统研究了该区域湖滨地貌的空间分布。同时,结合OSL测年结果,基于SRTM DEM数据,利用GIS空间分析手段重建了不同时期古大湖的空间信息,探讨了各主要时段“吉兰泰-河套”古大湖空间演化的过程以及历史时期水系格局的变迁。在此基础上,利用水量平衡模型,初步计算和分析了古大湖发育时期的入湖径流量,以期为理解“吉兰泰-河套”古大湖的演化历史及过程提供科学依据,为了解该区域环境变化的历史及水资源的合理开发与利用提供参考资料。本研究所取得的主要结论如下:1、利用NASA Astronaut Photographs、Landsat-7 ETM+影像,在三维可视化技术的支持下,判读出了吉兰泰-河套地区一系列的古湖岸堤、古冲积扇、古河道及断裂构造等信息,为研究“吉兰泰-河套”古大湖的空间演化提供了第一手的基础资料。影像判读表明:(1)古湖岸堤呈线状(或条带状)的影像特征,以吉兰泰盐湖周围保存最为完整。根据DGPS测量和DEM数据的分析,吉兰泰-河套地区的古湖岸堤共分五级,即1070～1080 m、1060 m、1050 m、1044 m和1035 m。高出现代盐湖47～57 m(海拔1070～1080 m)的古湖岸堤,是该地区保存的最高湖面遗迹,在盐湖西南道扣梁以南和盐湖西部剖面S32～S34之间保存较为完整;海拔1060 m的古湖岸堤主要分布于盐湖西部至西北,延续性较好,长度超过20 km,仅个别部位为沟谷冲断,实测宽度在100 m以上;海拔1050 m的古湖岸堤主要分布于盐湖西北、西部和西南道扣梁一带,延续性好,在盐湖西北长度达20 km以上,实测宽度在100m以上。在道扣梁一带,长度约10km以上,实测宽度6～9m。遥感影像明确揭示,盐湖西北两条并行的主湖岸堤中均包含有次一级的湖岸堤;海拔1044 m和1035 m的古湖岸堤主要分布于盐湖西部,长度有限,均不超过3 km。在吉兰泰盐湖西岸的南砂场和乌兰布和沙漠腹地的贺日木西尼发育古砂嘴,以贺日木西尼古砂嘴影像特征最为明显。该砂嘴长约11 km,实测顶部宽约5 m,最宽处可达30 m,砂嘴顶部比两侧高出3～10 m,海拔从1050 m降低到1035 m,顶面平坦笔直,近岸边呈现典型的“V”字型特征;(2)吉兰泰-河套地区存在三个古冲积扇,乌兰布和沙漠北部和后套平原西部地区的两个古冲积扇规模较大,南扇地面坡降大于北扇。南、北冲积扇上不同时期、不同流向的古河道相互重叠、交叉。南冲积扇上的古河道近南北向展布,北冲积扇及五原一带则逐渐转为近东西方向。古河道在ETM+543合成影像上呈蓝黑色或鲜绿色的条带,形态特征多种多样,以后套地区影像特征最为明显。在巴音木仁(旧磴口)以西可能存在一个更老的古冲积扇;(3)河套盆地周缘断裂构造非常发育,以NE(NEE)、EW方向为主。盆地北缘一线主要存在狼山—色尔腾山山前断裂带、乌拉山山前断裂带、大青山山前断裂带,断层陡坎、断层崖、断层三角面等沿断裂带广泛发育,影像特征非常明显。盆地南缘受控于鄂尔多斯北缘断裂带及和林格尔断裂带,影像特征也比较明显。吉兰泰盐湖周围的断裂带比较发育,以NE和SN方向为主。2、建立了吉兰泰-河套地区的数字高程模型,该模型精确地再现了吉兰泰-河套地区的地形地貌特征。通过DEM分析并结合OSL测年表明,60～50 ka以来,吉兰泰-河套地区经历了四次高湖面时期,即60～50 ka之前、40 ka之前、22 ka之前以及早全新世。在60～50 ka之前的最高湖面阶段(海拔1080 m),“吉兰泰-河套”古大湖湖域辽阔,西至吉兰泰盐湖西南,东到呼和浩特以东,南以鄂尔多斯高原北缘为界,北至巴彦乌拉山—狼山—色尔腾山—乌拉山—大青山南麓一线,包括现今的乌兰布和沙漠与库布齐沙漠的大部分地区。现代地形条件下的平均深度约50 m,湖泊面积约34 757 km~2,整个湖盆容积可达6 000 km~3;在MIS3晚期的高湖面时期(海拔1060m、1050m),现代地形条件下的平均水深介于32～25 m,古湖面积介于30 818～28 121 km~2之间,整个吉兰泰-河套地区仍为一个统一大湖;进入全新世以来,在全新世早期虽然出现了又一次的高湖面,但现有证据表明,湖泊仅局限于吉兰泰盐湖周围及贺日木西尼一带;晚全新世时,吉兰泰地区已进入盐湖阶段,流沙侵湖,并迅速呈现出沙下盐湖的特征。从湖面退缩的空间过程来看,古大湖北缘沿巴彦乌拉山—狼山—色尔腾山—乌拉山—大青山南缘一线直到22 ka之前变化不明显,东部边缘、西南边缘退缩比较明显,退缩最严重的区域在鄂尔多斯高原西北缘;3、基于遥感影像并参考前人研究成果,确认出乌兰布和沙漠北部地区遥感影像上形似小鸟的区域为西汉至北魏时期屠申泽所在。该古湖湖口大致位于隆盛合到东海子附近,南大致以海子岗到东海子一线为界,北缘大致位于王外生苑旦到杨三圪旦一线附近,古湖面积约450 km~2,东西长约40 km,南北最宽约18 km左右。屠申泽形成于西汉之前,在其鼎盛时期可能覆盖了整个乌兰布和沙漠北部地区,范围是西汉至北魏时期的8-9倍以上。根据文献记载描述的历史时期河套段黄河从北向南、从西向东的变迁过程,尤其是清代河道的变迁过程,在遥感影像上得到了忠实的记录和反映;4、初步探讨了构造活动、水系变迁及气候变化在“吉兰泰-河套”古大湖形成演化过程中的作用。研究表明,第四纪以来,吉兰泰地区构造活动相对稳定,而河套地区构造活动非常强烈,高湖面的形成很可能受控于区域造陆隆起和局部构造变形。剔除构造抬升的影响,60～50 ka之前古大湖的水位介于1080 m～1050 m之间,面积约30 000 km~2左右,吉兰泰-河套地区仍为统一大湖所覆盖;区域对比发现,“吉兰泰-河套”古大湖的高湖面记录与青藏高原区的“泛湖面”(溢流面)具有非常好的一致性,与古里雅冰芯、深海氧同位素曲线、北半球太阳辐射量曲线及洛川剖面的磁化率曲线具有较好的一致性。40 ka之前、22ka之前和全新世早期的高湖面与古里雅冰芯及深海氧同位素阶段所反映的暖期基本一致,尤其是与古里雅冰芯的对比较为一致,60～50 ka之前的高湖面与氧同位素的低谷相一致,可能反映在暖期后冰水融化而形成的高湖面;晚第四纪以来多次高湖面的形成,很可能是截留了黄河水,黄河很可能外流减少或停止以至成为内流河才使湖面能够保持稳定;5、根据水量平衡模型,以研究区现代的降水量、蒸发量为参考,通过子区划分赋权重的方法,初步地计算了古大湖发育时期的入湖径流量。结果表明,60～50 ka之前“吉兰泰-河套”古大湖发育时期,年入湖径流量约为420.55×10~8 m~3,其中黄河年入湖径流量达410×10~8 m~3以上。由于当时气温较低,降水较高,从而使古大湖的水位在海拔1080 m左右维持着一种动态平衡;6、研究证明,遥感技术在湖泊演化研究中具有独特的优势。与单源遥感影像数据相比,多源遥感影像数据所提供的信息具有互补性和合作性,在古湖演化研究中可以取长补短,提供更加全面的信息。将遥感技术、数字高程模型及GIS技术运用于古湖演化研究中,具有精度高、速度快、信息全面的特点,利于大区域研究和宏观规律的把握,同时还可以实现古湖演化的可视化和定量化,是研究湖泊演化极为有效和值得推广的方法之一。更多还原

【Abstract】 Jilantai Salt Lake, located on the northeastern margin of the Alashan Plateau, Inner Mongolia, China, is a typical salt lake in northwestern China. It belongs to the Hetao fault-depression basin tectonically, which was formed in Cenozoic and is limited to the south and north by the Ordos Plateau and Yinshan Mountains respectively. The Yellow River flows through the Hetao basin from west to east.The wider region covered by this research lies across a critical climatic boundary between the influence of the Asian summer monsoon and westerly airflow. The extensive Quaternary lacustrine sediments and its sensitive response to climate change due to its location have attracted much research interests here. Previous studies suggest that the existence of Jilantai paleolake and Hetao paleolake based on some local shoreline features and lacustrine sediments records. However, no comprehensive studies of the relationship between the Jilantai paleolake and the Hetao paleolake was addressed. A full understanding of the Paleo-Megalake ’Jilantai-Hetao’ needs more systematic and interdisciplinary studies.Based on remote sensing images, field geomorphological and sedimentary investigations, this research first confirmed the spatial distribution of paleoshorelines in the Jilantai-Hetao region. Meanwhile, Digital Elevation Model (DEM) was analyzed by means of GIS spatial analysis technologies to extract the spatial information of Paleo-Megalake ’Jilantai-Hetao’. Furthermore, the evolutionary processes and the water system shift processes were discussed in details. Finally, a simple water balance model was built to reconstruct the past natural runoff to the Paleo-Megalake. The results presented in this study have significant implications for improving our knowledge of Paleo-Megalake evolution and regional environment change. This study is also the first step for a remote sensing and DEM based reconstruction of late Quaternary paleolake evolution in this region, which is also important for the sustainable development and utilization of water resources in the Jilantai-Hetao region. The preliminary conclusions are as follows. 1. Series of paleoshorelines, paleoalluvial fans, old river valleys and fault systems were identified on remote sensing images, which are encouraging enough for us to use these data as the basic information for paleolake evolution studies in this region. Image interpretation indicates that(1) With clear linear or belt shape on remote sensing images, paleoshorelines are well preserved around Jilantai Salt Lake. Five shoreline groups at elevations of 1070～1080 m, 1060 m, 1050 m, 1044 m and 1035 m were confirmed based on DGPS measurements and DEM analysis. The highest shorelines at elevation of 1070～1080 m presented very well to the southwest of Daokouliang, which is located to the southwest of Jilantai Salt Lake, as well as the western profiles between S32 and S34. On the west to northwest margin of Jilantai Salt Lake, paleoshorelines at elevations of 1060 m and 1050 m extended more than 20 km, with width more than 100 m. In addition, paleoshoreline at elevation of 1050 m was also well preserved near Daokouliang and was about 10 km long and 6～9 m wide. Subshorelines existed in the above-mentioned two major shorelines. We also recognized some remnant paleoshorelines at elevations of 1044 m and 1035 m to the west of Jilantai Salt Lake. Two spits are clearly visible on the image. One is near the South Sand Quarry, west of Jilantai Salt Lake. The other is at Herimuxini, near the threshold separating the Jilantai basin from the Hetao basin, extends east from a high paleoshoreline to near the center of the modern Ulan Buh Desert. The spit is 11 km long and drops in elevation from 1050 m to 1035 m rapidly. The spit landform is well preserved, with a 5 m wide flat and straight crest and a height of 3 to 10 m above the playa floor. It has a typical "V" shape near the shore, with a maximum width of 30 m.(2) Three paleoalluvial fans were identified on the image. Two huge fans were located on the northern part of Ulan Buh desert and the western margin of the Houtao Plain where distributed numerous old river valleys. With blue-black or fresh green color on ETM+ 543 composite image, old river valleys orientated almost in SN direction on the south fan, while nearly in EW direction on the north fan and around Wuyuan. An older alluvial fan was also identified to the west of Bayinmuren (Jiudengkou).(3) Series of fault systems were clearly displayed on 3D images, on which the fault systems orientated mainly in NE (NEE) and EW direction. On the northern margin of the Hetao Plain, along the Langshan-Seertengshan-Wulashan-Daqingshan piedmont fault system, fault scarplets, fault escarpments and fault facets developed extensively and can be easily identified on remote sensing images. While the Ordos and Helingeer fault systems on the southern margin of the Hetao Plain can only be identified but with much ambiguous geomorphological features on the image. Around the Jilantai Salt Lake, some fault systems orientated in NE and SN were also documented.2. The 2000 Shuttle Radar Topography Mission (SRTM) data have been used in this study. SRTM DEM produces much more sharper images of the region’s topography and provides new insights into debates about the nature and extent of late Quaternary Paleo-Megalake here. Combined with OSL dating, a paleolake named as Paleo-Megalake ’Jilantai-Hetao’ developed before 60～50 ka was vividly sketched. The megalake covered a considerable area about 34 757 km~2 geographically, extending from the southwest of Jilantai Salt Lake to the east of Hohhot. It was bordered towards the south and north by the northern margin of the Ordos Plateau and the southern piedmont along Bayanwulashan-Langshan-Seertengshan-Wulashan-Daqingshan. The Paleo-Megalake basin has a volume about 6 000 km~3 and with an average depth of 50 m under modern topographic conditions. During the late MIS3, two highstands of paleolakes were also documented at elevations of 1060 m and 1050 m. The paleolakes still covered most of the Jilantai-Hetao region with an area about 30 000 km~2. During the early Holocene, firm evidences existed for another high lake stand but with limited extent only including Jilantai and Herimuxini. Arid climate gradually prevailed in this region during the late Holocene. Strong evaporation and serious desertification further enhanced the rapid shrinkage of Jilantai Salt Lake. Spatially speaking, the Paleo-Megalake ’Jilantai-Hetao’ regressed rapidly on the northwestern margin of the Ordos Plateau.3. Based on image interpretation and previous studies, we confirmed that the bird shape feature on the image represented the extent of Tushenze from Xihan to Beiwei Dynasty. The paleolake is bounded to the south from Haizigang to Donghaizi and from Wangwaishengyuandan to Yangsangedan on its northern margin. The lake mouth is near Longshenghe to Donghaizi. With a length of 40 km from west to east and a maximum width near 18 km, Tushenze occupied an area of 450 km~2. We postulated that Tushenze was formed before Xihan Dynasty and probably occupied most of northern Ulan Buh desert during its maximum period. Shifts of old river valleys from north to south and from west to east on the Houtao Plain were documented distinctly on the image.4. We postulated that several highstands since the late Quaternary were controlled by the regional epeirogenic uplift events. The Paleo-Megalake ’Jilantai-Hetao’ developed before 60～50 ka represented the hugest paleolake ever reported in this region and the lake level fluctuated between 1080 and 1050 m in spite of strong tectonic activities. The highstands in Jilantai-Hetao region not only show the same climatic pattern as in the Qinghai-Tibet Plateau, but also agree well with records from the Guliya Ice Core, the Marine Isotope Stages, and the susceptibility from Luochuan Loess as well as the Northern Hemisphere insolation curve. The Yellow River was probably an inland river or at least with very limited outflow, which contributed to the formation of several highstands in this region.5. A simple water balance model based on modern precipitation and evaporation was built to quantitatively reconstruct the natural runoff during the geological periods. Natural Yellow River runoff into the Jilantai-Hetao basin was estimated to be more than 410×10~8m~3/yr, which is necessary to maintain the Paleo-Megalake ’Jilantai-Hetao’ near equilibrium.6. With the characteristics of complementary and cooperative, multi-source remote sensing images have proved to be powerful tools in lake evolution studies. This research demonstrates that new technologies such as remote sensing, DEM and GIS have the potentials to significantly improve our knowledge of lake evolution and environment change. High accuracy, high efficiency and substantive information extracting from these technologies are of great benefit to understanding the macro geographical phenomena, to visualizing and quantifying the results. We believe that as complementary means to the traditional Quaternary research methods, these technologies can surely provide us more valuable information and deserve more applications.更多还原