湖泊与河流的形成演化是地貌学与第四纪环境演变研究的基本内容。已有研究表明，无定河上游地区第四系沉积具有以冲积、湖积交替，并夹有风积物的特点，说明该地区湖泊的形成演变与河流的发育关系密切。研究无定河上游湖泊消亡与河流演变的关系，有助于深入认识鄂尔多斯高原湖泊与河流的演化过程，不仅在区域地貌和环境演变研究方面具有理论意义，也可为鄂尔多斯高原湖泊保护及湖泊生态建设提供理论依据。 通过研究区全新世湖沼相沉积露头剖面的野外观察与年代样品AMS 14C测年，结合前人已有研究成果，辅以等高线地形图和遥感影像分析，本文探讨了无定河上游地区全新世湖沼相的沉积特征、空间分布以及湖泊消亡的可能方式，得出主要结论如下。 （1）无定河上游干流萨拉乌苏河的河床纵剖面总体接近直线形，具体表现为由基岩裂点分割的若干略呈下凹形的地段，河流两岸冲积-湖积台地顶部同期堆积面的地形剖面却呈“上凸形”，说明与台地顶部全新世湖沼相沉积相对应的古湖形成于具有加积堆积性质的冲积平原上。 （2）各沉积剖面柱状图的对比显示，全新世湖沼相沉积层具有高差显著，空间相变大，常尖灭于风沙层或过渡为古土壤层的特征，其下伏地层大多为河流相冲积物，上覆沉积主要是风成沙，说明该地区全新世湖泊并非统一大湖。其性质与现代湖泊一致，是以河迹湖和沙丘间洼地为主的大小不一的离散湖泊群，湖间高地常为末次冰期以来发育的沙丘或沙垄占据，构成低矮的沙丘分水岭，湖泊消亡后常被沙丘覆盖。多期遥感影像对比分析发现，研究区存在活动沙丘掩埋干河床的现象。在末次冰期及全新世气候较干旱的时期，活动沙丘隔断河道进而积水成湖的现象同样存在，湖泊干涸后被沙丘掩埋也属常态。 （3）根据本文及前人对沉积剖面湖沼相样品的测年结果，研究区冲积-湖积台地顶部的古湖大多开始形成于气候温暖湿润的中全新世时期，但持续历史较短，大多介于1000～3000a之间。以各剖面最上部湖沼相沉积的结束年代作为湖泊的消亡时间，萨拉乌苏河沿岸从统万城（～5000 a BP）向上游至三叉沟湾（～2500 a BP）、邵家沟湾（～1600 a BP）、滴哨沟湾（～1200 a BP），存在下游湖沼消亡较早，上游消亡较晚的变化趋势，仅大沟湾（～6500 a BP）与巴图湾（＜5000 a BP）出现反常。芦河、榆溪河等支流沿岸湖沼相沉积结束的时间大多处于1000～3000 a BP之间，部分地段存在湖沼消亡下游较早，上游稍晚的现象，但总体规律不明显。多数沉积剖面湖沼相沉积顶部没有泥炭层，少数剖面泥炭层很薄且不典型，表明湖泊消亡过程迅速，除受气候干旱影响之外，应主要与河流下切有关。 （4）河流导致湖泊消亡主要有两种形式，其一河流切穿湖盆，湖水外泄而亡；其二河流下切降低地方性潜水位，湖水下渗而亡。研究区现代湖泊无论是河迹湖还是沙丘间洼地，与河流的关系分为两类，一是沿河串珠状分布的吞吐湖，二是有低矮沙质分水岭相隔的独立湖泊。串珠状吞吐湖在河流溯源侵蚀过程中必然是从下游向上游依次消亡；与河流存在沙质分水岭的湖泊，既可以因河流侧蚀切开分水高地而消亡，也可以因河流下切降低潜水位而干涸。因此，无定河上游全新世湖沼的消亡过程，以河流溯源侵蚀下切为主，但也受河流侧向侵蚀影响。河流两岸台地顶部全新世湖沼相沉积结束年代的分布格局是不同湖泊消亡过程的结果。

The formation and evolution of lakes and rivers is a basic theme in geomorphology and Quaternary environment research. It has been shown that the Quaternary sediments in the upper reaches of the Wuding River have the characteristics of interbedded fluvial, lacustrine and aeolian sediments, indicating that the evolution of lakes there are closely related to the formation of rivers. Thus, studying the extinct lakes from a perspective of river development in the upper reaches of the Wuding River will help to deepen the understanding of the evolution process of lakes and rivers in the Ordos Plateau. It has a significance not only in the theoretical study of regional geomorphology and environmental evolution, but also in the practice of lake protection and lake ecological construction in this region. Based on outcrop observation and AMS 14C dating of the Holocene lacustrine and paludal sediments, combined with previously published research results, this paper deals with the characteristics and distribution of the Holocene lacustrine and paludal sediments and then discusses the possible ways of lake extinction in the research area, supplemented by topographic map and remote sensing image analysis. The main results and conclusions are summarized as follows. (1) The longitudinal profile of the Sarawusu River, the main stream of the Wuding River in the upper reaches, is nearly a straight type, which is composed of several slightly concave sections divided by bedrock knickpoints. However, the topographic profile along the concurrent surface of the alluvial-lacustrine platform shows a convex type, indicating that the ancient lakes corresponding to the Holocene lacustrine and paludal sediments exposed at the top of the valley shoulders has formed on an alluvial plain with aggradation properties. (2)The correlation of the sedimentary sections shows that the Holocene lacustrine and paludal sedimentary layers at different places have no consistency in elevation, but an obvious change in facies. They often thin out in aeolian sands or gradually change into paleosol layers. Most of their underlying strata are alluvial deposits and the overlying sediments are mainly aeolian sands. These features indicate that the Holocene lakes in this area were scattered lakes of different sizes, other than a conjoined large lake. The ancient lakes were mainly fluvial lakes and aeolian lakes, same as the modern ones. The interfluves between lakes were quite low and often occupied by sand dunes or dune chains, developed since the last glaciation. After the lakes dried up, sand dunes would invade and cover the previous lake areas. By comparing the multi-phase images, the phenomena that active sand dunes pass through a dried riverbed is identified in the study area. Hence, there was no doubt that during the last glaciation and relatively arid periods of the Holocene, active sand dunes could block the river course and form dammed lakes. It was normal also that a lake basin was buried by sand dunes after drying up. (3) According to the dating results of the sediment samples by both this study and other researchers, most of the ancient lakes formed at the top of the alluvial platform in the study area started to appear in the Middle Holocene with a warm and humid climate. Their duration was short and was mostly limited to 1000 and 3000a. Defining the age of the lake sediments at the top of each section as the time of lake extinction, there is a decline trend that the lakes vanished earlier downstream than upstream along the Sarawusu River. The lake extinct time at Tongwancheng was about ~5000 a BP and became younger upstream at Sanchagouwan (~2500 a BP), Shaojiagouwan (~1600 a BP), Dishaogouwan (~1200 a BP) respectively. There were some anomalies which were found at Dagouwan (~6500 a BP), located upstream to Dishaogouwan, and Batuwan (<5000 a BP), downstream to Tongwancheng. The end of the lacustrine and paludal sedimentation along the tributaries of the Wuding River, such as the Luhe River and the Yunxi River, was mostly between 1000 and 3000 a BP. The decline of lake extinct time from downstream to upstream can be found at some segments, but the trend was not steady and obvious as in the main stream. The fact that there are few typical peat deposits, which mark the last stage of a normal history of lake evolution, formed on top of lacustrine layers in most sections implicated that the process of lake extinction is rapid and it was highly possible to be the result of river development, besides the influence of a arid climate. (4) There are two main ways of lake extinction caused by river development. The first is a cutting through of the lake basin by river and the draining out of lake water. The second is a dropping of local groundwater table caused by river incision, which leads to a heavy leakage of lake water. The modern lakes, whether alluvial or aeoline ones in the study area, have two kinds of relationships to the river. The one is a series of throughput lakes along river course. The other is scattered lakes apart from river and divided by low sandy ridges. The extinction of the throughput lakes will inevitably start from downstream to upstream during the process of headward erosion of rivers. The independent lakes with sandy interfluves can be destroyed by lateral erosion of rivers or be dried up by groundwater lowering due to the river down cutting. Therefore, the disappearance of the Holocene lakes and marshes in the upper reaches of the Wuding River was caused mainly by river headward erosion, but it was also affected by lateral erosion of the river. The distribution pattern of the end time of the Holocene lacustrine and padulal sedimentation at the top of the alluvial platform on both sides of the river is the combination result of different processes of lake extinction.