【作者】 李智佩；

【导师】 薛祥煦；

【作者基本信息】 西北大学 ， 地层学与古生物学， 2006， 博士

【摘要】 我国北方地区不仅荒漠化土地面积大、发展变化大，与之有关的各种地质灾害频繁发生。今年4月底前北方地区已经发生了9次强沙尘暴，首都北京在4月16日一夜之间降尘量达30万吨!据估计，我国荒漠化危害的直接经济损失约642亿元/年。2004年北方地区风蚀荒漠化占全国风蚀荒漠化土地总面积183.94万km~2的97％以上，形势非常严峻。由于历史上的原因，荒漠化的地质环境背景研究重视不够，片面强调人为因素，造成许多地方治理成本高而收效甚微。开展土地荒漠化的地质环境研究，对于丰富我国荒漠化调查研究的理论、提出科学合理的荒漠化防治对策措施等均具有重要意义。基于对北方地区地质环境和各种地质营力对荒漠化形成发展的控制特征的研究，参照当前主要的荒漠化分类体系，首次提出了荒漠化土地类型的地质成因分类，包括风力作用下的荒漠化土地(风蚀荒漠化)、流水作用下的荒漠化土地(水蚀荒漠化)和物理化学作用下的荒漠化土地(土地盐渍化)。据风蚀荒漠化的形成特点将其划分为沙漠化(风力堆积型)和戈壁化(风力侵蚀型)等两个基本类型。风力堆积型沙漠化根据风沙的移动特征可分为就地起沙型和风沙侵入型和侵蚀残积型。根据水蚀荒漠化地区岩性特征，将其分为石灰岩地区以内的石漠化和以外的岩漠化以及黄土区的土漠化。根据化学成分的不同，将土地盐渍化划分为盐渍化、碱化等两种类型；根据成因还可分为灌溉型(次生盐渍化)、非灌溉型和残余积盐型等。荒漠化土地所处的地质构造和地貌部位，也是荒漠化土地分类的重要依据，例如冲积平原型、高原洼地型、平原洼地型、河流滩地型、山地残坡积型、高原残坡积型、梁峁型、塬面型、河流谷地型等。荒漠化土地的地质成因分类丰富了土地荒漠化的理论研究，为从地质学角度探讨土地荒漠化的形成和发展提供了理论基础。根据地质构造、地貌、气候、水文和水文地质条件特征，将北方地区划分为7个一级荒漠化地质环境区和23个二级荒漠化地质环境区。7个一级荒漠化地质环境区是：①内陆干旱盆地荒漠化地质环境区、②中西部高原荒漠化地质环境区、③中东部高原荒漠化环境地质区、④黄土高原荒漠化地质环境区，⑤东部平原荒漠化地质环境区，⑥青藏高原(东北部)荒漠化地质环境区和⑦山地荒漠化地质环境区等。荒漠化地质环境分区是环境地质调查与研究和荒漠化土地治理分区的基础。全新世以来的气候环境变化是北方地区土地荒漠化形成发展的主要因素。西部内陆盆地以干旱气候为主要特征，中部高原是受季风系统中夏季风和冬季风的消长变化影响最为显著的地区，东部地区则以暖湿气候为主，受夏季风控制。气候格局的形成造就了荒漠化土地的分布，气候的波动则是沙漠化发展或逆转的控制因素。末次间冰期以来一直持续的大约以1500a为周期的气候振荡对中国北方地区的沙漠化有重要的影响或控制作用。北方地区约在10000aBP、8000aBP、5500aBP、4000aBP、3000aBP、1500aBP的沙漠化过程分别与北大西洋第7、5、4、3、2和1次的浮冰事件相应，沙漠化扩大过程与全球气候变化的主要事件相一致。同时，北方不同地区10世纪或百年以来的人类活动，对荒漠化的影响起到了重要的决定性作用。新生代的构造隆升对全球气候变化有重大的影响。在我国，青藏高原隆升是造成北方地区气候环境变化的根本。青藏高原使西风环流发生变化，一方面使水汽多以固态形式降在高原及山体西侧，到达北方高原及东部平原地区的降水明显减少；另一方面使西风急流发生分支绕流，造成高原北侧的西风环流终年呈反气旋性质，加强西北的干旱气候。青藏高原隆升加强了西伯利亚一蒙古高压，造成北方冬季风强盛，导致西北地区冬半年气候异常干燥、大风频繁。水环境是控制荒漠化形成发展的决定性因素。内陆干旱盆地荒漠化的发展，一是取决于周围山地降雨和融雪所形成的地表和地下水径流的多少；在较短时间尺度上，人类活动导致水资源的重新分配是造成内陆河中上游人工绿洲区荒漠化程度减轻、下游天然绿洲区荒漠化迅速加剧的主要因素。河流的改道是促使冲积平原生态环境变迁、荒漠化发展的重要原因。内陆干旱盆地的植物生长所需的水分主要依靠地下水供给，地下水对荒漠化发生发展起到决定性作用。当潜水埋深＞6.0m时，植被开始衰败，沙漠化程度增加。中部高原处于季风边缘的半干旱地带，生态环境相当脆弱，土地荒漠化程度与降雨量存在明显的关系，地下水对荒漠化的影响减弱。在人类活动强烈影响下，植被破坏严重，冬春季节短暂的干旱就会造成土壤的极其干燥，为沙漠化扩大造成有利因素。黄土高原的水蚀荒漠化主要与气候和地表水环境有关，夏季的集中降雨和黄土区水的入渗速度低形成较强的地表径流是水蚀荒漠化主要土壤侵蚀形式。地下水的埋藏深度是决定土地盐渍化的重要因素，在内陆干旱区则更加明显。当地下水埋深小于2m时，地表蒸发强烈，土壤积盐迅速。一般当潜水埋深＞3.5m时就不会产生盐渍化。目前，严重缺水地区利用较高矿化度的地下水灌溉也是造成北方地区土地盐渍化迅速发展的原因之一。不同类型沉积物是决定荒漠化类型的主要因素。残积物、坡积物和洪积物分布区的低洼地带常形成沙漠化，地势较高的剥蚀地区形成砾漠化。现代和古河流阶地上的沙质堆积物是冲积物分布区沙漠化的物质基础。北方(古)湖盆地区是沙漠、沙漠化土地及沙尘暴的主要分布区或发源地，也是盐渍化土地的集中分布区。现代或古湖泊的化学沉积物也是构成盐尘暴的重要来源。第四纪风沙堆积的广泛发育是土地沙漠化的根源之一。以流动沙丘为主的塔克拉玛干、腾格里、巴丹吉林、库布齐等沙漠的边缘地带是沙漠化发生的主要地区；以固定沙丘或半固定沙丘为主的地区，如古尔班通古特沙漠，科尔沁、浑善达克、呼伦贝尔等沙地土地沙漠化以沙丘的活化或固定、沙地或沙漠边缘的扩张或缩小为特征。黄土堆积的则是水蚀荒漠化最主要的物质基础。此外，中新生代砂岩分布区不仅是土地沙漠化和水土流失最为严重的地区，如陕西和内蒙古交界处的砂岩分布区，也是黄河泥沙的主要来源。总之，本研究以资料综合为主，结合重点地区剖面、沙漠化变化的深入剖析，系统研究了中国北方土地荒漠化形成的地质成因类型与特征、气候变化及其周期性、第四纪地表沉积物、不同环境地质分区水文和水文地质系统等地质环境要素对荒漠化的控制作用，提出了内陆干旱盆地、中部高原和东部平原三种不同类型的土地荒漠化地质成因模式。在此基础上，提出了我国荒漠化防治的五项原则和若干对策建议。五项原则即地质环境背景决定荒漠化治理方案、生态环境自然恢复优先、资源有限高效利用和社会经济可持续发展，以及系统工程原则，这是使我国向经济节约型、知本型、环境和谐型社会发展的重要途径。更多还原

【Abstract】 Desertification is a serious environment problem in northern China, not only because of its large area and great changes, but also of varies kinds of geologic disasters and giant loses related to it. In 2004, wind effected desertification in the north occupies more than 97% of 1,839,400km in the whole country. The reasons for that research on geological environment of desertification have not been paid enough attentions and that the human factors been overemphasized could be found in the last 50 years of history. Thus led to the result that the costs of combating desertification are very high and the fruits are little in many places. This research would be of great importance in enriching theory of desertification investigation and study and proposing scientific and suitable measurements for combating desertification and finally realizing human nature harmonics target.On the basis of studying geo-environment and geologic forces that controlling the formation and development of desertification and referring to modern classification system, it has been put forward by the first time the geologic formation classification of land desertification in northern China. For example, wind effected desertification is divided into wind erosion type (i.e. sandy desertification) and accumulation type (i.e. gobi desertification) according to forming process characteristics. Water effected desertification is divided into karstification in limestone area and rocky desertification in other basement rock areas. Desertification related to physical chemical process is divided into salinization and alkalization. It could be divided also into irrigation type, non-irrigation type as well as relic accumulative salty type. The structural and morphologic units could also be use as important basis in the classification. For example, desertification of alluvial plain, plateau and plain depression, river valley and flood land, mountain and plateau residual, loess replat and Yuan types. The geologic classification laid theoretical foundation of studying the formation and development of desertification in the view of geologic aspect.Northern China is divided into seven desertification geo-environment regions and twenty three sub-regions according to geologic tectonics, morphologic, climatic, hydrologic and hydrogeology conditions. The geo-environment regions are as follows, inland arid basin, mid-western plateau, mid-eastern plateau, loess plateau, east plain, northeast Qinghai-Tibet plateau and mountain regions. This classification is both the fundamental of desertification geo-environmental investigation and research and combating district division.Holocene climate variation is the main cause to the formation and development of desertification in northern China. The climate in inland basins and mid-plateau are respectively arid and semi-arid which effected prominently by the East Asian monsoon system. The east plain is dominated by worm and humid climate. The climate pattern of northern China controls the distribution of desertification. But the climatic variations control the expansion and reverse of desertification. Since the last ice age, the 1500a cyclic climate oscillations dominate the desertification in northern China. Desertification at about 1000aBP, 8000aBP, 5500aBP, 4000aBP, 3000aBP and 1500aBP are respectively corresponded to the Holocene events numbered 7, 5, 4, 3, 2, and 1. This suggests that the sandy desertification processes in northern China are identical with main climate events. However, desertification in recent 100 years and in some places from 10th century is affected predominantly by human beings.Cenozoic tectonic uplift controls global climate changes. The uplift of Qinghai—Tibet plateau is the basic force of northern China climate changes. Qinghai—Tibet plateau makes the westerly wind circulation changed, leading to moisture rainfall at the west side of mountains and remarkable reduced that in the east basins on one side. On the other side, Qinghai—Tibet plateau divided westerly jet into two branches, leading to the north branch become to anticyclone all the year round, and enhanced arid climate in Northwest China. Finally, the uplift of Qinghai—Tibet plateau enhanced also Siberian—Mongolian high pressure, led to powerful winter winds and extraordinary dry in Northwest China.Aquatic environment is the decisive factor in controlling desertification. In inland arid basins, it is controlled mainly by the surface and ground water flows formed from rainfall and melting snow in surrounding mountains. In short time scale, the redistribution of water resources in endorheic drainage between manmade oasis in mid-upper reaches where desertification lightened and natural oasis in lower reaches where desertification worsened could be the dominantly factors in controlling the clearly different trends of desertification in these regions. In arid basins, waters required for plants grow are mainly from groundwater. Thus, bury and quality of groundwater dominates desertification development. When the ground is below 6.0 m, vegetation start dying, and sandy desertification develops. The middle plateaus stands in the edges of monsoon system, semi-arid climate causes ecologic environment very fragile, and desertification grades have clear relations to precipitation and groundwater levels become the second factor. In these regions, severe destroy of vegetations by human activities could led to sandy desertification expansion if there is a short dry in winter and spring seasons. The water erosion desertification in loess plateau is mainly related to climate and surface water environment. The concentrated rainfalls and low infiltration velocity in loess area make it possible that strong flows can be formed in a short time, and this is the main water erosion pattern. Ground water level dominates the formation of salinization, especially in the inland arid areas. When bury of groundwater is smaller than 2m, strong evaporation in surface led to rapid accumulation of salt in soil. In general, when bury of groundwater is bigger than 3.5m, salinization would probably do not occur. At present, salinization in many severe water shortage areas is caused by irrigation using high TDS groundwater.Different kinds of sediments lead to different desertification types. In depression belts of residual, talus and diluvium distribution areas may be occupied by sandy desertification, while the higher erosion regions would be occupied by gobi desertification. Sandy accumulation in modern and ancient river terraces is the materials of sandy desertification in alluvial areas. Lacustrine deposit in lake basins of both modern and ancient times are the major materials of desert, desertification and sand storms. Lake basins are also the concentrated areas of salinization. Quaternary aeolian sediments are the main materials of sandy desertification in all and around deserts, such as Taklimakan, Tengger, Badain Jaran, Gurbantunggut deserts and Mu Us, Hunshandake, Horqin, Hulun Buir sandy lands. Loess accumulations are the basic materials of water erosion desertification. In addition, Mesozoic and Cenozoic sandstone areas are characterized by both sandy and water erosion desertification, such as the juncture between Shaanxi Province and Inner Mongolia Autonomous Region.In summary, on the basis of data and important sections analysis, it has been studied systematically geo-environment of desertification in northern China, including the types and characteristics of geologic genesis desertification, climate changes and periodicity, Quaternary sediments, surface and groundwater conditions. It has been put forward for the first time the geologic genetic models of desertification in northwest arid basins, middle plateaus and eastern plains. Finally, five principles of combating desertification and a number of counter desertification measurements are proposed.更多还原