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2.
晚新生代青藏高原的隆升对其周围地貌格局和沉积产生了重大影响。地处高原东北构造边界的六盘山受其影响产生明显的地貌分异，造成黄土高原东西两部分巨大的风成沉积差异。最近对位于六盘山西侧陇中盆地东北边缘黄河最高阶地之上的山麓剥蚀面上的黄土磁性地层学研究表明该剥蚀面形成于约1.8 MaBP，与陇中盆地西南隅的兰州、临夏两地山麓剥蚀面的年龄一致 〔1〕，表明在约1.8 MaBP 以前六盘山以西普遍遭受剥蚀，可能形成一级统一 的山麓剥蚀面，即所谓的甘肃期准平原，并指示在约1.8 MaBP 时，六盘山和青藏高原曾产生进一步强烈抬升，该剥蚀面发育结束，黄河出现，黄土开始堆积 〔1，2〕。 相似文献
3.
Polygonal ridge patterns with intervening hollows some 400 m across and with a relief of about 100 m are common as low hills on the northern dissected part of the Sepik piedmont. They are developed in Pliocene mudstone and sometimes in marl and greywacke. The crests of the highest flat‐topped hills have a veneer of Pleistocene fanglomerate on them. The polygons were formed by water infiltrating through the fanglomerate on the former piedmont surface moistening and softening the sediments beneath. Swelling from centres of more intense weathering caused expansion. As the pressure centres impinged on each other a polygonal framework of rock under pressure took in less water and so remained least hydrated. On dissection the polygonal framework was exhumed and then differentially eroded to its present form. Tensional stress fields or tectonic causes do not appear to help in explaining the origin of the polygons. 相似文献
4.
Extensive and well‐developed pediments and pediplains in western New South Wales have hitherto received less than due attention in the literature. This paper records the details of instrumental survey and of excavation at The Pinnacles, near Broken Hill. It presents observation and analysis of slope, rock‐type, structure, and surficial cover, and discusses the significance of a peripediment which contains multiple soil profiles. 相似文献
5.
Soil water conservation is essential to the sustainability of sandy farming. In this paper, long-term observation of soil water, dry soil thickness and soil chemical changes are evaluated at eight locations in sandy soil. This paper subdivides the sandy lands and deserts of China into three climate zones: arid (hyperarid and extremely arid), semiarid, and humid (subhumid and subtropical humid), with respect to the bioclimatic zone, aridity, soil water content, and soil chemical characteristics. The water movement conditions, and chemical variations in each zone are analyzed. The paper also estimates the spatial and temporal correlation function of arid soil thickness and soil moisture. Sandy soils organic matter content, CaCO 3 content, soluble salts content are investigated. Afforestation and selection of tree species in different sandy areas are suggested to regulate sandy land soil moisture. Sandy land in China can be divided into the four sand stabilization regions according to the shifting sand conditions and the techniques advanced: regions I, II, III, and IV. These results have important implications for remote sensing of soil moisture and soil organic carbon, and soil moisture parameterization in climate models. 相似文献
6.
In arid and semiarid regions from the southwestern USA and vast areas of northwestern Mexico, Santa Ana wind events modify the environment with high temperatures, very low humidity, and dust storms representing a recurrent phenomenon that triggers asthma and other respiratory diseases. While research has emphasized Santa Ana wind effects on the USA side, northwestern Mexico has been less investigated. Numerical modeling of a severe dust storm in November 2018, applying the Weather Research and Forecasting model coupled with a chemistry module (WRF-Chem), revealed that erosion, transport, and dust storms extend along the peninsula and the Gulf of California. Santa Ana winds eroded large areas, transported desert conditions to urban zones, causing high dust concentrations and reducing the relative humidity below 10%, deteriorating climatic conditions favorable to wellness. In Tijuana, Mexicali, Ensenada, San Diego, and Los Angeles, PM10 and PM2.5 concentrations (particle matter with diameter below 10 µm and 2.5 µm) reached values over 2000 µg/m3 for PM10, with daily mean concentrations well above national standards, leading to poor air quality and representing a health threat even in short-term exposure. This Santa Ana event transported dust particles several hundreds of kilometers over urban areas, the Gulf of California, and the Pacific Ocean. Severe soil deterioration was simulated within the study area, reaching dust emissions above 700,000 t, including croplands from the northern part of Baja California and Sonora's coastal area. 相似文献
7.
Coober Pedy provides an example of slope development in an arid area. There are two plains separated by slopes which are the subject of this paper. The upper plain is duricrusted and this hard layer has an important protecting effect on the underlying rock. The slopes are gullied and water erosion was important in the formation of both the lower plain and the slopes. Both plains are covered by lag deposits of gibbers indicating considerable wind action. Landslides and desert gilgai are of minor importance. Many slopes take the form of “J” curves, with an upper straight section and a lower concave slope. There is a general parallelism of slopes, but there is variation in detail. Debris is nowhere more than a veneer, and accumulations of debris are not responsible for any slope elements. Slope development takes place largely by parallel retreat. 相似文献
8.
The impact of high-intensity coal mining on water resources has drastically affected the local environment in the Yushenfu mining area, Northwest China. Many studies have ascertained that coal mining has caused reduction of the phreatic water level and vegetation death, which has deteriorated the fragile arid and semiarid ecosystems. However, at Jinjitan coal mine, it has been observed that the phreatic water level rose due to coal mining, which has been beneficial for the local ecology, especially the vegetation. In this study, the variation of the phreatic water table and its ecological effects were investigated by in-situ tests and remote sensing. The results suggest that the recovery of the permeability of the loess aquitard controls the vertical leakage of phreatic water, whereas horizontal recharge is controlled by land subsidence. An ecological impact evaluation, using the normalized difference vegetation index (NDVI), demonstrates that the vegetation is being gradually improved. Compared to a small improvement of ~9.7% in the unexploited area, a?~23.3% improvement occurred in the exploited area where low-density shrubs transformed to high-density shrubs and herbs. Emergence of phreatic water at the land surface in low-lying areas of the working faces may induce the formation of an oasis and wetland system in arid and semiarid areas. These findings could change the conventional negative impression around mining and improve ecological restoration practices. 相似文献
9.
Farmlands and rivers have been seriously polluted by cyanide from a goldmine tailings dam that collapsed in early spring of 1995 in Yining County, Xinjiang Autonomous Region of China. The cyanide distribution in the polluted farmland and the abandoned tailings dam was studied, three and 4 years after the accident occurred. The results indicated that natural degradation of cyanide in soils is slower than in natural water bodies. The cyanide transport in the soil section is similar to freely soluble salts. In arid and semiarid areas, cyanide can be highly enriched in the salt crust in which the concentration is even higher than the fresh tailings debris though cyanide has decomposed for 4 years. In the polluted farmland, the sticky layer in the soil section can highly adsorb and enrich cyanide so it can partly prevent cyanide transfer to groundwater. According to the characteristics of cyanide natural degradation in soil, the measures for prevention and cure of soil polluted by goldmine tailing dam collapse have been discussed. 相似文献
10.
The existence of a small population of ‘relict rock glaciers’ scattered across the main British mountain areas has previously been inferred from published cases of individual sites or local clusters. Discrete debris accumulations (DDAs) of widely differing character have been identified as ice‐debris landforms (whether ‘rock glaciers’ or ‘protalus lobes’) partly from morphological, sedimentological and topo‐locational evidence, but principally by analogy with both active and relict examples in present‐day arctic/alpine environments, with consequent palaeoclimate inferences. However, re‐interpretation of several supposed rock glaciers as rock slope failures has cast doubt on both the palaeoclimatic reconstructions and the origin of the remaining features. Issues of polygenesis and mimicry/equifinality have contributed to some previous misidentifications. We re‐evaluate the 28 candidate cases based on new field and image‐analysis evidence and place them on a continuum from no ice presence through passive ice presence and glacial shaping to emplacement onto glacier ice with consequent melt‐out topography. A null hypothesis approach (that there are no relict rock glaciers in the British mountains) is pursued, and the evidence indicates that none of the 28 cases clearly warrants classification as a relict rock glacier; their characteristics can be explained without recourse to any significant forward debris movement controlled or facilitated by incorporated or underlying ice as it deforms and melts out. However, only one‐third of the candidate DDAs are attributed in whole or part to rock slope failure ( sensu stricto), with other debris sources including incremental rockfall, bedrock knolls with coarse debris veneer, protalus rampart and moraine. A few cases deserve more detailed investigation of their structure, morphology and sediments within a broader local glaciological/topographical context, with multitemporal/polygenetic evolution in mind. But it is for future researchers to demonstrate that deforming ice played an incontestable part in shaping these often enigmatic DDAs, given that other causes are simpler and commoner. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
11.
For many years the results of regional geochemical surveys in arid and semiarid regions of China were not satisfactory. Therefore, we selected eight areas in the middle and western part of Inner Mongolia and the northwestern part of Gansu Province to study this problem from 1982 to 1985. The contents of our study include: the migration and distribution of elements in an arid environment; the interference of aeolian sand; the applicability of different sampling mediums; and the development of effective sampling techniques. Pilot surveys were carried out covering several hundred or more than a thousand square kilometres in every test area after the orientation study.Very good results were obtained in the surveys carried out in mountainous and hilly regions. The only problem was to eliminate effectively the interference of aeolian sand. To accomplish this we collected elastics of −5 + 2 mm or − 10 + 0.9 mm coarse grain size in the dry valley. In the stony Gobi desert region and the eroded peneplain region, a rock survey and residual soil survey produced the results expected. However, we had to consider the following influencing factors: (1) the caliche in the loose soil layer forms a barrier, hindering the migration of most of the elements in a vertical direction. Only where the caliche was rather thin was the influence of little significance; (2) in the residual soil of the background area and non-mineralized zone, almost all trace elements are enriched secondarily. The enrichment factors are generally between 1.3 and 1.8. In the residual soil of the mineralized zone, almost all ore-forming elements are impoverished. The well-water geochemical survey and the deep-root system plant survey have a peculiar function in finding ore deposits in the arid region. These two methods are discussed elsewhere. 相似文献
12.
根据有关台站的水文气象观测资料及"九五"国家科技重点攻关项目"96－912"专题有关成果,对甘肃省河西内陆干旱区地表水、地下水资源的数量、分布特征与变化规律及相互转化关系进行了分析和研究。结果表明,内陆干旱地区的地表径流主要形成于中、高山区,散失于山前平原和沙漠。径流的补给来源主要为大气降水、冰雪融水和地下水。降水量及其时空分布对水资源的形成有着重要的影响。这里降水、河川径流与地下水转化关系十分明显。内陆干旱地区水资源最主要的特征就是从山区到平原地表水与地下水在不同地质地貌单元间的相互转化,并且由径流源区的山区到河流下游的平原,不同区域、不同地段地表水与地下水的转化关系及地下水的流动模式亦不相同：即由降水与冰雪融水下渗所形成的山区地下水绝大部分以基流形式排泄,形成地表径流进入盆地;而河流在进入盆地或平原区流经透水性极强的山前冲、洪积平原后又大量渗漏补给地下水,山前冲、洪积扇平原的地下水沿地形坡降向冲积平原运动至冲积扇缘地带后,由于含水层土壤颗粒变细,导水性减弱,形成地下水溢出带,地下水沿沟壑呈泉水大量溢出地表,汇集成泉沟进入河流而转化成为地表水。在冲、洪积扇以下的冲积平原上,潜水含水层土壤颗粒细,地下水埋藏浅,径流水平流动缓慢,地下水以垂向水量交替为主。在自然状态下,冲积平原下游直到尾闾湖;洪水季节（洪水季节外,河川径流量很小甚至没有）河流泻洪通过河道补给地下水,余水进入尾闾湖。正是水量不大的河水及其所转化形成的地下水维系着西北内陆干旱地河流下游地区的绿州的存在和这里十分脆弱的生态环境。这些地表水与地下水之间的转化过程的这种特征直接影响本地区水资源的开发利用模式。目前,在上游地区大规模发展经济、开发水资源的情况下,随着地表径流利用率的不断提高和地下水得到的补给减少,许多地方泉水量减少甚至枯竭,原来的泉灌区被迫变为井灌区。冲积平原下游即使在洪水季节也很难接受上游地表径流的补给,造成地下水位持续下降,植被死亡,土壤荒漠化。因此,内陆干旱区的水资源开发利用必须从整个流域的角度出发进行统一的合理的规划,总结不同类型地区水资源开发利用过程中的经验教训,逐步建立不同类型最优化的水资源利用模式,这将对今后干旱区的水资源开发利用具有重要的意义。 相似文献
13.
世界上近一半的国家都不同程度地受到干旱问题的影响,因而干旱、半干旱区的水文地质研究多年来一直是世界水文地质学界的研究热点。本文根据几年来所阅读的关于该方面的近百篇国内外文献资料,对干旱和半干旱地区地下水开发利用概况、地下水形成机理研究进展、干旱区大型盆地地下水运移所采用的两种模型、环境同位素技术在干旱区地下水研究中的应用、地下水流系统研究进展、地下水数值模拟及管理模型现状、干旱区包水带水文地质研究 相似文献
14.
基于对长白山天池及邻区火山地质和次生火山灾害的编图结果,从岩性、断裂、地形地貌和水系等方面,分析火山喷出物的地质特征与这些火山物质所导致的次生火山灾害之间的相关性。研究表明,崩塌发生在柱状节理发育的硬质岩中,多期火山喷发以及伴生的地震活动剥蚀掏空坚硬岩层间的松散堆积体,使岩体失稳发生崩塌,局部陡崖地貌在地震影响下亦会发生崩塌灾害。软质岩和松散堆积体受流水侵蚀,河谷下切,河流两岸斜坡前缘形成开阔的滑动空间,火山地震引起山体变形,斜坡岩体结构遭到破坏发生滑坡灾害。火山先期喷出的碎屑物和崩塌滑坡产生的碎石是火山泥石流的重要物质来源,火山喷发或强地震引发的洪水灾害以及地形地貌对火山泥石流的形成、搬运和分布范围起关键性作用。 相似文献
15.
Towards the end of the Carboniferous period, several isolated basins were eroded into Carboniferous sediments lying within the Lower Palaeozoic Southern Uplands massif. Eruption of basaltic lava flows ensued, followed by deposition of thin pediment breccias as desert conditions became established, leading to the development of extensive aeolian sands which interfinger with alluvial fan breccias at the basin margins. Such intermontane desert basins have rarely been documented in the stratigraphic record and the Permian deposits are here compared to similar deposits and processes operating in Recent intermontane desert basins. A number of breccia types have been distinguished, some attributable to secondary reworking of deflation areas on alluvial fans, and the deposits of streamfloods, braided streams, sheetfloods and desert-floor ephemeral streams have been recognised. 相似文献
16.
The Redan Geophysical Zone forms a regional magnetic high in contrast to the regional magnetic low defined by the main part of the Broken Hill Block. The magnetic rocks are interpreted to dip below the remainder of the Broken Hill Block and there has been speculation that they are significantly older than the Early Proterozoic Willyama Supergroup. Evaluation of lithological mapping and aeromagnetic data permitted interpretation of a stratigraphic sequence within the Redan Geophysical Zone, consisting of three new formations: the Redan Gneiss, Ednas Gneiss and Mulculca Formation, plus the Lady Brassey Formation, part of the Thackaringa Group. The rocks are considered to belong to the lower part of the Willyama Supergroup and are not an older basement. Although the Redan Geophysical Zone contains some rock types not found elsewhere in the Broken Hill Block, there are some lithological similarities with the lower part of the Willyama Supergroup: an abundance of albite‐rich rocks, the presence of quartz‐magnetite rocks with Cu and trace Co, and abundant amphibolite/ basic granulite in the Lady Brassey Formation. The boundary between the Redan Geophysical Zone and the remainder of the Broken Hill Block appears to be conformable, with no evidence of major faulting. Similarly no evidence of unconformities or major displacement of stratigraphic boundaries has been found within the Redan Geophysical Zone. Structural history, fold style and orientation, and metamorphic grade within the Redan Geophysical Zone are similar to adjacent areas of the Broken Hill Block. It is concluded that the Broken Hill Block contains no outcropping equivalent of the first cycle of sedimentary/ igneous rocks recognized in the Early Proterozoic of northern Australia. Albite‐quartz‐hornblende‐magnetite rocks unique to the Redan Geophysical Zone most likely comprised detritus derived directly from an intermediate volcanic suite. Some were altered considerably, while other rocks retained the dacite/andesite composition, except for the addition of Na, an increase in the oxidation state, and partial leaching of some of the more mobile elements. These modifications could have taken place in shallow alkaline evaporitic lakes. The Redan Geophysical Zone contains some of the elements of a foreland basin adjacent to a continental volcanic arc: a thick stratigraphic sequence, oxidizing evaporitic conditions, and intermediate volcanic detritus. The change from intermediate‐acid volcanism in the earliest formations, to bimodal acid/basic volcanism in the Thackaringa and Broken Hill Groups could correspond with a change from initial continental arc volcanism into bimodal rift volcanism. The case for the arc volcanism is weakened, however, by the relative scarcity of rocks with andesitic compositions and the lack of basaltic andesite compositions. The alternative is that the intermediate to acid volcanism represents only a variation on the later bimodal rift volcanism. 相似文献
17.
中、西太平洋海山区是富钴结壳的重要富集区,钙质远洋沉积、碳酸盐岩沉积及重力作用引起的滑塌沉积是海山山顶和斜坡的主要沉积类型,它们的空间分布规律对于富钴结壳的分布至关重要.在国内首次利用EM122多波束回波强度资料对中太平洋潜鱼海山进行了底质类型研究,对回波强度资料进行处理和统计分类,并与浅地层剖面和地质取样结果对比,分析得出了4种底质类型,即富钴结壳、钙质远洋沉积、碳酸盐岩基底及碎屑流沉积.这几种底质类型具有不同的回波强度特征,其中富钴结壳区表现为均一的回波强度高值特征;钙质远洋沉积区表现为均一的回波强度低值特征,二者回波强度值相差约20 dB.结果显示潜鱼海山山顶仅局部发育钙质远洋沉积,大部分为碳酸盐岩基底出露区,山顶边缘及侧翼山脊处为主要的富钴结壳分布区.此外,该海山存在3处较大规模的重力滑塌沉积区,主要为碎屑流沉积. 相似文献
18.
干表层（DSL,Dry Surface Layer）是干旱半干旱地区土-气界面的重要组成部分,影响着陆地水分循环。文章以土壤物理学、土壤水动力学、土壤热力学和水文地质学的基本理论为指导,在综合分析前人资料的基础上,结合室内物理试验的部分观测成果,界定了干表层的概念,探讨了此概念的内涵与外延;辨析了干表层和（下伏）土壤干层两个概念的关系;阐明了干表层与地下水位埋深的关系,干表层对降雨入渗、蒸发和植被的影响。 相似文献
19.
北京山区地质环境条件复杂,发育大量突发地质灾害隐患,既直接威胁山区村庄、道路、景区的人员及设施的安全,又会对城镇的规划建设构成威胁。通过开展地质灾害易发性评价工作,划分出地质灾害易发区,以评价结果指导城镇建设规划,减轻地质灾害的威胁,这是一项十分重要的工作。文章在阐述北京山区崩塌、滑坡及泥石流突发地质灾害发育情况的基础上,选取了坡度、起伏度、工程地质岩组、地质构造、地貌类型及降水等6个影响因子,采用综合信息量模型方法,分别对北京山区斜坡类灾害（崩塌、滑坡）和泥石流灾害的易发性进行评价,并根据“就高不就低”的原则,叠加各灾种的易发性评价结果划分出北京山区突发地质灾害易发性分区图,为城镇建设适宜性评价、编制国土空间规划及完善空间治理提供科学的依据。 相似文献
20.
Jiuzhaigou, located in the transitional area between the Qinghai–Tibet Plateau and the Sichuan Basin, is highly prone to geological hazards (e.g., rock fall, landslide, and debris flow). High-performance-based hazard prediction models, therefore, are urgently required to prevent related hazards and manage potential emergencies. Current researches mainly focus on susceptibility of single hazard but ignore that different types of geological hazards might occur simultaneously under a complex environment. Here, we firstly built a multi-geohazard inventory from 2000 to 2015 based on a geographical information system and used satellite data in Google earth and then chose twelve conditioning factors and three machine learning methods—random forest, support vector machine, and extreme gradient boosting (XGBoost)—to generate rock fall, landslide, and debris flow susceptibility maps. The results show that debris flow models presented the best prediction capabilities [area under the receiver operating characteristic curve (AUC 0.95)], followed by rock fall (AUC 0.94) and landslide (AUC 0.85). Additionally, XGBoost outperformed the other two methods with the highest AUC of 0.93. All three methods with AUC values larger than 0.84 suggest that these models have fairly good performance to assess geological hazards susceptibility. Finally, evolution index was constructed based on a joint probability of these three hazard models to predict the evolution tendency of 35 unstable slopes in Jiuzhaigou. The results show that these unstable slopes are likely to evolve into debris flows with a probability of 46%, followed by landslides (43%) and rock falls (29%). Higher susceptibility areas for geohazards were mainly located in the southeast and middle of Jiuzhaigou, implying geohazards prevention and mitigation measures should be taken there in near future. 相似文献
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