The chemical compositions of the desert sediments collected from Taklimakan Desert, China, were studied and their chemical characteristics are elucidated. 1) SiO2, Al2O3, K2O, Na2O and Ba are abundant in coarser fractions of most of sediments, and CaO, MgO, Fe2O3, MnO, P2O5, Cr, Sr, C, S and V are abundant in finer fractions. 2) Effect of sedimentary environment on chemical compositions is not clear, but regional effect is suggested by geochemical map. The chemical composition of finer fraction of dune sand is homogeneous, suggesting that the fine particle is supplied from wide area of the desert. 3) In view of chemical weathering, Na2O and K2O might dissolve in water and deposit as chloride or sulfate in the sediments related to river, whereas CaO and MgO might be immobile or retained in fine fractions as salt.
Power Reactor and Nuclear Fuel Development Corporation (PNC) has been conducting uranium exploration in the Rudall region, Western Australia, since 1989. The geological setting of this region is similar in age, rock types and structure to the Alligator River region in the Northern Territory, Australia and to the Athabasca region in Saskatchewan, Canada, where are currently the most important uranium province in the world. The Kintyre uranium deposit is located in this region and hosted in the Lower Proterozoic metasediments. Consequently, it is important to delineate these rocks, especially chlorite schist, for the first stage of uranium exploration in this region. Landsat Thematic Mapper (TM) data analysis was performed to delineate the Lower Proterozoic metasediments in this region. TM band combinations which were thought to be useful to delineate these rocks were examined on the basis of mineral content and conditions of rock surface of the host rocks in the Kintyre uranium deposit and the inter-band response pattern of each rock type which was distributed in this region. As the result of the examination band ratios band 3/band 1, band 3/b and 5 and band 5/band 7 were selected and combined in blue, green, red respectively to create a ratio color image. Metasediments were shown by yellow green on the ratio color image and apparently discriminated from other rocks. These results were also confirmed by the ground truth. In order to clarify the reason why metasediments were shown by yellow green on the ratio color image, reflectance spectra of the host rocks in the Kintyre uranium deposit were measured by the IRIS spectroradiometer. It was found that the cause which the host rocks were shown by such distinctive color on the ratio color image was due to the flat pattern of reflectance spectrum from the visible to the short-wavelength-infrared (0.6-1.6 μm).
Sultanat of Oman located at the south-eastern edge of Arabian Peninsula covers an area of 300, 000 km2. Though almost of the area consists of desert, she has 5, 000 year history of irrigation agriculture by groundwater. Although the country produce oil, Omani people, having been aware of the limitation of the resources, have made efforts to the pervation of education and agricultural development. The country is geographically characterized by the existence of two lines of mountain range. Oman mountain chain extending 600 km long in a direction paralle to the Batinah coast consist of many steep 3, 000 m class high peaks. Dohar mountain chain facing to Arabian sea and extending east-west direction has an altitude of about 1, 000 m. Southern side of the mountain chain shows steep topographic feature of fault scarp. Contrary to the fact, northern side of the mountain ridge show very gentle slope and dips toward the Rube al Khali desert. Although Sultanat of Oman climatically belongs to the tropical dry zone, it rarely severe rains in the steep slope of mountain region caused by the upstream air current. The precipitation is the source of ground water of the country. In the Batinah coastal region, irrigation water have been drawn up by small scale wells and in recent years by deep wells with Submarin pumps. Accompany with the increase of irrigated farm, excessive pumpages have outstripped natural recharge of groundwater resulting in the intrusion of sea water. In order to prevent salinitization of groundwater a number of recharge dams which reserve flood temporary and percolate the water under the gound have been constructed. There are no cultivation in the Nejd region located at the northern gentle slope of Dhar mountain chain, owing to very poor available water resources. Only a few nomads are found here and there near the water shed. In Nejd groundwater was first found out by exploration drilling for oil in 1955. In recent years it has been clarified that plenty of good quality groundwater is confined in Tertially limestone aquifers lie 300-600 m under the ground. Hydrological and hydrogeological conditions show that recharge to the aquifers is small, development would inevitably involove mining of groundwater from aquifer storage. It was decided agricultural development must be carrid out step by step appraising the volume of groundwater resoces. Pilot farm 50 ha in area accompany with 2 production wells and 4 monitoring wells is now under construction in technical cooperation with Japan.
The desertification of Sahel region along the southern Sahara desert result in the most serious environmental problems in west Africa. One of the proposed countermeasures against the desertification is afforestation in this area. We, authers, set up the anti-desertification project in this region, utilizing undeveloped subsurface water resources and solar energy which are used for the irrigation of tree-plantation and agriculture. Two years research and field survey on the underground water involved in the fossil valley of the Sahel region clarified the feasibility of construction of subsurface dam. In this paper, some characteristics of the water resources and of the proposed afforestation project in this region are summerized in view point of utilization of water. Hydrological characteristics of fossil valley are also described in relating with the construction of underground dam. The fossil valley distributing in the Sahel region cut the basement rocks downward and are filled with sand and grabel which are most suitable container for the storage ofsubsurface water. This type of water which is not developed for the present is supplied by rain fall in the corresponding area. Subsurface water stored in the fill materials of the fossil valley can be supplied enough in the dry season for the plantation, even if it is in the draught continuing a few years. The subsurface water storage system described in this paper is the most effective method for utilizing water in the Sahel region where the evaporation rate exceed some thousand millimeter a year.
Desert environment has the characteristic of being further deterioratedand some non-desertified land has changed into desertified one in Xinjiang. The main styles of deseritfication are: dunes activated, wind-sand current and moving dunes get into the non-desertified land, under the action of wind, form wind erosion and shifting sand land. According to the degrees of mobile dunes and wind-sand current and to the coverage of vegetation, the desertified land in Xinjiang is divided into 5 degrees as follows: the most severe desertified, severe desertified, middle desertified, light desertified and latent desertified lands. As Xinjiang has had great achievement on desertification prevention, desertification has been controlled in some areas, and the comprehensive management models have been set. But it still spreads in some area. Desertification and its prevention will be the important subject in the future.
Using scanning electron microscope (SEM), the modification and superposition of quartz surface textures of sandy sediments in the Taklimakan Desert are observed and analyzed. Based on field occurrence characteristics, sand materials can be divided into river-sand, dune-sand and stratum-sand. The features of surface texture of quartz grains are as follows: (1) On quartz grain surfaces in river-sands, the imprints by mechanical actions of glacier and running water are retained, i. e., conchoidal fracture, straight steps, arcuate steps. V-shaped depression, striation and so on. The imprints by chemical action are slighter. (2) The quartz grains in dune-sands can be divided into newer and older eolian sands. On the surfaces of newer eolian quartz sands, the imprints by glacial and river actions are clearly retained and the solution-precipitation textures are the results of low-energy chemical environment. The grain surfaces of older eolian quartz are covered with wind abrasion textures, and the earlier imprints on the surfaces caused by glacial and running water actions have been strongly rounded. This type of quartz sand often develops honeycombed hollows, scaly exfoliation surface and solution-precipitation textures in high-energy chemical environment. It should be indicated that the content of older eolian quartz grains in dune-sands is very low. (3) The quartz grains of stratum-sands can also be divided into newer and older eolian sands. Their surface patterns and textures are respectively similar to the newer and older eolian quartz grains in dune-sands. Above features show the sand materials of the Taklimakan Desert are modified by wind abrasion and chemical weathering after they are transported to the desert area by glacier and running water. According to observation and analysis under SEM, we can find that the surface textures of quartz grains in river-sands are mainly compound imprints by glacial and subaqueous mechanical actions. The quartz grains of dune-sands, based on the strength of eolation to surface textures formed in earlier period, can be divided into older eolian quartz sands and newer ones. The older ones suffer a lasting abrasion by wind, so that the surface textures caused by glacial and river actions in earlier period have been rounded, or wind abrasion textures such as pitted surface and dish-shaped concavity, etc. are superposed on their surfaces. This makes the earlier surface textures unclear. On the newer ones, imprints by glacial and river actions are clear, because the time in which these imprints are modified by wind is not long. The surface texture features of quartz grains in subsurface stratum-sands are similar to those of dune-sands. The features as above further confirm the discussion-the recent rivers still supply the Taklimakan Desert with sand. Chemical solution-precipitation textures of quartz grains surface in dune-sand and stratum-sand are mainly products of low-energy chemical environment, i. e., they are solution pits, solution holes and tiny SiO2-precipitates. This is related to the climate condition that it is dry and the temperature varies greatly between day and night in the Taklimakan Desert. However, in few area, such as Mazhatag Mountain Region and the core T. C. No. 1 (bellow 78m), products of chemical weathering in high-energy chemical environment are often found, i. e., honeycombed surface and scaly exfoliation chemical solution textures developed on quartz surfaces of the sand samples. The reason is that part of sand materials in the Mazhatag Mountain Region come from the bedrock of Tertiary System, and in Tertiary Period, relative warm-humid climate had appeared.