Duricrust development and valley evolution: Process–landform links in the kalahari     

David J. Nash  Paul A. Shaw  David S. G. Thomas 《地球表面变化过程与地形》1994,19(4):299-317

Duricrusts are an important landscape component of the Kalahari region of central southern Africa. Their exposures within the dry valleys (mekgacha) of the Kalahari provide some of the most widespread surface outcrops of the terrestrial Jurassic to Holocene Kalahari Group sediments. Exposures have been extensively used in the construction of lithostrati-graphic sequences, on the assumption that valley systems have incised their courses through a pre-existing duricrust sequence. Recent work, however, has identified the role of groundwater erosion processes in valley development, which may have influenced duricrust formation. Studies of duricrusts from boreholes drilled within two mekgacha show that duricrust type is intrinsically related to the presence of a valley. Analyses of calcretes and silcretes in a series of profiles and thin sections from the Letlhakeng area of Botswana also indicate extensive alteration and diagenesis in association with former higher water tables. Sedimentary sequences within duricrust host materials can be identified but there is no evidence for correlation of duricrust cements between exposures. Profile studies from the Auob Valley in Namibia, however, suggest that this valley has incised through a sequence of duricrusts. Caution is advised in future attempts to correlate duricrust types on the basis of valley exposures, with the recommendation that where such exposures are used in a lithostratigraphic context, only duricrust host material characteristics and not cementing materials should be considered.  相似文献   

河北坝上地区脆弱生态环境特征   总被引：23，自引：1，他引：23  

孙建中  杨明华 《中国沙漠》1994,14(4):37-46

坝上地区为典型的脆弱生态环境地带，这种地带易发生环境退化，但也存在着逆转的可能性。由于全球气候变化和人类活动的影响，近几十年来生态环境严重退化。土地风蚀沙化调查研究表明，影响风蚀沙化的因素很多，尤其是外部环境因素相互关系更为复杂，如大风和尘暴日、风速、降水、植被生长状况、土地封冻与融冻、土地耕翻等。但重要因素仍是风日、风速和地表物质。由于气候干旱，降水少等原因，本区最大的湖淖──安固里淖，在不断萎缩，该湖历史上比现在大十几倍，并且萎缩一直是自东向西进行，可能与新构造运动有关。坝上地区生态环境的退化是可以逆转的，近几年，一系列生态建设工程的实施，已初步收到了较好的效果。  相似文献   

坝上高原土壤不可蚀性颗粒与耕作方式对风蚀的影响   总被引：20，自引：3，他引：20  

哈斯 《中国沙漠》1994,14(4):92-97

对河北省坝上高原农田土壤风蚀及其三个主要影响因素（土壤不可蚀性颗粒、土壤微地形和作物残余物）的野外观测和研究结果表明，在棵露平坦的秋翻地，土壤风蚀量随不可蚀性颗粒含量的增加而减少；春翻地土垄高度（犁沟深度）和留茬地作物残余物盖度的增加使土壤风蚀量大大减少，而且土壤微地形作物残余物和土壤不可蚀性颗粒的综合影响，对降低土壤风蚀量更为有效。据此认为，在防护林体系很不完善的坝上高原，只要实行合理的耕作方式，即秋季留茬、增加作物残余物，春季深翻，增高土垄（或加深犁沟深度）可有效地控制土壤风蚀、减轻风蚀危害。  相似文献   

软岩风化粗颗粒土填料的工程特性   总被引：1，自引：0，他引：1  

徐榴胜 《水文地质工程地质》1993,20(2):23-26,19

在贵州潮湿多雨亚热带环境中,红粘土的起始含水量高,一般较难满足填筑要求,而软岩风化粗颗粒土是解决这一关键问题的最好填料,本文较翔实地论述了粗颗粒土填料的工程特性。  相似文献   

钱塘江护堤抛石铺盖的探地雷达试验   总被引：1，自引：0，他引：1  

邓世坤  王惠濂 《地球科学》1993,18(3):345-351

  相似文献   

中国海岸侵蚀述要   总被引：91，自引：1，他引：91  

夏东兴  王文海 《地理学报》1993,48(5):468-476

中国近代海岸侵蚀自50年代末期日渐明显,70年代末期加剧。目前约有70％的沙质海岸和大部分开敞的粉砂淤泥质海岸遭受侵蚀。人工挖沙和河流输沙减少是侵蚀发生的主要原因。海岸侵蚀已危及沿岸房舍、道路、海岸工程、旅游资源。  相似文献   

一维泥沙数学模型在黄河下游应用的讨论          下载免费PDF全文

万兆惠  宋天成 《水科学进展》1993,4(2):120-126

对黄河下游的河床演变特点进行了分析,并对目前已用于黄河规划设计中的3个一维泥沙数学模型作了剖析,指出各自的特点以及有待改进之处.据此,提出研究用于黄河下游的泥沙数学模型应注意的问题.  相似文献   

A simple field-portable rainfall simulator for difficult terrain     

A. C. Imeson 《地球表面变化过程与地形》1977,2(4):431-436

A small portable rainfall simulator is described which is inexpensive to construct and use and which requires relatively little water. Although drops are produced by drop-formers a satisfactory drop-size distribution is obtained by allowing the drops to break-up by falling onto a 3 mm wire mesh. The kinetic energy of the simulated rain is lower than that of natural rainfall because of the low fall height. Characteristics of the simulated rain are described and the use of the simulator briefly illustrated by results obtained from forested areas in Luxembourg.  相似文献   

Preliminary estimates of intertidal limestone erosion,one tree island,southern great barrier reef,australia     

Stephen T. Trudgill 《地球表面变化过程与地形》1983,8(2):189-193

Estimations of surface lowering of 0.2-3.8 mm a^?1 were gained from measurements of pedestal heights under sedentary organisms. The role of erosion by chitons, estimated at 0.2-2.9 mm a^?1 for home scars and 0.2-0.7 mm a^?1 for grazing, and other bioerosive organisms, is briefly discussed.  相似文献   

Suspended sediment in rapid subsurface stormflow on a large field plot     

David H. Pilgrim  Dale D. Huff 《地球表面变化过程与地形》1983,8(5):451-463

The occurrence of rapid movement of suspended sediment in subsurface stormflow on a large field plot in California is described. Concentrations of over 1000mgl^?1 were recorded in storms of only low to moderate intensity. The observed sediment was composed of uniformly fine-sized particles 4 to 8 μm in diameter. The mode of transport seems different from processes previously reported. Differences in sediment concentrations in different events, levels of ¹³⁷Cs on the sediment, and several other types of evidence indicate that the sediment was detached and entrained at the ground surface by raindrop impact and that the water and sediment flow occurred mainly through macropores in the soil. As conditions similar to those at the study site are not uncommon, it seems probable that the phenomenon may occur in many regions.  相似文献