ETCHING AS A PROCESS OF LANDFORM DEVELOPMENT *     

C. R. Twidale  Jerry E. Mueller 《The Professional geographer》1988,40(4):379-391

Bedrock forms of etch origin result from the interaction of groundwaters and bedrock at the weathering front at the base of the regolith. They are significant for general theories of landscape and landform genesis because they are azonal with respect both to climate and lithology. Two stages of etch form development are recognized: one involves weathering and the formation of a regolith; the second consists of stripping of the regolith and the exposure of the bedrock forms. Although etch forms have been recognized for some two centuries, the concept of etching as a process of landform development has been neglected, particularly in North America.  相似文献   

自动综合的结构化实现     

毋河海 《武汉大学学报(信息科学版)》1996,(3)

以河系、地貌及点群目标为例，建立了一个基于图论、分形学和计算几何的完整的结构化制图综合理论体系，并提供了有序化的操作方法  相似文献   

土壤包气带土体无机氮的吸附与微生物作用影响试验方法   总被引：5，自引：1，他引：5       下载免费PDF全文

张胜  张翠云  叶思源 《地球学报》2003,24(2):187-192

文章通过河北平原山前地区包气带土体的氮素循环及硝酸盐污染地下水的过程，对包气带土体与微生物细菌对三氮的运移转化作用进行了实验研究，介绍了用于溶质运移的预测与准确估算进入地下水的氮素含量求其参数的实验方法及特点。  相似文献   

Composition and flux of nutrients transport to the Changjiang Estuary     

ZHANG Shen  JI Hongbing  YAN Weijin  DUAN Shuiwang 《地理学报》2003,13(1):3-12

Based on the results of water sample measurements of nutrient concentrations at the Datong Station of the Changjiang River from 1998 to 1999, combined with historical data of water quality, seasonal variations of nutrient concentrations and nutrient transports are discussed.The following results have been obtained: (1) the fluxes of the nitrate nitrogen, ammonium nitrogen and nitrite nitrogen increased by time-series from 1962 to 1990, even if runoff volume had a little variation; (2) the concentrations and fluxes of the dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) increased notably with time, but those of the dissolved silicon (DSI) decreased pronouncedly; and (3) the concentrations and fluxes changed synchronously with time between the Datong Station and the Changjiang Estuary.  相似文献   

土壤中元素有效态分析质量管理实践   总被引：2，自引：1，他引：2  

李锡坤  李鉴伦等 《岩矿测试》2001,20(4):294-296

根据土壤中Cu、Pb、Zn、Co、Fe、Mn、Cd、K、Ca、Mg、P和Mo12种元素有效态测定偏差的来源和偏差分布，探讨土壤元素有效态测试结果允许的“偏差范围”及“质量管理办法”。  相似文献   

元素活动态测量法及其在铀矿勘查中的应用前景   总被引：5，自引：1，他引：5  

叶庆森 《铀矿地质》2001,17(5):289-294

本文简单论述了元素活动动态测量找矿技术的发展背景、方法系列、地表疏松介质中元素活动态的形式及其主要提取方法，并对该技术的原理及元素活动态的形成机理进行了初步探讨，认为地气找矿法应列入元素活动态测量法这一范畴。找矿应用试验表明，元素活动态测量法找矿效果显著，在铀矿勘查中应用前景十分广阔。  相似文献   

中高含硫量煤中硫的形态分析   总被引：5，自引：0，他引：5  

饶竹  梁汉东等 《岩矿测试》2001,20(3):183-186

利用超声提取、高速离心分离和加入助分散剂等手段，实现了中，高含硫量煤中单质硫，硫酸盐硫，硫化物硫，有机硫等主要形态硫的分步提取和顺序测定。所建分析方法测定了国家一级标样，统样样品和部分有分析结果的样品，其主要形态硫的加和与标准样品参考值，统检样品定值，原样品的总硫分析结果相符，RSD（n=3)为0．80％－4．23％，方法可用于煤中各主要形态硫的测定。  相似文献   

Vegetation as a tool in the characterisation of geomorphological forms and processes: an example from the Abisko Mountains   总被引：2，自引：0，他引：2  

Anna Koz&#;owska  & Zofia R&#;czkowska 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):233-244

  相似文献   

The hydrogeochemistry of the Kärkevagge Valley, Lapland, Sweden     

Iréne Malmsten  & Kurt Boström 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):245-259

The Kärkejokk (jokk = Lappish for brook) is rich in sulfate and calcium, both elements having been considered enigmatic. To resolve these problems we collected waters at 13 sites during 27 June to 1 September 1996. Nine sites were in the Kärkevagge, and the others in the drainage towards lake Torne Träsk. Rain waters were collected the same period. Conductivity, pH, and temperature were measured in the field, whereas salt load and the elements Na, K, Ca, Mg, S, Si, Fe, Al, Mn, Zn, Sr, and Ba were determined in the laboratory.
Mixing models based on rain water and leaching products of the major bedrocks do not explain observed element patterns except in the lower parts of the jokk. However, oxidation of pyrite has formed acid, sulfate–rich solutions that released Ca and Mg from limestones, and Fe, Mn, Al, and Si, from black shales (Malmsten 1998; Malmsten et al. 2000). Conservative mixing models, using rain water, leached bedrock and pyrite, match the jokk waters quite well, and sulfur isotope data corroborate these findings. The nearby Låktajokk, and Vassijokk also contain much S.
Where these waters debouch they may deposit Si, Al, and Ca, but only little S on various rocks. Total rock analyses, thermodynamic and X–ray data suggest that gypsum, barite, or alunite are not formed in major quantities.
These models show that the hydrogeochemistry of the Kärkejokk may be less enigmatic than often assumed.  相似文献   

Shelf-edge deltas and drowned barrier–island complexes on the northwest Florida outer continental shelf     

J.V. Gardner  P. Dartnell  L.A. Mayer  J.E. Hughes Clarke  B.R. Calder  G. Duffy   《Geomorphology》2005,64(3-4):133-166

A high-resolution multibeam survey of the northwest Florida shelf mapped six relict shelf-edge deltas, each with a drowned barrier–island system developed on its south and southwestern rims. The deltas appear to have formed during periods of sea-level stasis that occurred between 58,000 and 28,000 years ago. The barrier islands formed on the deltas during periods of slow regression during this same time interval. Large fields of asymmetric dunes are found on the delta surfaces as well as on the south and southwestern flanks of the deltas. The asymmetry and orientation of the dunes suggest that a northward-flowing current was sheared by the presence of the delta topography, and as a result, the upper layer of the flow continued to the north, whereas the lower layer was steered by the topography. The topographic steering accelerated the northward flow around the south and southwestern flanks with speeds adequate to form large dunes. The flow slowed after rounding southwestern flank but accelerated again as it encountered the next delta flank to the north. The age of the dune formation is unknown, and no northward-flowing geostrophic flow has been reported in the literature from this area.  相似文献