The deposition of stony colluvium on clay soil as a cause of gully formation in the Rif Mountains,Morocco     

J. W. Den Van Brink  P. D. Jungerius 《地球表面变化过程与地形》1983,8(3):281-285

V-shaped gullies are formed on slopes in the Rif Mountains where stony colluvium covers a truncated Luvisol in finegrained, early pleistocene slope deposits. The colluvium resulted from large-scale deforestation of summit areas in recent times. A number of properties related to the response of soil material to rainfall were investigated. Colluvium has a high infiltration capacity compared to the Luvisol. Consequently, the deposition of colluvium reduced overland flow and erosion by surface wash. Gully-forming processes on the other hand were activated by the superposition of permeable over impermeable material.  相似文献   

中国陆架第四纪地质学研究的最新进展   总被引：3，自引：0，他引：3  

于洪军  刘敬圃 《地球科学进展》1995,10(6):531-536

自本世纪５０年代以来，中国的陆架地质学的研究已经取得了长足的进步。尤其是９０年代以来对于晚第四纪的陆架环境的研究，出现以“陆架沙漠化”为首的一系列最新理论和重大发现。综述和总结了这一领域的最新成就：①末次冰期盛时中国陆架区的环境演变特点；②末次冰期盛时出露的陆架平原上的沙漠化现象、成因及证据；③陆架区海底埋藏黄土的发现与沿岸出露黄土的对比分析及意义。  相似文献   

A semi-analytical method of stress-strain analysis of buried steel pipelines under submarine landslides     

《Applied Ocean Research》2016

A semi-analytical method of the stress-strain analysis of buried steel pipelines under submarine landslides was proposed, considering the nonlinearities of the pipe-soil interaction and mechanical properties of the pipe steel. The pipeline was divided into three parts according to different loading conditions, and the corresponding differential equations were established based on a combination of the beam-on-elastic foundation and elastoplastic-beam theories. According to the second-order central difference method, the transverse horizontal displacement was calculated, and then the bending strain was obtained based on the relation between bending strains and curvatures. Considering the interaction between the axial and bending strains, the axial strain can be derived from the equilibrium condition by equating the axial force. The proposed method was verified through the comparison of obtained solutions to ANSYS results, with minor deviations which do not exceed about 4.6%. Additionally, the effects of the slide width, the buried depth of pipelines, the internal friction angle of soils, the cohesion of soils and the bulk density of soils are investigated through parametric studies.  相似文献   

Environmental significance of bedrock jointing in Southern Ontario,Canada     

N. Eyles  A. E. Scheidegger 《Environmental Geology》1995,26(4):269-277

The bedrock surface of many glaciated areas is obscured by thick drift deposits. In southern Ontario, Canada, the buried bedrock surface is dissected by channels, infilled with glacial deposits as much as 150 m thick, that are part of a wider mid-continent preglacial fluvial system that predates formation of the modern Great Lake basins. The infills of bedrock channels form major groundwater aquifers, influence regional groundwater flows and contaminant migration to Lake Ontario, and may localize the release of thermogenic methane and radon within heavily urbanized surface environments. A quantitative comparison of the regional pattern of bedrock joints and the orientation pattern of buried bedrock channels and modern river valleys shows that all these orientation patterns are virtually coincident. Buried bedrock channels in south-central Ontario are not part of a simple antecedent drainage system but were likely predesigned by bedrock joint patterns that have subsequently been propagated upward into overlying Pleistocene sediments. Joints in sediments are of considerable environmental significance (for example, subsurface contaminant and gas migration in fine-grained clayey sediments) and of many origins (stress release, desiccation, etc.) but are widely assumed to be a predominantly surface-related phenomena; the existence of deeper joints has been noted by some authors but their origin is obscure. Data presented herein from south-central Ontario confirm that, in addition to surface-related joints, a second population of bedrock-related joints, reflecting the upward propagation of bedrock fractures, is present in Pleistocene sediments of south-central Ontario.  相似文献   

千米桥古潜山岩溶地貌演化及古岩溶洞穴发育特征   总被引：2，自引：0，他引：2  

齐振琴  程昌茹  孙秀会  李泽敏  卢清净  郭秀丽 《海相油气地质》2008,13(4)

运用印模法和残厚法以及地震相位追踪对比等古地貌分析法研究揭示,千米桥古潜山岩溶地貌的演化形成先后经历了加里东—海西暴露发育期、印支—燕山暴露改造期、喜马拉雅埋藏定形期等演化阶段。古岩溶洞穴的发育和分布不仅受地貌形态及潜水面的控制,而且与岩性组合、古水文环境及断裂构造密切相关。加里东—海西暴露期地壳的持续抬升和区域潜水面的不断下移,造成古岩溶洞穴的多旋回层状分布,孔洞多被砂泥质充填,有效孔洞保存较少;印支—燕山暴露期发育的古岩溶洞穴受断裂体系影响,分布具有一定随机性,并且多被埋藏期化学半充填,成为目前古潜山油气储层的主要储集空间。利用钻井和测井信息及洞穴充填物,可在生产现场识别古岩溶洞穴的存在及分布,为古潜山油气储层的综合评价提供依据。  相似文献   

Properties of a 5500-year-old flood-plain in the Loup River Basin, Nebraska     

David W. May   《Geomorphology》2003,56(3-4):243

Flood-plain aggradation within the Loup River Basin of central Nebraska was episodic and alternated with incision throughout much of the Holocene. A widespread episode of flood-plain stability, however, occurred about 5700–5100 cal. year BP. The purpose of this paper is to describe the properties of this buried flood-plain at six sites in the basin, to consider why the properties of the buried flood-plain vary from site to site, and to evaluate possible reasons why the Loup River flood-plains stabilized 5500 years ago. Episodic valley-bottom aggradation was common during flood-plain formation at five of the six sites. The radiocarbon ages, particle-size data, and organic-carbon data for the buried flood-plain reveal that valley-bottom aggradation generally slowed between about 5700 and 5100 cal. year BP. Erratic down-profile changes in percentages of sand, clay, and organic matter indicate flood-plain sedimentation and soil formation were often episodic. Sand and clay rarely show a steady fining-upward trend. Organic matter fluctuates with depth; at some sites multiple, incipient A horizons were buried during waning valley-bottom aggradation. At two localities, the buried flood-plain is evident as a clay-rich stratum that must have been deposited in a paleochannel. Flood-plain stabilization between 5700 and 5100 cal. year BP probably occurred in response to the effects of external climate forcing on vegetation and hydrologic changes. Flood-plains of other rivers in the central Great Plains also stabilized at this time, further supporting a climatic explanation for slowing of valley aggradation and formation of a flood-plain at this time. Recognition of buried flood-plains is important to both soil mapping in valleys and to the discovery of cultural resources in valleys.  相似文献   

新疆境内部分地质年代数据反映的现代构造运动   总被引：2，自引：0，他引：2  

刘景元  阮成雯 《内陆地震》2003,17(1):39-46

由地质样品的年代及其埋深，得到样品所在地的沉降速率。一般情况下，一个剖面上只有一个数据，可得到一个地区的沉降速率。昆仑山的沉降速率最大，阿尔泰山次之，天山最小，但特克斯是个例外。少数剖面上有2—3个数据，由同一剖面上的不同数据，可得到阶段性的沉降速率。阶段速率图(the picture of phase rate—PPR图)清楚地表示了晚更新世至全新世4不同阶段不一样的沉降速率。  相似文献   

Subglacial Lake McGregor, south-central Alberta, Canada     

Mandy J. Munro-Stasiuk   《Sedimentary Geology》2003,160(4):325-350

It is proposed that a lake, here named “Subglacial Lake McGregor”, existed beneath the Laurentide Ice Sheet at, or near, the last glacial maximum. The lake resided in the ancient buried McGregor and Tee Pee preglacial valleys, which are now mostly filled with glacigenic deposits. The greatest thickness of sediment in the valleys is in the form of chaotically deposited lake beds that were laid down in a subaqueous environment by a number of process: gravity flow, water transport, and suspension settling. Topographic, sedimentary, and stratigraphic evidence point to a subglacial, not a proglacial, origin for the beds. During the early stages of lake existence, ice movement was significant as there are numerous sets of shear planes in the sedimentary beds. This indicates that the lake filled (lake sedimentation) and drained (shearing of the beds by overlying ice when ice contacted the bed) often. Thus, early in its history, the lake(s) was/were ephemeral. During the later stages of lake existence, the lake was relatively stable with no rapid draining or influx of sediment. Gradual drainage of the lake resulted in lowering of the ice onto the lake beds resulting in subglacial till deposition. Drainage was not a single continuous event. Rather it was characterized by multiple phases of near total drainage (till deposition), followed by water accumulation (lake sedimentation). Water accumulation events became successively less significant reflected by thinning of lake beds and thickening of till beds higher in the stratigraphic sequence. Since subglacial lake sedimentation appears to be restricted to the subglacial valleys, it is suggested that the valleys acted as a large-scale interconnected cavity system that both stored and transported water. It is also suggested that these acted as the main routes of water flow beneath the Laurentide Ice Sheet.  相似文献   

The application of the transient electromagnetic method in hydrogeophysical surveys   总被引：3，自引：0，他引：3  

Jens E. Danielsen  Esben Auken  Flemming Jrgensen  Verner Sndergaard  Kurt I. Srensen 《Journal of Applied Geophysics》2003,53(4):181

The transient electromagnetic (TEM) method has been used extensively for hydrogeophysical exploration in Denmark for the past decade. Innovative instrumentation combined with multi-dimensional modelling and interpretational insights based on experience gained through numerous case studies have proven to be a successful strategy. In the case study reported here, the combination revealed an unknown and unexpected buried valley complex. Drill hole data were in good agreement with estimates of both the bearings and depths of valleys defined by the TEM surveys. The Pulled Array Transient Electromagnetic (PATEM) system was built to provide high data density for increased lateral resolution. A High moment Transient Electromagnetic (HiTEM) system was developed for delineation of aquifers to depths up to 300 m. Because both of these systems provide high data density, data quality can be assessed as part of the interpretational strategy. When acquiring TEM measurements in areas as densely populated as the Danish countryside, precautions must be taken to minimize coupling between the TEM system and man-made conductors. Modelling the slope of the flanks of buried valleys has challenged the adequacy of the one-dimensional (1-D) assumption for inversion of TEM data. The study shows that for a valley structure in a low-resistive layer, the 1-D assumption is sufficient to track the presence of rather steep slopes. For a valley structure in a high-resistive layer, however, the insensitivity of the TEM method to resistors makes it difficult to determine a slope with a 1-D inversion, and only the overall structure is defined.  相似文献   

Geophysical investigation of buried Pleistocene subglacial valleys in Northern Germany   总被引：1，自引：0，他引：1  

Gerald Gabriel  Reinhard Kirsch  Bernhard Siemon  Helga Wiederhold 《Journal of Applied Geophysics》2003,53(4):159

Buried Pleistocene subglacial valleys are extensively used as groundwater reservoirs by waterworks in northern Germany, although little is known about the locations and size of these valleys and the internal structure of the sediment fill. This lack of knowledge about important groundwater reservoirs is a challenge for geophysics.This paper summarizes the geophysical investigation of two buried Pleistocene subglacial valleys in northern Germany—the Ellerbeker Rinne and the Bremerhaven–Cuxhavener Rinne—including seismic, gravity, and airborne electromagnetic (AEM) surveys. Seismic sections show the detailed structure of the paleovalleys. The reliability of interpretation is enhanced by vertical seismic profiles in wells. The maximum depths of the Ellerbeker Rinne and the Bremerhaven–Cuxhavener Rinne were found to be 360 and about 400 m, respectively. Gravity survey revealed Bouguer anomalies above the sediment fill of both buried valleys. The Ellerbeker Rinne produces a negative residual anomaly of −0.5 mGal, whereas the sediments of the Bremerhaven–Cuxhavener Rinne produce a positive anomaly. The latter one is superimposed by negative gravity anomalies due to near-surface structures. The Bremerhaven–Cuxhavener Rinne can be mapped by airborne electromagnetics at locations without saltwater intrusion, which would affect the measurements. The electrical conductivity of the clay layer at the top of the valley fill differs significantly from that of the surrounding sand. The combined use of these three geophysical methods, which measure different physical parameters, leads to a better understanding of the subsurface geology and the hydrogeology of the Pleistocene subglacial valleys.  相似文献