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1.
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2.
Different mountain shapes in sedimentary sequences in the Canadian Rockies were enhanced by glacial erosion and have been modified postglacially by gravity-driven slope processes. Slope modification by both glacial erosion and postglaciation landslides is related to rock structure, particularly bedding dip, rock mass strength and slope geometry. Five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips. Castellate (1) and matterhorn (2) mountains occur in sub-horizontal beds and their slopes on all sides follow combinations of bedding planes and joints. The overall slopes are generally 37 to 65° and oblique to both bedding and joints. Slopes in sub-horizontal beds may be controlled by their rock mass strength. Cuestas (3) develop in gently to moderately dipping beds. Dip slopes and steeper, normal escarpments form their cataclinal and anaclinal sides respectively, with the dihedral angle between them about 90°. Hogbacks (4) in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes. Cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments; the dihedral angle between the slopes is usually less than 90°. Dogtooth (5) mountains occur in steeply dipping to sub-vertical beds and the dihedral angle can be as low as 60°. Slope gradients in inclined beds are closely related to landslides, whose modes are controlled by bedding dips. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

3.
Slope frequency distributions are computed from Digital Elevation Models (DEMs) of 18 areas from five different geographic and physiographic regions. Over 160,000 slope estimates are used in the definition of the slope frequency distribution for each area. Analysis of several transformations of the slope data indicates that no single transformation is capable of normalizing all slope distributions. This is, in part, due to the arbitrary placement of the boundaries of the map sheets used in the data collection. The square root of sine, however, provides better results than sine, log-tangent, or several other transformations. The degree of (positive) skewness of gradients in degrees correlates with the proportion of slopes below 2° or 5° (rs = + 0·93), as does the kurtosis (rs = + 0·91).  相似文献   

4.
It has been shown that the major clay minerals of the biothermocatalytic transitional zone source rock are montmorillonite, illite/montmorillonite (I/M) interlayer mineral, illite, kaolinite and chlorite. Within the depth of the transitional zone, montmorillonite could convert to the I/M ordered interlayer mineral via the I/M disordered one, i.e. in the intercrystalline layer of montmorillonite, A13+replaces Si4+abundantly, resulting in a surface charge imbalance and the occurrenec of a surface acidity. By means of the pyridine analytic method, the surface acidity of these aluminosilicate clay minerals is measured. The catalysis of aluminosilicate clay minerals, such as montmorillonite, illite and kaolinite to the thermo-degraded gas formation of the transitional zone is simulated in the differential thermal analysis-gas chromatography system and the alcohol dehydration catalyzed by clay minerals is employed to discuss this catalytic mechanism. Experiments have shown that montmorillonite is the major catalyst in the formation of the transitional zone gas and it lowers the thermo-degraded temperature of organic matter by 50°C.  相似文献   

5.
Soil erosion plays an important role in plant colonization of semi‐arid degraded areas. In this study, we aimed at deepening our knowledge of the mechanisms that control plant colonization on semi‐arid eroded slopes in east Spain by (i) determining topographic thresholds for plant colonization, (ii) identifying the soil properties limiting plant establishment and (iii) assessing whether colonizing species have specific plant traits to cope with these limitations. Slope angle and aspect were surrogates of erosion rate and water availability, respectively. Since soil erosion and water availability can limit plant establishment and both can interact in the landscape, we analysed variations in colonization success (vegetation cover and species number) with slope angle on 156 slopes, as a function of slope aspect. After determining slope angle thresholds for plant colonization, soil was sampled near the threshold values for soil analysis [nitrogen, phosphorous, calcium carbonate (CaCO3), water holding capacity]. Plant traits expressing the plant colonizing capacity were analysed both in the pool of species colonizing the steep slopes just below the threshold and in the pool of species inhabiting gentler slopes and absent from the slopes just below the threshold. Results show that the slope angle threshold for plant colonization decreased from north to south. For the vegetation cover, threshold values were 63°, 50°, 46°, 41° for the north, east, west and south slope aspect classes, respectively, and 65°, 53°, 49° and 45° for the species richness and the same aspect classes. No differences existed in soil properties at slope angle threshold values among slope aspects and between slope positions (just below and above the threshold) within slope aspect classes. This suggests that variations between slope aspect classes in the slope angle threshold result from differences in the colonizing capacity of plants which is controlled by water availability. Long‐distance dispersal and mucilage production were preferably associated with the pool of colonizing species. These results are discussed in the perspective of a more efficient ecological restoration of degraded semi‐arid ecosystems where soil erosion acts as an ecological filter for plant establishment. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

6.
Although a number of studies of the variation of soil transport with increase in slope angle have appeared, few include an information on the interaction of sheetwash and rainsplash on high slope angles, which is necessary to test Horton's proposed polynomial relationship. Virtually no studies are available which compare the influence of changes in soil type or antecedent moisture on established relationships. This paper reports the testing of eight soils from Alberta, Canada, under simulated rainfall on ten slopes from 3° to 30°. Material eroded was separated into that transported by rainsplash and that by sheetwash. In general, it was found that the influence of changes in slope angle on soil transport is best described by polynomial relationships, but these are shown to vary considerably between rainspash and sheetwash, between different soil types and for different antecedent moisture conditions. Despite careful control of all factors other than slope angle very high variability of results was experienced. Causes of variability are examined and the need for evaluation of the effect of test plot size on variability of results is suggested.  相似文献   

7.
The Sarma Stream is located in Turkey, southwest of the town of Akcakoca in the Duzce Province. It was decided that the Sariyayla reservoir should be built on the Sarma Stream in order to address the water needs of Akcakoca. This research was conducted in the Sarma Stream basin to determine the effects of environmental and hydrological processes. Samples of rocks, soil, stream water, rain, snowmelt and bed and suspended sediment were collected in the Sarma Stream basin. Geochemical and water chemistry analyses of the samples were performed at the ALS Global laboratories in Canada. The sandstone, which is easily weathering and rich by clay minerals, and soil samples cause the Sarma Stream to flow muddy in rainy season. The kaolinite, illite, montmorillonite and clay minerals that type of chlorite is found in the bed and suspended sediments of the Sarma Stream. The water of the Sarma Stream is rich in calcium and bicarbonate, the water type is Ca–HCO3. Acid rain affects the dissolution of geological units and the abundance of principal ions. Some heavy metal and elements in the Sarma Stream basin waters exceed the drinking water limit values (e.g. Al, Fe, Mn, NH4 and NO3). Hence, water in the Sariyayla Reservoir should be treated.  相似文献   

8.
This paper represents a systematic investigation of slope evolution diffusion models and has the following sections: (1) The model of slope development with linear coefficient k = k0x; (2) The model of slope development with quadratic coefficient in x; (3) Slope development model with vertical lowering of base level (downcutting); (4) Slope development model with the base level a horizontal variable (undercutting); (5) Steady-state regime of undercut slopes; (6) Model of a pediment and scree slope formation. The comparison is made between mathematical and classical methods of slope evolution analysis.  相似文献   

9.
Observations on an Early Quaternary slope deposit in the Massif Central indicated that the texture and mineralogy of this deposit have been seriously altered by post-depositional subsurface weathering. Analyses of clay fractions and water samples show that the montmorillonite present is a stable mineral in this environment and is, and has been, newly formed. As shown by water analyses from nearby sites, the chemical environment is strongly dependent on local factors. Consequently it can be seen that great care should be taken firstly in correlating different slope deposits on the basis of texture and clay mineralogy and secondly in using these parameters as (paleo) climatic indicators.  相似文献   

10.
The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic Vp and Vs profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

11.
Structure of weathered clastic crust and its petroleum potential   总被引：1，自引：0，他引：1  
Weathered clastic crust can be subdivided into weathered clay and leached zone in terms of variable weathering of different minerals and mobility of weathered products.On the basis of clastic outcrops and well cores in the Junggar Basin,the dark red Fe-rich weathered clay is formed in an arid environment,whereas the light blue Al-rich weathered clay under humid conditions.According to the geochemical analysis,a new weathering index for weathered clastic crust is built mainly on Fe and Al contents,accurately indicating the weathered clay,sandy leached zone,and muddy leached zone in the Junggar Basin.The breaking pressure of weathered clay is rather large,the same as that of normal muddy cap,effectively to seal oil or gas.The porosity of underlying leached zone is greatly enhanced by weathering and leaching,but its permeability is a function of clay mineral content,i.e.,the higher the clay content,the worse the permeability.Weathered crust provides effective sealing conditions for both top and bottom layers of a petroleum reservoir,and is important in the clastic hydrocarbon exploration.  相似文献   

12.
Landslides and rockfalls are key geomorphic processes in mountain basins. Their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution. We used digital photogrammetry to produce a multi‐temporal record of erosion (1963–2005) of a rock slope at the head of the Illgraben, a very active catchment prone to debris flows in Switzerland. Slope failures affect 70% of the study slope and erode the slope at an average rate of 0.39 ± 0.03 m yr¯¹. The analysis of individual slope failures yielded an inventory of ~2500 failures ranging over 6 orders of magnitude in volume, despite the small slope area and short study period. The slope failures form a characteristic magnitude–frequency distribution with a rollover and a power‐law tail between ~200 m³ and 1.6 × 106 m³ with an exponent of 1.65. Slope failure volume scales with area as a power law with an exponent of 1.1. Both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock. Our data suggest that the magnitude–frequency distribution is the result of two separate slope failure processes. Type (1) failures are frequent, small slides and slumps within the weathered layer of highly fractured rock and loose sediment, and make up the rollover. Type (2) failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre‐determined potential failure surfaces, and make up the power‐law tail. Rockslides and rockfalls of high magnitude and relatively low frequency make up 99% of the total failure volume and are thus responsible for the high erosion rate. They are also significant in the context of landscape evolution as they occur on slopes above 45° and limit the relief of the slope. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

13.
Calculations of absolute elemental gains and losses based on isovolumetric bedrock alteration are applied to deep weathering profiles and silcrete developed on Dwyka Tillite and Bokkeveld Shale. Bedrock weathering to kaolinite and illite yields sufficient SiO2 to account for observed thicknesses of associated silcrete. Absolute accumulation of SiO2 in silcrete is complemented by substantial absolute depletion of Al2O3. Absolute accumulation of TiO2 in both silcrete and associated weathered material together with authigenic anatase concentrations in silctete recorded during micromorphological investigations indicate TiO2 mobilization in a low pH environment (pH < 3·75) during silcrete formation. Under these low pH conditions increased Al2O3 solubility led to replacement of kaolinite and illite by a proportion of SiO2 retained in the weathering profile through restricted drainage.  相似文献   

14.
Obtaining a continuous sedimentary record of Cenozoic East Asian paleoclimate change is key to understand the origin, evolution and driving mechanism of the East Asian monsoon and climate change. Based on the continuous Cenozoic fluvial and lacustrine sedimentary sequence in the Weihe Basin, central China, we carried out research on the content and crystal parameters of clay minerals. The paleoclimate change since the middle Eocene was reconstructed accordingly. The results show that smectite and illite are the dominant clay minerals in fluvial-lacustrine sediments of Weihe Basin. The crystallinity of illite,the chemical index of illite, the ratio of smectite to illite and chlorite decrease gradually, which indicates that chemical weathering in the Weihe River watershed stepwise weakened since the middle Eocene, under the background of a semi-arid and semi-humid climate. The formation of palygorskite may be affected by a weak diagenesis. In this case, the content of smectite and the illite crystallinity caused by the weathering in the corresponding period may be actually higher than that of the current,which indicates that the climate in the Weihe Basin region was relatively warm and humid from the middle Eocene to Pliocene.With the decrease of Cenozoic global temperature and the continuous accumulation of sediments, the intensity of chemical weathering in the Weihe Basin gradually weakened, and the East Asian monsoon climate gradually evolved until becoming dry in the Quaternary. Evidence from clay minerals also indicates that the aridification in the Weihe Basin from the late Eocene to the Oligocene may be a response to the global cooling event at the Eocene-Oligocene transition.  相似文献   

15.
Characteristic badlands are incised into Plio‐Pleistocene clays in Basilicata, southern Italy, creating steep, scarp slopes with knife‐edge ridges (calanchi) and small dome‐shaped forms (biancane). Erosion pin data for the period 1997–2003 give mean annual erosion rates for dome‐shaped biancane in the range 9–19 mm a?1, while rates for the calanchi scarps are lower, at 7–10 mm a?1. The erosion pin data also show a non‐linear relationship with slope angle. Maximum erosion rates coincide with a slope angle of 35°, within an envelope defined by combining the theoretical effects of both rainsplash and surface weathering. Monitoring of surface changes and erosion rates for two 0·5 m2 cleared swathes on biancane forms reveals a complex relationship between weathering and erosion. Characteristic forms can develop from large blocks of intact clay bedrock over a time period of less than 30 a. The implications of the measured erosion rates for the landform association of mountain front/pediment/domed inselberg are explored. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

16.
Soil erosion is one of the most severe land degradation processes in the Mediterranean region. Although badlands occupy a relatively small fraction of the Mediterranean area, their erosion rates are very high. Many studies have investigated to what extent vegetation controls soil erosion rates. This study, however, deals with the impact of erosion on vegetation establishment. In semi‐arid badlands of the Mediterranean, soil water availability constitutes the main limiting factor for vegetation development. As a consequence, south‐facing slopes are typically less vegetated due to a very large water stress. However, these findings do not necessarily apply to humid badlands. The main objective of this paper is to determine the topographic thresholds for plant colonization in relation to slope aspect and to assess the spatial patterns of vegetation cover and species richness. We surveyed 179 plots on highly eroded badland slopes in the Central Pyrenees. We defined four aspect classes subdivided into slope angle classes. Colonization success was expressed in terms of vegetation cover and species richness. Slope angle thresholds for plant colonization were identified for each slope aspect class by means of binary logistic regressions. The results show that a critical slope angle exists below which plants colonize the badland slopes. Below this critical slope angle, plant cover and species richness increase with a decreasing slope angle. The largest critical slope angles in humid badlands are observed on south‐facing slopes, which contrasts with the results obtained in semi‐arid badlands. North‐facing slopes however are characterized by a reduced overall vegetation cover and species richness, and lower topographic threshold values. The possible underlying processes responsible for this slope‐aspect discrepancy in vegetation characteristics are discussed in terms of environmental variables that control regolith development, weathering and erosion processes. Moreover, possible restoration strategies through the use of vegetation in highly degraded environments are highlighted. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Previous studies of weathering generally started with geochemistry[1—8] and mineralogy[9—12], and have been focused on chemical weathering rates[1—3], removability-enrichment of elements[3—6] during chemical weathering, and the age of weathering profi…  相似文献   

18.
利用FLAC3D软件模拟地震作用下不同岩层倾角的顺倾向边坡,对比坡面峰值加速度放大系数、峰值位移、地震作用结束后坡体剪应变增量的变化规律,探讨岩层倾角对顺倾边坡地震效应的影响。研究表明:(1)在水平地震波作用下,坡面水平峰值加速度放大作用随岩层倾角增大而线性减小;(2)当岩层倾角小于软弱岩层内摩擦角时,坡面峰值位移较小且变化规律受岩层倾角影响不明显,当岩层倾角大于软弱岩层内摩擦角且小于30°时坡面峰值位移增大,大于60°时减小;(3)岩层倾角小于坡角时,残余剪应变增量最大值集中在坡面中下部软弱岩层处,反之,剪应变增量最大值出现在整个坡面并呈弧形区。  相似文献   

19.
以承张高速某顺层页岩边坡工程为依托,首先采用单轴压缩模拟实验与宏观力学参数值对比的方法确定出边坡各岩土层的细观参数。进而建立其离散元模型,分析其稳定状态,并对其失稳过程进行研究。结果表明:边坡中的全风化页岩层向下滑动,并在坡脚堆积;强风化页岩层和中风化页岩层未发生滑动,滑动面为全风化页岩层与强风化页岩层的交界面。模型中出现的裂纹主要以压裂纹为主,且主要分布在全风化层,而其他两层未产生裂纹。离散元模拟结果与赤平投影法分析结果一致。该模拟结果对工程的设计、施工具有指导意义。  相似文献   

20.
Chert and other hard monomineralic quartz grains weather mostly by mechanical processes in modern environments. Their clasts are overrepresented in conglomerates and sands relative to their sources regions. Conversely, macroscopic dissolution features, including quartzite karst, are rare but not nonexistent. The similar rarity of quartz dissolution in Archean deposits provides a paleothermometer for climate on the early Earth. For example, chert is overrepresented in conglomerates and sands of the ∼3.2 Ga Moodies Group (South Africa) relative to the source region. Features related to the far-from-equilibrium dissolution rate are particularly diagnostic as it increases an order of magnitude over 25 °C, much more than solubility. Extrapolating from observed dissolution rates in modern environments that weather at ∼25 °C, we expect obvious dissolution features in ancient climates above ∼50 °C. Polycrystalline quartz and chert would readily disaggregate by solution along grain boundaries, yielding silt and clay. Quartz grains within slowly weathering granite would become friable, yielding silt and clay, rather than sand. At still higher temperatures, Al2O3-rich clays from weathered granite would stand above solution-weathered chert on low-relief surfaces. The observed lack of these features is evidence that the Archean climate was not especially hot.  相似文献   

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