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1.
The multistage concept is explained and illustrated, with particular reference to a bornhardt from the southern Yilgarn Block of southwestern Western Australia. Hyden Rock is a complex inselberg developed on Archaean granite. It probably developed through fracture-controlled differential subsurface weathering in the Cretaceous, followed in the Eocene by erosion of the lateritic regolith and exposure of the massive compartment as an inselberg. But the variations in fracture density to which Hyden Rock owes its origin developed long before the Cretaceous, probably in the latest Archaean or earliest Proterozoic. The relief amplitude of the residual has increased through the Cainozoic.
A rich assemblage of minor forms (basins, runnels, tafoni, pitting, displaced slabs, A-tents) is developed on the bornhardt and, though their mode of development varies, the origin of many can be traced back to magmatic and tectonic events of Late Archaean and earliest Proterozoic times. Others were initiated at the weathering front during the later Mesozoic, and many have developed since exposure, beginning in the Eocene. A few are related to tectonism during the later Quaternary.
The residual is a multistage form. Its development as a major landform can be traced back some 120 million years, and the structures to which the outlines of the bornhardt, and those related to several minor features, originated in later Archaean times. The geomorphological evolution of landforms of the shield lands and cratons extends over vast ages and cannot be regarded as a geologically recent phenomenon. 相似文献
A rich assemblage of minor forms (basins, runnels, tafoni, pitting, displaced slabs, A-tents) is developed on the bornhardt and, though their mode of development varies, the origin of many can be traced back to magmatic and tectonic events of Late Archaean and earliest Proterozoic times. Others were initiated at the weathering front during the later Mesozoic, and many have developed since exposure, beginning in the Eocene. A few are related to tectonism during the later Quaternary.
The residual is a multistage form. Its development as a major landform can be traced back some 120 million years, and the structures to which the outlines of the bornhardt, and those related to several minor features, originated in later Archaean times. The geomorphological evolution of landforms of the shield lands and cratons extends over vast ages and cannot be regarded as a geologically recent phenomenon. 相似文献
2.
SOIL CATENAS,TROPICAL DEFORESTATION,AND ANCIENT AND CONTEMPORARY SOIL EROSION IN THE PETéN,GUATEMALA
Timothy Beach 《自然地理学》2013,34(5):378-405
The Petexbatún region of Guatemala's Petén tropical forest lowlands has been largely deforested since the early 1980s as landless peasants have turned even national parks into milpas. The soils of these tropical forest, karst landscapes are known mainly from small-scale maps and archaeological investigations. This paper investigates soil catenas and natural slope processes from the region's last virgin tropical forests and compares these with catenas and processes on slashed and burned slopes. Soils were sampled and analyzed for physical, fertility, and taxonomic measures. This primary forest toposequence forms a typical downward translocation catena, with the thickest soils (>200 cm) in depressions, the thinnest soils on shoulder slopes, and moderately thin soils on the crests and backslopes. Most crest and sloping soils are Lithic Rendolls and contain simple O-A-C horizon sequences, and most soils have little sign of either eluviation or illuviation. A few deeper soils on the slopes are Vertic Rendolls and have moderate slick-ensides, whereas footslopes and seasonally drained depressions are well developed Vertisols. The primary forest soil catena was compared with two slash-and-burn milpas, one with comparable slopes and one with steeper slopes. The comparably sloped milpa had soil thicknesses that were 7.9 to 13.8 cm thinner, truncated horizons, and physical evidence of erosion. The steeper milpa had soil thicknesses that were 11.1 to 18.2 cm thinner and also had truncated horizons and physical evidence of erosion. Where ancient Maya terraces (Late Classic, ca. 550 to 830 A.D.) are present in the slash-and-burn landscape, an average of 25 to 46.5 cm soil remain upslope and 9.3 to 16.1 cm remain downslope. The findings show high soil truncation rates and erosion to bedrock in a decade in one place, though ancient Maya terraces are still holding 2.7 to 3.6 times more soil than the surrounding hillslopes. Despite high modern erosion, lake sediments show surprisingly low soil losses in the Maya Late Classic during the period of the most intensive land use. In contrast, studies at Copán, Honduras and in the northern Petén, where terrace evidence is scant, show high rates of erosion during this period. [Key words: soil catenas, tropical deforestation, milpa, soil erosion, Maya Lowlands.] 相似文献
3.
Wolfgang Rmer 《Geomorphology》2007,86(3-4):349-368
A morphometric analysis of inselberg systems in southern Zimbabwe indicated that there are two types of inselberg systems that differ in the mode of development. Inselberg systems characterized by backwearing tend to occur on granitoid rocks that are foliated, highly fractured, and prone to grusification. The inselbergs are mostly of the koppie-type and are covered to a great extent with regolith or debris. The second type of inselbergs consists of sparsely fractured granitoid rocks, and areas underlain by these rocks are characterized by clusters of closely spaced rock domes. In the case of these inselbergs, backwearing is not indicated. They appear to be the result of the exposure of structurally pre-designed, highly resistant rock compartments.The hypothesis that differences in lithology and structure may influence the rate and style of inselberg development was tested by means of a simulation model. The simulations are run under the same boundary conditions with differing assumptions concerning role of divergent weathering. The results show that both modes of inselberg development may occur alongside one another as long as a critical relief is maintained. The modelling provided also indicates that, although the inselberg systems must have integrated several sequences of environmental changes during their development, these changes were not able to divert the general trend of the process–response system away from its steady course. Lithological and structural factors, which are responsible for the differences in the mobility of material on the inselberg sideslopes, are thus considered to be the primary source of influence of the different modes of inselberg development. It is suggested that the compositional and structural diversity in granitoid rock terrains is what enables inselbergs to pass through different development modes and sequences as rocks of differing resistance become subject to weathering during the development of the landscape. 相似文献
4.
河湖相沉积是一种非固结沉积物,是风蚀地貌发育的一种重要地质基础。在塔克拉玛干沙漠中发育在这种沉积物上的风蚀地貌分布非常普遍,但相关研究较少,尚缺乏风蚀地貌发育过程方面的研究。基于野外调查信息和理论分析,结合相关文献,分析了塔克拉玛干沙漠河湖相平原风蚀地貌发育的外营力作用机制。研究结果表明：（1）风蚀地貌发育的外营力作用主要有：风化作用、流水作用、风蚀作用以及重力作用;（2）风蚀作用是风蚀地貌发育的主要外营力,但是风化作用、流水作用和重力作用也发挥着重要的作用,它们的关键作用是形成风蚀突破口,而重力作用和风化作用是促进风蚀地貌后期快速发展的重要作用;（3）各种外营力协同作用和互为条件,它们在风蚀地貌发育的各阶段的重要性不同;（4）沉积层特殊沉积构造和外营力作用共同造成了风蚀地貌形态特征。 相似文献
5.
《自然地理学》2013,34(3):285-302
Uluru is an inselberg shaped in arkosic sandstone located in the arid plains of central Australia. The indigenous people believed it rose out of a sand hill and has since remained unchanged. The various minor landforms represented mythological animals, people, and events of the Dreamtime. Later investigators interpreted the residual as remaining after long-distance scarp retreat, or as due to scouring by the wind or by the waters of a huge lake. The inselberg and its decorations have been construed in terms of climatic variations. Uluru also has been interpreted as a compressed and resistant compartment that was exposed as a low rise in the latest Mesozoic. The initial rise shed runoff. The steep flanks were shaped in the Eocene by deep subsurface weathering followed by stripping of the regolith and exposure of bedrock forms. Large tafoni and breaks of slope were formed on the southern side where permeable sediments abutted the residual. Following their exposure, basal flares and footcaves were shaped during a later period of subsurface weathering. The inselberg has grown as a relief feature not by uplift, but by the lowering of the surrounding plains. The morphology of Uluru is an expression of episodic exposure. 相似文献
6.
基于地理探测器的喀斯特不同地貌形态类型区土壤侵蚀定量归因 总被引：15，自引：0，他引：15
土壤侵蚀形成机制与影响因素识别是当前研究的核心与前沿议题,然而从多因素综合作用的角度进行定量归因仍需加强。以喀斯特典型峰丛洼地流域为研究区,基于GIS手段和RUSLE模型模拟土壤侵蚀,综合土地利用、坡度、降雨、高程、岩性、植被覆盖度等影响因子,应用地理探测器方法针对喀斯特不同地貌形态类型区进行土壤侵蚀的定量归因研究。结果表明,各影响因子对土壤侵蚀的解释力及因子间耦合作用程度在不同地貌形态类型区差异显著,其中土地利用和坡度是决定土壤侵蚀空间异质的主导因子,但在山地丘陵区,随着地形起伏度的升高,坡度的控制作用下降,即地理探测器q值表现为中海拔丘陵>小起伏中山>中起伏中山;生态探测器显示土地利用对土壤侵蚀的影响相比于其他因子有显著差异;双因子交互作用有助于增强对土壤侵蚀的解释力,土地利用与坡度的协同作用对土壤侵蚀的解释力达到70%以上;对于土壤侵蚀空间分布的差异性检验,风险探测器显示在小起伏中山、中起伏中山等地貌形态类型中,具有显著差异的影响因子分层组合数占比至少55%。因而,喀斯特地区土壤侵蚀的治理应综合考虑不同地貌形态类型区土壤侵蚀影响机制的空间异质性。 相似文献
7.
黄土丘陵区坡面形态和植被组合的土壤侵蚀效应研究 总被引：7，自引：0，他引：7
以位于陕北黄土丘陵区的羊圈沟流域为重点研究区,针对不同坡面类型（坡长、坡形、坡度）和植被组合进行野外土壤采样,利用137Cs元素示踪方法评估坡面的土壤侵蚀效应。研究发现：① 坡面形态对土壤侵蚀具有重要影响。自坡顶至坡脚,“直-凹”组合的坡型一般具有相对较低的土壤侵蚀模数,整体上起到“汇”的作用;但“凹-直/凸”组合的坡型具有相对较高的土壤侵蚀模数,在土壤侵蚀方面起到“源”的作用;其他坡型,如直坡、凸坡、“直-凸”和复杂性坡型的土壤侵蚀模数介于两者之间。② 坡面不同植被空间配置对土壤侵蚀的影响具有明显差异。研究发现,坡面植被组合（自坡顶至坡脚）为荒草地-果园、有林地-其他植被类型组合和荒草地-其他植被类型的坡面具有相对较低的土壤侵蚀模数,起到了一定“汇”的功能,但人为干扰较为强烈的景观坡面（无水土保持措施）具有相对较高的土壤侵蚀模数,整体上表现为土壤侵蚀的“源”区。 相似文献
8.
风化洞穴在全球不同气候区广泛发育,其形成过程和主控因素是地貌学研究的热点问题,但形成机制至今仍存在不少争议,尤其对丹霞地貌区风化洞穴的研究还较少。丹霞山是世界自然遗产地“中国丹霞”的典型代表,陡坡上发育形态和规模各异的风化洞穴,是丹霞地貌的重要景观要素,为认识亚热带湿润气候风化洞穴成因提供了良好的机会。文章以丹霞山砾岩和砂岩陡坡上的5处典型风化洞穴为研究对象,利用野外考察、形态测量、气象监测、样品显微观察及盐化学实验等方法,在已有研究的基础上进一步对湿润气候丹霞地貌区风化洞穴的特征和成因进行探讨。结果表明：1）在砾岩中发育的洞穴一般个体形态较大,洞穴具有较明显的向上和向内生长趋势;砂岩中发育的洞穴大多密集排列,形态较小,常具有蜂巢结构。2）岩石性质是洞穴发育的基本影响因素,在宏观尺度上决定了洞穴的发育位置和排列方式,也决定了不同岩性下发育的风化洞穴的形态特征。在微观尺度上,岩石含有较多长石、钙质胶结物等易溶矿物组分,在酸性雨水渗流过程中发生化学溶解,加上盐结晶作用导致岩石微观结构破坏,诱发洞穴初始形成。3）洞穴尺寸变大后,洞穴内适宜的微气候是洞穴演化的关键因素,为水和盐的聚集及盐风化提... 相似文献
9.
Roland Schmidt Christian Kamenik Richard Tessadri Karin Anne Koinig 《Journal of Paleolimnology》2006,35(3):491-505
Major and trace elements, minerals, and grain-size were analysed from the early to mid-Holocene (12 to 4 ky BP) period of
a sediment core from the Alpine lake Oberer Landschitzsee (ObLAN, 2076 m a.s.l.), which is located on predominantly crystalline
bedrock on the southern slopes of the Austrian Central Alps. Geochemistry and mineralogy were compared with diatom-inferred
(Di-) ‘date of autumn mixing’ (Amix), DOC, pH, and selected indicator pollen species from the same sediment core. Principal components analysis (PCA) indicated
a positive correlation between processes triggered by temperature and precipitation (e.g., lake mixing, DOC). PCA grouped
indicators of physical weathering and enhanced catchment run-off (sand, quartz, feldspar), elements of weathering (e.g., Ti,
Rb, Mn) under dryer conditions (clay to silt fractions), and elements that probably were related to changes in redox conditions
(Cu, Fe, S, Zn). The duration and height of the snow-pack played an important role in this high-alpine environment, affecting
weathering, erosion, pH, and lake stratification. Low Alnus viridis pollen abundance, together with markers for increased elements of erosion, indicated extensive snow-pack. Changes in S coupled
with As, and elements indicating increased weathering, reflected climate oscillations. LOI was affected by productivity and
erosion. High (late) Di–Amix coupled with increased Di-DOC indicated prolonged summers with increased productivity. Cold and wet (snow-rich) phases and
subsequent melting caused low pH and a decoupling of the significant linear correlation between sedimentary Ca and Di-pH.
Weathering and leaching during climate deteriorations opposed the long-term trend in a loss of cations and forced in-lake
alkalinity generation during the following lake warming. Overall, the multi-proxy study indicated complex climate-driven processes
within different time-scales (long-term trends, climate oscillations, seasonality). The climate oscillations within 12–5 ky
BP corresponded well with the cool and wet phases known from central Europe suggesting a dominant common Atlantic climate
impact. When Mediterranean climate established between 5 and 4 ky BP, its influence on the southern slopes of the Alps increased. 相似文献
10.
《地理学报(英文版)》1997,(1)
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11.
Chemical weathering studies in relation to geomorphological research in southeastern Canada 总被引：1，自引：0，他引：1
Although chemical weathering provides fundamental information relevant to geomorphology, the subject has been overlooked during the 20th century in Canada. This paper provides an overview of the current state of Canadian research on chemical weathering in southeastern Canada and takes into account three spatial and temporal contexts: (1) the formation of bedrock morphology by chemical weathering, (2) occurrences, characteristics and age of saprolites and (3) contemporary chemical denudation rates. Long-term geomorphological evolution of southeastern Canadian landscapes shows that chemical weathering has played an important role. An example is taken from the Laurentide region of the Canadian Shield north of Montréal (Québec). The present topography resulted from the stripping of the former weathering mantle and from the probable subsequent modification of the weathering front, first by the action of hillslope processes and rivers and then by glaciers, before and during Plio-Pleistocene times. The present landscape reflects the timing of the formation of erosion surfaces, and of the stripping of the Paleozoic cover rocks and exposure of the Shield. Since the late seventies, several isolated occurrences of saprolite-soil profiles have been discovered in eastern Canada and prompted a renewal of the study of these materials about the Cenozoic evolution of these regions. One of the problems in this field of research is the dating of saprolites and their inclusion in a chronostratigraphic framework, along with the other Cenozoic surficial deposits and landforms. Because of the multiple factors involved in the development of secondary minerals in saprolites during the course of weathering, it is preferable to distinguish the dating of saprolites from the study of their mineralogical and geochemical evolution. Fortunately, several new techniques are becoming available for the absolute dating of surficial deposits and saprolites, including the use of cosmogenic radionuclides. Saprolites provide a strong potential field of research for our understanding of the geological evolution of eastern Canada during the Cenozoic. Contemporary weathering and erosion rates are fields of research that have gained increasing interest recently, since modeling landscape geochemical response can be applied to various environmental stress situations, such as acidification by rain and forest harvesting. Rock-type may be the main factor explaining the large differences between watersheds. In fact, variability of cation removal in the temperate zone is probably most closely related to flow-paths of water. Investigations, at different scales, from entire watersheds to slopes to individual pedons, highlight the problem. In the Catamaran Brook watershed (New Brunswick), water chemistry is explained by a mix of groundwater and soil solution from the horizons at the base of the floodplain soils. Geochemical mass-balances based on net outputs give little information on the weathering reactions of primary minerals, the weathering products or on the nature of the weathering processes that provide the dissolved load of streams. Mineralogic and petrographic analysis of selected soil pedons are necessary to determine weathering reactions and their role as sources or sinks for bases, silica, aluminum and iron in the various compartments through which water percolates before it reaches the stream. 相似文献
12.
The Southern Alps lie along the convergent Pacific-Indian plate boundary. Geomorphically distinct eastern, axial and western regions reflect the east-west gradient in tectonic uplift (1 to 10 mm a−1) and precipitation (600 to 10,000 mm a−1). The eastern region is divided into front-ange and basin-and-range subregions. Soil-sequence studies on terraces established temporal contrasts in pedogenesis within and between eastern and western regions encompassing Entisols, Inceptisols and Spodosols. On Late Pleistocene and early Holocene terraces Dystrochrepts are persistent soils in the eastern region and Aquods in the western region. These soil sequences are used in the interpretation of relative soil age, stratigraphy and erosion history in hill and mountain drainage basins of the eastern and western regions. In the subhumid to humid eastern front-range subregion, simple soil forms occur as catenary sequences, and there is little evidence of erosion following the destruction of forests in the last millenium. Mollisols are dominant in the subhumid, and Dystrochrepts in humid areas, respectively. Soil-debris mantle regoliths date from the early Holocene and are still developing on slopes. The soil pattern on mountain slopes in the humid, eastern basin-and-range subregion is a complex array of simple, eroded, composite and compound soils. This pattern has resulted from erosion following forest destruction within the last millenium. The oldest surface or buried forest soils are Dystrochrepts dating from the Late Pleistocene to early Holocene. Wind erosion of these low-fertility soils contributes to the loessial sediments in which younger soils have formed. In the western region, soil patterns and soil stratigraphy indicate continous instability with a complex pattern of highly leached, shallow Orthents and bedrock outcrops on slopes. The soils are eroded from slopes within 2 ka. These contrasts in soil development and erosion periodicity in the eastern and western regions of the Southern Alps parallel the east-west contrasts in erosion rates of ca. 1–10 mm a−1. 相似文献
13.
三峡库区坡地地貌过程的速率 总被引：1，自引：0，他引：1
在重庆奉节至湖北巴东一带三峡库区,存在两类坡地,分别是深层风化坡地与崩积—残坡积坡地。这两类坡地上,堆积物的稳定性差,表现为剥蚀、堆积的速率大。堆积物的累积速率可粗略地依据热释光年龄来估计。据此我们推测深层风化坡地的浅层滑坡周期大约是1.5ka,对应的堆积速率大约是33cm/ka。崩积—残坡积坡地上主要的陡崖崩塌发生周期是40ka60ka,坡地中部的累积速率大约是4cm/ka。在崩积—残坡积坡地上常见生长的树木因堆积物蠕滑而变形,树木变形程度反映了蠕滑速率,据此估算的蠕滑速率是非常可观的,这既是坡地中部的剥蚀速率,可能也在一定程度上反映了坡地下部堆积物的物质供应速率。这些认识可能对滑坡与水土流失的治理有参考价值。 相似文献
14.
土地利用/土地覆盖变化与土壤侵蚀关系研究进展 总被引：34，自引：7，他引：27
土壤侵蚀作为LUCC引起的主要环境效应之一,是自然和人为因素叠加的结果。不合理的土地利用和地表植被覆盖的减少对土壤侵蚀具有放大效应。土地利用/土地覆盖变化与土壤侵蚀关系的研究已逐渐成为LUCC研究和土壤侵蚀研究的一项新的重要课题。目前,涉及土地利用/土地覆盖的土壤侵蚀研究方法有很多,本文介绍了基于模型的定量研究、基于GIS和RS的研究、基于放射性同位素的研究以及基于湖泊(水库)沉积物的研究的基本原理与研究进展,同时指出了每种方法中存在的不足。 相似文献
15.
Soil distribution in high mountains reflects the impact of several soil-forming factors. Soil geomorphologists use key pedological properties to estimate ages of Quaternary deposits of various depositional environments, estimate long-term stability and instability of landscapes, and make inferences on past climatic change. Once the influence of the soil-forming factors is known, soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected.The Front Range of Colorado rises from the plains of the Colorado Piedmont at about 1700 m past a widespread, dissected Tertiary erosion surface between 2300 and 2800 m up to an alpine Continental Divide at 3600 to over 4000 m. Pleistocene valley glaciers reached the western edge of the erosion surface. Parent rocks are broadly uniform (granitic and gneissic). Climate varies from 46 cm mean annual precipitation (MAP) and 11 °C mean annual temperature (MAT) in the plains to 102 cm and −4 °C, respectively, near the range crest. Vegetation follows climate with grassland in the plains, forest in the mountains, and tundra above 3450 m. Soils reflect the bioclimatic transect from plains to divide: A/Bw or Bt/Bk or K (grassland) to A/E/Bw or Bt/C (forest) to A/Bw/C (tundra). Corresponding soil pH values decrease from 8 to less than 5 with increasing elevation. The pedogenic clay minerals dominant in each major vegetation zone are: smectite (grassland), vermiculite (forest), and 1.0–1.8 nm mixed-layer clays (tundra). Within the lower forested zone, the topographic factor (aspect) results in more leached, colder soils, with relatively thin O horizons, well-expressed E horizons and Bt horizons (Alfisols) on N-facing slopes, whereas soils with thicker A horizons, less developed or no E horizons, and Bw or Bt horizons (Mollisols) are more common on S-facing slopes. The topographic factor in the tundra results in soil patterns as a consequence of wind-redistributed snow and the amount of time it lingers on the landscape. An important parent material factor is airborne dust, which results in fine-grained surface horizons and, if infiltrated, contributes to clay accumulation in some Bt horizons. The time factor is evaluated by soil chronosequence studies of Quaternary deposits in tundra, upper forest, and plains grassland. Few soils in the study area are >10,000 years old in the tundra, >100,000 years old in the forest, and >2 million years old in the grassland. Stages of granite weathering vary with distance from the Continental Divide and the best developed is grus near the sedimentary/granitic rock contact just west of the mountain front. Grus takes a minimum of 100,000 years to form.Some of the relations indicated by the soil map patterns are: (1) parts of the erosion surface have been stable for 100,000 years or more; (2) development of grus near the mountain front could be due in part to pre-Pennsylvanian weathering; (3) a few soil properties reflect Quaternary paleoclimate; and (4) a correlation between soil development in the canyons and stream incision rates. 相似文献
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17.
Norikazu Matsuoka Cline E. Thomachot Chiaki T. Oguchi Tamao Hatta Masahiro Abe Hiroyuki Matsuzaki 《Geomorphology》2006,81(3-4):408-420
Rates and processes of rock weathering, soil formation, and mountain erosion during the Quaternary were evaluated in an inland Antarctic cold desert. The fieldwork involved investigations of weathering features and soil profiles for different stages after deglaciation. Laboratory analyses addressed chemistry of rock coatings and soils, as well as 10Be and 26Al exposure ages of the bedrock. Less resistant gneiss bedrock exposed over 1 Ma shows stone pavements underlain by in situ produced silty soils thinner than 40 cm and rich in sulfates, which reflect the active layer thickness, the absence of cryoturbation, and the predominance of salt weathering. During the same exposure period, more resistant granite bedrock has undergone long-lasting cavernous weathering that produces rootless mushroom-like boulders with a strongly Fe-oxidized coating. The red coating protects the upper surface from weathering while very slow microcracking progresses by the growth of sulfates. Geomorphological evidence and cosmogenic exposure ages combine to provide contrasting average erosion rates. No erosion during the Quaternary is suggested by a striated roche moutonnée exposed more than 2 Ma ago. Differential erosion between granite and gneiss suggests a significant lowering rate of desert pavements in excess of 10 m Ma− 1. The landscape has been (on the whole) stable, but the erosion rate varies spatially according to microclimate, geology, and surface composition. 相似文献
18.
福建长乐屏山风化坑与河流壶穴的成因及其证据 总被引：1，自引：0，他引：1
风化坑和壶穴是一种常见的岩石坑穴地形,其形成原因和形态完全不同,但容易被误解和混淆.结合对福建长乐三溪河地区这两种坑穴地形的实地考察,本文从地貌学,沉积学,岩石化学和矿物学等各个方面对两者的形成过程、影响因素进行了论证和对比.研究表明：风化坑形成于岩石面积水的风化作用,壶穴则是由河流的旋转水流对河床产生的侵蚀作用形成;山顶风化坑的发育与河流流水作用没有关系,河流壶穴的形成与河谷的发育过程有关,河谷中的风化坑只能在河流深切后,流水不再作用到的河床部位发育;只要条件合适,风化坑或壶穴随时可以生成;风化坑与河流壶穴的形态,坑内沉积物的磨圆度、粒度特征等反映出各自不同的形成过程.风化坑内碎屑与周边岩石的化学蚀变指数CIA 值的差异反映了风化坑的化学风化成因;风化坑内碎屑与周边岩石石英长石比例的差异说明风化坑是矿物差异风化的结果;用CIA 值和英长比均无法区分河流壶穴和风化坑中的碎屑颗粒,但两者化学元素迁移特征的差别反映了风化坑的风化作用和河流壶穴的流水搬运作用的成因差别;风化坑的风化程度达不到当地风化壳的风化程度,但不同气候带风化坑碎屑的CIA 值能反映不同气候带风化作用的强度差异. 相似文献
19.
Walter G Whitford 《Journal of Arid Environments》1998,40(4):453-457
The densities of pits made by goannasVaranus gouldiiwere estimated in the three distinct zones of banded mulga landscapes (erosion slope, interception zone, and mulga grove) in paddocks of a grazing study in north-western New South Wales, Australia. In light and moderately grazed paddocks, soil pits were significantly more abundant in the interception zones (M=119.057 m−2) than in the groves and erosion slopes (M=16.057 m−2). In the overgrazed paddock there were no differences in densities of pits in any of the zones. In the groves and erosion slopes approximately 70-80% of the pits contained litter, seeds, and fruits. However, on the erosion slopes less than 20% of the pits contained litter and seeds. The data support the hypothesis that soil disturbance byVaranuslizards produces a positive feedback mechanism for the viability of the interception zone and the functioning of banded vegetation landscapes. 相似文献
20.
Soil erosion is a complex process determined by mutual interaction of numerous factors. The aim of erosion research at regional scales is a general evaluation of the landscape susceptibility to soil erosion by water, taking into account the main factors influencing this process. One of the key factors influencing the susceptibility of a region to soil erosion is land cover. Natural as well as human-induced changes of landscape may result in both the diminishment and acceleration of soil erosion. Recent studies of land-cover changes indicate that during the last decade more than 4.11% of Slovak territory has changed. The objective of this study is to assess the influence of land-cover and crop rotation changes over the 1990–2000 period on the intensity and spatial pattern of soil erosion in Slovakia. The assessment is based on principles defined in the Universal Soil Loss Equation (USLE) modified for application at regional scale and the use of the CORINE land cover (CLC) databases for 1990 and 2000. The C factor for arable land has been refined using statistical data on the mean crop rotation and the acreage of particular agricultural crops in the districts of Slovakia. The L factor has been calculated using sample areas with parcels identified by LANDSAT TM data. The results indicate that the land-cover and crop rotation changes had a significant influence on soil erosion pattern predominately in the hilly and mountainous parts of Slovakia. The pattern of soil erosion changes exhibits high spatial variation with overall slightly decreased soil erosion risks. These changes are associated with ongoing land ownership changes, changing structure of crops, deforestation and afforestation. 相似文献