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1.
Thermoluminescence (TL) measurements on the present organic surface soil and two buried soils in loess and colluvium derived from loess at Pegwell Bay, Kent, suggest that the signal is almost completely zeroed during soil development, mainly by optical bleaching. The technique may therefore be used to date buried soils developed in loess and possibly other terrestrial sediments. Decalcification, gleying and other soil-forming processes may also affect the TL signal of the soil parent material, and seem to be the main reasons why the Btg horizons of the Early Holocene buried soil at Pegwell Bay give more recent TL dates than the parent calcareous loess. 相似文献
2.
Gully incision as a key factor in desertification in an arid environment, the Negev highlands, Israel 总被引：3，自引：2，他引：3
Gully incision has been eroding the alluvial sediments and loess soils deposited and developed along the valleys in the arid and semiarid regions of Israel. This phenomenon is critical in the arid regions of the Negev Highlands where the agricultural fields, the main floral biomass and the areas which have the highest grazing value, are limited to narrow valleys filled with redeposited loessial sediments. The headcut migration and gully development in the region were studied between 1990 and 2001 in three representative drainage basins (Zipporim, Revivim and Sekher). During flood events, the runoff penetrates the alluvial cover of the valleys, forming vertical headcuts, which gradually retreat up the valley. The runoff is channeled into narrow gullies, preventing the floodwater from spreading over the whole width of the valley. The change in irrigation efficiency along the valleys is reflected in a sharp estimated drop of 70–90% in the floral biomass, causing the reduction of the range value by 83–99%. During the monitoring time interval (1990–2001), the linear gully retreat in the study area ranged between 12.3 and 250 m an average rate of 1.12–22.7 m year− 1 for each gully head. The process is accompanied by erosion of soil, which has high agricultural and range value. The total soil losses in these sites ranged between 800 and 9000 m3 at an average rate of 81–818 m3 year− 1 for each gully head, which is equivalent to 121–1227 Mg year− 1. During the monitoring period, approximately 0.11–0.87 ha of land lost its agricultural and range value in each basin under study, at an average rate of 0.01–0.079 ha year− 1. Since the Byzantine period (1400 BP), approximately 6.5 ha, which is 10% of the land that had high agricultural and range value in the Zipporim valley, lost its value due to gully erosion. No recovery effects of the gully channels were found in the nearby region. The soil erosion is generated by a long-term natural dynamic change in the soil / rock ratio evolving within the drainage basins through time since the termination of the last glacial phase. The loessic sediments, originally deposited within the drainage basins during the late Pleistocene glacial stage, are being removed under the present Holocene climate in several erosion stages. This ongoing phenomenon is causing degradation of soil and biomass and is severely reducing the agricultural and range potential of the region. These parameters indicate that an ongoing process of desertification is active in the arid environment of the Negev Highlands, and is advancing in proportion to the headcut retreat rates in the region. The soil erosion and headcut retreat have been active in the Negev Highlands for the last few millennia. If these processes continue in the future, the Negev Highlands region will lose its agricultural potential within a few millennia. However, the fact that the ancient inhabitants of the region implemented successful long-term land conservation techniques already 3000 years ago, implies that a sustainable land management policy can be adapted to the Negev Highlands, as well as to other semi-arid regions in the Middle East. 相似文献
3.
Micromorphological characteristics indicate that in southwestern Wisconsin pedogenesis transgressed the Sangamonian-Wisconsinan chronostratigraphic boundary in conjunction with colluvial and eolian sedimentation. The use of micromorphology helps to distinguish between pedological, colluvial, and eolian components in the paleosol horizon sequence, which can be difficult to resolve and interpret solely from field investigations and from other laboratory analyses. Results show that a basal loess “mixed zone” within the welded paleosol profile contains features that are the products of colluvial reworking processes. We present micromorphology data which support stratigraphic relationships suggesting that colluvial processes were important in the formation of basal loess “mixed zones” in addition to other possible mixing processes such as pedoturbation and bioturbation. 相似文献
4.
Late Quaternary alluvial fans and paleosols of the Kangra basin,NW Himalaya: Tectonic and paleoclimatic implications 总被引：1，自引：0，他引：1
The paper describes Late Quaternary pedosedimentary sequences of the alluvial fans from the Kangra basin of NW Himalayas for tectonic and paleoclimatic implications. In the proximal part of the Kangra basin three coalescing alluvial fans, namely Rait-Rihlu fans (~ 65 km2), Kangra fans (~ 200 km2), and Palampur fans (~ 170 km2) from west to east evolved due to reactivation of longitudinal and transverse faults and climatic changes during the Late Quaternary. The fans are characterised by subsidence of Rait-Rihlu fans, uplift of Kangra fans and tilting of Palampur fans. The thick (~ 90 m) pedosedimentary sequences exposed along the rivers characterise the dominant formative processes over the fans. The stream flow sediments dominate the Rait-Rihlu fans, whereas the debris flow sediments dominate the Kangra and Palampur fans. The fan sequences are also marked by the formation of strongly developed paleosols on loess (L1–L3 loess paleosols) and weakly developed paleosols on fluvial deposits in response to the tectonics and climate change in NW Himalayas. 相似文献
5.
6.
This study is based on a sequence of soils on a typical slope of the Himalayas in central Nepal from 2300 m to 4000 m. Above 2300 m the land is forested and at 4000 m forest gives way to alpine meadows.The soils have developed in silty loam materials derived from weathering of micaschists. They are humic, acid and strongly desaturated. Their spatial distribution is related to the bioclimatic zonation: acid brown soils and deep humic acid soils occur in the mountain zone and podzols and brown podzolic soils in the subalpine and alpine ones.Biological activity and “maturation” of humus decrease with increasing elevation. The podzolization process dominates. There is intense weathering of ferruginous phyllosilicates in eluvial horizons and accumulation of amorphous products in B horizons. 相似文献
7.
This work was done in three different research areas In order to determine the loess content in the periglacial strata, there has been taken a profile catena on gneis, granite and ignimbrite as solid rock. At first the rock material including the loess of the upper Rhine plain was described. The admixed loess in the layered solifluction profiles was qualitatively and quantitatively determined by its differentiating values By grain-size-distribution the “total loess” including far and local transport was calculated. Because the “far transported loess” differes in geochemical values and heavy minerals it was possible to select it from the local loessThe maximum in loess content was found in the so called Hauptfolge (main series) of the Periglacial. The “Decksediment” (top layer) has got similar contents but is less important because of his minor thickness and smaller spread. The dense “Basisfolge” (basic series) is almost free of loess The amount of far transported loess in a distance of 1 km from the glacial terrace of the Rhine is about 1000 kg/m2 (300 m above sea level). It decreases sharp into the mountains and reaches at 1000 m and 12 km from the plain the detection limit of about 30 kg/m2. The local component in contrary is not important on the lower slopes and has its maximum of 150 kg/m2 at the mountains top (1300 m, 15 km). According to this features total loess has a minimum in an altitude between 800 and 1000 m.At the footslope of Black Forest loess accumulation was favoured at least at the end of the last glacial period. On the mountains kryoclastic silt production and local transport have been more important.
Zusammenfassung
Die Untersuchungen wurden in drei Teilgebieten mit den anstehenden Gesteinen Gneis, Granit und Ignimbrit durchgeführt. Die Lößbeimengung wurde in je einer Catena von Schuttprofilen erfaßt. Zuerst wurden die unveränderten Ausgangsgesteine einschließlich Rheintallöß beschrieben. Mit den hier dargestellten Kennwerten wurden die Lößanteile in den Schuttprofilen qualitativ und quantitativ ermittelt. Mit Hilfe der Korngrößenverteilung wurde der aus Ferntransport und Lokalverwehungen bestehende “Gesamtlöß” bestimmt. Fern- und Lokallöß ließen sich aufgrund ihres unterschiedlichen Chemismus und Mineralbestandes trennen.Die höchsten Lößanteile hatten die als Hauptfolge bezeichneten Schuttschichten. Das Decksediment, welches ähnliche Gehalte erreicht, hat wegen geringerer Mächtigkeit und kleinerem Verbreitungsgebiet weniger Bedeutung. Die meist dichte Basisfolge ist nahezu lößfrei. Die Fernlößmengen, welche in 1 km Abstand von der Niederterrasse des Rheins noch ca. 1000 kg/m2 betragen, nehmen gebirgseinwärts rasch ab und erreichen bei 1000 m und 12 km die Nachweisgrenze um 30 kg/m2. Die Lokalkomponente ist an den unteren Hängen am niedrigsten und erreicht auf den höchsten Höhen mit 150 kg/m2 ihr Maximum. Der Gesamtlöß hat also zwischen 800 und 1000 m sein Minimum.Am Fuße des Schwarzwalds waren die Bedingungen der Lößakkumulation zumindest gegen Ende des letzten Glazials günstig (Vegetation, wenig Bodenfließen). Auf den Höhen dagegen war offensichtlich die Kryoklastik aktiver und lokale Umlagerungen waren stärker begünstigt. 相似文献8.
Many alpine gravel-bed rivers have been altered in the past due to human interventions. A typical transboundary alpine river in Central Europe flowing over Austria, Slovenia, Croatia and Hungary is the Mura River (length: 465 km, catchment area: 14,304 km2). The main problem of the river before leaving Austria is bed degradation (average 0.5 m from 1970 to 2000) as a combined consequence of river regulation works and the reduced sediment supply from the upstream reaches due to the construction of hydro power plants. River restoration measures for the river reach on the border between Austria and Slovenia (SLO–A Mura reach) were proposed in 2000 to support both ecological and flood protection purposes that apply the concept “of self-restoration”. In order to apply similar process-oriented restoration strategies in the Mura River downstream in Slovenia, we consider the potentials for self-forming river processes. We have analysed the sediment granulometry and morphology of the Mura River in Slovenia, and discussed morphodynamic processes to detect potential for the Mura River recovery into a more diverse morphological structure. The cross section area increased by 8% between 1979 and 2005 on average, mainly due to riverbed degradation. On average, the thalweg of the Mura riverbed in Slovenia had degraded by 0.28 m in the 1979–2007 period, with the highest degradation of 2.28 m in one cross section and some cross sections being stable. The high river degradation trend from the SLO–A Mura reach is slowly shifting to the downstream direction into the Mura River in Slovenia. Nevertheless, the clear downstream coarsening of river sediments turns into the normal trend of sediment fining in the Mura River reach in Slovenia. The “self-restoration” potential in the Mura River reach in Slovenia is larger than on the SLO–A Mura reach due to still active morphological fluvial processes. These processes can be enhanced by the inflow of fresh coarse sediments from the SLO–A Mura reach, where active measures for re-establishing sediment transport are under way. In the long term, this will not work as proposed, if no sediment inflow is re-established from the Mura headwaters in Austria. 相似文献
9.
Sedimentological characteristics of aeolian soil parent materials in the Río Sauce Grande basin, southern Buenos Aires province, were analysed using grain-size distributions, transport mechanisms, dynamics of the sedimentary process and the nature of calcareous layers. Samples were collected from C horizon of 13 profiles distributed over all the piedmont areas and plains. Calcium carbonate in these materials is either inherited from the parent material or was redistributed by pedogenic processes. Their amounts in Ck horizons increase from the upper to the lower basin, and are inversely related to the thickness of soil parent material, to mean annual rainfall and to the calcrete depth.The cumulative grain-size plots show that the sediments were transported by both aeolian saltation and aeolian suspension. Most of them have coarser and more heterogeneous grain size distributions than typical loess of the northern hemisphere, indicating a larger and more fluctuating wind energy than is required for the formation of typical loess. Deposits in the upper and middle basins were deposited in two main aeolian episodes which can be related to the dry periods of the Late Pleistocene and the Late Holocene recorded in southern Buenos Aires province. In some thin profiles of the middle and lower basins, the large clay content of the calcic C horizon was probably inherited from one or more previous pedogenic events. There is a systematic increase of particle size towards the lower basin, which may be related to an increase of energy towards the lower basin or to the influence of littoral dune fields along much of the Atlantic coastal zone. 相似文献
10.
Soils derived from loess are extensive in Europe and are well suited for forestry. They are suspected to be poor acid buffers, however. We have estimated the weathering stage and acid neutralizing capacity of acid soils under forest in a toposequence on loess in the Belgian silt belt. The soils vary distinctly in morphology and physico‐chemical properties according to their topographic position. Dystric Cambisols have developed in colluvial deposits in the dry valley floors, whereas Dystric Luvisols have formed on the slopes in a rejuvenated material. The Cambisols are more acid and less saturated in bases than are Luvisols. They are strongly depleted of clay and contain less weatherable minerals. Easily weatherable minerals are concentrated mainly in the clay fraction of both soil types. Clay minerals of size < 2 μm therefore act as major sinks for protons in these soils. A simplified expression taking into account the total reserve in bases, total aluminium and iron occluded in silicates is used to estimate acid neutralizing capacity. Our estimates confirm that these acid loessic soils are indeed poor acid buffers. They show that the Dystric Cambisols depleted of clay are sensitive to potential acidification, whether natural or man‐made. 相似文献
11.
新集黄土剖面位于陕西扶风县境内渭河第四级阶地上。剖面出露有马兰黄土（Q3）和离石黄土上部（Q22）,厚38m,见有五层古土壤。根据黄土的性质,剖面处于碳酸盐风化壳阶段。黄土中碳酸盐含量10.0—16.5%,古土壤则为0.19—6.0%,全剖面的 SiO2、Al2O3和 Fe2O3含量分别为54.0—66.6%、11.6—15.8%、4.8—6.6%。古土壤中的铁铝含量均较黄土为高。但在减去碳酸钙后,差别不甚明显。黄土和古土壤中的粘土矿物主要为伊利石,剖面呈盐基饱和。根据古土壤的结构和性征,这些埋藏的土壤属褐土类土壤。 相似文献
12.
Loess grain size data used to infer transport direction or wind strength are generally derived from vigorously disaggregated samples. However, these data may not adequately represent the effective particle size distribution during loess transport, if the transported dust contained aggregates of fine-grained material. Thin sections of minimally altered C and BC horizons in the late Pleistocene Peoria Loess of Nebraska, USA, indicate the presence of aggregates with diameters of 30–1000 μm. The larger aggregates (>250 μm) are unlikely to have been transported, and are interpreted as the result of soil faunal activity and other pedogenic processes after deposition. Aggregates smaller than 250 μm could have a similar origin, but laser diffraction particle size analysis suggests that many are sedimentary particles. Comparison of minimally and fully dispersed particle size distributions from each sampling site was used to estimate the modal diameter of aggregates. The aggregate modal diameter becomes finer with decreasing loess thickness, representing increasing distance from the source. A similar trend was observed in the modal diameter of fully dispersed particle size distributions, which represents the mode of sand and silt transported as individual grains. We interpret both trends as the result of sorting during transport, supporting the interpretation that many of the aggregates were transported rather than formed in place. Aggregate content appears to increase with distance from the source, explaining a much more rapid downwind increase in clay content than would be expected if clay were transported as particles smaller than 2 μm diameter. Although the Peoria Loess of Nebraska contains sedimentary aggregates, many of the coarse silt and sand grains in this loess were transported as primary particles, were thoroughly exposed to sunlight and are potentially well suited for luminescence dating. 相似文献
13.
A 5-m-wide soil pit at the base of a forested hillslope in coastal British Columbia was instrumented for studying subsurface flow processes during rainstorms. Three typical, low-intensity autumn rainfall events with different antecedent moisture conditions are assessed. Outflow from the organic horizon was captured and measured by a single trough, and outflow from the mineral horizon (above compact glacial till and bedrock) was measured separately for three adjacent sections of the soil pit. For two storms that were preceded by dry conditions, lateral outflow from the organic horizon occurred, although the water table did not rise up to the organic horizon. However, the calculated effective contributing area was small (<0.7 m2) and the effective contributing slope length was short (<0.15 m). Furthermore, volumes of outflow from the organic horizon during these storms were more than 400 times less than during a later storm with wet antecedent conditions. During this later storm, a portion of the outflow from the organic horizon may have been generated as saturated overland flow due to the rising water table. The calculated effective contributing area (>170 m2) and the effective contributing slope length (>36 m) were substantially greater for the “wet” antecedent storm compared to the “dry” storm events. Shallow lateral flow over unsaturated soil is therefore unlikely to be a significant contributor to storm runoff at such forested sites. Flow at the organic horizon–mineral soil interface may contribute to interconnected preferential flow pathways during wetter antecedent conditions. 相似文献
14.
The evolution of clay soil porosity is currently demonstrated via the shrinkage curves in a large water content domain spreading from a shrinkage limit to a liquidity limit. In fact, the parallel between in situ profiles and the shrinkage curves in such a large water content range is difficult to obtain because of the lack of earth pressure in the laboratory tests and in situ limited water contents. The vertical distribution of porosity throughout a clay-rich marsh soil profile was studied in a grassland field with samples taken from the soil surface characterized by water contents near their shrinkage limit down to 2.00 m deep saturated sediments over their liquidity limit. The depth of the plasticity limit isolates a soil in a solid state characterized by a vertical prism-like structure from a plastic to pseudo-liquid state in depth. The porosity was calculated from the measurements of the density of intact samples by double weighing and image analysis of 100 cm2 polished sections. The initial structure of clay soil was maintained by impregnation based on water–acetone–resin exchange. An ultraviolet photo luminescent pigment added to the resin allowed the capture of images from which shrinkage cracks and microporosity of the clay matrix were easily separated. The distribution of porosity between the shrinkage crack mesoporosity and the clay matrix microporosity was evaluated after the mathematical decomposition of the grey level curves characteristic of each level. Vertical evolution of the porosity distribution from the soil surface in a solid state to the plastic and pseudo-liquid sediment in depth was presented on the shrinkage curve of the clay material. The measurements point out how the clay matrix microporosity and mesoporosity of shrinkage cracks are complementary and the role of the scale effect on the shrinkage curve. The analysis of images captured on an optical microscope under polarized and analyzed light and the SEM observation of freeze-dried samples demonstrated the isotropic arrangement of the clay particles in typical “honey-comb” architecture in the in situ plastic-to-liquid saturated domain. Eventually the distribution of porosity through the profile results from the evolution of the initial “honey-comb” microstructure of the sediment induced by the desiccation phenomenon. It is governed by the depth of plasticity limit of the clay material and by the depth of the water table. 相似文献
15.
The paper presents an analysis of the Sudan clay plain. Total plain area is 500,000 sq. km., but the paper focuses on an area of 90,000 sq. km.In the east-central Sudan an old erosion surface between600m× 730m above sea level is probably Miocene in age. The main plainlands lie 200 – 300 m below this and date from entertiary times. Evidence of an “African” surface may occur on skeletal volcanoes near Gedaref.Downwarping along NNW-SSE lines formed distinctive basins including the Blue Nile basin. Sediments accumulated in the basins and a sequence of arkose, paludal sandy clay, alluvial sand, silt and clay in the Blue Nile basin is capped by modern silt and clay which has weathered to form a clay soil.The clays on the plain vary in age from upper Pliocene to modern though the weathering seems in balance with a somewhat wetter climate than at present. The clays dominantly on almost level plains are alluvial or lacustrine. The remainder is residual or colluvial weathered material on flat but extremely gently sloping interfluves on higher ground.The clay of the aggradational plains in the Blue Nile basin has been reworked continuously by the rivers and is therefore, much younger than the clay on the degradational plains which is upper Pliocene to Middle Phistocene in age. The present Blue Nile flows in a wide alluvial valley with the channel incised up to 24 m below the general plain. 相似文献
16.
Advances in characterization of soil structure 总被引：4，自引：0，他引：4
A.R. Dexter 《Soil & Tillage Research》1988,11(3-4)
Soil structure is defined as “the spatial heterogeneity of the different components or properties of soil”. Aspects of soil structure which are important for plant development, soil water balance and soil workability are reviewed briefly. The different types of soil structure which occur on different size scales are placed in a hierarchical order. Different mechanisms give rise to the different hierarchical orders. Similarly, different physical/chemical/biological processes are involved in the stabilization of the different hierarchical orders.A number of methods for measuring soil structure are described. Preference is given to methods involving direct observation of structural features by scanning electron microscopy and by optical scanning of impregnated sections and fracture surfaces. These need to be supported by assessments of the stabilities of compound particles in water and of the mechanical strengths of compound particles as a function of water content.“Good” soil structure is described as one where all the hierarchical orders are well-developed and stable. The greatest lack of knowledge appears to be in the 2–100 μm size range which is too large to have been studied by colloid chemists and too small to be visible to the naked eye. It is suggested that more observations of soil structure should be made in this size range, as it may hold many important clues on how to manage soil structure in the field. 相似文献
17.
D. L. MOKMA J. K. SYERS M. L. JACKSON R. N. CLAYTON R. W. REX 《European Journal of Soil Science》1972,23(2):147-162
The particle-size distribution of the whole sample and the content, particle-size distribution, and oxygen-isotope abundance (δ18O) in quartz were employed to determine the extent to which aeolian materials such as aerosolic dust (10 to I /μm) from Australia, loess (50 to 10μm) in New Zealand, and flöttsand (250 to 20 μm) in Australia have been accreted into soils and sediments in the South Pacific area. Although aeolian material from both local and more distant sources has been deposited on the Franz Josef, Fox, and Tasman glaciers, the extent to which aeolian materials have been added to soils in South Westland, New Zealand, could not be determined because the oxygen-isotope abundance (12.9 to 13.5 0/00 in quartz from the soils was similar to that (13.1 to 13.9 0/00) in quartz from the dust samples. The quartz from loess added to two basaltic soils in North Auckland, New Zealand, had an oxygen-isotope abundance (12.9 to 13.9 0/00) slightly lower than that (15.0 to 15.4 0/00) in quartz from a greywacke-derived soil and the underlying rock also in North Auckland. The oxygen-isotope abundance (13.6 to 15.4 0/00) in quartz from a chronosequence of soils developed in basalt in Victoria, Australia, indicates that the quartz did not originate from the parent basalt, but probably was transported by aeolian processes from stranded beach ridges and dunes and added to the soils in the form of flöttsand, an aeolian material coarser than loess and finer than dune sand. Most particles of the pelagic sediments fell within the aerosolic dust size range. The oxygen-isotope abundance (12.1 to 15.1 0/00) in quartz isolated from several pelagic sediments between latitudes 35 and 45° S. was similar to that (12.9 to 15.4 0/00) in quartz from New Zealand and Australian soils located between these latitudes. An aeolian source of quartz explains the above relationship and also the decreasing delta values of quartz from sediments and soils with increasing latitude in the South Pacific area. Oxygen-isotope abundance in quartz refutes a volcanic origin of quartz in pelagic sediments but supports the deduction of Griffin et al. (1968) from mineralogical analyses that the quartz and associated minerals were transported from lands to seas. 相似文献
18.
通过团粒分析、电子显微镜 (SEM/EDX)扫描等元素分析扫描方法和手段 ,对黄土高原西北部自然黄土中的团粒数量及其与碳酸钙的溶解量的关系、团粒表面和内部碳酸钙的分布进行了研究。结果表明 :碳酸钙大约参与了 99%的团粒形成 ,呈现团粒越大 ,碳酸钙含量越多的趋势 ;反之 ,团粒数量与碳酸钙的溶解量成反比 ;随着团粒表面碳酸钙分布的减少 ,附着在团粒表面的微团粒及粉粒、粘粒减少 ;在团粒内部 ,碳酸钙与矿物颗粒之间存在 3种胶结方式 ,分别为碳酸钙附着在矿物颗粒表面、碳酸钙分布于矿物颗粒之间以及碳酸钙表面附着矿物颗粒。实验结果证明了黄土团粒的主要胶结物是碳酸钙这一理论。 相似文献
19.
Due to northwestward attenuation of the summer monsoon and northwestward intensification of loess deposition during the last interglacial, the last interglacial pedocomplex S1 gradually differentiated from the northwest to the southeast. The three paleosols (S1S1, S1S2, S1S3) corresponding to the marine isotope sub-stages 5a, 5c, and 5e and the two intercalated loess units (S1L1, S1L2) corresponding to the marine isotope sub-stages 5b and 5d are completely preserved at northwestern sections. Towards southeast, both the S1L1 and S1L2 were annexed by the subsequent paleosol development (S1S1 and S1S2) and the three paleosols (S1S1, S1S2, and S1S3) were partially welded. At the southeasternmost site, the three soil-forming events (S1S1, S1S2, and S1S3) repeatedly occurred in a single paleosol profile. The three observed orders of particle-size variations are interpreted to have imprinted important chronological and pedogenic signatures. First-order variations, i.e., a remarkable difference between the interglacial pedocomplex S1 and the glacial loess units (L1 and L2), implies that the S1 parent material was considerably finer in the source areas or/and the proximity to the source areas was much farther during interglacial period than during the preceding (L2) and following (L1) glacial periods. Second-order variation, i.e., the parenthetical trends in > 63 μm and < 10 μm fraction curves, might have resulted from the delayed response of the source material supplies to the climate changes. The third-order variations in < 10 μm fraction correspond well to the variations in frequency-dependent magnetic susceptibility, suggesting that pedogenically formed finer particles (i.e., < 10 μm fraction) and the associated ultra-fine paramagnetic minerals as expressed by the frequency-dependent susceptibility occurred only as a minor component of the < 10 μm fraction. The third-order variations seem to be obscured by soil welding and annexation at southeastern sections where the paleosols within the S1 were partially or completely welded. The laboratory data-indicated < 10 μm fraction peaks of the third-order and field-observed clay coatings on ped-faces, together with carbonate leaching and accumulation, in the paleosols within the S1 indicate occurrence of within-S1 material translocation. To sum up, it is unrealistic to reconstruct high-resolution climatic records from the S1 pedocomplex because a number of factors might have undermined the validity of the particle size as a winter monsoon proxy. These factors include weathering in the source areas, in situ post-depositional weathering and fine fraction translocation, and downward penetration of soil formation into underlying previously deposited materials on stable land surfaces. 相似文献
20.
黄河中游流域产沙量随降雨变化的区域分异 总被引：3，自引：0，他引：3
在黄河中游地区选择 5 0多个位于不同自然地理地带和地域的水文测站流域 ,流域面积从 5 0 0 km2 至 2 5 0 0km2 ,代表 6种不同自然地理类型。在流域降雨、泥沙及环境特征数据获得基础上 ,以不同自然地理类型流域为参数 ,建立了流域产沙量与降雨季节性、年际变化和年降雨量之间关系。结果表明 ,对于不同类型流域 ,产沙量与降雨季节性变率和年际变率之间有相当好的正相关关系 ,不同类型流域曲线的斜率各不相同 ,在图中所处的位置也不相同。由沙黄土、砒砂岩流域 ,经黄土流域、黄土 基岩流域 ,到基岩山地 黄土流域和基岩山地流域 ,曲线的斜率渐趋减小 ,曲线的位置由上而下呈有序的排列。流域产沙量与年降雨量之间关系遵循 L angbein— Schumm曲线 ,但是由沙黄土、披砂岩流域向基岩山地流域过渡 ,流域产沙量峰值趋于减小 ,而峰值出现所需要的降雨量渐趋增大。流域产沙量随降雨变化的特征是流域降雨、地面物质、植被和地貌发育程度等因素共同作用的结果。 相似文献