Influence Of Bedrock Research Articles

Factors Controlling the Spatial Variability of Mercury Distribution in Spanish Topsoil

This study characterized the sources and scales of mercury variability in agricultural soils of the river Ebro (9.5 million ha) using geostatistical methods and data from 624 samples. The Ebro basin (20% of Spanish land mass) is an important agricultural area that is industrialized. Spatial analysis was done on a local scale (20 km) and indicated that high Hg concentrations were related to mining and specific agronomic practices, such as sewage effluents from irrigation. The intermediate scale (100 km) was associated with mercury from atmospheric deposition (mining, smelting, and industrial activities). The regional scale (220 km) corresponded to mineralogical structure and bedrock influence. The analysis demostrates that while geographical and geochemical processes and anthropogenic influences, such as industrialization and agricultural practices, can influence the content and distribution of mercury in the valley, the calcareous nature of the soils (alkaline pH and low organic matter) minimize the effect of the mercury load.

Resistivity measurements as a tool for outlining quick-clay extent and valley-fill stratigraphy: a feasibility study from Buvika, central Norway

Thick, marine clay deposits in valleys along the Norwegian coast are occasionally subjected to large landslides involving quick clay. Detailed mapping of the extent of quick clay is of great interest for planning and protection purposes, as the position of quick clay within slopes has a major impact on the landslide risk. Ground conditions in the small valley of Buvika, mid-Norway, are characterized by thick occurrences of quick clay, which are documented in numerous geotechnical investigations. The resistivity method is potentially well suited for outlining pockets of quick clay since quick clay has a slightly higher electric resistivity (10–80 Ωm) than intact unleached clay (1–10 Ωm). This is due to a higher salt content in the latter. These relations are supported in this study by pore-water salt content measurements. The acquired resistivity profiles are compared with other geophysical data and geotechnical drilling information. Results are promising, and acquired resistivity profiles are interpreted in terms of quick-clay extents, stratigraphy, bedrock influence, and groundwater drainage patterns. Mismatch between intersecting resistivity profiles may be an indication of local geological variations.

Trace elements contamination of agricultural soils affected by sulphide exploitation (Iberian Pyrite Belt, Sw Spain)

Agricultural soils of the Riotinto mining area (Iberian Pyrite Belt) have been studied to assess the degree of pollution by trace elements as a consequence of the extraction and treatment of sulphides. Fifteen soil samples were collected and analysed by ICP-OES and INAA for 51 elements. Chemical analyses showed an As–Cu–Pb–Zn association related with the mineralisation of the Iberian Pyrite Belt. Concentrations were 19–994 mg kg−1 for As, 41–4,890 mg kg−1 for Pb, 95–897 mg kg−1 for Zn and of 27–1,160 mg kg−1 for Cu. Most of the samples displayed concentrations of these elements higher than the 90th percentile of the corresponding geological dominium, which suggests an anthropogenic input besides the bedrock influence. Samples collected from sediments were more contaminated than leptosols because they were polluted by leachates or by mining spills coming from the waste rock piles. The weathering of the bedrock is responsible for high concentrations in Co, Cr and Ni, but an anthropogenic input, such as wind-blown dust, seems to be indicative of the high content of As, Cu, Pb and Zn in leptosols. The metal partitioning patterns show that most trace elements are associated with Fe amorphous oxy-hydroxides, or take part of the residual fraction. According to the results obtained, the following mobility sequence is proposed for major and minor elements: Mn, Pb, Cd, > Zn, Cu > Ni > As > Fe > Cr. The high mobility of Pb, Cu and Zn involve an environmental risk in this area, even in soils where the concentrations are not so high.

Influence of Bedrock and Aspect on Soils and Plant Distribution in the Holyoke Range, Massachusetts

and 24 pairs on the north side of the range. For each plot we measured slope, plot aspect, soil pH and soil nutrients, the importance value for trees, within-plot frequency for shrubs and recorded presence/absence for herbaceous taxa. Soil on basalt had a higher pH and was richer in nutrients, particularly exchangeable Ca and Mg than soil on arkose. Principal Components Analysis of plots using soil variables indicated that those associated with bedrock accounted for 51% of the variance while soil differences related to aspect accounted for 22%. The multi-response permutation procedure indicated significant differences in distribution in all vegetation layers with respect to both bedrock and aspect. Species richness on basalt was significantly higher for both trees and herbaceous plants, and was also higher on the south side of the range for herbaceous plants. Of the 89 species present in more than 5% of the plots, 32% had significantly different distributions with respect to bedrock alone, 21% differed significantly with respect to both bedrock type and aspect while only 9% differed significantly with aspect independent of bedrock. The largest differences were in the herbaceous layer. Canonical correspondence analysis using soil and site variables indicated that for all vegetation layers the strongest gradient was related to bedrock.

Morphological Classification of Fluvial Environments: An Investigation of the Continuum of Channel Types

Bedrock‐controlled channel systems exhibit considerable morphological variation. Both bedrock‐influenced and alluvial morphological units coexist to form a system of changing channel patterns in response to changes in the relative influence of the controlling process variables. This article investigates the morphological composition of the bedrock‐influenced Sabie River, Mpumalanga Province, South Africa, mapping 25 km of river channel at the scale of individual morphological units. Cluster and discriminant analyses define objective reach–scale “channel type” assemblages based on morphological unit composition. A number of robust clusters emerged that could be broadly classified into five channel types, namely, bedrock anastomosed, mixed anastomosed, pool‐rapid, braided, and alluvial single‐thread. The cluster analysis revealed that these channel types fit on a continuum from bedrock‐dominated channels to fully alluvial systems. Each channel type could also be characterized by a certain set of “dominant” morphological units, which changed from bedrock‐influenced at one end of the continuum (bedrock anastomosed, pool‐rapid) to alluvial deposits at the other (braided, alluvial single‐thread). An investigation of the role of controlling process variables in defining these channel types revealed a broad link between the degree of bedrock influence and the amount of available energy within the system as defined by indices such as the flow regime and water‐surface slope variation. It is clear that the bedrock‐dominated channel types are characterized by energy levels in excess of those accepted for alluvial systems, and an extended river classification is presented for the Sabie River that includes these bedrock channels. The mixed anastomosing channel type on the Sabie River is characterized by higher available energy levels than braided or alluvial single‐thread reaches. As such, it appears to be a higher‐energy example of an anabranched system, probably formed as a result of sediment accumulation on top of a high‐energy bedrock anastomosed channel template.

The contemporary geomorphology of the Sabie River in the Kruger National Park

The Sabie River in the Kruger National Park has been described as the most pristine in South Africa. It has remained largely free of direct alteration along its 110 km length within the reserve and as such displays a high geomorphic diversity. This physical vari- ability supports a great diversity of flora and fauna including a number of species endemic to the river. The diversity in fluvial form is the result of a high degree of bedrock influence coupled with a rapidly changing energy regime. Steeper bedrockinfluenced areas alternate with more gently sloping alluvial segments to create a series of channel types ranging from bedrock anastomosing through to alluvial single thread and braided sections. Each channel type is part of a continuum that relates to the degree of alluviation of the river on the bedrock template. Descriptions of the characteristic channel types associated with the Sabie River, together with associated morphologic units are given together with the areal extent of the changing morphology in the Kruger National Park. Each morphologic unit is characterised by size, shape, sedimentology and flow influence. Recent research into the degree and direction of morphologic change in the Sabie River is also summarised in the light of possible catchment management.

Riparian vegetation‐environment relationships: complimentarity of gradients versus patch hierarchy approaches

Abstract. Two prominent conceptual frameworks, environmental gradients and patch hierarchies, are used in combination to describe vegetation patterns along a riparian corridor in a semi‐arid South African system. We adopt both approaches, since riparian corridors are characterized by both strong environmental gradients above, away from and along the river, as well as a mosaic of patches in the geomorphology at multiple hierarchical scales. Constrained and unconstrained ordinations were used to determine the variability in vegetation pattern accounted for by the gradient and the geomorphic patch hierarchy data sets. The gradient data set consisted of vertical, lateral and longitudinal dimensions of the macro‐channel, while the patch hierarchy data set consisted of substratum type, morphological unit and channel type. Elevation up the macro‐channel bank, of the gradient data set, explained the main variation in vegetation pattern, and alluded to overriding processes of flooding frequency and water availability as determinants of vegetation pattern. Along the fluvially dynamic macro‐channel floor (lower elevation range), patchiness at the scale of the morphological unit best explained vegetation pattern. This relationship with morphological units suggests that the formation of well developed alluvial bars, and the degree of bedrock influence are important processes. The nested hierarchical framework used provided a good basis for identifying scale specific pattern in a relational manner. In systems characterized by strong environmental gradients as well as a patch mosaic at different spatial and temporal scales, the combined use of both perspectives to develop a fuller understanding of vegetation pattern is imperative and is encouraged.

Cover-beds as soil parent materials in midlatitude regions

In parts of southern France, the Russian Plain, south central Turkey, the western USA and in Germany, slopes are covered by deposits (cover-beds) formed by geomorphic processes not limited to linear discharges. Often, loess material is mixed into them. Cover-beds usually form sequences of two or more distinct layers, and their distribution depends on the geomorphic, climate-driven processes of their formation. As they influence pedogenesis, they contribute to the understanding of soil properties and soil distribution. Horizon boundaries occur at depths where cover-bed properties change. Where aeolian matter is mixed in, podzolisation is buffered but depletion of clay may occur; loess-rich cover-beds may entirely decouple pedogenesis from bedrock influence. In humid areas, soil-water stagnation is often associated with varying cover-bed bulk densities, particularly upon flat relief. In semiarid areas, deep soil profiles consist of multiple layer sequences often with argillic and calcic properties within the same horizons. They reflect several cycles of cover-bed deposition and incorporation of loess, alternating with decalcification accompanied and followed by clay translocation. This led to the overprinting of buried soils by pedogenic carbonate leached from younger sediments. Synchronous sediment and/or airborne carbonate accretion and pedogenesis, which is usually invoked to explain soil profiles with several calcic horizons, cannot apply to cover-beds.

Periglacial slope deposits and their pedogenic implications in Germany

Disconformities within soil-parent materials are frequently reported from locations throughout the world, but they are rarely within the goals of systematic research. This article provides an overview of the current state of knowledge on such materials and their pedogenic relevance in Germany. It intends to encourage further discussion on stratified soils in other parts of the world. The slope deposits in Germany are divided into (1) the upper layer that is ubiquitously distributed and displays a relatively constant thickness; (2) the intermediate layer that is restricted to flat relief, to hollows, and to lee-ward facing slopes; and (3) the basal layer that is rather widespread again. Both the upper and intermediate layer contain intermixed loess, while the basal layer is free of loess. These layers were mainly formed by periglacial solifluction. Such deposits are referred to as cover-beds. The upper layer formed during the Younger Dryas within a relatively short episode. In contrast, the lower layers may be diachronous; nevertheless, they display recurring vertical sequences. This is probably due to the fact that loess-free layers usually could not deposit as long as there was loess in the environs. Thus, the last phase of surface wash, during which older loess was removed, determines the age of the lower layers. The composition of the layers differs, reflecting the varying portions of loess and of rock allocated from upslope. In twofold sequences, the cover-beds influence the formation of the soils as they provide weathered material, and as their boundaries, where properties such as texture and bulk density abruptly change, determine the soil-horizon boundaries. Some pedogenic processes are favored (oxidation, depletion of clay), or hindered (podzolization) due to the loess content of the upper layer. Even exceeding this, the dominant loess content of an intercalated intermediate layer in threefold sequences may completely decouple pedogenesis from bedrock influence. In all, soil formation is largely influenced by the constellation of cover-beds at any given site.

Aspects of climatic influence on the clay mineralogy and geochemistry of soils, palaeosols and clastic sedimentary rocks

Climate strongly influences soil clay mineralogy and bulk chemical composition. In humid climates chemical weathering is at its most intense and virtually all ‘primary’ bedrock minerals suffer complete breakdown. They are replaced by authigenic hydrated oxides of Fe and Al together with halloysite and kaolinite in deep profiles. These minerals develop where the residence time of water in the soil is slight. Longer residence times lead to higher solute concentrations and the stabilization of smectite. Authigenic palygorskite and sepiolite may form in highly saline, alkaline soils. The stability of these precipitated minerals is problematic: they may be metastable or even unstable. All other clays found in soils are unstable, being incomplete, solid-state hydrolysis products of substrate minerals. The balance between stable, metastable and unstable minerals and the rate of profile development are both much influenced by temperature, rainfall and activities of soil biota; themselves reflecting climate. Bedrock influence is greatest under conditions of low to moderate precipitation where unstable minerals persist. Local topography, however, also strongly influences both the rate and products of chemical weathering, quite independently of climate. On the grand scale, tectonic factors may constrain the time available for profiles to develop, hence the extent to which bedrock minerals survive or are altered. Mountain soils reflect local climate and bedrock composition much more than latitude. The sediments delivered to major basins today do not reflect global soil distribution patterns. The bulk composition of suspended sediment entering the Indian Ocean, for example, is rather similar to that entering the Arctic Ocean. Sediment dispersal patterns can also confuse climatic signals: a problem not encountered with palaeosols. Authigenic clays formed within sedimentary basins and post-depositional (burial) alteration of both sediments and buried soil profiles must lead to interpretational ambiguities. Climatic signals are likely to survive best in bulk compositional data (although diagenetic reactions at depths in excess of about 2 km do not appear to be isochemical) and in the distribution of more stable yet climatically sensitive minerals (kaolinite as opposed to illite, chlorite).

Bedrock Influence on the Quaternary Geology of Essex County, Southern Ontario: ABSTRACT

Bedrock Influence on the Quaternary Geology of Essex County, Southern Ontario: ABSTRACT

Lithology and trace-metal content in till in the kuhmo granite-greenstone terrain, eastern Finland

Rocks of the Archaean Kuhmo greenstone belt and the fine fraction (− 63 μm) of 236 till samples were analysed for Co, Cr, Cu, Mn, Ni, Pb, Zn and Fe mainly with the AAS method. The influence of bedrock upon the lithology and geochemistry of till is clear, and can be seen immediately at the proximal contact. Expected trace-metal contents for the fine fraction of till were calculated using the average metal contents of the rock types and the proportions of these rock types in the till (2–6 cm pebbles). The expected values were then compared with the measured values in the fine fraction of till at the same locality. This approach seems effective for lithological comparison between various grain-size fractions of till. In general, the measured metal contents are clearly lower than expected. This indicates that the proportion of the greenstone material in the fine fraction of the till is smaller than in the coarse fraction. Correlations between measured and expected values of individual trace metals as well as their correlation with the different rock types are low, in most cases indicating inconsistent variation in the lithology of the coarse and fine fraction of the till. Good positive correlations between the number of pebbles of mafic metavolcanics and contents of Cu, Co, Mn and Fe in the fine fraction of till show that the influence of these rocks on the trace-element geochemistry of the tills in the study area is most significant as might be expected.

The behaviour of rainwater on a forested hillslope(I) The properties of vertical infiltration and the influence of bedrock on it

The behaviour of rainwater on a forested hillslope(I) The properties of vertical infiltration and the influence of bedrock on it

The Influence of Local Bedrock: An Important Consideration in the Interpretation of Textural and Mineralogic Analyses of Till

ABSTRACT Bedrock produces variations in texture and composition of tills not only on a regional scale but also on a local one. Bedrock influence is evident in Wisconsinan tills in an area as small as a township in the Allegheny Plateau of northeastern Ohio. Generally till sheets of the Plateau fine upward with decreasing age. Within the Mogadore and Northampton tills, samples from borings terminating in sandstone bedrock on the upland contain significantly more sand and have higher quartz-feldspar ratios than those from the same tills overlying lacustrine silts and clays in the valley. On the upland samples from the Northampton till, overlying sandstone contains slightly more sand than that from the same till overlying shale and siltstone. However, quartz-feldspar ratios increase down ice from sandstone bedrock highs. A few kilometers of transport may have been required for ice to crush plucked sandstone fragments which added more quartz to the fine sand fraction of the Northampton till. Geologists mapping tills using soil associations should be aware of textural and lithological variations produced by local bedrock.

The influence of bedrock on heavy mineral content of streams within a glaciated area of Perthshire

Synopsis A systematic collection and comparison of heavy minerals from stream sediments, glacial deposits and bedrock in the Glen Artney–Glen Lednock area shows that, despite glaciation and the influx of foreign material, the present heavy mineral distributions in streams clearly reflect the local geology.

Past and present uplift in Sweden: Glacial isostasy, tectonism and bedrock influence

Abstract Recent studies in Sweden of the classical Fennoscandian uplift have revealed many new facts. The past and present uplift is affected by old fault lines and bedrock seams. The Pre-Svecofennian/Gothian bedrock seam across southern Sweden is a major, still active, structural—dynamic boundary. Shore-line data of the past uplift and geodetic data of the present uplift agree very well and indicate that the Fennoscandian uplift is complex and composed of two factors: (1) a glacial-isostatic factor that died out some 2000–3000 years ago, and (2) a “tectonic” factor of uncertain origin that is responsible for the present uplift.

A KINEMATIC DISCUSSION OF THE FORMATION OF GLACIAL FLUTINGS

ALTHOUGH MANY STUDIES have been made of so-called ice-moulded landforms, drumlins, drumlinoids, and flutings, their mode of genesis remains unsolved. The form of drumlins is quite distinctive; a quotation from Alden (1905) used by Chorley (1959) clearly sets down their salient features: “We may regard as a typical drumlin a hill of glacial drift which approximates the form of a segment of an elongated ovoid, of which the widest part of the basal outline and the highest point of the crest are not more distant from the stoss-end than one-third the length of the major axis and whose major axis is oriented parallel to the direction of movement of the glacier which formed it.” With extension of the length of the characteristic drumlin a gradation occurs into extensive linear features known as flutings. The longitudinal profile of flutings differs from that of drumlins in that the maximum crest elevation is maintained for large distances. However, flutings show the same parallelism with ice-flow direction and general streamlined form as drumlins. In this paper flutings refer to both the ridges and the adjacent grooves that make up the total landform. Generally this paper will be confined to larger-scale flutings as described by Smith (1948), Gravenor and Meneley (1958), Lemke (1958), and Freschauf (1971). The large-scale features range in scale from two to three metres high and several kilometres in length. Such flutings appear to be confined to North America. Smaller-scale features have been described from a variety of recently deglaciated areas (Hoppe and Schytt 1953; McPherson and Gardner 1969; Baranowski 1970), but these are not analogous with the large-scale features. Drumlins and flutings clearly differ in form, and it is pertinent to consider other properties which may provide information on their mode of origin. A wide variety of internal composition has been noted. Till is most commonly observed, but stratified drift is often found in both drumlins and flutings. The influence of bedrock may also be important; drumlins with bedrock cores have been widely described (Chamberlin 1883; Crosby 1934), and flutings in Alberta, Saskatchewan and the Northwest Territories, Canada, may also be developed in crystalline bedrock (Smith 1948). Long-axis orientation of stones in drumlins has been shown to parallel drumlin axes approximately (Hoppe 1951; Donner and West 1955; Wright, 1957). Hill (1971) shows similar results but emphasizes a significant scatter in mean directions obtained from different samples from a single drumlin. Andrews and King (1968) show increasing deviation between stone and drumlin orientations in samples taken from successively higher positions in a drumlin section. However, micro-fabric analysis on samples from glacial flutings (Gravenor and Meneley 1958) gave orientations of silt and sand particles parallel to the fluting crest to a depth of three metres. Below three metres particle long axes were found to deviate from the fluting crest. Some authors have proposed that there is a relationship between the occurrence of drumlins

Oahe Dam: Influence of Shale on Oahe Power Structures Design

Oahe dam site is a soft-rock site. The shale bedrock is badly faulted, has bentonite sliding planes, a low modulus and low compressive strength. Power structures are located in positions relative to faulting to afford minimum construction difficulty. Structures design is controlled by influence of bedrock as much as by functional requirements. Designers develop a pessimistic attitude in working with this material. Pierre shale disintegrates rapidly when exposed to air. Exposed foundation areas are protected by bituminous sealing, guniting, and concrete slab cover. Exposed tunnel rock is protected by humidity control or by pneumatically placed mortar. Foundation areas are stitched with anchorages to prevent differential rebound. Construction sequence is carefully controlled to prevent overstressing of foundation slope faces.