bluuebunny/crossref_metadata_2025_split huggingface dataset:
Importance of environment on the order of mineral weathering in olivine basalts, Hawaii
Authors: Wasklewicz Thad A. 
Published: February 2007

AbstractExamination of weathering rinds from lava flows on Hawaii with backscatter electron microscopy and electron micro‐probe analysis reveals that olivine weathers more slowly than adjacent clinopyroxene and plagioclase in environments with a paucity of organic acids. Yet when weathering rinds are in contact with abundant organic acids secreted by lichens, olivine weathers before clinopyroxene and plagioclase weathers last. The exception to Goldich's widely accepted mineral stability series in organic‐poor environments runs counter to a thermodynamics explanation for the order of mineral weathering and illustrates the importance of the biogeochemical environment.
Effects of atmospheric conditions on wind profiles and aeolian sand transport with an example from white sands national monument
Authors: Frank Andrew , Kocurek Gary 
Published: February 2007

AbstractQuantifying aeolian sand transport rates relies upon the computation of the near‐surface shear velocity (u*) determined from velocity profiles of the wind. While it has been recognized that various conditions, such as saltation, surface roughness, surface slope and atmospheric conditions, have an effect on the velocity profile, it is commonly assumed that measurements made above the surface will be representative of the near‐surface shear velocity. Airflow and temperature data collected over a flat substrate at White Sands National Monument in New Mexico, however, show the significant effects that atmospheric conditions have on velocity profiles. During the day, when solar insolation is heating the surface, atmospheric conditions in the lowest several metres become unstable, resulting in enhanced convection and vertical mixing so that the velocity gradient changes little with height. As a result, the shear stress in this region of vertical mixing lessens, while the near‐surface shear stress is increased because the higher wind speeds are now nearer the surface. At night, the near‐surface atmospheric conditions are stable, thereby reducing convection and vertical mixing, resulting in stratified airflow and increased shear velocity away from the surface. Unless this atmospheric effect is accounted for, estimates of sediment transport rates may be in error by as much as a factor of 15 times when wind speeds are near threshold velocity. At wind speeds approaching 10 ms1, at 5m above the surface, this error in computing sediment transport is reduced to a factor of only two to three times, and may be within the range of measurement error.
Response of tide‐dominated mangrove shorelines in Northern Australia to anticipated sea‐level rise
Authors: Woodroffe C. D. 
Published: February 2007

AbstractThe exact response of mangrove shorelines to anticipated sea‐level rise will depend upon the balance between sedimentation and sea‐level change. Within the Top End of the Northern Territory of Australia there are extensive, relatively unmodified, tide‐dominated mangrove forests, where tidal processes redistribute sediment. Harbours, such as Darwin Harbour, and tidal rivers, such as the South Alligator River with its associated coastal and estuarine plains, represent opposite extremes in terms of Holocene sedimentary infill, and will respond differently to sea‐level rise. In Darwin Harbour, mangrove assemblages can be recognized in geomorphologically defined habitats. Similar topography within and between creeks implies morphodynamic equilibrium with tidal processes. Tidal reworking of sediment may maintain an equilibrial profile under gradually rising sea level, with resuspension of lower intertidal and subtidal muds and their redeposition within upper intertidal mangrove habitats. In contrast, the plains along the coast and tidal rivers draining into van Diemen Gulf developed during the post‐glacial marine transgression, and since sea level stabilized, around 6000 years ago, coastal plains have prograded. These broad plains are presently not extensively influenced by salt water, but are often at elevations close to, or even below, modern high‐tide levels. They may, therefore, revert to saline conditions particularly rapidly if the sea rises. The pattern of change may not be directly analogous to marine incursion experienced in the early Holocene, because broad plains have been able to prograde during the last 6000 years of relatively stable sea level.
Rapid entrenchment of stream profiles in the salt caves of Mount Sedom, Israel
Authors: Frumkin Amos , Ford Derek C. 
Published: February 2007

AbstractRock salt is approximately 1000 times more soluble than limestone and thus displays high rates of geomorphic evolution. Cave stream channel profiles and downcutting rates were studied in the Mount Sedom salt diapir, Dead Sea rift valley, Israel. Although the area is very arid (mean annual rainfall ≈ 50 mm), the diapir contains extensive karst systems of Holocene age.In the standard cave profile a vertical shaft at the upstream end diverts water from a surface channel in anhydrite or clastic cap rocks into the subsurface route in the salt. Mass balance calculations in a sample cave passage yielded downcutting rates of 0–2 mm s−1 during peak flood conditions, or about eight orders of magnitude higher than reported rates in any limestone cave streams. However, in the arid climate of Mount Sedom floods have a low recurrence interval with the consequence that long‐term mean downcutting rates are lower: an average rate of 8·8 mm a−1 was measured for the period 1986–1991 in the same sample passage. Quite independently, long‐term mean rates of 6·2mm a−1 are deduced from 14C ages of driftwood found in upper levels of 12 cave passages. These are at least three orders of magnitude higher than rates established for limestone caves.Salt cave passages develop in two main stages: (1) an early stage characterized by high downcutting rates into the rock salt bed, and steep passage gradients; (2) a mature stage characterized by lower downcutting rates, with establishment of a subhorizontal stream bed armoured with alluvial detritus. In this mature stage downcutting rates are controlled by the uplift rate of the Mount Sedom diapir and changes of the level of the Dead Sea. Passages may also aggrade. These fast‐developing salt stream channels may serve as full‐scale models for slower developing systems such as limestone canyons.
Geomorphic evolution of the Southern Alps, New Zealand
Authors: Tippett J. Mark , Kamp Peter J. J. 
Published: February 2007

AbstractThe Southern Alps are the topographic expression of late Cenozoic (<8 Ma ago) uplift of the crust of the leading edge of the Pacific plate in South Island, New Zealand. New fission track data on the basement exposed in the Southern Alps quantify the age, amount, and rate of rock uplift, and in combination with geomorphic parameters permit the construction of a new model of the geomorphic evolution of the Southern Alps. The model emphasizes the development over time and space of rock uplift, mean surface elevation, exhumation of crustal section, and relief. The earliest indications of mean surface uplift are between 4 and 5 Ma ago at the Alpine Fault. Mean surface uplift, which lagged the start of rock uplift, propagated southeastward from the Alpine Fault at a rate of 30 km/Ma. By about 4 Ma ago, exhumation had exposed greywacke basement adjacent to and east of the entire 300 km long central section of the Alpine Fault. At 3 Ma ago, greenschist was exposed in the southern parts of the Southern Alps near Lake Wanaka, and since then has become exhumed along a narrow strip east of the Alpine Fault. The model infers that amphibolite grade schist has been exhumed adjacent to the Alpine Fault only in the last 0·3 Ma. The age of the start of rock uplift and the amount and rate of rock uplift, all of which vary spatially, are considered to be the dominant influences on the development of the landscape in the Southern Alps.The Southern Alps have been studied in terms of domains of different rock uplift rate. At present the rate of rock uplift varies from up to 8–10 mm/a adjacent to the Alpine Fault to 0·8–1·0 mm/a along the southeastern margin of the Southern Alps. This spectrum can be divided into two domains, one northwest of the Main Divide where the present rock uplift rates are very high (up to 8–10 mm/a) and exceed the long‐term value of 0·8–1·0 mm/a, and another to the southeast of the Main Divide where the long‐term rate is 0·8–1·0 mm/a. A domain of no uplift lies immediately to the east of the Southern Alps, and is separated from them by a 1·0–1·5 km step in the basement topography. We argue that this spatial sequence of uplift rate domains represents a temporal one.The existing models of the geomorphic development of the Southern Alps—the dynamic cuesta model of J. Adams and the numerical model of P. Koons—are compared with the new data and evolutionary model. Particular constraints unrealized by these two earlier models include the following: the earlier timing of the start of rock uplift of the Southern Alps (8 Ma ago); the spatial variation in the timing of the start of rock uplift (8 Ma ago to 3 Ma ago); the lower long‐term rock uplift rate (0·8–1·0 mm/a) of the Southern Alps for most of the late Cenozoic; the lag between the start of rock uplift and the start of mean surface uplift; and the patterns of the amounts of late Cenozoic rock uplift and erosion across the Southern Alps.
Use of magnetic and radiometric measurements to investigate erosion and sedimentation in a British upland catchment
Authors: Hutchinson Simon M. 
Published: February 2007

AbstractIn response to the potential shortcomings of single‐technique strategies in the investigation of erosion and sedimentation, a combined magnetic and radiometric (13Cs and 210Pb) approach has been undertaken in the upland, watershed‐lake system of Howden Reservoir, Derbyshire. By combining these techniques, some assessment of sediment sources and the erosion status of the catchment has been achieved. Alone, each approach would have been unable to determine unequivocally sediment provenance. Furthermore, the parallel use of these measurements has highlighted limitations and/or uncertainties in both the magnetic and 137Cs techniques. These problems reflect the particular soil characteristics and drainage conditions of this upland catchment. Despite the documented severity of peat erosion in the region, Howden Reservoir has a mixture of sediment sources and a relatively moderate rate of sedimentation. Sediment yields (total 127·7 t km−2 yr−1 including organic fraction 31·3 t km−2 yr−1) are, however, higher than in other British upland areas.
Air flow over foredunes and implications for sand transport
Authors: Arens S. M. , Van Kaam‐Peters H. M. E. , Van Boxel J. H. 
Published: February 2007

AbstractMore than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed. Wind flow over the foredunes is studied by means of the relative wind speed: the ratio between wind speed at a certain location and the reference wind speed at the same height. Relative wind speeds appear to be independent of general wind speed but dependent on wind direction. For perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness. Accelerations dominate over decelerations on the seaward slope. The pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes, but the magnitudes differ. An increase in foredune height from 6 to 10m leads to an increase in speed‐up near the top of the seaward slope from 110 to 150 per cent during onshore wind, but further increase of foredune height from 10 to 23m appears to have little effect, due to increased roughness and deflection of flow.Topography also influences the direction of the flow. Between beach and top, the flow deflects in the direction of the normal during onshore winds. During offshore winds the flow is deflected to the parallel. Near the dunefoot, deflection is always in the direction of the parallel, and increases with steeper topography. The maximum deflection near the dunefoot was 90°, over a 23 m high dune, observed during offshore winds.Patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations. Owing to speed‐up on the seaward front of the foredune, sand transport capacity of the wind increases, which results in erosion if vegetation is absent. During strong onshore wind, sand is lifted near the dunefoot and moves over the foredune in suspension. During weaker winds, vertical wind velocities do not exceed fall velocities of the sand grains, and most of the sand is deposited near the dunefoot.
Floodplain sedimentation: Quantities, patterns and processes
Authors: Asselman Nathalie E. M. , Middelkoop Hans 
Published: February 2007

AbstractThis paper presents the result of measurements of floodplain sedimentation using sediment traps. The study was carried out on two embanked floodplains along the Rivers Rhine and Meuse in The Netherlands during a 3 day flood in January 1993. Raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging. The sediment maps show clear patterns in sediment accumulation, together with the estimated interpolation errors. Average sediment accumulation ranges between 0·57 and 1·0 kg m−2. High sediment accumulation is found on the levees (4 kg m−2 or more) and on low lying areas (1·6 kg m−2); sediment accumulation decreases with distance from the main channel. The sedimentation patterns are related to floodplain topography and sediment transporting mechanisms. Sediment transport by turbulent diffusion as well as by convection can be recognized. Also, flood duration and the process of sediment settling out in ponding water in closed depressions are important. The applied method allows comparison of the results with raster‐based sedimentation models.
Adjustment and recovery of unstable alluvial channels: Identification and approaches for engineering management
Authors: Simon Andrew 
Published: February 2007

AbstractThe management of riverine environments is shown to require a knowledge and awareness of the complex interactions between fluvial and mass‐wasting processes, riparian vegetation, and channel form. Identification of the cause of instability rather than the local symptoms, and knowledge of the temporal and spatial aspects of channel adjustment are central to the application of (1) appropriate analyses to estimate future channel changes, (2) appropriate mitigation measures, and (3) the protection of river‐crossing structures and adjacent land. Conceptual models of channel evolution and bank‐slope development are particularly valuable for interpreting past and present processes, applying appropriate computational techniques to estimate future channel changes, and implementing strategies to mitigate the impacts of processes likely to dominate the channel in the future.Techniques for identification and analysis of channel instability are interdisciplinary and provide a mechanism for estimating changes in channel‐bed elevation and channel width with time. Features of channel form and associated riparian vegetation can be used as diagnostic criteria to identify channel processes, the stage of channel evolution and the magnitude and extent of instability. Changes in bed elevation with time can be represented using an exponential function; changes in channel width with time can be calculated using slope stability equations and (or) projection of a temporary angle of stability from a low‐angle surface termed the ‘slough line’ that supports re‐establishment of woody vegetation. These techniques, in combination with knowledge of the state of channel evolution, can then be used to assess the appropriateness of various mitigation measures to control on‐going channel adjustments and to protect river‐crossing structures.
Concentrated flow erosion in cultivated catchments: Influence of soil surface state
Authors: Auzet A. Véronique , Boiffin Jean , Ludwig Bruno 
Published: February 2007

AbstractConcentrated flow erosion is the dominant form of winter erosion in northern France. This study correlates the ephemeral rill and gully volumes measured in 20 cultivated catchments (4–95 ha) for three consecutive winters with the size of the potential runoff‐contributing areas. These areas were identified by characterizing soil surface state through crust development stage, importance of surface wheel tracks and roughness grade. A single and significant relationship was found between the size of runoff‐contributing areas, estimated by this criterion, and the rill and gully volumes. This identified the proportion of the catchment area occupied by fields with a degraded surface structure as the main factor controlling the variability of erosion in a context of concentrated flow erosion on cultivated land. The extension of degraded areas was shown to be controlled by dynamic interactions between weather, land occupation and soil physical properties. This criterion accounts for the uneven distribution of rainfall in space and time. Morphological factors, such as talweg length and slope, are believed to determine part of the residual variability.
Variation with respect to petrological differences in a thin band of upper carboniferous non‐marine lamellibranchs
Authors: Eagar R. M. C. 
Published: February 2007

AbstractThe development of an impersistent band of non‐marine shells immediately underlying the Gastrioceras subcrenatum marine band and referred to Carbonicola ? lenisulcata (Trueman) and C. ? aff. bellula (Bolton) is traced over much of the area of outcrop of the Lower Coal Measures in Yorkshire and Lancashire. The fauna of an underlying local leaf in the Sheffield area is referred to Carbonicola aff. protea Wright. The shells of both faunas show allometric growth with respect to their height and length.Differences in the petrology of the main non‐marine shell band in five localities have been investigated optically by Professor K. C. Dunham and Mr. T. Deans, and by chemical analysis. What appear to be regional changes in the nature and range of variation of the shells reveal a correlation with petrological change closely comparable with that found in passage upward through the lower parts of cyclic units of sedimentation in the Soft Bed — Bassy Mine succession (Eagar 1947). Changes in the variation of the faunas, when they are traced horizontally on this single horizon, are however, of considerable smaller magnitude than those of the latter. Thus a fauna of dominantly anthraconaioid elongate shells, occurring in fine‐grained richly carbonaceous shale, shows greater variation and an increasing proportion of relatively short Carbonicolae? as it is followed into shaly mudstone with larger detrital constituents and less carbonaceous matter. The relative proportions of carbonaceous matter, varying inversely with thickness of the band and amount of shells per unit thickness, suggest that sedimentation caused reduction in size in two localities. The significance of the clay‐mineral content and of pyrite, which is unusually abundant and present with framboidal texture in the band, is brieflly discussed. It is suggested that the water was brackish during the formation of the band and that possibly unusually saline or near‐marine conditions may have obtained.
Hebridean notes: Rhum and Skye
Authors: Bailey E. B. 
Published: February 2007

AbstractI. Black's dating of the Tertiary lavas of Rhum as later than the Tertiary granophyre is accepted, as also his tracing of a fault along the contact of granophyre and Torridonian. This fault is interpreted as part of the Rhum ring‐fault, and a local transition between granophyre and Torridonian arkose is discussed.II. King's discovery of dissimilar contacts on the two sides of a Tertiary basalt dyke cutting Tertiary granophyre in Skye is explained on a mobilisation hypothesis.
Diagenetic fabrics in some British Dinantian limestones
Authors: Bathurst R. G. C. 
Published: February 2007

AbstractDiagenetic fabrics (textures and structures) have been examined in thin sections of Dinantian limestones mainly from the Avon Gorge, North Wales and Yorkshire. Six processes are shown to have been responsible for the change from unconsolidated sediment to limestone. These are: (1) granular cementation and drusy growth, (2) rim cementation (secondary enlargement), (3) pressure solution, (4) grain growth sensu stricto, (5) mechanical deposition in cavities of post‐depositional age, and (6) post‐depositional formation of cavities by erosion and solution in a carbonate mud.Grain growth, a process well known to metallurgists, acts in monomineralic fabrics of low porosity in the solid state. The intergranular boundaries wander so that some grains enlarge while others shrink and disappear, so bringing about a general increase in coarseness.In all the limestones the mosaic between the mechanically deposited particles (skeletal debris, pellets, ooliths) is one of three types. These are granular cement, rim‐cemented detrital crystals, and a mosaic caused by grain growth.
The stratification of the Great Scar Limestone in the Settle district of Yorkshire
Authors: Schwarzacher W. 
Published: February 2007

AbstractThe Great Scar Limestone in the Settle district and near the Stainmore syncline has been studied in eight representative sections. The sequence of D1 age in this area is divided by pronounced master bedding planes into nine lithological cycles, which can be traced from section to section.Fossils are concentrated near the master bedding planes and indications of increased current activity are recorded. The regularity with which the master bedding planes occur suggests a climatic rather than tectonic control of the cycles.
The lower Ludlow Grits in Wales
Authors: Cummins W. A. 
Published: February 2007

AbstractDevelopments of arenaceous beds in different parts of North and Central Wales are shown to be contemporaneous and are grouped together as the Lower Ludlow Grits. Directions of transport based mainly on flute cast measurements are recorded. It is shown that the Welsh Basin was divided into two distinct troughs. In the northern, Denbigh Trough, greywackes were deposited by currents flowing from west to east. In the southern, Montgomery Trough, no greywackes are found, but calcareous siltstones were deposited by currents flowing from south to north. Turbidity current flow was along the lengths of the troughs. Contemporaneous slumping was down the sides of the troughs.
Some aspects of radiogeology
Authors: Davidson C. F. 
Published: February 2007

AbstractWithin recent years studies of the natural distribution pattern of the radioactive elements have been developed as a prerequisite to explorations for the raw materials of atomic energy. One important result of this activity is an improvement of our geochronological knowledge of the stratigraphical succession. Memorable bench‐marks are Lower Cambrian at 600 million years, Upper Carboniferous at 300 m.y., Middle Cretaceous at 100 m.y. So‐called Proterozoic rocks may locally be more than 2,000 m.y. old (Witwatersrand System) and may pre‐date several orogenies in so‐called Archaean rocks elsewhere. Some ore deposits provide factual evidence for theories of reworking: for example, ores apparently of late Mesozoic age can derive from Hercynian granites. Radiogeological studies now play an important part in prospecting for ore deposits and for coal and oil fields, and they can be of much significance in evaluating the health hazards arising from artificial radioactivity.