bluuebunny/crossref_metadata_2025_split huggingface dataset:
Groundwater movement and water chemistry associated with weathering profiles of the African surface in parts of Malawi
Authors: McFarlane M. J. 
Published: April 2008

Abstract
This paper summarizes the main results of recent geomorphological research on the hydrogeology of weathering profiles on the African erosion surface in Malawi. Deep regolithic profiles have developed by protracted and aggressive weathering and differential leaching. In the advanced stages of weathering, congruent kaolinite ‘dissolution’ causes the saprolite to collapse, forming a thick residuum of the most resistant materials, dominated by silica in the form of quartz and iron as goethite. Aluminium has been extensively leached. Such profiles pertain to a mechanism of land surface formation dominated by the activity of infiltrating water rather than direct surface runoff and it results in terrain with a generally basined configuration. Low-lying areas are occupied by dambos. These are clay-filled bottomlands which are seasonally waterlogged and are located where lithology favours leaching and saprolite collapse. The contemporary fluviatile-like configuration of the dambos is attributed to post-incision modification of the ancient land surface. As a result, their area is reduced and they become inset into it, following geological controls which express integrated groundwater movement within the saprolite. The infill is shown to be essentially an alumino-silicate evaporite rather than of alluvial origin.
Analysis of dambo and dambo-peripheral profiles supports this genetic model, identifying the continuity of the contemporary dambo infill with a ‘palaeodambo’ clay wedge below the surficial sands in peripheral situations. The very low permeability of the clay is held to be responsible for the marginal seepage zone, fed by shallow throughflow from topographically higher profiles and augmented by upward discharge of deep water.
Elements lost from the interfluves were identified in evaporites which occur on the dambo floors in the dry season. These include aluminium. Analysis of water discharging into the dambos failed to identify this element. There is a need for reassessment of technique to determines element mobilization in tropical groundwater, where organic binding is implicated.
The hydrogeology of crystalline aquifers in northern Nigeria and geophysical techniques used in their exploration
Authors: Hazell J. R. T. , Cratchley C. R. , Jones C. R. C. 
Published: April 2008

Abstract
The large number of rural water supply boreholes sited and drilled in northern Nigeria during the ground water decade of the eighties has provided much data on the hydrogeology of the Basement regolith and has led to the development of new techniques in locating aquifers. Regolith aquifer characteristics and their dependence on geology and environment are reviewed with particular emphasis on lithology, weathering pattern and fracturing in Bauchi, Kano and Sokoto States. Specific capacity is shown to be related to both lithology and grade of weathering; dry season water levels and frequency of occurrence of successful holes are related to lithology. Water quality data for Kano State show some high nitrate concentrations.
The process of borehole siting begins with desk study (records and photointerpretation), then field reconnaissance of lithology, structure, water points, topography and soils. EM traverses and resistivity soundings follow in targeted areas. Maximum regolith thicknesses are estimated from the vertical to horizontal coil (EM) response using computed model graphs for 40 m and 20 m coil spacings. VES measurements at these sites give regolith resistivities, hence some estimate of its suitability as an aquifer. In addition EM traverses have located steeply-dipping fracture zones, dykes and pegmatites and interpretation of these in terms of strike and dip has been aided by results from a computer-controlled modelling system.
Borehole siting in an African accelerated drought relief project
Authors: Barker R. D. , White C. C. , Houston J. F. T. 
Published: April 2008

Abstract
In response to recent droughts in central Africa, an accelerated well drilling programme was commissioned in Victoria Province, Zimbabwe. Geophysical techniques involved in the siting of 370 boreholes included electromagnetic profiling and resistivity sounding, the latter using the offset sounding system. An analysis of the field data showed that although observed errors were low, a significant proportion of the soundings were affected by strong lateral changes in resistivity, this probably indicating the presence of a very irregular bedrock surface. Nevertheless, mean regolith thickness and lithology were reliably estimated.
Geomorphological features which were found to have the greatest potential for water supply boreholes include valleys and zones of weathering around bornhardts. In these situations geophysical surveys proved useful in locating areas of thickest regolith. Borehole yield could then be estimated from the measured formation resistivity although a precise relationship was somewhat masked by the clay mineralogy of the regolith and the type of bedrock which must be taken into account when siting boreholes.
Rural water supplies: comparative case histories from Nigeria and Zimbabwe
Authors: Houston John 
Published: April 2008

Abstract
Two rural water supply projects based on groundwater sources are described and compared. One in Nigeria aimed to provide yields of greater than 1 l/s using electric submersible pumps to villages and towns with populations from 2000 to 30 000; the other in Zimbabwe aimed to supply yields greater than 0.2 l/s using hand pumps to small communities and villages from 100 to 2200 people. The higher yields in Nigeria are examined in relation to geology and aquifer characteristics, aquifer recharge, siting methods and borehole design. It is found that the higher yields are partly due to the criterion used to define a ‘successful’ borehole and partly due to other factors. Geology and aquifer characteristics appear to be similar in both places but recharge is much higher in Kwara State, leading to higher water levels and higher potential yields. A greater use of geophysics in Kwara State leads to a higher success rate and greater drilled depths into the bedrock in Kwara State also contribute to higher yields.
Detection and prediction of Lower Cretaceous sandstone distribution in the Scapa Field, North Sea
Authors: Harker Stuart D. , Chermak Andrew 
Published: April 2008

Abstract
The Scapa Field is a combination structural/stratigraphic trap located in UK North Sea Block 14/19, 112 miles northeast of Aberdeen. The productive intervals consist of turbidite sandstones in the lower part of the early Cretaceous Valhall Formation. Three discrete sandstone bodies have been identified during the development of the Scapa Field, ranging in age from early Valanginian to late Hauterivian. The sandstones are interbedded with marls, limestones and conglomerates that filled the early Cretaceous northwest-southeast trending syncline between the Halibut Shelf and Claymore tilt block, on the southwest flank of the Witch Ground Graben. The combination of lithofacies, wireline log correlation, palaeontological, reservoir production and pressure studies led to the recognition of a five-fold subdivision (‘SA’ to ‘SF’) of the Scapa Sandstone Member. Detailed seismic studies, in particular amplitude extraction mapping using the 3D data set, have enhanced the interpretation of the distribution of the sandstone bodies. Tight conglomerate facies dominate the Lower Valhall sequence to the south in a narrow fringe bordering the Halibut Shelf. Reservoir sandstones interfinger with these conglomerates and thin to the north, changing facies to sandy marls onto the Claymore tilt block. Within the main Scapa syncline, sandstone distribution was controlled by clastic input associated with subtle structural control. The gravity-driven turbidite system concentrated deposition in the bathymetric lows. Lime muds were deposited in a constant hemipelagic rain, both over the intervening highs and interbedded with the sands.
Quantitative analysis of pore structure and its effect on reservoir behaviour: Upper Jurassic Ribble Member sandstones, Fulmar Field, UK North Sea
Authors: Clelland W. D. , Kantorowicz J. D. , Fens T. W. 
Published: April 2008

Abstract

Image analysis has been used to quantify the pore structure of dolomite-cemented sandstones in the Ribble Member of the Fulmar Field, UK North Sea. This technique was used because the data obtained from conventional petrography did not enable quantification of the controls on permeability. Three-quarters of the sandstones in the Ribble Member have high measured porosity and permeability (ø17–29%,
K
h
40–1800mD). In these poorly cemented sand-stones, intergranular porosity predominates and permeability reflects (depositional) sediment texture. One quarter of the sandstones contain > 20% dolomite. The dolomite (mean δ
13
C PDB +0.8‰, mean δ
18
O PDB −2.3‰) formed from sea water trapped and buried within the sediments and occurs as patches or nodules that should not form reservoir scale barriers to fluid flow. These cemented sandstones are less permeable (ø15–25%,
K
h
0.4–600mD). They contain grain-dissolution pores created by the dissolution of sponge spicules and intercrystalline pores between the dolomite rhombs.

Backscattered electron imaging and automated image analysis have enabled quantification of the differences in pore structure between the poorly cemented and cemented sandstones. Permeability is not only related to the amount of porosity present, but also to the amount of dolomite cementation. The degree of cementation influences average pore area and pore connectivity, which in turn controls permeability. Permeability is lower in the cemented sandstones because the dolomite rhombs have occluded the intergranular pores, creating restricted flow paths through small intercrystalline pores. As a result of these differences in pore structure, hydrocarbon production from the cemented sandstones will be slower than from the poorly cemented sandstones.
The permeability of the cemented sandstones cannot be predicted from porosity logs alone but also requires knowledge of the amount of dolomite cement present. In uncored wells this information should be obtainable using modern wireline log evaluation techniques. This study demonstrates the importance of combining a detailed understanding of the rock’s pore structure with a sound geological model in order to predict reservoir behaviour.
Sedimentological and reservoir characteristics of a fluvial-dominated delta-front sequence: Ferron Sandstone Member (Turonian), East-central Utah, USA
Authors: Lowry Philip , Jacobsen Torgrim 
Published: April 2008

Abstract
Exposures of the Ferron Sandstone Member (Turonian) of the Mancos Shale Formation in east-central Utah offer an opportunity to examine the dimensions of delta-front reservoir elements and their associated heterogeneities. Field mapping within the Ferron Sandstone has demonstrated that distributary mouth-bar facies have maximum lengths of 8–9 km and maximum widths of 4–6 km. Distributary channel width-to-thickness ratios commonly have values between 10:1 and 20:1. Distal bar sandstone thicknesses and shale lengths are dependent upon their location within the mouth-bar. Distal bar shales are shortest within the proximal region of the mouth-bar, where amalgamation of distal bar sandstones is greatest.
850 field minipermeameter measurements were obtained from the various facies elements of a distributary mouth-bar sandbody. The data display significant correlation between facies elements and permeability structure. Trough cross-bedded upper mouth-bar facies exhibit the highest means and lowest coefficient of variation. Muddy and bioturbated distal bar facies exhibit the lowest means and highest coefficient of variation. The permeability distributions appear to be related to the degree of heterogeneity, and show increasing left-skewness with increasing heterogeneity.
Fluid flow simulations of two geological models of a distributary mouth-bar were conducted to assess the effect of permeability contrasts on predicted reservoir behaviour. One of the models depicts a lithologically homogeneous mouth-bar, while the other depicts a mouth-bar that is composed of two internal facies elements (lower and upper mouth-bar). Results of the simulations show that up to 30–45% difference in predicted water breakthrough can occur between the two models.
The late Cenozoic
Globorotalia truncatulinoides
datum-plane in the Atlantic, Pacific and Indian oceans
Authors: Jenkins D. Graham , Gamson Paul 
Published: April 2008

Abstract

Since 1967 it has been thought that the planktonic foraminiferal taxon
Globorotalia truncatulinoides
(d’Orbigny) evolved in the oceans at about 1.9 Ma, with an anomalous date of 2.5 Ma for its first appearance in the Southwest Pacific. A new model is presented which demonstrates that
G. truncatulinoides
evolved in the Southwest Pacific at 2.5 Ma and later spread, while still evolving, into the South Atlantic via Drake Passage and then into the North Atlantic arriving there at 1.9 Ma; it also migrated and arrived in the Central and North Pacific at this time. The diachronous nature of the first appearances of both
G. truncatulinoides
, and
Globorotalia inflata
(d’Orbigny) which also evolved in the Southwest Pacific and later spread to other oceans, has implications for first appearances of species in the Cenozoic that have been labelled ‘datum-planes’.
Geochemical correlation of marl bands in Turonian chalks of the Anglo-Paris Basin
Authors: Wray David S. , Gale A. S. 
Published: April 2008

Abstract
Geochemical analysis of a series of laterally correlative Middle and Upper Turonian marls collected from exposures in Kent, Sussex and on the French coast reveal that it is possible to chemically fingerprint individual marls. The fingerprint is derived from four elements (scandium, titanium, vanadium and yttrium) which are believed to be located within detrital clay minerals. The true potential of this method is demonstrated by applying it to a series of Turonian marls within and below the condensed succession overlying the London Platform and western edge of the Wessex Basin (the Chalk Rock and Spurious Chalk Rock). Previously, correlation of these marls with those in the main part of the Basin was difficult and tentative. Using the geochemical fingerprinting method it is possible to make accurate marl band correlations which demonstrate that, on the London Platform, much of the Middle and Upper Turonian is condensed into a series of closely spaced hardgrounds.
Gain function analysis of sand transport in a turbulent air flow
Authors: Hardisty Jack , Rouse Helen L. , Hart Samantha 
Published: April 2008

Abstract
Recent work on the modelling of sand transport processes in the wind is concentrating on the effects of turbulence and, in particular, on flow accelerations and particle inertia. An approach is developed here in which the problem is cast in the frequency domain using the particle momentum equation which balances grain inertia against resultant steady and acceleration related fluid forces. A transport gain function is defined which relates the normalized transport spectrum to the normalized, turbulent flow spectrum. Experiments are reported in which the gain function was determined using a hot wire anemometer and a new pin impact probe to make high-frequency measurements of the velocity and sand transport profiles within the saltation layer in a small laboratory wind tunnel. The results were subjected to frequency analysis and the corresponding wind and transport spectra were obtained. Preliminary calculations suggest that the transport gain function is reasonably flat over the range up to 0.4 Hz and, therefore, models based upon gain function analysis may more properly account for sand transport within a turbulent boundary layer.
Desert dune dynamics and the evaluation of shear velocity: an integrated approach
Authors: Wiggs Giles F. S. 
Published: April 2008

Abstract
Few empirical measurements have been undertaken of shear velocity, sand transport or dune morphology in the upwind basal regions of dunes. This study compares field measurements in this region from a barchan dune in Oman with calculations from a complex flow model using linearised equations (FLOWSTAR) and measurements in a wind tunnel.
The calculations of shear velocity from wind velocity observations in the field and those predicted by the FLOWSTAR model reflect the observations of previous studies in exhibiting the widely reported upwind reduction in shear velocity. Despite these observations, measurements of sand transport did not reduce at the base of the dune. The implications of these findings for the predictive power of typical saltation flux equations and the dynamics of the dune itself are discussed.
Wind tunnel modelling using a pulse wire probe suggests that the conventional methods of shear velocity derivation are inadequate. The pulse wire measurements exhibited no reduction in shear at the toe. An argument is presented to explain the maintenance of shear velocity in this position. It is suggested that the reduction in shear stress due to the fall in wind velocity is counteracted by an increase in shear stress due to streamline curvature. The adequacy of field methods for determining shear velocity in this respect is considered.
Aeolian processes and deposits in northwest Ireland
Authors: Carter R. W. G. , Wilson Peter 
Published: April 2008

Abstract

The exposed Atlantic coast of northwest Ireland supports numerous dunefields derived largely from glacigenic deposits in the area of the present continental shelf. The present-day dunes began to form about 5000 to 6000 years
bp
at, or just after, the mid-Holocene sea-level peak which reached a maximum of + 3 m OD on parts of the County Antrim coast. As the sea-level fell so sediment was transferred onshore accumulating as beach ridges and dunes. Some dunes are perched on gravel ridges of marine origin that were exposed long enough to aeolian processes to allow the formation of ventifacts. Since about 4000 years
bp
the primary sediment budget has become strongly negative, allowing morphological reworking of many dune systems. The processes of erosion may well have been triggered by climatic changes or human impacts or a mixture of both. Periods of dune instability are marked by the widespread engulfment of former soil surfaces by large-scale mobile bedforms, the transport of sand inland and the formation of extensive sand sheets. At Maghera, County Donegal and Downhill, County Londonderry there are ramp dunes against former sea cliffs, and between Portstewart, County Londonderry and Portrush, County Antrim extensive cliff top dunes formed in the late Holocene which are now isolated from their original sediment source. Non-coastal aeolian sands are of limited extent in northwest Ireland, but some local examples are described.
Use of cement types in the palaeoenvironmental interpretation of coastal aeolianite sequences
Authors: McLaren Susan J. 
Published: April 2008

Abstract

The interpretation of palaeodune sequences is an important component in palaeoenvironmental analyses. Studies of the diagenetic alteration of palaeodunes is one of the main ways of determining post-depositional environmental conditions. This paper questions the long-held and generally accepted ideas that cement types/fabrics are a ‘major method of recognising the original mineralogy of the cements and by inference their origin under marine, vadose or phreatic conditions’ (Arthur
et al.
1982). A detailed study of last interglacial aeolianites from Mallorca, Tunisia and the Bahamas has shown that although many cement types may be characteristic of the meteoric vadose zone, none are unique. No single cement type is diagnostic of the vadose zone.
Occurrence and palaeoenvironmental implications of the Late Pleistocene loess along the eastern coasts of the Bohai Sea, China
Authors: Li Pei-Ying , Zhou Li-Ping 
Published: April 2008

AbstractLoess is found to blanket various landforms of different altitudes in the eastern coastal areas of the Bohai Sea, from Liaodong Peninsula to the Miaodao Islands and Jiaodong Peninsula in eastern China. Two major lithological units have been recognized: the Penglai Loess and the Dalian Loess. Recent studies reveal a weathered unit within the Dalian Loess and confirm the occurrence of Holocene loess. Random distribution of marine microfossils and concomitant occurrence of contrasting species in the loess rule out the possibility of the coastal loess being a marine sediment. The coastal loess is coarser and contains a higher content of unstable minerals compared to the inland equivalents. Regional variations in texture and heavy mineral assemblage within the coastal loess zone are also observed, suggesting that the primary source of the coastal loess is not northwestern China but is more likely to be from the coastal areas and the adjacent Bohai Sea basin. When the coastline was displaced a few hundred kilometres eastwards during the last glacial period, vast areas of the continental shelf of the Bohai Sea were exposed. Coastal dunefields may have been expanded and perhaps developed locally into a desert shelf environment. With intensified aeolian process, fine particles in the ancient fluvial and marine sediments were transported by small-scale low-level northwesterly and northerly winds and deposited along the eastern coasts of the Bohai Sea. The basal age of the Late Pleistocene Dalian Loess was previously estimated to be 11–25 ka, but preliminary thermoluminescence dating results suggest that it started to accumulate at least 30 ka earlier.
Palaeosols and sandbody prediction in alluvial sequences
Authors: Kraus Mary J. , Bown Thomas M. 
Published: April 2008

Abstract
Diverse palaeosols in the Eocene Willwood Formation illustrate how overbank deposits can help predict the location of fluvial sandbodies. Palaeosols of differing maturity formed in response to local fluvial processes and tectonically controlled sediment accumulation rates. The various palaeosols can be distinguished using criteria including colour, pedogenic nodules, and grain size trends, all of which should be observable in core.
Palaeosol maturity increases laterally with increasing distance from a coeval channel sandbody. Consequently, a specific type of Willwood palaeosol provides an estimate of the relative distance to a channel sandbody at a specific stratigraphic level. Vertical sequences of overbank deposits also show changes in palaeosol type as a result of channel avulsion. The vertical changes can thus help predict the position of channel sandbodies within a fluvial package. On a basin-wide scale, the rate of subsidence influenced both palaeosol maturity and the location of channel sandbodies. Areas of the basin that subsided rapidly (thus sediment accumulated rapidly) are commonly rich in channel sandbodies and also contain relatively immature palaeosols. In contrast, areas that subsided more slowly and in which channel sandbodies are not concentrated are characterized by relatively mature palaeosols.