bluuebunny/crossref_metadata_2025 huggingface dataset:
Insights into the hydraulic performance of landfill-lining clays during deformation
Authors: Peters M. G. , Maltman A. J.
Published: April 2008

The low hydraulic conductivities of mudrocks are widely utilized in the waste disposal industry, where clays are commonly employed as a lining to landfill sites. The hydraulic conductivity of these clays is well characterized, but only under steady-state conditions. In reality, as with many situations in geology, landfills are dynamic environments and the lining materials are subject to temporal and spatial stress variations. These fluctuating stress conditions are likely to lead to deformation of the liner, which may in turn lead to changes in its hydraulic performance. To assess the behaviour of clay lining materials under operational stresses, samples of actual liner clays have been subjected to anisotropic loading in a triaxial cell while monitoring their hydraulic performance with a constant-rate-of-flow permeameter. The clays show marked changes in hydraulic conductivity during deformation, with increases and decreases being seen in different samples. However, the measured changes are probably not large enough to breach the minimum performance specification for landfill linings (current legislation calls for a maximum saturated hydraulic conductivity of 1 × 10
−9
m s
−1
). The fluctuations in hydraulic conductivity can be linked to the consolidation state and changes in the pore volume of the samples during deformation. The results and interpretations detailed here for three representative tests provide models of the hydrological behaviour of clays during deformation that may be applicable to poorly lithified mudrocks in other dynamic situations.
Gas transport properties of clays and mudrocks
Authors: Harrington J. F. , Horseman S. T.
Published: April 2008

Controlled flow rate gas injection experiments have been performed on clay and mudrock samples using helium as a permeant. By simultaneously applying a confining stress and back-pressure, specimens were isotropically consolidated and fully water saturated under predetermined effective stress conditions, before injecting gas at a very slow rate using a syringe pump. Ingoing and outgoing gas fluxes were monitored. All tests exhibit a conspicuous threshold pressure for gas breakthrough. All tests showed a post-peak negative transient leading to steady-state gas flow. On the basis of a stepped history of flow rate, the flow law was shown to be nonlinear (i.e. non-Darcian). With the injection pump stationary (i.e. zero flow rate), gas pressure declined with time to a finite value. No gas flow was ever detected at excess gas pressures less than this lower threshold. When gas flow was re-established, the threshold for gas breakthrough was found to be significantly lower than in the virgin clay. There is strong evidence to suggest that the capillarity restrictions on gas penetration of the intergranular pores of saturated clays and mudrocks are of such a magnitude that normal two-phase flow is impossible. Gas therefore does not occupy, or flow through, the intergranular porosity of the clay matrix. In the absence of pressure-induced cracks, water-saturated clays and mudrocks are totally impermeable to gas. The measured gas permeability of a clay-rich medium is a dependent variable rather than a material property, as it depends on the number of pressure-induced pathways in the plane normal to the flow, together with the width and aperture distributions of these pathways. The experiments suggest that the flow pathways open under high gas pressure conditions and partially close if gas pressure falls, thus providing a possible explanation of the nonlinearity of the flow law. Reliance on conventional two-phase flow theory is inadvisable when attempting to quantify gas transport in initially water-saturated clay-rich materials.
Origin of overpressures on the Halten Terrace, offshore mid-Norway: the potential role of mechanical compaction, pressure transfer and stress
Authors: Skar T. , Van Balen R. T. , Arnesen L. , Cloetingh S.
Published: April 2008

The Halten Terrace, a structural element on the mid-Norwegian margin, is characterized by distinct spatial variations in subsurface fluid pressure. Jurassic formations on the western part of the Halten Terrace are highly overpressured (> 30 MPa), whereas the same formations have fluid pressures close to hydrostatic in the central and eastern parts of the terrace. The cretaceous formations are moderately overpressured in the whole area. The porosities in the overpressured middle Jurassic formations and lower Cretaceous shales are only slightly influenced by the present-day overpressures, suggesting that most of the overpressure development was recent. Overpressure generation as a result of mechanical compaction, induced by the weight of the Plio-Pleistocene sediments, is not sufficient to explain the overpressure magnitudes in the Jurassic and Cretaceous formations. Results from forward modelling of mechanical compaction suggest that the deep Rås Basin adjacent to the Halten Terrace has been highly overpressured since Cretaceous time. Pressure transfer from this basin to the western part of the Halten Terrace is therefore a possible explanation for the observed overpressures. Migration of the overpressured fluids may have occurred through the Klakk Fault Complex separating the basin from the terrace, during an event related to a basinal stress reorientation in early Pliocene time.
The recognition of artefacts from acoustic and resistivity borehole imaging devices
Authors: Lofts J. C. , Bourke L. T.
Published: April 2008

Image artefacts, that is, non-geological features present on acoustic or micro-resistivity borehole image logs are a fact of life. In poor quality image logs, they can constitute the bulk of the data-set although fortunately, such features generally constitute the minority of a data-set. The recognition of artefact features must form part of the log quality control process and should also form part of the interpretation process. By applying sound log quality control principles, these artefacts can be identified systematically and the remaining image data will be geologically related. This paper provides an up-to-date summary of borehole image artefacts, their cause and recognition. It also, for the first time, considers artefacts arising from acoustic (ultrasonic) as well as micro-resistivity images. Four main artefact image categories related to data acquisition, borehole wall condition, post processing of data and measurement physics form the basis for the systematic identification procedure. These are discussed and developed herein.
A methodology for applying a non unique, morphological classification to sine wave events picked from borehole image log data
Authors: Trice Robert
Published: April 2008

Sine wave events are interactively picked as a representation of planar and pseudo-planar events within a borehole. This paper presents a logic and terminology by which sine wave features can be assigned a classification based on their morphological character. This morphological classification is non unique with respect to geological interpretation but can act as a template from which geological interpretations can be applied. The methodology presented has been written as a result of working on problematic image interpretations from a range of sedimentological, structural and petrophysical case studies. Application of the technique is considered of specific benefit to geoscientists with limited practical experience in image log analysis, to practising image log specialists when dealing with problematic data sets and as a methodology by which a base case interpretation can be derived in equity or shared data sets. An application of the technique is provided as a short case study.
Geology and reservoir description of 1Y1 reservoir, Oso Field, Nigeria using FMS and dipmeter
Authors: Thompson Laird B. , Snedden J. W.
Published: April 2008

Mobil Producing Nigeria’s Oso Field produces 120 000 barrels of oil per day from late Tertiary sands in the Niger Delta offshore. The reservoir consists of anastomozing fluvial deltaic sands which are difficult to correlate from well to well using traditional log correlation techniques. Image log data from Formation MicroScanner (FMS) logs and dipmeter data tied directly to cores permit detailed analysis of channel thickness, orientation, and distribution. This geographic understanding of the sand bodies enables geoscientists to construct a detailed ‘plumbing’ diagram of this complex reservoir, thus allowing for better exploitation.
Fault visualization from borehole images for sidetrack optimization
Authors: Grace L. M. , Newberry B. M. , Harper J. H.
Published: April 2008

Missing pay sections in faulted areas is a common occurrence. An accurate measurement of the fault plane and surrounding bed distortion can substantially reduce the risk involved in the sidetrack decision. The measurement of the fault plane includes the dip and strike as well as the sealing nature of the fault plane. Our experience indicates mineral-filled fault planes are always sealing. This has lead to several interesting sidetracks, many of which are against conventional wisdom. Case studies included show an extensional fault sidetrack to the downthrown block; a perforating determination based on the location of the actual sealing fault; an extensional fault sidetrack based on the non-sealing properties of the fault plane. In these cases the distortion of the surrounding blocks are modeled using enhanced computer techniques (Etchecopar 1992). The input of the actual fault plane dip and strike is shown to be the key to an accurate cross-sectional projection. The visualization of the fault model is critical to the resolution of the sidetrack azimuth and distance. Whether a fault plane is sealing is also an important contribution to any sidetrack analysis. This technique has accurately predicted the sidetrack location for many successful wells.
Manganiferous ironstones in the early Ordovician Manx Group, Isle of Man: a protolith of coticule?
Authors: Kennan P. S. , Morris J. H.
Published: April 2008

Spessartine-garnet quartzites (coticule) are now widely recognized as extremely useful marker horizons throughout the Appalachian-Caledonian Orogen. In many instances, they appear to be of early Ordovician age. They reflect a syn-sedimentary, volcanic exhalative origin and in many areas, e.g. the Leinster region in southeast Ireland, they are intimately associated with,
inter alia
, base metal mineralization and with tourmalinite. However, though the metamorphic coticule is common, the pre-metamorphic coticule precursor has proved difficult to recognize.

Manganiferous ironstone rocks of coticule aspect are a distinctive feature in parts of the Manx Group exposed along the west coast of the Isle of Man. Though they lack any trace of the characteristic manganese garnet, perhaps reflecting a relatively low metamorphic grade, they do bear a strong morphological resemblance in outcrop to the typical coticule lithology of the Ribband Group in southeast Ireland. In both places, tourmaline-rich rocks occur nearby. On the Isle of Man, a major tourmalinite occurrence is linked to an important shear zone.

In briefly reviewing the field occurrence, petrography and chemistry of the manganiferous ironstone beds, and by comparison with coticule elsewhere, the possibility that these ironstones are a coticule precursor or a coticule facies variant is introduced. That a lithology now termed coticule might be a significant component in the Manx Group (‘Slates’) was noted no less than 70 years ago. Any recognition of coticule rock would have an important bearing on the understanding of the stratigraphy, metamorphism and mineralization of the Manx Group.
The definition of sandstone-bearing formations in the Isle of Man and correlation with adjacent areas — evidence from sandstone chemistry
Authors: Barnes R. P. , Power G. M. , Cooper D. C.
Published: April 2008

The outcrop of Lower Palaeozoic rocks on the Isle of Man is dominated by thin- to medium-bedded sand-rich turbidites over most of the southeast side of the island (Lamplugh’s Lonan and Agneash Grits, comprising greywacke and quartz arenite, respectively, interbedded with mudstone) and on the northwest coast south of Peel (the Niarbyl Flags). Recent work has shown that the latter, the Niarbyl Formation, is Silurian in age and thus distinct from the otherwise early Ordovician sequences. The composition of the Niarbyl sandstone is also distinct, with comparatively low silica (SiO
2
60–66%) but elevated CaO, MgO and Cr, relative to the Ordovician sandstones.

The Ordovician sandstones fall into two compositional groups: a very mature, silica-rich (SiO
2
78–95%) quartz arenite (Agneash type) and a greywacke (Lonan type) with lower silica (SiO
2
65–78%). Most element contents vary with silica but there is a compositional hiatus. It is here inferred that the two sandstone groups represent material from separate source areas. The three tectonostratigraphical sequences distinguished in the southeast of the island all include sandstone of both compositional types in different proportions. These usually occur as units of one or other composition, but in one sequence the two are locally closely interbedded while remaining compositionally distinct. Sandstone in two possibly equivalent units may, however, vary gradationally between the two types, implying more intimate mixing. In the absence of biostratigraphical control, the geochemical data are used to constrain the various ways in which the tectonostratigraphical sequences might correlate.

The chemical signature of the Isle of Man sandstones also provides constraints on possible correlatives in adjacent areas. The Lonan type is very similar to mid-Arenig sandstone in the upper part of the Skiddaw Group of the English Lake District. The more siliceous Agneash type has no compositional comparative in the main Skiddaw Group outcrop, although sandstone comprising the enigmatic Redmain Formation is similar in composition. The Wenlock Niarbyl Formation is lithologically and chemically comparable with Wenlock turbidite sequences in the Southern Uplands terrane and in the Windermere Supergroup in the Lake District, and they may all be closely related. None provides a precise match but compositionally the Niarbyl sandstone closely resembles the sandstone of the same age in the Birk Riggs Formation of the Windermere Supergroup. Subject to a number of constraints, the chemical composition of sandstone can also provide information on the probable tectonic environment of the source rocks. On this basis, the Lonan and Niarbyl sandstones include substantial components of first- or second-cycle volcanic debris, whereas the Agneash type is dominated by mature debris reworked from older sedimentary rocks or derived from a granite/gneiss basement source.
The Silurian succession of the Isle of Man: the late Wenlock Niarbyl Formation, Dalby Group
Authors: Morris J. H. , Woodcock N. H. , Howe M. P. A.
Published: April 2008

Interpretation of the stratigraphy and structure of the Lower Palaeozoic Manx Group has been strongly influenced by the assumed equivalence of distinct sandstone sequences, the Niarbyl and Lonan Flags, exposed along the west and east coasts of the Isle of Man, respectively. However, new palaeontological evidence confirms an Arenig age for the Lonan Flags and indicates a mid-Silurian age for the Niarbyl Flags, thereby necessitating a complete revision of previous interpretations. The Niarbyl Flags are formally defined here as the Niarbyl Formation and are assigned to a new group, the Dalby Group. A previously unrecognized lithofacies in the formation, laminated hemipelagite, is also distinguished and described and this indicator of anoxic deposition is compared and contrasted with the Manx Group and other Lower Palaeozoic sequences. Combined turbidite facies, palaeocurrent and petrofacies analysis of the turbidite suite further serves to reinforce the distinction with the Manx Group, in particular palaeocurrent and petrofacies data that indicates provenance from a magmatic-arc source to the west-northwest. The turbidite sequence is interpreted as a mid-lower fan, slope-apron sequence of interlobe and sandy lobe packets. Finally, the regional correlation and significance of the formation in its Iapetus Ocean setting, as well as the significance of the Niarbyl Shear Zone that defines its lower contact with the Manx Group, is considered and compared.
Relationships between metamorphism and structure on the northern edge of eastern Avalonia in the Manx Group, Isle of Man
Authors: Power G. M. , Barnes R. P.
Published: April 2008

The early Ordovician rocks of the Isle of Man, comprising fine-grained clastic sedimentary rocks at low regional metamorphic grade, contain a range of variably developed porphyroblasts. These are used to establish the relationship between the metamorphism and early Devonian deformation. Evidence for pre-deformation mineral growth is limited to diagenetic chlorite-mica stacks which may occur in most lithostratigraphical units. The first deformation (D
1
) is marked by a pervasive cleavage, related to folding at various scales. Subsequent events formed crenulation cleavages in association with generally minor folding, including a gently dipping fabric developed relatively widely in response to the second phase of deformation (D
2
). The main metamorphic peak, represented by growth of ilmenite, Mn-rich garnet, chloritoid and cordierite in muddy facies in the Manx Group, occurred after D
1
and before the onset of D
2
. Local heating contributions are also recognized in restricted metamorphic aureoles around dioritic dykes and intermediate size granitic intrusions of syn-D
1
(Dhoon Granodiorite), syn-D
2
(Black Hut Dyke) and post-D
2
(Crosby and Foxdale Granite) ages.

Porphyroblast phases are best developed along the spine of the island and previous workers have suggested a metamorphic pattern related to underlying granitic intrusions. However, the timing of the growth of porphyroblasts within and outside the aureoles around exposed granites in this zone are very different, militating against any simple relationship between porphyroblast growth and igneous activity. Metamorphic mineral maps reveal a strong lithological control on the distribution of porphyroblasts. Chloritoid, in particular, is largely restricted to two prominent carbonaceous black mudstone units, the Barrule and Glen Rushen Formations, which strike northeast-southwest along the central part of the island. Cordierite is developed in the mudrocks of the Injebreck and Maughold Formations which crop out either side of the Barrule Formation. Further out across-strike, the absence of porphyroblasts (other than ilmenite) in the turbidite sandstone-rich parts of the sequence may again be, at least in part, related to composition. Here, however, low grades in the outermost tectonic tracts may be a real feature resulting from early D2 extensional reactivation and subsidence relative to the elevated central tracts.
Trans-Iapetus contrasts in the geological development of southern Scotland (Laurentia) and the Lakesman Terrane (Avalonia)
Authors: Barnes R. P. , Stone P.
Published: April 2008

The Iapetus Ocean was a major feature separating Laurentia and Avalonia in the early Ordovician. The early Palaeozoic, Laurentian margin of the ocean is preserved in the UK in inliers in the Midland Valley of Scotland and in the Southern Uplands Terrane. The oldest rocks, of similar age to the deep-marine facies of the Skiddaw and Manx Groups opposite on the Avalonian margin, form the fragmentary ophiolitic sequences preserved in the Ballantrae and Highland Border complexes. These, together with equivalents displayed more extensively in Newfoundland, show that a succession of volcanic arcs and back arc basins formed and were accreted onto the Laurentian margin as a result of subduction during the late Cambrian and early Ordovician. In contrast, a suprasubduction zone extensional regime may have dominated the Avalonian margin at that time.

Evidence for the progressive destruction of the ocean by northward directed subduction is preserved in the Caradoc-Wenlock rocks of the Southern Uplands. The tectonostratigraphic configuration, with fault-bound slices containing thick turbidite sandstone sequences, of individually restricted duration, resting southwards on progressively younger oceanic mudrocks, is suggestive of an accretionary complex, although the precise situation is debated. Interpretation of the structural complexity of the Southern Uplands is reliant upon extensive biostratigraphical data, prior to the availability of which the understanding was at a level comparable to that of the Manx Group at the present time.

The late Llandovery-Wenlock Hawick and Riccarton Groups in the Southern Uplands continue the general tectonostratigraphical pattern. These younger turbidites are, however, of distinctive lithological character and show similarities with Wenlock to Ludlow sandstone-dominated sequences in the Windermere Supergroup in the southern Lake District and the Niarbyl Formation on the Isle of Man. This correlation between the Laurentian and Avalonian margins confirms that the Iapetus Ocean was no longer a significant feature by the mid-Silurian. The Southern Uplands accretionary thrust front migrated southwards on to the Avalonian foreland during the late Silurian as the Avalonian plate was subducted beneath Laurentia. Deformation in the Southern Uplands was largely complete prior to emplacement of
c.
400 Ma granite plutons, whereas the Acadian deformation of the Skiddaw and Manx Groups was concentrated in the early Devonian at
c.
390 Ma. However, similarities in structural style in the two areas seem to arise from the operation of similar mechanisms.
Characterization of tephras using magnetic properties: an example from SE Iceland
Authors: Gonzalez Silvia , Jones Jennifer M. , Williams David L.
Published: April 2008

Mineral magnetic techniques have been applied to two different stratigraphic profiles excavated in the Oraefi Volcano area, SE Iceland. The profiles include sequences of soils and tephra layers of inferred age. Each profile includes the distinctive pumice tephra layer associated with the eruption of Oraefi in 1362, which is a stratigraphic marker for the area. Detailed magnetic measurements included: magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization (IRM) acquisition, back-field IRM’s and strong field thermomagnetic behaviour (Curie temperature). The results indicate that the most useful magnetic properties for distinguishing between soils and tephras are the back-field IRM’s and the Curie temperatures. Principal component analysis has been applied using all the measured magnetic properties. In this way it is possible to discriminate between different types of material in the sections, and even more importantly to correlate some tephras between the two sections. The potential of this technique to correlate tephras is promising, but further evaluation is required.
Inherited landscapes of the Sudetic Foreland (SW Poland) and implications for reconstructing uplift and erosional histories of upland terrains in Central Europe
Authors: Migoń Piotr
Published: April 2008

This paper provides evidence of the very varied denudation topography that had developed in the Sudetic Foreland by the end of the Palaeogene and which has survived up to the present day because of partial burial by Neogene sediments. The Sudetic Foreland comprised different landscape units and the range of relative relief within it may have been up to 600 m; 150–200 m seems to be a figure typical for the mid-Tertiary. This stands in apparent contrast to the widely held opinion that the landscape subjected to the Neogene uplift represented a planation surface. It is argued that much of the present-day topography of Central European uplands and mountains, including the adjacent Sudetes, may be inherited from the Early Cenozoic. In many cases there is generally no need to invoke complicated uplift histories, for which scarce independent geological evidence exists, to explain the origin of landsurfaces.
Palaeolandsurfaces and neotectonic analysis in the southern Sierras Pampeanas, Argentina
Authors: Costa Carlos H. , Giaccardi Aldo D. , González Díaz Emilio F.
Published: April 2008

The Sierras Pampeanas of northwestern Argentina are ranges underlain by crystalline basement rocks bounded on their western margins by N-S trending reverse faults along which uplift took place during the Andean orogeny. A pre-uplift regional erosion surface is commonly preserved on the eastern slopes which have been tilted in most cases towards the east. No stratigraphical units of Neogene age have been preserved on this surface. The remnants of this palaeolandsurface have been used in the southernmost Sierra de San Luis for reconstructing the palaeotopography, dismembered during Neogene tectonism. This analysis facilitated the identification of minor blocks and the calculation of the vertical component of neotectonic faults as well as a rough estimate of the rates and amplitudes of uplift along the range front. Simple geometrical techniques were applied for a preliminary balancing of cross-sections and for estimating shortening and the detachment depth of faults.
Cosmogenic isotope data support previous evidence of extremely low rates of denudation in the Dry Valleys region, southern Victoria Land, Antarctica
Authors: Summerfield M. A. , Sugden D. E. , Denton G. H. , Marchant D. R. , Cockburn H. A. P. , Stuart F. M.
Published: April 2008

Quantitative estimates of denudation rates in different tectonic and climatic environments are of fundamental importance to an understanding of long-term landscape development. Little quantitative information is currently available on minimum denudation rates, although this is important in placing constraints on the maximum survival potential of individual landforms or erosion surfaces in terrestrial environments. The persistence for up to >15 Ma of a hyper-arid, polar climate in the ice-free Dry Valleys area of southern Victoria Land, Antarctica, makes this a highly probable environment for minimum terrestrial denudation rates.
40
Ar/
39
Ar dating constraints on the mimimum formation ages of individual landforms indicates generally little modification of even minor features over the past few million years. Relatively, the highest rates of denudation occur at low elevations near the Ross Sea coast. By contrast, rates of landscape change are exceedingly slow at elevations above
c.
1500 m in the western Dry Valleys where landforms with a relief of a only a few metres have survived with minimal modification since the mid-Miocene. Measurements of
in situ
-produced cosmogenic isotopes indicate that even on rectilinear slopes maximum denudation rates may be only
c.
1 m Ma
−1
, with rates falling to <0.2m Ma
−1
at some locations on low relief surfaces at high elevation.
Source and fate of Chernobyl-derived radiocaesium on floodplains in Ukraine
Authors: Van Der Perk Marcel , Burrough Peter A. , Culling Adrian S. C. , Laptev Gennady V. , Prister Boris , Sansone Umberto , Voiteskhovitch Oleg V.
Published: April 2008

The accident in the Chernobyl nuclear power plant on 26 April 1986 has resulted in radiocaesium contamination in the Dnieper-Pripyat catchment in Ukraine, Belarus and Russia. As radiocaesium tends to be readily adsorbed by soil particles, by illitic clay minerals in particular, sedimentation and erosion of fine soil particles are the major radiocaesium redistribution processes that have occurred since initial deposition. A part of the eroded material is transported to and through the river channel. The seasonal character of fluvial transport causes deposition of this sediment on the river banks and floodplains. This is particularly relevant if floodplains are used for agriculture. The geochemical characteristics of the floodplain soils determine to what extent radiocaesium is taken up into food chains. In this paper, we try to identify the source and fate of radiocaesium on a floodplain along the Slučc River and its tributaries in the Dubrovitsa district, Ukraine, some 350 km west of the Chernobyl nuclear power plant. In July 1993, a major summer flood occurred, which inundated the floodplain for about 3 weeks. The observed provisional increase of radiocaesium contamination in soil and cow’s milk in this area after this flood is discussed in relation to soil type and proximity to the river channel.
Scientific and institutional constraints on the restoration of European floodplains
Authors: Adams W. M. , Perrow M. R.
Published: April 2008

Most river restoration (or often more appropriately rehabilitation) projects have focused on the river channel, in-stream and channel-edge environments. The desirability of extending restoration to the active floodplain is now widely recognized, because of the critical importance of the floodplain-riparian zone in river structure and function. However, the extension of river restoration to floodplain environments presents the environmental manager with complex scientific and institutional challenges. This paper considers the constraints on floodplain restoration as a result of scientific uncertainty, the ways in which scientific and technical knowledge are applied, the complexity of formal institutions of floodplain governance, and the complexity of informal institutions influencing floodplain environments.
Identification of an ecologically based floodway: the case of the Cosumnes River, California
Authors: Andrews Elizabeth S.
Published: April 2008

The opportunities for restoring natural floodplain function along the Cosumnes River in California, USA, were evaluated by integrating traditional methods of engineering floodplain analysis with geomorphological analysis. The specific goal for floodplain restoration was the reestablishment of physical processes that would lead to the creation of cottonwood forest, and ultimately the generation of riparian oak woodland, while preserving or reducing current off-site flood hazards. Long-term trends, current hydraulic conditions, anticipated ecological value, and expected future conditions were evaluated to identify an appropriate floodplain restoration goal for the river.
The use of floodplain sedimentation measurements to evaluate the effects of river restoration works
Authors: Asselman Nathalie E. M.
Published: April 2008

Over the past century, many rivers throughout Europe have been channelized. The channel of the River Rhine in the Netherlands was straightened, groynes were built, and minor river dykes were constructed to prevent inundation of parts of the embanked floodplain during minor floods. More recently, however, ecological rehabilitation of the rivers Rhine and Meuse and the reduction of flood risk have become major issues for river management in the Netherlands. Various projects for restoration of the embanked floodplains to a more natural state and for the improvement of the discharge capacity of the high-water floodway have been initiated. Proposed measures include the construction of side channels through the floodplain, lowering of the floodplain surface by several decimetres, removal of minor river dykes, and reintroduction of floodplain forests. These measures will alter floodplain sedimentation rates. The aim of this paper is to evaluate the possible effects of such river rehabilitation measures on sediment accumulation using the results of overbank sedimentation measurements. The measurements were carried out during several floods at different floodplain sections along the rivers Waal and Meuse in the Netherlands. Sediment traps made of artificial grass were used to collect the deposited sediment. By comparing amounts and patterns of sediment deposited at floodplain sections characterized by different topography, the possible effects of rehabilitation measures on floodplain sedimentation are assessed. The findings are compared with model predictions. Results indicate that removal of minor dykes and lowering of the floodplain surface will significantly enhance sedimentation, whereas the impact of changes in vegetation cover from grass to grass with clusters of trees will be small.
Island topography mapping for the Brahmaputra-Jamuna River using remote sensing and GIS
Authors: Hassan A. , Martin T. C. , Mosselman E.
Published: April 2008

The significance of river morphology and the need to develop reliable morphological prediction methods require better knowledge of river-bed and island topography. This study focuses on techniques for determining the topography of exposed chars (char is defined here as a vegetated island (island-char) or an area of vegetated land within the braid belt that is attached to the floodplain (attached-char)) within the braid belt of the Brahmaputra-Jamuna River, based on land cover and age of the land surface. Traditionally, char topography is assessed from widespread field surveys, which are both costly and time-consuming. In addition, the river is highly dynamic and the utility of field survey is limited beyond 1 year. This study explores the use of remote sensing as a cost-effective and rapid method of acquiring synoptic data on land elevations in the low relief of the Brahmaputra-Jamuna braid belt. The land elevations assessed indirectly by remote sensing are combined with ground surveys for calibration. The results indicate that the rate of char elevation growth is initially high, but decreases as the char matures. It appears that growth ceases after about 7 years, and that char elevation reaches a level that is maintained, provided the char is not subjected to erosion. A multitemporal satellite image database and field survey measurements at corresponding dates are required to develop the method. Extensive survey data are not available, hence verification of the method is limited. Despite this limitation the results give approximate char heights, which can be used for sediment budgeting and other morphological studies.
The contribution of a multiproxy approach in reconstructing floodplain development
Authors: Dinnin Mark , Brayshay Barbara
Published: April 2008

This paper discusses the results of palynological, fossil insect and sedimentological investigations of floodplain deposits in the lower reaches of the River Trent. The results demonstrate the value of using multiproxy records by enhancing the resolution of a model for the development of the Trent floodplain during Holocene time. In particular, these data provide evidence for ecological and hydrological process-response relationships within the catchment. The combined results highlight the role of anthropogenic disturbance in major changes in floodplain ecology and hydrology during the later prehistoric and historical periods. The results and their implications for nature conservation management of floodplain natural resources are discussed in their national contexts and with reference to the implications for habitat restoration.
Geochemical characteristics of overbank deposits and their potential for determining suspended sediment provenance; an example from the River Severn, UK
Authors: Bottrill L. J. , Walling D. E. , Leeks G. J.
Published: April 2008

The sources of suspended sediment are an important factor controlling sediment yield and sediment budgets. Sediment provenance is an essential prerequisite for elucidating the overall sediment delivery system. Only a proportion of the suspended sediment transported by a river during floods may reach the river mouth, and lowland floodplains frequently represent important sediment sinks. The geochemical properties of floodplain sediments have been used in stratigraphic studies of long-term environmental changes in river basins, but their potential for investigating recent and contemporary sediment sources has not been fully exploited. This paper reports the results of a study that has used the geochemical properties of overbank deposits, including heavy metal, trace metal and cation exchange elements, to establish the main suspended sediment sources within the 10 000 km
2
basin of the River Severn, UK. The results confirm the importance of the upland catchments of the rivers Teme, Vyrnwy and Upper Severn as sources, providing 70% of sediment in the Basin, and of the River Avon as a source of 27% of the <63 μm material. The catchments of the rivers Perry, Stour and Tern, which drain the central areas of the Severn Basin, are shown to be insignificant sources of sediment, contributing only 0–4% to sediment deposited at Haw Bridge. An attempt was also made to establish historical sediment source contributions, although changes in sediment geochemistry during storage in floodplain sinks cause this to be largely unsuccessful.
Alluvial architecture of the Mississippi valley: predictions using a 3D simulation model
Authors: Bridge John S.
Published: April 2008

The 3D alluvial-architecture model of Mackey & Bridge (1995,Journal of Sedimentary Research,B65, 7–31) is used to simulate the nature of avulsion and alluviation of the Mississippi River in its lower alluvial valley and delta plain during the Holocene period, a time of relative sea-level rise. An important objective of these simulations is to examine the controls on the relative proportion of channel-belt deposits and floodplain deposits within the alluvium. Although the model cannot predict the exact avulsion behaviour of the Mississippi, the timing and location of avulsions are predicted well in a general sense. In the lower Mississippi valley, avulsions commonly originate in an up-valley location near Memphis, and the mean avulsion period is 1000–1500 a. This avulsion frequency, combined with large channel-belt width relative to valley width, has resulted in large channel-deposit proportion along the length of the lower alluvial valley. On the delta plain, the model predicts that avulsions are relatively frequent (intervals of decades to centuries) on active deltas where deposition rate on alluvial ridges is greatest and down-valley slopes are least (related to relative sea-level rise). Avulsions originating from locations on the delta plain more distant from the coast occur at longer time intervals (hundreds to thousands of years), because alluvial-ridge topography develops more slowly in these regions. Such avulsions give rise to discrete delta lobes or subdeltas (e.g. Teche, Lafourche). Channel-deposit proportion is generally low on the delta plain, and decreases towards the Gulf of Mexico. This is primarily due to down-valley increase in floodplain width relative to channel-belt width. However, channel-deposit proportion is locally high near avulsion points. These results indicate that change in alluvial architecture during relative sea-level rise in near-coastal settings is more complicated than suggested by recent sequence-stratigraphic models where the proportion of channel-belt deposits is postulated to be controlled primarily by only two factors: deposition rate and valley width.
The Makapansgat Australopithecine site from a speleological perspective
Authors: Latham Alf G. , Herries Andrew , Quinney Patrick , Sinclair Anthony , Kuykendall Kevin
Published: April 2008

Remains of
Australopithecus africanus
from the Limeworks Cave, Makapansgat, South Africa, are believed to belong mainly to a metre-thick, bone-rich, speleothem layer. The flowstone is one stratum among a sequence of speleothems, muds, silts, sands and fine and coarse breccias, the study of which has evoked some disagreement. The limeworkers’ excavations revealed some stratigraphic relationships but they have obscured others. Partly because of this, controversy surrounds the supposition about whether there are separated depositional basins within the overall site and, if so, whether strata can be securely correlated. This is important because a reconstruction of an overall stratigraphic sequence was used as a basis for a magnetostratigraphic reversal record and by which the site has been tentatively dated. There is qualification and disagreement about the origin of the various flowstones and the actual depositional environment of the muds and silts. Evidence is presented which rules out some previous interpretations. From the point of view of the Australopithecine fossils themselves, it can be said that the calcite matrix in which they were provenanced was a low-energy environment and that the dense bone accumulation of this layer almost certainly did not arise by the action of floods, as previously supposed. The most likely main cause of the dense accumulation was hyena denning activity. It is clear that further work is needed to see how a reliable overall sequence can be established and that closer sampling is required for magnetostratigraphy.
Tracing the record of early alluvial tin mining on Dartmoor, UK
Authors: Thorndycraft Varyl R. , Pirrie Duncan , Brown Anthony G.
Published: April 2008

Although there has been considerable speculation, there is as yet no conclusive evidence to confirm Dartmoor as a tin producing region in prehistory. This is in part due to extensive tin mining on the moor during the Medieval period destroying evidence of earlier mining activity. This paper presents the preliminary results of an integrated mineralogical and geochemical geoarchaeological approach to identifying the record of early mining activity. Floodplain sedimentary successions, that have not themselves been mined, and are downstream of known areas of tin streaming, retain a geochemical record of the mining activities because the early tin streaming released large quantities of mine waste tailings. Where these successions can be dated, they provide an indirect means of testing the record of mining activity on Dartmoor. Geochemical and mineralogical analyses of datable fluvial sediments aimed to (a) distinguish between natural and mine contaminated sediments, and (b) to date the onset of sediment aggradation caused by tin mining activity in the headwaters. Results from the Avon Valley show negligible Sn concentrations in basal silts that are dated to pre-2845 ± 45 yrs
bp
. Overlying silts are enriched in Sn and were deposited after 1560 ± 40
ad
, suggesting that the Sn enrichment corresponds with tin streaming in the 16th century. In the Erme Valley, significant Sn enrichment post-dates an organic-rich silt dated at 1280 ± 45
ad
. At both sites there is sediment aggradation coupled with an enhancement in Sn concentration consistent with mine waste contamination as a result of Medieval tin streaming.
Geochemistry and the early alum industry
Authors: Millard Andrew R.
Published: April 2008

One of the earliest chemical industries in Britain was the alum production industry. The early alum industry relied on a complex series of extractions from suitable shale deposits, until the rise of alternative methods in the 19th century, based on industrially produced sulphuric acid. Relatively little is known about the actual processes involved. This paper discusses the evidence that can be gleaned for the chemical processes involved and reports investigations on residues recovered from waste tips at the 17th–18th century alum works at Carlton Bank, North Yorkshire. For the first time it can be said that the sulphur content of the alum shale would have limited yields from the alum production process. Wide variability in the sulphur content of unworked shale implies variable yields in the alum production process, which may have contributed to the historically recorded boom and bust of individual alum works. Analyses of waste calcined shale were shown to be of limited value without experimental reconstruction of shale processing. Future investigations need to concentrate on waste residues recovered from alum works during excavations, and on reconstructions of the process.
Geophysical imaging of the shape of granitic intrusions at depth: a review
Authors: Améglio L. , Vigneresse J. L.
Published: April 2008

This review deals with direct evidence (field statements and geochemistry) and indirect observations (modelling experiments, analogical models, and geophysics) on granite plutons to model their shape at depth. 3D modelling of granite plutons can be achieved using geophysical tools. Amongst these tools, heat-flow and heat-generation data used earlier to estimate the thickness of granitic plutons appear inadequate. Electrical methods are strongly influenced by near-surface heterogeneities and temperature, which minimize their effectiveness at depth. Magnetic surveys provide information on contacts between pluton and country rocks, since magnetic halos are appropriate to delineate surface contours, but the technique lacks the resolution to reveal deep boundaries. Anisotropy of magnetic susceptibility is particularly well adapted to determine the internal structures of plutons. Seismic profiles at usual frequencies (30–80 Hz) define the layered structure of the floor of several bodies but fail to show the rock-type variations and their internal fabrics, because of their low impedance contrasts. Conversely, high-resolution seismic reflection profiles reveal fault structures in granites but the pluton’s floor remains transparent. Gravity measurements have been widely applied in granites and owing to the 3D inversion of data, the shape of the pluton at depth and depth of its floor may be derived with confidence from density contrasts.
Structure and geophysics of the Gåsborn granite, central Sweden: an example of fracture-fed asymmetric pluton emplacement
Authors: Cruden Alexander R. , Sjöström Håkan , Aaro Sven
Published: April 2008

The emplacement mechanisms of the Palaeoproterozoic Gåsborn granite, a satellite of the Transscandinavian Igneous Belt (TIB), are investigated using an integrated structural and geophysical approach. The pluton is discordant to
c
. 1.89 Ga folded supracrustal rocks that were deformed and metamorphosed at
c
. 1.85–1.80 Ga during the Svecokarelian Orogeny. Emplacement occurred at a depth of
c
. 10 km, within a regime of late Svecokarelian dextral transpression. Deformation of the pluton during cooling resulted in the formation of a variably developed foliation in the granite and deflection of less competent wall-rock units around its western and eastern contacts. Later E-W Sveconorwegian shortening resulted in the formation of shear zones that affect one of the pluton margins and may contribute to a component of the observed wall-rock distortion. The granite is situated above strong NNW-trending linear magnetic and negative gravity anomalies, which are interpreted to correspond to an important early Svecokarelian shear zone. The geophysical data indicate that the pluton is markedly asymmetric and modelling of the residual gravity field suggests that it consists of a deep root zone in the west and a thin sill-like body, which makes up most of the east and south parts of the body. Emplacement of the sill-like part occurred by lateral flow of magma from the root zone accommodated by downwarping of the underlying units. Intrusion of the thicker, discordant west part may have been accommodated by a combination of roof lifting and floor depression, aided by displacement on an active shear zone.