bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamics of a floodplain recirculation zone investigated by field monitoring and numerical simulation
Authors: Nicholas A. P. , McLelland S. J.
Published: April 2008

Results are presented from a combined field monitoring and numerical modelling study of flow dynamics within a floodplain recirculation zone. An array of four acoustic Doppler velocimeters (ADVs) was employed to monitor 3D flow velocities within a backwater site on the River Culm, Devon, UK. Patterns of measured mean velocity and turbulent kinetic energy are compared with the results of a numerical simulation of 3D flow carried out using the computational fluid dynamics software package
fluent
. Simulation results illustrate the presence of flow recirculation within the backwater zone, which is consistent with lateral flow convergence monitored in the field along the upstream portion of the channel-backwater interface. Both the simulation results and ADV data highlight the existence of a free-shear layer at the mixing interface between these flows, which is characterized by high levels of turbulent kinetic energy. However, simulated turbulent kinetic energy levels are significantly lower than those monitored in the field. In addition, ADV data illustrate deviations from isotropic turbulence that may not be simulated using a two-equation
k
-ɛ turbulence model. These results provide quantitative evidence of the hydraulic mechanisms responsible for promoting high rates of suspended sediment deposition in such backwater recirculation zones, and highlight several modelling issues that require further attention.
Variations in the quality of the thatching reed
Phragmites australis
from wetlands in East Anglia, England
Authors: Boar R. R. , Kirby J. J. H. , Leeming D. J.
Published: April 2008

Phragmites australis
(Cav.) Trin. ex Steud. (common reed) is an emergent grass that grows in a wide belt across the wetlands of North America and Europe. In many European wetlands, dead stems of
P. australis
are harvested annually to supply the roof thatching industry. This study has measured and compared the quality, in terms of mechanical strength and decay rate, of a reed harvest from 12 marshes in the floodplains of the Rivers Bure, Ant, Thurne Waveney and Blythe in East Anglia, UK. The marshes varied from fresh-water peat to marine alluvium and were in floodplains that have been managed traditionally to supply thatching reed. The decay rate of stems varied more within the floodplains than between them. Mechanical properties, however, varied between the different floodplains, with stems of greatest tensile strength from brackish reedbeds not flooded directly by sea water. As neither the mechanical properties, nor the shape and size of reed stems varied with their decay rate, the quality of roof thatch originating from particular growing areas cannot be predicted easily.
Biotic response to late Holocene floodplain evolution in the River Irthing catchment, Cumbira
Authors: Cotton J. A. , Heritage G. L. , Large A. R. G. , Passmore D. G.
Published: April 2008

This paper presents some results of a geomorphological and palaeoecological evaluation of late Holocene floodplain evolution at a site in the middle reaches of the River Irthing, a tributary of the River Eden, near Brampton, Cumbria, UK. Geomorphological mapping and survey have identified a minimum of seven Holocene alluvial terraces in this reach, each with well-defined palaeochannels developed on their surfaces. Sediment coring and radiocarbon dating of selected channel fills indicate that a large proportion of the Holocene valley floor has been deposited during and after the 3rd millennium
bc
. Detailed sedimentological and macrofossil analyses undertaken on late Holocene channel fill sediments reveal spatial and temporal variability in patterns of local vegetation development within palaeochannel environments. These reflect local changes in hydrology, the character and rates of sedimentation, and levels of disturbance. Results are interpreted in the context of regional records of Holocene climate and land-use change, as well as existing models of floodplain vegetation succession. The advantages of taking a holistic approach to palaeoenvironmental reconstruction and the utilization of macrofossils are discussed.
Historical background to floodplain morphology: examples from the East European Plain
Authors: Panin A. V. , Sidorchuk A. Yu. , Chernov A. V.
Published: April 2008

Floodplain morphology is described in relation to channel pattern changes in the past. The oldest segments of the present-day floodplains were formed in the Late Valdai (Weichselian). Their morphology is inherited from large palaeomeanders (macromeanders) formed under extremely high discharge conditions. A map of the spatial distribution of Late Valdai macromeander relics on the East European Plain is given. Various floodplain segments have a spectrum of ages that may reflect only selected portions of the river history. The most widespread morphological units correspond to the periods when the river was undergoing its widest lateral migration. Periods of stable channel position may result in a gap in the floodplain age spectrum. The channel pattern and rates of river migration are controlled both by hydrological conditions and by valley floor morphology inherited from the preceding river regime. Heterogeneity of floodplains is illustrated from three key sites: the Khoper River (Southern Russia), the Protva River (Central Russia) and the Vychegda River (Northern Russia).
Palaeochannels and ground-water storage on the North China Plain
Authors: Zhao Yingkui , Wu Chen , Zhang XiuQing
Published: April 2008

The North China Plain, on which there are many palaeochannels as a result of frequent river channel changes, consists of a complex of floodplains formed by the Yellow, the Haihe and the Luanhe rivers. The palaeochannels act as a significant store of fresh ground water. Most of the storage is within sand and gravel layers. The buried depth of these layers varies among palaeochannels formed in different periods. For example, those formed between the last principal stage of glaciation and early Holocene time are buried 20–40 m deep. Those formed in mid-Holocene time are found at a depth of 10–20 m and those formed in late Holocene time at 0–10 m depth. Ground-water storage and palaeochannel discharge was calculated for the North China Plain. Ground-water in palaeochannels is recharged mainly by rainfall. With good management practice, the water withdrawn can be balanced against recharge to achieve a sustainable level of use. In addition, the shallow-buried palaeochannels provide a suitable environment for water regulation and storage and can be used to develop underground reservoirs.
Floodplain palaeosols of the Cenomanian Dunvegan Formation, Alberta and British Columbia, Canada: Micromorphology, pedogenic processes and palaeoenvironmental implications
Authors: McCarthy Paul J. , Plint A. Guy
Published: April 2008

Floodplains represent both sedimentological and pedological entities that record a unique blend of potential environmental indicators in the rock record. Because floodplains develop in aggradational environments with a high preservation potential, they preserve a detailed record of the local pedosedimentary history. Assemblages of micromorphological features present in floodplain palaeosols record, with a high degree of temporal and spatial resolution, specific pedological processes that operated under particular environmental conditions. Detailed micromorphological analyses of floodplain deposits, in conjunction with their regional distribution, are required for accurate palaeoenvironmental reconstruction of these environments.

Micromorphological features are described from floodplain palaeosols in the Upper Cretaceous (Cenomanian) Dunvegan Formation in northwestern Alberts and northeastern British Columbia, Canada. The palaeosols developed on low-lying and generally poorly drained floodplains during a time when the tectonic subsidence rate was very low. High-frequency fluctuations in base level were superimposed upon this tectonic signature, resulting in at least seven phases of valley cutting and the corresponding development of mature interfluve palaeosols. The major pedogenic processes operating were clay illuviation, redox processes, precipitation of soluble salts (primarily FeCO
3
) and pedoturbation. Palaeopedological features in the Dunvegan Formation are consistent with features developed in modern cool temperate soils with a non-seasonal precipitation distribution, such as Brunisols and Luvisols. The presence of embedded grain argillans, compound silt-clay coatings and rounded aggregates suggests at least the possibility of limited frost penetration in inland soils. Floodplains of the mid-Cretaceous Dunvegan Formation (palaeolatidude
c.
65°N) record evidence for cool temperate conditions that supports other palaeobotanical and sedimentological evidence for cool Cretaceous palaeoclimates at high latitudes.
Nature and distribution of heavy minerals in the Natal Group, South Africa
Authors: Liu K. W.
Published: April 2008

The author provides an example of heavy minerals concentrated in floodplain sediments. Nine types of heavy mineral have been found in fluvial sediments of the Ordovician Natal Group, South Africa, among which ilmenite is the most abundant. These heavy minerals are concentrated mainly in the Eshowe and Inanda Formations of the succession, and vary in content from 1.6 to 20.1% (average contents of 3.86% and 4.18%, respectively). This is in contrast to the shallow-marine Kranskloof and Dassenhoek Members, with average contents of only 1.14% and 1.27%, respectively. Host rocks of the heavy minerals are mainly arkose and lithic arkose, with subordinate subarkose. Grain-size analysis shows that heavy mineral rich beds are composed mostly of fine to medium size sand and are better sorted than the host rocks. The main depositional environments for the heavy minerals are branched or braided channels, rather than the main channel, as the moderate hydrodynamic regime is more favourable for the accumulation of fine to medium arenaceous heavy minerals. Palaeogeography and mineral assemblages confirm that the main provenance of the heavy minerals lay to the north of the depositional basin, namely, the Archaean Kaapvaal Craton, with the Natal Structural and Metamorphic Province as a supplementary source.
Euler deconvolution methods used to determine the depth to archaeological features
Authors: Murdie Ruth E. , Styles Peter , Upton Paula , Eardley Phil , Cassidy Nigel J.
Published: April 2008

Field techniques, instrumentation and data processing for geophysical location of archaeological remains are now at such a standard that clear maps of the subsurface detail are readily obtainable. Magnetic gradiometry and resistivity plots are widely used to locate diverse features such as walls, ditches and burial areas. However, information concerning the depth to these features is not often extracted from such plots and would be useful in planning any following excavation. Here we use Euler deconvolution methods, on a reasonably high-resolution magnetic gradiometer data set, to determine the depth to a buried Romano-British villa at the Wroxeter archaeological site. The interpretation of these depth estimates is compared to GPR sections taken over the same site.
Geochemistry of ballast granites from Brouage and La Rochelle, France: evidence for medieval to post-medieval trade with Falmouth, Cornwall, and Donegal, Ireland
Authors: Lazareth Claire E. , Mercier Jean-Claude C.
Published: April 2008

Determination of the geographical origin of exotic ballast boulders found in various archaeologically dated constructions of medieval and post-medieval age along European shores provides evidence for early commercial sea links. However, ballast often consists of common granites. Some are identified here by combining multiple geochemical tools which support a first-degree classification into two groups, muscovite-bearing (with or without biotite) or muscovite-free (with biotite as the only mica), each one showing a remarkably very narrow and distinct range in mineral compositions. This suggests a single locality for the origin of each type of granites. Indistinguishable muscovite-bearing facies are found in La Rochelle and Brouage, with one representative sample geologically dated at 274 ± 6 Ma. In agreement with the evidence from bulk-rock and phase chemistry which are similar to those of the Carnmenellis intrusion, Cornwall, this geological age strongly supports early commercial sea links with nearby Falmouth, at least from the end of the 14th to the middle of the 16th century. For the muscovite-free granites found in Brouage in a different site dated
c.
1650, similar investigations and a 393 ± 9 Ma geological age, strongly suggest ballast loading north of Ros Eoghain Point, Ireland, and direct trade with nearby Donegal.
Zinc isotope fractionation in liquid brass (Cu-Zn) alloy: potential environmental and archaeological applications
Authors: Budd Paul , Lythgoe Paul , McGill Rona A. R. , Pollard A. Mark , Scaife Brett
Published: April 2008

A preliminary study of zinc isotope fractionation in brass melting suggests that the process can be modelled by simple Rayleigh fractionation. Brass melting experiments at 1100°C followed by quadrupole ICP-MS isotope ratio measurements of the resulting alloys suggest that the model is appropriate and that a useful approximation of the fractionation factor (α) is 1.0064. The data indicate that the change in isotope ratio of the residual liquid alloy would be measurable for zinc losses by evaporation of more than about 30 wt.%. It is unlikely that measurements at the precision of the current study (∼0.55‰amu
−1
) would be sufficient to distinguish between the two principal historical brass-making processes, although more precise measurement using a multi-collector ICP-MS probably would be. The experimental data also suggest that zinc vapour evolving during the evaporation of the first few per cent of the metal will be significantly fractionated (∼1.5‰amu
−1
) with respect to the liquid. This might provide a basis to distinguish between environmental zinc from high-temperature industrial processes and that derived from natural and manufactured product sources.
Granitic melt viscosities
Authors: Dingwell Donald B.
Published: April 2008

The viscosities of granitic melts play a crucial role in controlling the kinetics and dynamics of magma transport including generation, segregation, ascent, differentiation and emplacement. No general theory of liquid viscosity has been successfully applied to date to the description of granitic melt viscosities. The approach in the earth sciences so far has been empirical and experiments designed to measure the viscosity of granitic melts have made considerable progress in improving our picture of the composition-, temperature- and pressure-dependence of granitic melt viscosities. This chapter summarizes the recent progress in parameterizing the viscosity of granitic melts with respect to the most important compositional variables such as alkali/aluminium ratio, silica content, water content, anorthite content. The pressure-dependence of granitic melt viscosities is very slight. The temperature-dependence, in contrast, is a very strong and non-linear function of the reciprocal absolute temperature (i.e. non-Arrhenian). Indirect determinations of the viscosity of granitic melts have also contributed substantial information on the composition-, pressure- and temperature-dependence of melt viscosity. These measurements are particularly useful where direct viscosity determinations are difficult or impossible to perform. The outlook for a more complete picture of granitic melt viscosities in the next years is excellent. The combination of several factors, including conceptual advances in the quantitative understanding of relaxation in silicate melts, experimental advances in the measurement of viscosity of silicate melts, and the identification in the experimental studies to date of the areas of investigation where the effort should be concentrated in the future, give reason to expect a more or less complete picture, fully adequate for the purposes of modelling the dynamics of granitic magmas, in the near future.
Geometry of granite emplacement in the upper crust: contributions of analogue modelling
Authors: Román-Berdiel Teresa
Published: April 2008

Granite emplacement in the brittle crust can be modelled by means of the injection of a Newtonian fluid (low-viscosity silicone putty) into sandpacks. This paper describes dynamically scaled analogue models of granite intrusions in the upper crust under different tectonic regimes. Experiments analyse three boundary conditions: (1) static conditions, with different rheological profiles (single sand-layer system, two-layer silicone-sand system, three-layer sand-silicone-sand system and five-layer sand-silicone-sand-silicone-sand system), (2) extensional regime, including gravitational sliding and divergent basal plate, with both mobile and fixed velocity discontinuities and (3) strike-slip regime, induced by two mobile basal plates. The results obtained indicate that: (1) a soft level between two competent units is necessary for laccolith formation—the critical thickness of the soft layer necessary for laccolith formation decreases with increasing depth, (2) when there are two soft layers in the brittle crust, laccolith emplacement occurs in the deeper soft level, even when this is thin and the overburden does reach its critical thickness, (3) in extensional regimes the geometry of intrusions is mainly controlled by normal faults and at the same time intrusions determine the location of faults within the cover and (4) in strike-slip zones intrusions are elongate and their long axis tends to track the principal stretching direction associated with the strike-slip regime. Some natural examples of granitic bodies were considered to test the applicability of experimental results.
A multidisciplinary approach combining geochemical, gravity and structural data: implications for pluton emplacement and zonation
Authors: Hecht L. , Vigneresse J. L.
Published: April 2008

Granitic pluton emplacement and zonation are controlled, among others, by regional deformation and the rate of magma supply. The latter has consequences for the disposition of successively emplaced, more chemically evolved, batches of magma. Our general interpretation is based on a multidisciplinary approach combining field observations, gravity data, internal structures and geochemical variations. Magma feeders are identified in the plutons as the deepest zones, inferred from gravity measurements, when they also correspond to vertical lineations. Correlation of the root zone location with compositional zoning indicate how the magma evolved during emplacement. Two case studies of Hercynian granite plutons illustrate the interpretations: the normally zoned Cabeza de Araya pluton (Spain), and the multiphase Fichtelgebirge pluton (Germany) which displays both normal and reverse zoning. It is proposed that reverse zoning reflects discontinuous magma injection due to a tectonic rate slower than the rate of magma supply. Conversely, normal zoning can occur when magma injection is continuous in time, with successive magma batches entering within not yet crystallized magma. The two case studies illustrate how the understanding of compositional zoning and emplacement of granitic plutons can be improved by multidisciplinary approaches combining classical and modern techniques.
Contrasts in morphogenesis and tectonic setting during contemporaneous emplacement of S- and I-type granitoids in the Eastern Lachlan Fold Belt, southeastern Australia
Authors: Trzebski R. , Lennox P. , Palmer D.
Published: April 2008

Integrative gravity and structural modelling of Ordovician-Silurian granitoids in the Eastern Lachlan Fold Belt (southeastern Australia) revealed contrasts in emplacement mode and deformation style between coeval S- and I-type granites. The NNE-SSW directed contraction during the Benambran event of the Lachlan Orogen caused dextral movement along two major strike-slip faults (Carcoar Fault/Copperhannia Thrust) and simultaneous formation of both transtensional pull-apart and transpressional shear zones. The geometry and deformation style of the plutons and country rock, their spatial relationship at depth to adjacent faults and the structural history of both the granites and country rocks suggest a genetic linkage between magma emplacement and synmagmatic deformation. Synchronously, the Carcoar Granodiorite was emplaced into a transtensional pull-apart structure and the Barry Granodiorite and Sunset Hills Granite intruded transpressional shear zones. The I-type Carcoar and Barry granites are square to tabular, wedge-shaped bodies exhibiting a weak deformation; whereas the S-type Sunset Hills Granite is an elongated, tabular to sheet-like pluton showing a moderate deformation degree. The contrasts in 3D shape, emplacement mode and deformation style between the I- and S-type granites are due to differences in nearfield stress regime, geometry of the emplacement sites, intrusion level with respect to thermal and rheological conditions, and in their response to deformation. This response is in part controlled by the proportion of resistant/non-resistant minerals in the granite and host rock. This study demonstrates that distinctive emplacement modes can operate simultaneously in different parts of a fault system under contrasting deformation conditions.
Origin of megacrysts in granitoids by textural coarsening: a crystal size distribution (CSD) study of microcline in the Cathedral Peak Granodiorite, Sierra Nevada, California
Authors: Higgins Michael D.
Published: April 2008

Microcline megacrysts in the Cathedral Peak Granodiorite and other parts of the Tuolumne Intrusive Suite were formed by textural coarsening (Ostwald Ripening) of earlier formed crystals. The early-formed crystals nucleated and grew in an environment of increasing undercooling, probably during the ascent of the magma. Emplacement of the magma into warm host rocks promoted textural coarsening. Crystals smaller than a certain size (the critical size) dissolved in the interstitial melt whilst large crystals grew. Microcline was most sensitive to this effect as the magma temperature was buffered close to its liquidus for a long period by the release of latent heat of crystallization. Positive feedback between textural coarsening and magma permeability channelled the flow of interstitial melt to produce a heterogeneous distribution of megacrysts. Megacryst growth was halted when cooling resumed at the end of the intrusive cycle. K-feldspar nucleation was then renewed and K-feldspar crystals grew to form part of the groundmass. It was the particular thermal history of this pluton that promoted textural coarsening—chemically similar plutons that lack megacrysts probably did not have the pause during cooling that was necessary for the development of this texture.
Granitic magma ascent and emplacement: neither diapirism nor neutral buoyancy
Authors: Vigneresse J. L. , Clemens J. D.
Published: April 2008

It is probable that granitic magma ascent does not result from the intrinsic properties of the magmas. Within the uppermost crust, neither the reduced viscosity nor the density contrast between magma and surroundings are themselves sufficient to induce either low-inertia flow (diapirism) or fracture-induced magma propagation (dyking). Igneous diapirism is intrinsically restricted to the lower, ductile crust. Dyking is therefore the most probable ascent mechanism for granitic magmas that reach shallow crustal levels. A neutral buoyancy level in the crust, at which magma ascent should stall, is never observed. This is demonstrated by coeval emplacement of magmas with different compositions and densities, and the negative gravity anomalies measured over many granitic plutons. We suggest that deformation, through strain partitioning, is necessary to magma ascent. Pluton formation is controlled by local structures and rock types rather than by intrinsic magma properties. As a result of its intermittent character, deformation (both local and regional) induces magma pulses, and this may have important consequences for the chemical homogeneity of intruded magmas.
Experiments on granite intrusion in transtension
Authors: Román-Berdiel T. , Aranguren A. , Cuevas J. , Tubía J. M. , Gapais D. , Brun J.-P.
Published: April 2008

Granite intrusion in transtensional regime is modelled by injecting a Newtonian fluid into a sand pack containing a ductile layer. The transtensional regime is obtained using two plastic sheets sliding along two rigid horizontal plates, and diverging from two narrow spaces (two fixed velocity discontinuities). The injection tube is located in a central space between these plates. Both symmetric experiments (when the two sheets were displaced with equal and opposite velocity vectors) and asymmetric experiments (in which only one sheet was displaced) were performed. Transtension was applied with a systematic variation (every 15°) of the divergence angle (α), between 15° and 90°. Experiments showed that: intrusions localize strain from the first stages of deformation; intrusions result in partially conformable laccoliths with bowler-hat geometry in cross-section; intrusions show an important offset towards the mobile basal plate for asymmetric transtensional regime, and are more symmetric and centred on the injection point for symmetric transtensional regime; the geometry of intrusions is controlled by the faults developed in the overburden. The significance of this control depends upon the angle of divergence α. Examples of the Hombreiro and Los Pedroches granites of the Variscan belt of Spain have been addressed to test the applicability of these experimental results.
Salt extrusion at Kuh-e-Jahani, Iran, from June 1994 to November 1997
Authors: Talbot Christopher J. , Medvedev Sergei , Alavi Mehdi , Shahrivar Hassan , Heidari Esmael
Published: April 2008

Kuh-e-Jahani is one of the largest extrusions of salt currently active in the Zagros mountains. Salt rises from about 4 km below sea level to nearly 1.5 km, above, where, unable to support its own weight, it spreads over the surrounding scenery in a process responsible for present and past allochthonous salt sheets elsewhere. We report vertical movements and apparent horizontal displacements of 43 markers dispersed over this mountain of salt for 4.5 years in three consecutive intervals, the first of 18 months and two others of 12 months. The geometry and inferred flow rate of the salt changed between surveys emphasizing that the gravity spreading is not steady. Our field readings of the dimensions and velocities of the salt at Kuh-e-Jahani are used to tune a simple numerical model and constrain the viscosity of the salt to between 10
16
and 10
17
Pa s
−1
, its rate of surface dissolution to 2–3 cm a
−1
, and its rate of rise out of its orifice at 2–3 m a
−1
for
c.
55 ka. These results imply that vigorous extrusion of salt at Kuh-e-Jahani is probably close to evacuating its deep source and that this mountain will soon begin to waste as salt dissolution overtakes extrusion. This progress report is warranted because our results have significant implications for sophisticated engineering in salt.
Salt tectonics in and around the Nile deep-sea fan: insights from the PRISMED II cruise
Authors: Gaullier Virginie , Mart Yossi , Bellaiche Gilbert , Mascle Jean , Vendeville Bruno C. , Zitter Tiphaine ,   Second Leg Prismed II Scientific Party
Published: April 2008

The recent PRISMED II geophysical survey has documented various styles of salt tectonics in and around the Nile deep-sea fan (Eastern Mediterranean Sea). The first main type of salt-related structures comprises listric normal growth faults and grabens, trending roughly perpendicular to the slope line of the Nile Cone. These faults and associated salt structures result from thin-skinned extension, driven by gravity gliding and spreading as a result of sediment loading of the Plio-Quaternary overburden above the Messinian evaporites, which acted as a décollement layer. The second major type of salt structures consists of lineaments that obliquely intersect the continental slope of the Nile deep-sea fan. These structures may have had some strike-slip movement, and salt diapirs grew reactively or were deformed by fault-block movement. In the western distal part of the Nile deep-sea fan, compressional tectonics of the adjacent Mediterranean Ridge caused the formation of a series of salt-cored folds and reverse faults above the Messinian evaporites. In the eastern distal part of the Nile Cone, sediment progradation progressively expelled salt northward, first forming small folds and tight diapirs, then a scarp of 400 m height around the Eratosthenes Seamount, corresponding to the basinward limit of salt deformation.
Influence of extension and compression on salt diapirism in its type area, East Carpathians Bend area, Romania
Authors: Stefanescu Mihai , Dicea Oprea , Tari Gabor
Published: April 2008

The East Carpathians Bend area has a very complex structure characterized by the presence of nappes, their post-tectonic cover and salt diapirs. The salt forming the studied diapirs is Early Miocene (Burdigalian) in age. After its accumulation the salt was more or less continuously involved in alternating extensional and compressional stages that deformed it from its original tabular position to the present-day diapir. Five stages of salt deformation have been established: initial, pre-nappe emplacement, nappe emplacement, post-nappe emplacement and Wallachian. During all of these stages the salt was configured into different shapes: it formed a truncated cone during the initial stage, a mushroom head during the prenappe emplacement stage, and an increasingly more tapered shape with nappe emplacement and during the post-nappe emplacement stages. Finally, it was squeezed out and refashioned by strike-slip faulting during the Wallachian compressional stage of Pleistocene age.
Holocene coastal dune initiation in Northumberland and Norfolk, eastern UK: climate and sea-level changes as possible forcing agents for dune initiation
Authors: Orford J. D. , Wilson P. , Wintle A. G. , Knight J. , Braley S.
Published: April 2008

Relative sea-level (RSL) control on dune initiation during the Holocene is examined in the context of chronostratigraphies established from 43 vibracores through dunes and into sub-dune sediments taken from the Northumberland and Norfolk (UK) coasts. The chronology is based on 23 accelerated mass spectroscopy and conventional
14
C dates, and 37 infra-red-stimulated luminescence dates. The oldest dunes in Northumberland are
c.
4 cal. ka
bp
with phases of dune development at 2.8 and 1.5–1 ka
bp
. Most dune deposition is of last millennium age, with a concentration, especially in Norfolk, around 500–200 a
bp
. The initiation and survival of coastal dune sequences relate to macroscale RSL changes over the last 4 ka. Northumberland dunes reflect a gradient of RSL change from a northern RSL fall (forced regression) through to a southern RSL rise (normal regression through sediment supply). The north Norfolk coast has been dominated by a rising RSL through the Holocene, though associated with a sediment supply sufficient to offset the transgressive tendency and allow normal regressive deposition at numerous positions along the coast over the last 1 ka. It is suggested that the development of Little Ice Age (LIA) dunes in both Norfolk and Northumberland identifies the onset of specific conditions in which intertidal sediment sources were exposed (falling sea-level) to onshore winds (LIA circulation changes), which reflect a brief west North Sea period in dune initiation and deposition rates. A comparison of this consolidated dune chronology with statements of RSL elevation and climate conditions in the last 2.5 ka leads to some recognition of RSL fall preceding major dune building in two phases post 1.5 ka
bp
and post 0.6 ka
bp
.
Holocene sedimentary evolution and palaeocoastlines of the Fenland embayment, eastern England
Authors: Brew David S. , Holt Tina , Pye Ken , Newsham Rhonda
Published: April 2008

The Holocene sedimentary facies of the Fenland are described using a lithological database and new cores recovered as part of the Land-Ocean Interaction Study. Landward, the Holocene sequence is dominated by mud facies with intercalated peat layers, whereas the seaward areas are sand-dominated. The sedimentological characteristics of the mud facies are homogeneous and are similar for the whole sequence. Glacial deposits located north of The Wash are thought to be the main sediment sources. The sand facies generally fines upwards and the chemistry reflects this change. However, elemental ratios show only slight variations between the two facies implying a general constancy of sediment provenance. The evolution of the Fenland has been dominated by three main events. Firstly, the initial post-glacial transgression, which started
c.
7850 cal.
bp
. Secondly, the sedimentary infilling of the embayment with rising sea-level; deposition of intertidal clastic sediments alternating with peat accumulation. Thirdly, renewed expansion of tidal flat areas between
c.
2750 and 1500 cal.
bp
forming the final clastic fill.
Late Cretaceous and Tertiary structural evolution of the northeastern part of the Vøring Basin, Norwegian Sea
Authors: Mogensen Tommy Egebjerg , Nyby Rune , Karpuz Ridvan , Haremo Pål
Published: April 2008

The Late Cretaceous-Tertiary structural evolution of the northeastern part of the Vøring Basin, mid-Norway, is highly complicated. Although tectonic activity occurred throughout Cretaceous time in much of the Vøring Basin, including the Gjallar Ridge and along the Fles Fault Zone, in the Vema Dome-Nyk High area evidence of such activity is not observed until the latest Maastrichtian time. In the Vema Dome-Nyk High area, several faults with both a NW-SE orientation and a NE-SW orientation have experienced lateral movements. The NE-SW orientation is the old Caledonian trend. The complex structural evolution of the Vema Dome-Nyk High area is probably related to the existence of continental weakness zones, which are the onshore extension of known oceanic fracture zones. The two lineaments that delineate these weakness zones, and that delineate the Vema Dome-Nyk High area, namely the Bivrost and Surt Lineaments, diverge slightly from one another toward the SE. This complex structural framework of NW-SE oriented lineaments and NE-SW oriented deep-seated basement structures of Caledonian compressional and/or Mesozoic rift origin, facilitated minor clockwise rotation of the area between the two lineaments during the extensional regime before the break-up of the North Atlantic, as well as during the compressional regime that has been proposed after the break-up.
Norwegian-Greenland Sea thermal field
Authors: Sundvor Eirik , Eldholm Olav , Gladczenko Tadeusz P , Planke Sverre
Published: April 2008

Thermal gradient and thermal conductivity measurements carried out in the Norwegian-Greenland Sea and in the western Eurasia Basin from 1967 to 1996 have yielded 436 heat-flow values which have been stored on a UNIX-platform database,
heat
, to facilitate retrieval, documentation and display.
heat
contains all public domain data for the region, and the database and application programs are freely available. The heat flow on oceanic crust reveals a clear, first-order heat-flow-crustal-age relationship. The thermal conductivity is relatively uniform and consistent, with values in the 0.85–1.15 W m
−1
K
−1
range. The lower values are from the ocean basins and the higher values from the continental margins. Local, very high heat flow along the present spreading axis may imply active volcanism or venting. We also document local continental slope maxima on the Møre and western Barents Sea margins, contrasting greatly with the typical low heat flow, generally <75 m W m
−2
, on old oceanic and thinned continental crust. The abnormally high heat flow, exceeding 1000 m W m
−2
, on the ‘Håkon Mosby’ gas-seeping mud volcano on the Barents Sea margin suggests that also other local slope maxima may be related to active seeps.
A comparison of the geometry, spatial organization and fracture patterns associated with forced folds and buckle folds
Authors: Cosgrove J. W. , Ameen M. S.
Published: April 2008

In this paper the three-dimensional geometry and spatial organization of folds (both buckle folds and various types of forced folds) are considered, together with their associated fracture patterns, in an attempt to determine if these features can be used in regions of poor exposure or in areas where the geologist must rely on seismic data to indicate the type of folding that has occurred. This study of the relationship between the various fold types and associated fracture patterns draws on theoretical considerations of ideal conceptual models of folds, analogue models and field studies.
Forced-fold development within Tertiary sediments of the Alba Field, UKCS: evidence of differential compaction and post-depositional sandstone remobilization
Authors: Cosgrove John W. , Hillier Rob. D.
Published: April 2008

It is argued that the present trapping geometry within the Eocene Alba Field of the Outer Moray Firth, UKCS, has combined structural-stratigraphic elements. The structural component formed by significant topographic inversion of the deep-marine channel sandstones that constitute the field’s reservoir. A study of core and three-dimensional (3D) seismic demonstrates that topographic inversion took place in response to two processes. The first was differential compaction of mudstone over the channel resulting in a forced fold. This structure was further enhanced by post-depositional sandstone fluidization and remobilization, the latter being focused toward the structural crest of the sandstone body which formed the core of the forced fold. The process of post-depositional remobilization caused significant sand injection into the mudstone overburden and the formation of seismic-scale dykes at the margins of the channel fairway. The growth of the forced fold (by sand remobilization) and the position of the peripheral dykes is analogous to that of igneous intrusions, specifically laccoliths.
Extensional forced folding and décollement of the pre-rift series along the Rhine graben and their influence on the geometry of the syn-rift sequences
Authors: Maurin Jean-Christophe , Niviere Bertrand
Published: April 2008

On the western margin of the Rhine graben, forced folding and décollement of competent Dogger strata occurred during the latest Eocene-Early Oligocene (Priabonian) as a result of normal faulting in the basement. The Dogger series are represented by NNE-striking thick layers of oolitic limestones strongly disrupted by extensional structures and incipient boudinage. To the east, the overlying Priabonian (syn-rift) sequences exhibit divergent onlaps, steeply dipping intraformational unconformities and a general drag syncline geometry. These syn-depositional structures attest to a close control by the progressive tilting and normal dip-slip sliding of the Dogger strata. Interpretation of a shallow seismic reflection profile reveals that this tilting is related to an underlying master normal fault which dips 60–70° to the east. This fault offsets the Variscan crystalline basement and the gently dipping Triassic cover by about 2 km. To be balanced, the structural arrangement requires the presence of a décollement layer located between the top of the Triassic series and the Dogger series, corresponding to the Late Triassic incompetent gypsiferous clays and marls. The response of the competent Dogger to the imposed forced folding is through the development of a large-scale extensional syncline in the hangingwall of the master detachment, compensated by the development of a piggy-back half-graben in the footwall. In the light of this new interpretation, a mechanical hypothesis is proposed including a two-stage evolution model of extension and subsidence for the Rhine graben.
Predicting patterns of strain from three-dimensional fold geometries: neutral surface folds and forced folds
Authors: Lisle Richard J.
Published: April 2008

The geometries and densities of fractures associated with fold structures can be predicted by assuming that the strains accommodated by fractures mimic the bulk strains induced in the strata during folding. This paper examines, from a theoretical standpoint, the distributions of bedding-plane strains expected in folds formed by various folding mechanisms. The relationship between the state of bedding-plane strain and fold-surface geometry is found to vary according to different fold types, distinguished on the basis of their curvature properties. The first type are developable fold surfaces, which have Gaussian curvature equal to zero. Folding mechanisms which are dominated by the mechanical strength of the layering, such as buckling, produce surfaces of this type. Folds of this type allow the possibility of estimating the bedding-plane strains from the geometrical features of the folded layer. Neutral surface folds and flexural-slip folds are discussed as examples. The other main class of folds have non-developable surfaces, which have non-zero Gaussian curvature. Folded surfaces with this form arise predominantly from mechanisms that involve the passive deflection of the layering in response to displacement gradients originating outside of the layer, e.g. drape folding. Although the geometry of these surfaces implies the presence of bedding plane strains, the quantification of these strains cannot be made from the fold geometry but requires additional information on these displacement patterns.
Structural evolution of the western margin of the Nanga Parbat massif, Pakistan Himalaya: insights from the Raikhot-Liachar area
Authors: Butler R. W. H.
Published: April 2008

There are several competing interpretations of the structure of the margins of the Nanga Parbat massif: that the massif is bounded by the original suture between the Indian continent and the Kohistan-Ladakh island arc—the Main Mantle Thrust; that the massif is entirely bounded by neotectonic faults; that it is bounded by a combination of early and late faults and shear zones. If the marginal structures of the massif are to be related to local and regional geo-tectonic evolution then their correct characterization is critical. The Raikhot Bridge area on the western margin of the massif is useful in this regard, as it provides accessible and near-continuous outcrops. This contact, sometimes called the Raikhot Fault, is composite. Sheared metagabbros of the Kohistan arc are juxtaposed tectonically against metasediments and orthogneisses of the Nanga Parbat massif along an early ductile shear contact, developed under amphibolite facies conditions. In this regard it may be a preserved segment of the Main Mantle Thrust. However, this ductile shear zone has been strongly modified, flattened and rotated, and is cut by younger shears and faults. The original kinematics of the shear zone have been largely overprinted by these subsequent deformations. The younger structures include NE-SW striking, dextral strike-slip faults and a major top-to-NW thrust and shear zone. A sequence of metamorphism, deformation and igneous emplacement may be used to study the history of structural evolution within the massif. The use of a single name (e.g. Raikhot Fault) for the present-day map contact between the Nanga Parbat massif and neighbouring Kohistan is misleading. The early contact (termed here the Phuparash Shear Zone, possibly the northeastern continuity of the Main Mantle Thrust) is modified by the Buldar Fault Zone (dextral strike-slip) and the Liachar Thrust Zone (top-to NW carriage of the Nanga Parbat massif across the Phuparash Shear Zone and onto Kohistan). The activity of the Buldar Fault and Liachar Thrust Zone continued during exhumation of the massif, through amphibolite facies to the Earth’s surface. The interaction between these structures is at present unknown. However, establishing these and similar interactions within the Nanga Parbat area remain central to establishing the role of regional NE-SW dextral transpression in the modern structure of the massif.
Geological structure of the southern part of the Nanga Parbat massif, Pakistan Himalaya, and its tectonic implications
Authors: Butler R. W. H. , Wheeler J. , Treloar P. J. , Jones C.
Published: April 2008

The Nanga Parbat massif lies in the core of the major north-south trending, broadly upright antiform that marks the NW syntaxis of the Himalayan arc. However, this antiformal structure is not evident in the trend of foliation and banding within the central and southern parts of the massif. Reconnaissance field studies in this region (Astor, Rama and Rupal areas) have delineated an important shear zone with top-to-the-south overthrust kinematics. This Rupal Shear Zone carries the migmatitic core of the massif onto nonmigmatitic metasediments locally termed the Tarshing Group. The shear zone traces north into a broad high strain zone of steep foliation with gently plunging mineral elongation lineations with no consistent sense of shear. A tentative model is proposed whereby top-to-the-south overshear in the Rupal area passes northwards into a steep belt of apparently constrictional N-S elongation. This type of large-scale transpression may record the early growth of the syntaxis. However, relating these structures to Himalayan orogenesis and the amplification of the NW syntaxis is problematic. The Nanga Parbat massif displays a long and complex history of polyphase deformation, metamorphism and magmatism, as might be expected of a terrane derived from the basement of the Indian sub-continent. Although at least the later part of the constrictional steep belt developed with syn-kinematic leucogranite intrusions (< 10 Ma), the old age limit on the Rupal Shear Zone remains unconstrained.
Geochronological constraints on the evolution of the Nanga Parbat syntaxis, Pakistan Himalaya
Authors: Treloar P. J. , Rex D. C. , Guise P. G. , Wheeler J. , Hurford A. J. , Carter A.
Published: April 2008

New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission track data are presented from the western margin of the Nanga Parbat syntaxis as well as from the Indus and Astor valley sections which cross the syntaxis. Amphibole data date a regional cooling through 500°C at 25±5 Ma and are inconsistent with earlier suggestions that the peak of regional metamorphism was Neogene in age, although there is no doubt that some rocks were still at upper amphibolite facies temperatures as recently as 5 Ma. The data can be used to constrain structural models for syntaxial uplift. After an initial phase of crustal-scale buckling, bodily uplift of the syntaxis was along subvertical shear zones developed along its margins, although with a significantly higher time-averaged strain rate for shears developed along the western margin than along the eastern margin. The latter may be antithetic to the former. These shears were operative from 10 to < 1 Ma. In the southwestern part of the syntaxis, this subvertical uplift was superseded, since 6 Ma, by uplift along moderately SE-dipping NW-vergent shears on the hanging wall of which are located Neogene-aged migmatites.