bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conduit flow and fragmentation
Authors: Mader H. M. 
Published: April 2008

Abstract
This chapter provides a critical overview of syn-eruptive processes between magma chamber and vent in magmatic, sustained, Plinian-type eruptions. Phreatomagmatic effects are largely neglected. The main sources of information derive from textural studies of ejecta, theoretical models and physical experiments of eruption dynamics. Textural studies commonly find bimodal vesicle populations, indicative of several discrete nucleation events. The degree of disorder increases with explosivity. Dynamical parameters, such as nucleation density and rate and bubble growth rate, can be inferred from studies of the moments of bubble size distributions. Vesicularity in pumices is observed to vary significantly both within and between deposits, which suggests that the vesicularity at fragmentation is affected by the flow dynamics. Vesicularity variations correlate most closely with changes in magmatic composition and viscosity, but not with discharge rate. Conduit flow models can be broadly grouped into first- and second-generation models; the former generally impose a lithostatic pressure gradient and a constant Newtonian viscosity, whereas the latter include equations for the rheological changes that take place during vesiculation and solve for the pressure. Second-generation models derive highly non-lithostatic pressure gradients with the result that most of the vesiculation occurs at a high rate over a short distance just prior to fragmentation. The mechanisms of brittle and ductile fragmentation have been investigated in separate studies in non-vesiculating magmas, but which mechanism operates in explosive eruptions is not known. Dynamical laboratory experiments provide observations of the physical processes operating in conduit flows. Gas-expansion experiments have shown that it is possible to generate violent explosions by unloading in cool magmatic materials. Expanding dusty flows are found to be stable only if the bulk density increases with height. Exsolution experiments have demonstrated that acceleration precedes fragmentation and that gas evolution is enhanced by advection and bubble deformation. Deformed vesicles similar to those found in ‘woody’ pumice have been generated in an analogue system that has similar rheology to that found in vesiculating magmas. Large-scale exsolution experiments suggest that explosive volcanic eruptions are inherently heterogeneous: the fluctuations in discharge rate and discrete pulses and shocks commonly observed are a consequence of the large physical scale of volcanic systems. The effect of the magma chamber and conduit geometry has also been investigated. Eruption of material from a spherical flask up a narrow cylindrical tube generates quasi-steady flow conditions after an initial transient during which the discharge rate grows, as frequently observed in volcanic eruptions. The fragmentation surface does not propagate down into the magma chamber.
Palaeosurfaces and associated saprolites in southern Sweden
Authors: Lidmar-Bergström Karna , Olsson Siv , Olvmo Mats 
Published: April 2008

Abstract
Saprolite remnants from different palaeosurfaces in southern Sweden have been analysed by XRD and SEM analyses. They represent two clearly different types. The first is a clay- and silt-rich saprolite with a kaolinite-dominated clay mineral association representative of mature saprolites and with chemically altered quartz grains. This saprolite type is associated with sub-Cambrian, sub-Jurassic and sub-Cretaceous denudation surfaces. The second type is gravelly and in a youthful stage of alteration with mainly vermiculitic clay minerals in the fine fractions. Microtextures developed on quartz grains indicate a mainly mechanical breakdown. Compared to overlying till beds this saprolite is in a more advanced stage of chemical alteration. It is not associated with any specific denudation surface. Its characteristics and thickness indicate a Plio-Pleistocene age.
The saprolites represent deep weathering of the bedrock surface at different times. The weathering resulted in thin kaolinitc saprolites during the Late Proterozoic, thick kaolinitic saprolites from the latest Triassic through the Jurassic and Cretaceous, and medium thick immature saprolites from the Pliocene and onwards. The depth of the deep weathering has been decisive for the shape of the present relief and thus etch processes have been of fundamental importance in shaping the relief, even in a formerly glaciated area.
Preservation of old palaeosurfaces in glaciated areas: examples from the French western Alps
Authors: Battiau-Queney Yvonne 
Published: April 2008

Abstract
Remnants of deeply-weathered rock have been recorded in many regions which were ice-covered during the Pleistocene. They generally belong to shields and Palaeozoic massifs. This paper presents an example from the French Alps which testifies to the good preservation of very old (> 200 Ma) landforms in a high relief area situated on the western side of the ‘Grandes Rousses’ which was entirely covered by ice 30 000 years ago. Sedimentary structures, such as ripples on sandstone bedding planes and other erosional near-shore features, dating back to the Late Triassic before the development of the north, passive, margin of the Tethys ocean, are found in this high relief area. These are remarkably well preserved and occur in close proximity to typical glacial landforms. More generally, widespread elements of a pre-Triassic erosional surface are still recognized in the present landscape. Evidently, ice was unable to obliterate these 200 Ma old features in a high mountain area which was strongly glaciated 30 000 years ago.
Rock weathering in blockfields: some preliminary data from mountain plateaus in North Norway
Authors: Whalley W. Brian , Rea Brice R. , Rainey Michelle M. , McAlister John J. 
Published: April 2008

Abstract

The formation of blockfields is a process usually attributed to weathering. In mountain areas this is generally assumed to be mechanical weathering (frost shattering). Evidence from two high plateaus [900 and 1350 m above sea level (a.s.l.)] in North Norway (
c.
70°N) suggests that chemical action is at least as important as mechanical activity in blockfield formation. The bedrock in both areas consists of complex banded gabbros. Blockfields circumscribe ice masses and are generally > 1 m thick. They contain high percentages of material in the silt and clay sized fractions, including a variety of clay minerals: gibbsite, chlorite, vermiculite and kaolinite, as well as magnetite/maghemite. The blockfield thickness and presence of these weathering products suggests both a considerable (pre-Pleistocene) length of time required for development as well as warmer conditions than are found now (mean annual air temperature
c.
0°C) or in the period since deglaciation. It is suggested that these blockfields represent a preglacial palaeosurface which formed initially under warmer conditions and has survived, largely intact, beneath all the Pleistocene ice sheets.
Environmental changes during the Tertiary: the example of palaeoweathering residues in central Spain
Authors: Borger Harald 
Published: April 2008

Abstract
In central Spain three main weathering phases are found which can be put in a chronological sequence with tectonic and sedimentation phases. Weathering intensity, as recorded by micromorphological analysis, has plainly decreased during the course of the Tertiary reflecting the prevailing environmental conditions.
During the Palaeogene intensive chemical activities produced, on the mineral grains of the deeply decomposed rocks, features typical of humid tropical climate.
In the Miocene the Palaeogene regolith of the southern Tajo Basin was truncated and partly incorporated into sediments which comprise reworked weathering residua of this basin and of the adjoining Montes de Toledo. After sedimentation another weathering phase started. During this phase the feldspars were heavily corroded, but in contrast to the Palaeogene residues, the quartz shows hardly any features caused by etching.
In the Pliocene the rañas were deposited during a second main transportation phase. Particularly in the SE of the Montes de Toledo, these sediments were subjected to intense weathering, but only where conditions were favourable. Due to sufficient soil humidity in intramontane basins, high temperatures, and presence of iron, quartz corrosion was locally possible once more during Pliocene times. The rañas of the Tajo Basin, however, were substantially less attacked.
Palaeoweathering profiles developed on the Iberian Hercynian Basement and their relationship to the oldest Tertiary surface in central and western Spain
Authors: Ballesteros E. Molina , Talegón J. García , Hernández M. A. Vicente 
Published: April 2008

Abstract

On the southwest border of the Duero Basin the Hercynian basement of the Iberian Peninsula is fossilized by a siderolithic sedimentary cover whose thickness increases progressively eastward. Two different palaeoweathering mantles have developed in this zone. From west to east, these mantles are progressively separated in the vertical sense. Whereas the lower mantle affects the Hercynian basement to a depth of > 18–20 m, being fossilized eastward by the siderolithic cover, the upper mantle affects both the Hercynian basement to the west and the siderolithic cover to the east to a depth of
c
. 3–5 m.

Mineralogical, petrographic and geochemical techniques have shown that the lower mantle shows an upward destruction of the parent minerals with the development of new 2 : 1 phyllosilicates (smectite-like minerals) in the middle levels of weathering and an enrichment in 1:1 phyllosilicates in the upper levels. By contrast, the higher weathering mantle shows important palaeosol features, an enrichment in CT opal, oxyhydroxides mobilizations and occasional concentrations of alunite dated at 58–67 Ma.
A planation surface appears related to the uppermost of these mantles, its remnants now uneven owing to the Alpine tectonic phases. Eastward, the Tertiary sediments of the Duero Basin unconformably fossilize the remnants of this palaeosurface.
The geochemistry of Indian bole horizons: palaeoenvironmental implications of Deccan intravolcanic palaeosurfaces
Authors: Widdowson M. , Walsh J. N. , Subbarao K. V. 
Published: April 2008

Abstract
Deccan intravolcanic bole horizons represent weathering products formed during major hiatuses of a major volcanic episode. In these quiescent periods weathering processes pervasively altered the newly formed volcanic landscape and subsequent flows covered and effectively fossilized the resulting weathered palaeosurfaces. The current work is a detailed geochemical study which examines patterns of element mobilization during these intravolcanic weathering events.
The bole horizons normally rest on top of altered basaltic lavas. Both boles and altered lavas represent a comparatively early stage in weathering because the content of chemically residual elements, such as aluminium and iron, are closer to fresh basalt than laterite. Nevertheless, these is clear evidence for significant chemical alteration because the more mobile elements such as calcium and sodium have been substantially removed. A chemically distinctive nature for some boles can be demonstrated from chondrite normalized REE plots and, in these instances, strontium and neodymium isotopic compositions demonstrate that the fine-grained bole material is derived from a chemically distinct source. In addition, thin sections reveal that these fine grained portions commonly contains glass shards and occasionally fresh phenocrysts. It is therefore suggested that many Deccan boles are in fact weathered pyroclastic material, and that the pyroclastic content of the basaltic succession may be greater than previously supposed. A significant pyroclastic input during the Deccan eruptions has important palaeoenvironmental implications for the fate of late Cretaceous flora and fauna in peninsular India.
Remote sensing for mapping palaeosurfaces on the basis of surficial chemistry: a mixed pixel approach
Authors: White Kevin , Drake Nick , Walden John 
Published: April 2008

Abstract
Palaeosurfaces are often characterized by distinctive surficial material compositions; for example, iron oxide in lateritic surfaces in India or calcium carbonate in calcreted surfaces in Africa. The chemical constituents of interest often play a significant part in the induration, and hence the preservation, of palaeosurfaces. Furthermore, these components often have distinct spectral reflectance characteristics, enabling them to be detected from multispectral remote sensing systems. However, traditional image processing techniques, such as classification, are inappropriate for mapping such phenomena, which usually exhibit a gradually-varying distribution. In studies of palaeosurface development, the requirement is for data that provide quantitative estimates of the surficial material composition (i.e. the proportions of a given component, such as iron oxides, within an image pixel). Algorithms based on compositional analytical techniques can be applied to unmix the pixel spectral response into estimates of the proportions of the image components (such as vegetation, iron oxides, etc.) within each pixel of an image. The resulting fraction maps provide a powerful technique for mapping palaeosurfaces and analysing their development. This paper demonstrates how these techniques have been applied to studies of Quaternary piedmont surfaces in the Tunisian Southern Atlas.
Orogeny through time: an overview
Authors: Burg Jean-Pierre , Ford Mary 
Published: April 2008

Abstract
As an introduction to a diverse set of papers on orogenic studies we present a personal overview of the most notable developments in orogenic studies since the 1960s. The impact of new techniques such as deep reflection seismic profiling, geochronology, analogue and numerical modelling is discussed. The major geodynamic models and concepts which have stimulated orogenic studies in recent years are also considered.
Rheology of the lithosphere in space and time
Authors: Ranalli Giorgio 
Published: April 2008

Abstract
The rheology of the lithosphere is a factor of primary importance in the kinematics and dynamics of mountain belts. This paper attempts to clarify the role of rheology in orogenesis, by applying simple physical principles to the analysis of tectonic processes. The emphasis is on broad generalizations leading to order-of-magnitude estimates. Since the rheology of lithospheric materials is strongly dependent on temperature, the discussion opens with a review of continental and oceanic geotherms and an assessment of their reliability. Then the brittle (frictional) and ductile (high-temperature creep) properties of the lithosphere are considered. In the brittle field, particular attention is paid to the problem of fault reactivation, which is shown to be more likely in extensional than in compressional regimes. In the ductile field, a summary of creep parameters for the most common lithospheric materials is presented. The central concept of rheological profiles (strength envelopes), essential to the estimation of the depth variations of lithospheric rheology, is discussed with reference not only to its applicability but also to its limitations (a two-dimensional example from the Canadian Cordillera is given). Processes related to the rheological properties and layering of the lithosphere — gravitational collapse in thickened and softened crust, tectonic inversion following the detachment of a lithospheric root, lower crustal ductile flow with consequent relaxation of Moho topography — are analysed semi-quantitatively, mainly to show that they are indeed likely to be important players in geodynamics. Finally, in a brief Archaean detour, some possible important differences between present-day and Archaean oceanic lithosphere are examined, and the conclusion is reached that in all likelihood plate tectonics, although at different rates, has been the main agent of orogenesis during most of the history of the planet.
Geodynamic evolution of the Proterozoic Mount Isa terrain
Authors: O’Dea M. G. , Lister G. S. , Maccready T. , Betts P. G. , Oliver N. H. S. , Pound K. S. , Huang W. , Valenta R. K. , Oliver N. H. S. , Valenta R. K. 
Published: April 2008

Abstract

The Proterozoic Mount Isa terrain records the effects of four periods of intraplate tectonism. The
c
. 1870 Ma Barramundi Orogeny was characterized by a massive felsic magmatic event, and global correlations suggest a physical link between Australia and Laurentia at this time. Thereafter, the terrain underwent an extensional history spanning 200 Ma involving repeated episodes of rifting, post-rift subsidence and associated depositional and magmatic phases. This protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25 km above attenuated continental crust. Rifting was interrupted prior to the formation of ocean crust by the compressional Isan Orogeny (1590–1500 Ma). The Isan Orogeny was synchronous with low-pressure high-temperature metamorphism and widespread metasomatism. In the waning stages of shortening, the Mount Isa terrain evolved into a wrench system characterized by an extensive network of strike-slip faults. The current level of exposure in this terrain provides spectacular examples of superimposed rifts, basin inversion, and wrench geometries developed at middle to upper crustal levels.
Climatic cyclicity and accommodation space in arid to semi-arid depositional systems: an example from the Rotliegend Group of the UK southern North Sea
Authors: Howell John , Mountney Nigel 
Published: April 2008

Abstract
The arid to semi-arid, continental deposits of the Permian Rotliegend Group of the UK southern North Sea (SNS) provide an ideal opportunity to test and further the concepts of sequence stratigraphy in fully non-marine depositional systems. Although these depositional systems are detached from the effects of sea-level change, cyclic fluctuations in the climatic regime result in variations in the vertical facies successions laid down. The effects of increasing or decreasing aridity upon depositional processes are considered. Climatic cycles, bounded at the point of lowest aridity are defined. These climatic cycles have been correlated between different, co-existent depositional environments. This enables depositional systems, such as those present in the Rotliegend, to be considered chronostratigraphically. The application of these concepts to an extensive data set illustrates that, whilst the internal architectures of sedimentary cycles are controlled by the depositional processes and their positions within the basin, the thickness of the cycles directly reflects the rate of accommodation creation.
The Penarth Group-Lias Group succession (Late Triassic-Early Jurassic) in the East Irish Sea Basin and neighbouring areas: a stratigraphical review
Authors: Warrington Geoffrey 
Published: April 2008

Abstract

Small, widely separated outliers of latest Triassic and Early Jurassic rocks in and around the East Irish Sea are preserved in the hangingwall blocks of faults that were active during post-Pliensbachian-pre-Cenomanian times. The successions preserved in the outliers comprise the Penarth and Lias groups, in typical facies and with characteristic microfloras and macrofaunas, and are vestiges of a formerly extensive cover of those rocks to the northwest of their main outcrops in England. The Penarth Group, of Rhaetian (Late Triassic) age, comprises the Westbury Formation and the succeeding Lilstock Formation; the latter is represented largely, or entirely, by the Cotham Member. Lias Group successions preserved in the outliers include, above the basal (‘pre-planorbis’) beds, of latest Triassic age, Early Jurassic beds ranging in age from Hettangian (
planorbis
Zone) to Pliensbachian (
spinatum
Zone) and are considerably thicker than their correlatives in eastern England, indicating that subsidence was slower there than in western Britain in Hettangian, Sinemurian and Pliensbachian times.
The Mesozoic and Tertiary history of the Irish Sea
Authors: Cope John C. W. 
Published: April 2008

Abstract
Uplift centred on the Irish Sea in latest Cretaceous times accompanied by a locally raised geothermal gradient is supported by apatite fission track analyses from the area, the outcrop patterns of the Mesozoic rocks of England and the positive gravity anomalies over the whole of the Irish Sea region. This conclusion allows more precise modelling of the history of the region and the lost Mesozoic cover can be reconstructed, with varying degrees of certainty, by combining the results of extrapolation from existing land and submarine outcrops and subcrops, with the amount of cover lost. Stratigraphical considerations suggest the occurrence of both Late Cimmerian and latest Cretaceous inversions of the Irish Sea area. Following rapid erosion of the central part of the domed area in the Palaeogene, alluvial plain sedimentation was established over the Irish Sea region, developing around valleys cut through the Mesozoic sediments of the area. Deflation of the dome and accompanying faulting allowed the sea to enter the area, initially primarily through St George’s Channel in the early Oligocene and into the whole of the basin in Neogene times.
Clastic sabkhas and diachroneity at the top of the Sherwood Sandstone Group: East Irish Sea Basin
Authors: Thompson Jillian , Meadows Neil S. 
Published: April 2008

Abstract
The identification of early evaporite sulphate cements with a marine isotopic signature within the Ormskirk Sandstone Formation supports previous models of diachroneity at the contact of the Sherwood Sandstone Group and the Mercia Mudstone Group in the East Irish Sea Basin. Basin-wide correlations suggest that, at the onset of transgression, a range of sandflat and aeolian dune environments co-existed on the margins of the basin with marginal marine environments toward the basin centre. One of the major implications of this model is that the high quality aeolian sandstone reservoirs encountered near the top of the Ormskirk Sandstone in the southern parts of the East Irish Sea Basin have no reservoir correlatives in large areas of the basin but can be predicted on the margins.
Fault analysis of the Cheshire Basin, NW England
Authors: Chadwick R. A. 
Published: April 2008

Abstract
The Cheshire Basin forms a segment of the N-S trending English Channel-East Irish Sea rift. The southern part of the basin has classic half-graben geometry, with the Wem-Bridgmere-Red Rock Fault system forming its southeast margin, whereas its northern part is much more symmetrical with much smaller basin margin faults. Fault strikes also show systematic differences between the southern and northern parts of the basin. In the south, dominant NE-SW (Caledonoid) fault-strikes indicate a strong degree of basement control, particularly at the faulted southeast margin. Farther north, numerous faults with N-S strikes constitute the majority of faults within the basin. They are interpreted to have formed perpendicular to the initial basin-forming extension (roughly E-W), and suggest a much weaker basement influence. Fault displacement analysis also reveals a N-S split, with two distinct fault populations showing different fractal (power-law) distributions. In the south, extension was concentrated on the large, dominantly oblique-slip basin margin faults, whereas in the north, extension was distributed on numerous small to medium-sized dip-slip faults. The two fault populations are attributed to a variable degree of basement control. Major reactivated Caledonian basement structures controlled basin faulting in the southern part of the basin, whereas farther north the basin faults developed more-or-less independently of a less faulted, more isotropic basement. Estimates of extension magnitude, incorporating the ‘hidden’ contributions of small faults, indicate local basin extension factors in the range 1.07–1.16 (7–16%). However, because of difficulties in measuring the true heaves of the basin margin faults, these values are likely to be minimum estimates.