bluuebunny/crossref_metadata_2025 huggingface dataset:
The Jabel Sayid complex, Arabian Shield: geochemical constraints on the origin of peralkaline and related granites
Authors: HARRIS N. B. W. , MARZOUKI F. M. H. , ALI S.
Published: December 2007

The Jabel Sayid Complex comprises two principal rock types which require distinct source regions. An earlier intrusion (572 ± 24 Ma) of biotite-hornblende monzogranite displays selective enrichment of
LIL
elements and depletion of
HREE
characterizing a calc-alkaline magma derived from a garnet-bearing source within a hydrated mantle wedge. The younger intrusion (534 ± 40 Ma) is an aegirine-arfvedsonite peralkaline granite which can be derived neither by fractionation of a calc-alkaline magma, nor by closed-system anatexis of a crustal source. This granite is enriched in HFS elements and strongly depleted in Sr, Ba and Eu, and requires the contribution of a fluorine-bearing fluid phase. This volatile phase has resulted in a range of metasomatic rock types including an aplitic rim which carries extreme levels of HFS elements and is a potential economic source of U, and a red granite characterized by widely ranging trace element abundances and strong Eu depletion. The peralkaline granite is typical of siliceous melts derived from an intra-plate tectonic environment, with trace elements strongly controlled by volatiles which are probably mantle-derived. The role of crustal contamination on such granites can neither be proved nor excluded.
The submarine eruption and emplacement of the Lower Rhyolitic Tuff Formation (Ordovician), N Wales
Authors: HOWELLS M. F. , REEDMAN A. J. , CAMPBELL S. D. G.
Published: December 2007

The Lower Rhyolitic Tuff Formation (up to 600 m thick) represents an eruptive cycle of acidic ash-flow tuff which is stratigraphically associated with marine sediments and subaqueously emplaced basalt lavas. The formation comprises volcaniclastic and pyroclastic megabreccias and breccias, massive welded and non-welded acidic ash-flow tuffs, reworked tuffs and tuffities, siltstones, rhyolite intrusions and extrusions. Its basal contacts vary from conformable, to disconformable and unconformable. The inter-relationships of these variations to pre-, syn- and post-emplacement structures define a submarine, asymmetric downsag caldera. The main eruptive centre, coincident with the thickest accumulation of intracaldera tuffs, lies close to its north margin, on the north side of the Snowdon Massif. To the SW, the intracaldera tuffs thin progressively and much of the formation comprises tuffs reworked in the vicinity of a Caradocian shoreline. To the NE and E, outflow tuffs escaped into a deeper marine basin. Many of the features of the caldera are similar to those of subaerial calderas, and it is concluded that the enveloping sediments and lavas, and the character of the reworked tuffs, hold the key to the recognition of its submarine development. Subsequent resurgence resulted in only local and short-lived emergence of the intracaldera tuffs.
The Sticklepath-Lustleigh fault zone: Tertiary sinistral reactivation of a Variscan dextral strike-slip fault
Authors: HOLLOWAY S. , CHADWICK R. A.
Published: December 2007

Dextral strike-slip movement on the Sticklepath-Lustleigh fault zone (SLFZ) is indicated by displacements of ?Permian and older rocks. Previous authors have inferred that the main dextral movement which caused these displacements was post- Permian and, noting the presence of small Tertiary pull-apart basins along the fault zone, probably of Tertiary age. However, the geometry of these early Tertiary pull-apart basins indicates sinistral rather than dextral strike-slip movement. We present an alternative model for the history of the Sticklepath-Lustleigh fault zone, summarized below:

1 Late Variscan strike-slip movement, with a total displacement of up to 10 km, produced the SLFZ and offset dextrally an earlier Variscan thrust.

2. Extensional reactivation of this thrust led to rapid Permo-Triassic subsidence in the Crediton Trough and a dextrally offset neighbour, the Hatherleigh outlier.

3. Approximately 6 km of early Tertiary sinistral movement on the SLFZ produced small pull-apart sedimentary basins, and reduced the net dextral offset across the fault.

4. In mid-Tertiary times, minor dextral movements on the SLFZ may have produced reverse faulting on the margins of the Tertiary basins.
Glasgow, a case study in urban geology
Authors: BROWNE M. A. E. , FORSYTH I. H. , McMILLAN A. A.
Published: December 2007

A long history of mining and quarrying in Glasgow has left a legacy of engineering problems. Thematic mapping by the British Geological Survey, which takes account of all the available evidence on the distribution of man-made hazards and relevant geological factors, is assisting local and national planning departments in the preparation of proposals for urban renewal and development. Key features described include: lithology, thickness and generalized engineering properties of the drift deposits; bedrock geology; and undermining, with the emphasis on workings close to rockhead.
High-pressure metamorphism of the Zermatt-Saas ophiolite zone, Switzerland
Authors: BARNICOAT A. C. , FRY N.
Published: December 2007

Within the Zermatt–Saas ophiolite zone of the western Alps a record of polystadial high-pressure metamorphism is well preserved. Early blueschist assemblages, retained as inclusions in garnets, were succeeded by eclogitic assemblages which in some rocks contained lawsonite, kyanite, talc and chloritoid. These eclogitic assemblages formed by prograde reaction from the early blueschists. Subsequently, reaction of these eclogites with a mixed H
2
O-CO
2
, vapour phase led to the replacement of kyanite by paragonite and the partial replacement of omphacite-garnet paragenses by assemblages containing glaucophane, paragonite and ankerite. High-pressure, eo-alpine metamorphism took place under conditions of 550–600°C and 17.5–20 kbar. Values of
a
H
2
O between 0.55 and 1 are high enough to accommodate equilibration with a water-rich vapour phase under the highest-grade conditions. The presence of such a fluid phase is locally indicated by the presence of quartz-rich veins containing omphacite and kyanite. This vapour phase was absorbed during retrogression. Later, rehydration is limited to areas close to albite veins, tectonic contacts and bodies of metasediment.

The metamorphic conditions determined for the Zermatt-Saas zone are compatible with those suggested for over- and under-lying units. These conditions, and the P–T path inferred by comparing the reaction histories with a petrogenetic grid for the system Na
2
O-CaO-MgO-A1
2
O
3
-SiO
2
-H
2
O, suggest that metamorphism occurred during subduction to depths of between 60 and 70 km and subsequent exhumation during the Alpine orogeny.
Major, minor and trace element mobility in the acidic upland forested catchment of the upper River Severn, Mid Wales
Authors: NEAL C. , SMITH C. J. , WALLS J. , DUNN C. S.
Published: December 2007

Variations in the major, minor and trace element concentrations in two streams within a coniferous forest are described and are related to hydrological and hydrogeochemical factors. The rainfall chemistry reflects a maritime influence although there are occasional pollutant inputs (pH 4–5). Streamwater chemistry variations are strongly dependent upon flow. Baseflow chemistry, determined by reactions in the inorganic soils and bedrock, is of a Mg-Ca-HCO
3
type (pH 6–7.5); mineralization yields up to a four-fold increase in Ca, HCO
3
, Zn and SO
4
concentrations (pH ~ 0.5 units higher). Stormflow chemistry reflects hydrogeochemical processes in the organic soil horizons; the stormflow waters are acidic (pH ~ 4.5) and are enriched, by an order of magnitude, in H
+
, AI, Y, Co and Mn. Mineral equilibrium calculations have been applied to aluminium hydroxides, crystalline and amorphous aluminosilicates and hydroxy aluminium sulphates to determine the degrees of mineral saturation in the streamwaters. Ion exchange reactions have been evaluated to describe the consequences of natural variations in atmospheric salt loadings and evapotranspiration on the stream water chemistry and to explain low Na/Cl ratios in storm waters.
Weathering rates of gneiss and depletion of exchangeable cations in soils under environmental acidification
Authors: PACES T.
Published: December 2007

Budgets of Na, K, Mg, Ca, Al and Si in two forested basins in central Europe indicate that the weathering rate of gneiss and the depletion of exchangeable calcium and magnesium are increased due to acidification caused by high deposition of SO
2
. The production of the pool of exchangeable cations is slower than its depletion. There is a coincidence of a very short time necessary to deplete the topsoil of the exchangeable Ca
2+
and Mg
2+
and the die-back of spruce. These conclusions are derived from a new mass-balance approach that enables a separation of hydrolysis of primary minerals, depletion of exchangeable ions and production of the exchangeable pool of cations in soils from data on elemental budgets in small hydrological basins.
GLORIA investigations of oceanic fracture zones: comparative study of the transform fault zone
Authors: SEARLE R. C.
Published: December 2007

The tectonic patterns of some twenty spreading centre offsets have been determined using the long range sidescan sonar GLORIA and are reviewed in this paper. Offsets of less than about 20 km fail to produce transform faults but are accommodated by short sections of oblique spreading (with overlapping spreading centres in the fast spreading case). At slow slip rates such offsets can be associated with topographic fracture zones that are indistinguishable from those produced at true transform faults. Such features may account for a significant proportion of spreading centre offsets on slowly spreading mid-ocean ridges. Offsets larger than about 30 km produce a true 'transform fault'. This comprises a 1 to 5 km-wide band of individual faults that are parallel or subparallel to the spreading direction. The band corresponds to the 'Transform Fault Zone' (TFZ) of continental wrench faulting. It includes the 'Principal Transform Displacement Zone' (PTDZ) and secondary structures such as Riedel shears. A narrow TFZ is normally associated with a prominent PTDZ, which appears to be either a narrow furrow or a single scarp; on the other hand wider zones often fail to show a clear PTDZ on GLORIA. Both types are common on the slowly spreading Mid-Atlantic Ridge, and may even occur at different points along the same large offset transform (such as Romanche), although the narrow type appears to occur preferentially where the local Ridge axis is oblique to the spreading direction. Narrow TFZs and prominent PTDZs appear to be more common on the fast spreading East Pacific Rise. It is suggested that broader TFZs and less prominent PTDZs may form in response to the complicating effects of small components of compression across the transform fault, perhaps as a result of departure of the transform fault trace from a true small circle. Such compression would be more easily supported in the thicker, stronger lithosphere of slowly spreading ridges, but could be relieved by tension due to the ridge-push force where the ridge is oblique to the spreading direction.
Strike-slip fault styles in slow-slipping oceanic transform faults—evidence from GLORIA surveys of Atlantis and Romanche Fracture Zones
Authors: PARSON L. M. , SEARLE R. C.
Published: December 2007

Long range sidescan sonar data covering active sections of two transform fault zones are presented to illustrate the range of structures observed during the surveying of several Atlantic fracture zones. The trace of the actively slipping component, the Principal Transform Displacement Zone, is identified and its configuration interpreted in terms of either extensional/compressional stress systems or oblique motion at the plate boundaries.
Anomalous oceanic lithosphere formed in a leaky transform fault: evidence from the Western Limassol Forest Complex, Cyprus
Authors: MURTON B. J.
Published: December 2007

Detailed studies in the Western Limassol Forest Complex, Cyprus have revealed plutonic and structural histories that differ markedly from the Penrose type ophiolite of the Troodos Massif to the north. A tectonized harzburgite of upper mantle origin acts as host to multiple mafic and ultramafic intrusions, forming a plutonic core complex. Mafic and picrite dykes cut and are cut by E–W trending shear zones, demonstrating syn-tectonic magmatism. A retrogressive metamorphic and progressive cooling history of the intrusive suite indicates uplift of the host, mantle harzburgite while in a sea-floor setting. It is suggested here that the geological evolution of the Western Limassol Forest Complex indicates formation of anomalous oceanic lithosphere in the active domain of an Upper Cretaceous, leaky transform fault.
Thrust tectonics, deep structure and crustal subduction in the Alps and Himalayas
Authors: BUTLER R. W. H.
Published: December 2007

The structural restoration of collision orogenic belts onto crustal templates provides important insights into the tectonic evolution, deep structure and amounts of plate convergence after the initial contact between two continental masses. Balanced cross-sections have been constructed, parallel to the local displacement directions, across the western Alps and western Himalayas and demonstrate very large amounts of crustal shortening above intra-crustal detachments. To achieve a balance, substantial volumes of lower crust must have been subducted beneath the two tectonic hinterlands. A model of eclogite metamorphism is invoked to facilitate this subduction and to explain the varying isostatic responses of the Alpine and Himalayan hinterlands. Patterns of eclogite metamorphism are controlled by the geometry of thrust profiles on a lithospheric scale: the development of crust-mantle detachments being of crucial importance. Such a profile is proposed for the Himalayas, suggesting that relatively small volumes of the footwall crust succumbed to eclogite metamorphism. In the Alps however, a steeper thrust profile apparently developed, emplacing mantle onto crust, causing wholescale eclogite metamorphism in the underlying Franco–Swiss crust. The resultant density increase would provide a mechanism of isostatic collapse and flexural subsidence in the Po plain region.
40
Ar–
39
Ar step-heating ages of the Tertiary igneous rocks of Mull, Scotland
Authors: MUSSETT A. E.
Published: December 2007

Twenty-one samples from throughout the Mull Tertiary igneous succession were dated. Of these, eight gave a satisfactory age plateau and the dates show a systematic decrease throughout the succession. Extrusion of the lavas began
c
. 60 Ma ago, contemporaneous with the bulk of activity in the British Tertiary igneous province. Igneous activity continued until
c
. 57 Ma. Probably the lavas were extruded during the reversely magnetized chron 26r; development of the central igneous complex continued into the normal chron 26, while the late dykes were intruded during 25r. If this is so then, according to the polarity timescale of Harland
et al.
1982, the duration of igneous activity lies between 0.7 and 4.7 Ma, consistent with the dates. The usefulness of the age plateau selection criteria of Lanphere & Dalrymple (1978) is supported by the results.
Post-Triassic continental hypsometry and sea level
Authors: WYATT A. R.
Published: December 2007

Application of modern hypsometric relationships to ancient continental groupings requires changes in ocean basin volumes through time and hence sea level. A global sea-level change curve, based on current knowledge of continental evolution from the base of the Jurassic, is presented. Variation in sea level for most of the Mesozoic, requiring explanation by mechanisms other than the area–elevation effect, was of the order of 160 m; a major lowering of sea level started in the late Cretaceous and continued into the Cenozoic. This major change can be explained by changes in ocean ridge volumes.
Dipping reflectors in the Norwegian Sea—ODP Leg 104 drilling results
Authors: ELDHOLM O. , THIEDE J. , TAYLOR E. , BJØRKLUND k. , BLEIL U. , CIELSIELSKI P. , DESPRARIES A. , DONNALLY D. , FROGET C. , GOLL R. , HENRICH R. , JANSEN E. , KRISSEK L. , KVENVOLDEN K. , LEHURAY A. , LOVE D. , LYSNE P. , MCDONALD T. , MUDIE P. , OSTERMAN L. , PARSON L. , PHILLIPS J. , PITTENGER A. , QVALE G. , SCHOENHARTING G. , VIERECK L. , MORTON A. , GIBSON I.
Published: December 2007

The following is an extended abstract of a paper presented at the Marine Studies Group meeting ‘Structure of Continent-Ocean Boundaries’
, 11
December
1985.

Ocean Drilling Program (ODP) Leg 104 successfully completed a number of deep drill holes on the Outer V0ring Plateau and the Vering Basin during July and August 1985 (Fig. 1; Eldholm, Thiede, Taylor et al. 1986). One of the principal objectives of the leg was to drill and sample a thick oceanward-dipping wedge of seismic reflectors, known to characterize much of the multichannel seismic (MCS) profile data recorded across ocean-continent transitions in the NE Atlantic north of 55°N. Elsewhere, these reflectors have previously been the target of deep drilling during Legs 48 and 81 of the International Phase of Ocean Drilling IPOD (Montadert, Roberts et al. 1979; Roberts, Schnitker et al. 1984). These efforts met with some success, sampling only the uppermost part of the sequence and identifying a series of tholeiitic lava flows. Over the Outer V~ring Plateau, a number of MCS profiles reveal a distinct change in seismic character at the base of the well-stratified dipping reflector sequence, where an irregular surface characterized by a band of low-frequency, high-amplitude reflectors occurs. This surface is referred to as K. Prior to Leg 104, therefore, relatively little was known regarding the variation in petrographic character of the flows at depth, their evolution and origin, and particularly the character of the material below the reflector sequence. A single deep drillhole (642E) successfully recovered a section through the
Sediment supply to the continental shelf by the major rivers of China
Authors: WANG YING , REN MEI-E , ZHU DAKUEI
Published: December 2007

The Yalu, Luan, the Yellow, Changjiang and Pearl Rivers, discharge 90% of China’s total annual input of 20.14 × 10
8
t of sediment to the sea. This huge volume of sediment is deposited in the river mouths and in the vicinity of the inner shelves in the form of deltas or submarine sandy ridges depending upon the dominant processes or dynamics of the area. Even though the continental shelves of the China Seas were coastal plains during the Late Pleistocene, modern river sediments rarely extend to the outer shelves except in response to changes in sea level.
The nautiloid cephalopods: a strange success
Authors: HOLLAND CHARLES HEPWORTH
Published: December 2007

The origin of the cephalopods from the Monoplacophora is briefly considered. The first rare Upper Cambrian
Plectronoceras
are now known to be succeeded by a later Cambrian radiation involving the Plectronoceratida, Ellesmeroceratida, and two other orders, all well documented from Chinese occurrences. The greatest success of the nautiloid cephalopods came in the Ordovician Period with three evolutionary pulses in the Tremadoc, Arenig, and later Ordovician. Three particular Palaeozoic problems are treated: gigantism in cephalopods, the orthocone operculum
Aptychopsis,
and the Chinese Pagoda Limestone as an example of an 'Orthoceras' limestone. Devonian developments included the origin of the ammonoids through their first suborder, the Bactritina; the origin of the coleoids; and the beginning of the long history of the coiled Nautilida. After a brief aside on the classification of the cephalopods, the Nautilida are treated in terms of their survival after the extinction of the ammonoids. Finally, there are comments on the living
Nautilus.
The three-dimensional morphology of arrays of echelon and sigmoidal, mineral-filled fractures: data from north Cornwall
Authors: NICHOLSON R. , EJIOFOR I. B.
Published: December 2007

Arrays of mineral-filled, echelon, sigmoidal fractures in cobbles of sandstone from the Crackington Formation of north Cornwall were examined by cutting serial sections. In three dimensions each array consists of a set of blade-like, mineral-filled fractures. These blades project as a fringe from the single but composite fracture that forms through their linkage. Linkage takes place as the strips of rock (bridges) between blades fail through cross-fracture. Cross-fractures give rise to the steps that mark the margins of the composite fractures so formed. Bridges show little penetrative deformation. Arrays are not zones of high ductile strain. Displacement is a consequence of dilatation. Echelon fractures were formed and opened by intruding hydrothermal fluid.
Geology and geochemistry of the Ojos del Salado volcanic region, Chile
Authors: BAKER P. E. , GONZALEZ-FERRAN O. , REX D. C.
Published: December 2007

Calc-alkaline volcanic rocks ranging in age from Miocene to Recent are encountered in the Ojos del Salado area (27°0'S, 68°45'W). They lie at the southernmost end of the Central Volcanic Zone, coinciding with a major morphological, seismic and volcanic discontinuity. It has previously been suggested that this Ojos del Salado lineament may represent a continental extension of the chain of islands and seamounts referred to as the 'Easter Hot Line'. The volcanic rocks of the area have been sub-divided into five groups based on K–Ar dates. The first three groups, all of Miocene age, show a progressive younging eastwards with a concomitant increase in K
2
O. The formation of Wheelwright and other caldera structures appears to date from the close of this phase (8–6 Ma). During the Pliocene the Group 4 volcanoes were constructed mainly along a line trending N65°E but a number of other cones developed around Wheelwright caldera which was partially filled by their products. Clockwise rotation of the volcanic axis continued in Pleistocene–Recent times with the eruption of the Group 5 volcanoes of Ojos del Salado. Extensive pumice flows were associated with this new volcanic chain and there is generally a shift to more acidic compositions, especially dacite. Apart from the increase in K and related elements from west to east in Groups 1 to 3, there is no evidence for any systematic compositional change. In particular, the youngest group of volcanoes with an east–west trend is geochemically indistinguishable from its predecessors on the dominantly north–south axes. Trace element ratios show similar trends, the rare earth element patterns are LREE enriched and the
86
Sr/
87
Sr initial ratios are all approximately 0.706. The Ojos del Salado volcanics are thus devoid of any compositional signature to link them with the Easter 'Hot Line'.
Biogenic indicators of suspended sediment transport in marginal marine environments: quantitative examples from SW Britain
Authors: MURRAY J. W.
Published: December 2007

Suspended sediment samples taken from the water column in the high energy Western English Channel and its Western Approaches contain size-sorted benthic foraminiferal tests, <200
μ
m in diameter, derived from the continental shelf sediments. Similar associations of small tests are found in estuaries where the indigenous living assemblages are totally different. Net transport from the shelf to the estuaries is therefore inferred to have taken place. Tests <200
μ
m in size are probably equivalent to quartz spheres of silt size and they indicate the net transport path for this size grade. An attempt has been made to quantify the transport budget and, in spite of the paucity of data, an order of magnitude estimate has proved to be possible.
Relationships between chemical and convective layering in the Earth
Authors: O'NIONS R. K.
Published: December 2007

This review principally addresses the question of convective isolation is the Earth's mantle as deduced from chemical and isotopic data. In particular it is shown that the isolation is imperfect and the interactions that occur account for a variety of geochemical phenomena.
Postulated restite fragments from Karoo picrite basalts: their bearing on magma segregation and mantle deformation
Authors: COX K. G.
Published: December 2007

Karoo picrite basalts from the Letaba Formation of SE Zimbabwe and the NE Transvaal contain rare but widespread multigrain aggregates of high-pressure orthopyroxene. These are of two types interpreted as (a) crystallization products of the host liquids, (b) restite fragments (refractory residue) from the zone of partial melting. The latter are characterized by strong lattice-preferred-orientation fabrics produced by simple flattening. It is speculated that such fabrics are generated either by the upward flow of magma through refractory residue or by earlier solid flow in the axial region of a diapir. Ultimately, magma segregation appears to be sufficiently vigorous to entrain restite fragments, and the apparent degree of partial melting may increase as restite is dissolved during ascent.
The role of fracture zones during early Red Sea rifting: structural analysis using Space Shuttle radar and LANDSAT imagery
Authors: CRANE K. , BONATTI E.
Published: December 2007

The structural pattern of the Red Sea region, an area where continental lithosphere is cut by a young oceanic rift, was studied by means of satellite and space shuttle radar imagery. The Space Shuttle Mission 2 made two passes over the Red Sea bracketing a region transitional between the southern Red Sea, where true seafloor spreading started about 5 Ma BP, and the northern Red Sea where crust is probably continental, though thinned and stretched. Structures on these passes define bands of shearing in the African and Arabian margins parallel to the Dead Sea Fracture Zone (000–020°). Combinations of these data with LANDSAT information reveal four shear bands along the margins of the Red Sea and one oblique to the Gulf of Suez. We have named the northern three Red Sea shear zones detected on the SIR-A data, the Brothers–Dead Sea Fracture Zone, the Zabargad Fracture Zone and the Shagara Fracture Zone. Two sets of normal faults were also detected, trending 330–340° (parallel to the northern Red Sea coastline) and 310–320° (parallel to the axial deeps in the Red Sea). A map of the 310–320° faults bordering the Red Sea resembles a V-shaped wedge narrowing to the north near the Gulf of Suez. These faults may have formed as a result of the most recent push of seafloor spreading. If this is so, then there may be a propagating tectonic wedge moving from south to north which thins the continental crust up to distances of 300 km from the axis of spreading. Following continental deformation, oceanic crust may be emplaced in 'hot points' along the rift axis. These 'punctiform' oceanic spreading centres should propagate in the same direction as continental rifting. During this episode palaeo-shear zones probably act as barriers ('locked zones') to the axial propagation. One such case is at the Zabargad Fracture Zone where the oblique impact of the propagating rift against the palaeo-shear may have placed the Red Sea's western side under compression and uplift while the eastern side may have been subject to oblique extension with the formation of pull-apart basins. The Space Shuttle imagery allows integration of some of the northern Red Sea morphotectonic features with structures on the continent.
Coal deposition in carbonate-rich shallow lacustrine systems: the Calaf and Mequinenza sequences (Oligocene, eastern Ebro Basin, NE Spain)
Authors: CABRERA LI. , SAEZ A.
Published: December 2007

Two main coal-bearing sequences developed during the Oligocene in the Tertiary Ebro Basin, the Calaf (early Oligocene) and Mequinenza (late Oligocene) coal basins. Coal deposition took place in shallow marsh-swamp-lake complexes which sometimes became closed and evolved under warm climatic conditions with fluctuating humidity. These shallow lacustrine systems are closely interrelated with the terminal parts of the distributive fluvial systems which spread from the tectonically active Ebro basin margins. Laterally extensive lignite-bearing sequences, including rather thin, lenticular autochthonous and/or hypautochthonous coal seams with high ash and sulphur contents, characterized coal deposition in the shallow lacustrine systems. Coal seam geometry, which makes them nearly subeconomic, resulted from the tectonic instability during basin margin evolution and the sometimes closed, arid conditions under which the lacustrine systems evolved. High ash and sulphur contents resulted from the inadequate isolation of peat forming environments from clastic influx and from the very low acidity and sometimes high sulphate contents of the lacustrine waters. Coal exploration in shallow lacustrine sequences similar to those described here must take into account that the spread of coal-forming environments and maxima of coal deposition are usually coincident with lake expansions and retraction or shifting of the terminal fluvial zones interrelated with the lacustrine areas.
A tidal origin for coarsening-upward sequences above two Wilcox lignites in East Texas
Authors: BREYER J. A.
Published: December 2007

Conventional palaeogeographic reconstructions show a large river system occupying the East Texas Embayment during the deposition of the Wilcox Group. Coarsening-upward sequences above Wilcox lignites in East Texas have been interpreted as floodplain splays. However, the bedding types, sedimentary structures and shallow scour surfaces in a coarsening-upward sequence above the main seam at the Martin Lake Mine in Panola County indicate deposition in water stirred by tidal and wave activity. The bedding types include sand streaks in mud and lenticular, wavy and flaser bedding. The sedimentary structures include abundant wave-ripple lamination and large-scale crossbeds with thin, closely-spaced mud drapes. These crossbeds suggest traction currents of short duration alternating with periods of slack water. Pollen from broadleaf hardwood trees is the most common element of the palynoflora from the coarsening-upward sequence at the mine. The upper reaches of riverine estuaries along the SE coast of the United States provide a modern analogue for the environment of deposition of the Wilcox sediments at the Martin Lake Mine. Here tidal currents extend inland to places where freshwater aquatic plants and forests border the estuaries. The same bedding types and sedimentary structures that occur in the sediments at the Martin Lake Mine occur in a coarsening-upward sequence above a lignite at the Big Brown Mine in Freestone County. Recognition of the tidal origin of the coarsening-upward sequences suggests an embayed coast or a shoreline within the East Texas Embayment during the deposition of the strata above the lignites.
The occurrence and diversity of Coal Measure insects
Authors: JARZEMBOWSKI E. A.
Published: December 2007

Insects are generally considered to be rare in the Upper Carboniferous Coal Measures. However, recent work in the Westphalian D of SW England suggests that many have been overlooked in the past. This is because wings, which are the most characteristic insect fossils, may be mistaken for detached ‘fern’ pinnules, which are much more common. The resemblance may be functional convergence rather than leaf-mimicry.

The earliest members of the class Insecta in the strict sense occur in the Upper Carboniferous. Eleven major divisions or orders are represented in the Coal Measures of which only four are still living. Primitively wingless insects (Archaeognatha) are present, relatives of familiar living insects such as the silverfish. There are numerous winged insects, some of which could fold their wings (Neoptera) and others which could not (Palaeoptera). Palaeopterous insects were more diverse than today. They include three extinct orders (Palaeodictyoptera, Megasecoptera, Diaphanopterodea) which were probably plant suckers like present clay bugs. Other extinct palaeopterous insects (order Protodonata) were probably aerial predators like modern dragonflies, and included some of the largest insects of all time (‘giant dragonflies’).

By far the most common neopterous insects were cockroaches (Blattodea) which outnumber all other insects in the Upper Carboniferous. This abundance is perhaps less surprising when one considers the general picture of the coal forests as warm, humid, and rich in organic matter. Another important neopterous group was the extinct order Protorthoptera, which is probably related only in part to extant Orthoptera (grasshoppers, crickets and locusts). There is no evidence at this time of higher insects such as flies, fleas, beetles, moths and butterflies, ants, bees and wasps.
The continental margin of central East Greenland in relation to North Atlantic plate tectonic evolution
Authors: BOTT M. H. P.
Published: December 2007

The East Greenland continental margin is inferred to have formed in three stages during the Tertiary evolution of the adjacent North Atlantic Ocean. The East Greenland basaltic volcanism occurred over a period of 2–3 Ma, which was just prior to the probable date of onset of seafloor spreading in the Early Eocene shortly before magnetic anomaly 24B (52 Ma). The associated coastal flexure is interpreted as marking the edge of a zone of stretched and thinned continental crust beneath the inner Denmark Strait shelf and Jan Mayen microcontinent; this represents a short-lived rifting phase just prior to break-up. According to the evolutionary model, the initial break-up produced the margins south of the Faeroe Transform Fault (68.5°N) and north of the Jan Mayen Fracture Zone (72°N), but in the intervening region the microcontinent remained attached to East Greenland. After break-up, the outer shelf of Denmark Strait formed from anomalously thick oceanic crust complementary to the Iceland-Faeroe Ridge. The Blosseville Kyst margin (68.5°N to 70°N) was initiated after anomaly 20 time (42 Ma) as the Jan Mayen microcontinent started to separate from Greenland with spreading on both sides. The new split occupied the line of the pre-existing coastal dyke swarm and flexure. The Liverpool Land margin (70°N to 72°N) was also initiated at this time, but the main separation of the northern part of the microcontinent only commenced after anomaly 7 time (26 Ma) when a single spreading axis was relocated west of the microcontinent.

It is suggested that the Blosseville lavas subsided during deposition by loading and slight crustal stretching. Doming occurred near Kangerdlugssuaq at the time of break-up. Otherwise the topography of the lavas remained subdued until the relocation of the spreading axis at 26 Ma, after which the main regional uplift took place.
Age of Feiran basement rocks, Sinai: implications for late Precambrian crustal evolution in the northern Arabian–Nubian Shield
Authors: STERN R. J. , MANTON W. I.
Published: December 2007

Basement exposed on the perimeter of the Red Sea was created during the Pan-African event at the end of the Precambrian. Pre-Pan-African crust in the northern part of this region has not yet been identified. This paper reports the results of Rb–Sr whole-rock and U–Pb zircon dating of gneisses and related basement units from the Wadi Feiran area in the Sinai peninsula, where the existence of such older basement has previously been suggested. A post-tectonic extensional dyke gives a Rb–Sr age of 591 ± 9 Ma with an initial
87
Sr/
86
Sr ratio of 0.7034 ± 0.0002. Rb–Sr whole-rock and thin slab dating of paragneisses gives ages of
c
. 610 Ma with an initial
87
Sr/
86
Sr ratio of 0.7035. A U–Pb zircon age of 632 ± 3 Ma is interpreted as either the time of formation of these gneisses or the age of the crust sampled by protolith sediments. Granodiorite to the east gives a U–Pb zircon age of 782 ± 7 Ma and is interpreted as representing the westernmost extent of a 780 ± 50 Ma terrane that extends across Sinai into Jordan. Uplift and erosion of the 780 ± 50 Ma terrane supplied detritus to flanking terranes in N and SE Sinai. This region thus acted as a foreland to the younger accretionary and extensional units to the south and west that were active later in the Pan-African event. There is still no evidence for pre-Pan-African basement in the Precambrian units around the northern Red Sea east of the Nile.
Thrust sequences
Authors: BUTLER R. W. H.
Published: December 2007

The sequential evolution of arrays of thrusts can occur by a number of geometric models: these models form the subject of this contribution. The most common of these is a simple foreland-directed (piggy-back) series which develops into either an emergent imbricate fan or, if the faults converge upwards, a duplex structure. Depending on the geometry and distribution of thrust ramps and the relative magnitude of displacements on the faults, a range of duplex geometries can result where the imbricate slices have either hinterland-dipping, antiformal stack or foreland-dipping attitudes. A frequently recognized complexity occurs when a later fault climbs across from the footwall into the hanging wall of an earlier one leading to a breached geometry. A less common generation of imbricate fans occurs by the hinterland-directed progression of thrusts in a break-back sequence. This can lead to an overstep geometry where earlier structures are truncated in the footwall of a later fault. The evolution of hinterland-directed, back-thrusts is also considered. Both internally piggy-back (regionally hinterland-directed) and break-back (regionally foreland-directed) sequences can develop, depending on the ability of the active displacement front to propagate forwards. Simple imbricate geometries can develop with an internally break-back sequence but piggy-back propagation will generally require substantial strains within the back-thrust slices or the generation of multiple detachment levels. The range of structures which can result from these fore-thrust and back-thrust sequences is illustrated using hypothetical cross-sections and natural examples from the Scottish Moine thrust belt and the western Alps. The implications of each geometry for estimates of orogenic contraction and the construction of balanced cross-sections are also emphasized.
Practical application of the sequential balancing technique: an example from the Irish Variscides
Authors: FORD M.
Published: December 2007

The process of sequential restoration presented by Cooper & Trayner (1986) is applied to a N–S cross-section through the Irish Variscides to demonstrate that this approach improves the accuracy of thin-skinned structural modelling and allows the progressive deformation of a marginal belt to be examined. The principles and methods of sequential restoration are illustrated. The cross-section is restored in four steps and gives a bulk shortening of 52%. In this model, the fold belt evolved as the basal décollement migrated northwards, and considerable ductile shortening by folding and cleavage formation preceded faulting, although faulting gradually became more important towards the north. The section is divided into four structural domains based upon different deformation histories. Each is restored independently by removing the ductile strain before restoring the faulting. From this example it is clear that many models derived from single-step balancing, especially those through ductile-deformed areas, should be re-examined.
Volcanic carbonatites of the Kaluwe complex, Zambia
Authors: TURNER D. C.
Published: December 2007

The Kaluwe carbonatite forms a thick, gently dipping sheet with a crescentic outcrop nearly 10 km long. It is composed largely of layered fragmental rocks and was originally interpreted as a sill-like intrusion, concordant with enveloping Karoo sandstones and emplaced episodically as fluidized suspensions of carbonatite fragments. The complex is re-interpreted as a sub-aerial volcanic accumulation of tuffs, agglomeratic tuffs, carbonatite lavas, and associated volcaniclastic sediments. Clasts in the tuffs include crystal and sövite fragments, and also fine-grained carbonatite fragments interpreted as blocks and lapilli of lava. The latter commonly have a trachytic texture with tabular calcite crystals and calcite pseudomorphs after nyerereite, indicating an original natrocarbonatite composition. A similar rock forms several non-fragmental layers, considered to be lava flows. The extrusive origin of the complex is shown by the presence of weathering and palaeosol horizons, of rubbly tops to lava flows, and of interbedded volcaniclastic arenites near the base of the succession. The entire upper part of the succession consists of conglomerates and arenites composed of re-deposited carbonatite volcanic material. Plutonic carbonatites, found as clasts in tuffs, are cumulates of calcite with layers in which apatite and magnetite are concentrated. The parent magma is considered to have been alkali carbonatite from which calcite and the minor non-carbonates crystallized to give sövite cumulates, with the residual alkaline melt being erupted as lavas and pyroclastics.
A gold and silver-bearing subvolcanic centre in the Scottish Caledonides near Lagalochan, Argyllshire
Authors: ZHOU J.-X.
Published: December 2007

Field investigation, petrographic studies and lithogeochemical sampling have defined an area of hydrothermal alteration and mineralization associated with a subvolcanic centre of late Caledonian age at Lagalochan near Kilmelford, Argyllshire, Scotland. The igneous rocks of an area of 2.5 km
2
comprise a large body of porphyrite, flow-banded dacitic rocks, pyroclastic rocks and several bodies of hydrothermal breccia. The close relationship between pyroclastic masses, dacites and discordant breccia bodies within and peripheral to the porphyrite is indicative of a subvolcanic level of emplacement near a volcanic vent. This subvolcanic zone evidently channelled mineralizing fluids leading to widespread alteration of the rocks and introduction of anomalously high concentrations of silver, copper, molybdenum, zinc, lead, arsenic and gold.
Interaction between faulting and sedimentation during Dinantian extension of the Solway basin, SW Scotland
Authors: ORD D. M. , CLEMMEY H. , LEEDER M. R.
Published: December 2007

The ENE-WSW-trending North Solway Fault acted as a northern marginal fault to the Solway Basin during Dinantian sedimentation. Structural, sedimentological and diagenetic relationships suggest syn-sedimentary Dinantian movement was dip-slip and normal. A later Carboniferous phase of dextral transtension is also indicated. Allokinetic deformation features increase in abundance and intensity towards the North Solway Fault, their presence and nature being strongly facies dependent. Syn-sedimentary fault deformation of the hanging wall sediments also increases towards this fault. Both distributed and localized shearing characterizes these early faults and is thought to be related to the water content of beds at the time of deformation. Local minor thrusting and reverse fault movement also occurred within the sediments during basin extension, due to dextral transtensional movement on the North Solway Fault. N–S– and NW–SE–trending faults appear to show no evidence for syn-sedimentary Dinantian movement and are interpreted as the products of 'Hercynian' basin shortening and Mesozoic basin formation.
Mesozoic extensional history of the southern Tethyan continental margin in the SE Aegean
Authors: HARBURY N. A. , HALL R.
Published: December 2007

The islands of Rhodes, Alimnia and Symi are situated at the eastern end of the Hellenic arc. Well exposed on these islands are a series of nappes composed of Mesozoic-early Tertiary, principally carbonate, sequences which formed the sedimentary cover of the southern Tethyan margin and were stacked during Alpine deformation in the late Palaeogene. The stratigraphy of these sequences is described and interpreted as preserving a transition from a carbonate platform through slope to basin. The sequences formed part of the cover of a passive continental margin but this margin differed from typical modern margins in recording several episodes of extension with no clear evidence of ocean crust formation in the SE Aegean. Three important episodes of extension are recorded: a platform-basin topography was initiated by Mid-Late Triassic rifting, late Liassic extension led to platform collapse and development of carbonate slopes, and renewed Late Cretaceous extension further reduced the size of carbonate platforms. The Late Cretaceous extension was probably linked to the formation of ocean crust further east, in Cyprus and Turkey. Sedimentological evidence indicates that the slope was eastward-facing and the platform-basin margin was orientated approximately north-south. This evidence is not consistent with previously proposed palaeogeographic reconstructions of the region based on tracing the isopic zones of the Hellenides through the arc. A new two-dimensional reconstruction of the form of the southern Tethyan margin in the SE Aegean is proposed.
The margins of the South Orkney microcontinent
Authors: KING E. C. , BARKER P. F.
Published: December 2007

Marine geophysical studies of the South Orkney microcontinent show two intersecting tectonic fabrics of different age. The older fabric is oriented E-W, and represents the magmatic arc and fore-arc created by subduction-related processes at the Pacific margin during the Mesozoic. The younger, oriented NNW to SSE, comprises half-graben related to E-W rifting at both the eastern and western margins of the microcontinent. Both fabrics provide constraints on a 40 Ma reconstruction, which shows a highly systematic distribution of arc and fore-arc provinces and points to the importance of E-W strike-slip in regional tectonic evolution. The rifting, apparently of Oligocene age, is associated with back-arc extension which created the oceanic basins to either side of the microcontinent. This strongly supports the existence of subduction with the same orientation as the present South Sandwich arc as far back as 35 or 40 Ma.
Deltas—sites and traps for fossil fuels
Authors: WHATELEY M. K. G. , PICKERING K. T.
Published: December 2007

Report of a joint British Sedimentological Research Group/Petroleum Group meeting held on 21 and 22 April 1987 at the Geological Society of London, Burlington House, Piccadilly. The meeting was organized by M. K. G. Whateley and K. T. Pickering.

This successful international meeting was convened to fill a considerable hiatus which has occurred since the flurry of conferences on deltaic sedimentation took place in the early and mid-1970s. It was felt that significant advances have been made in our understanding of deltas as sites and tra for fossil fuels and a timely forum was required to enable workers to disseminate their knowledge. The two-day meeting included
27
papers and 8 posters covering modern and ancient deltas in marine to fresh-water environments. Topics included: processes, facies models, petroleum, gas and coal related deltaic environments, together with general case studies. A Special Publication of the Geological Society of London will be published within about a year from the date of the meeting. The meeting attracted about 180 speakers and delegates from Germany, France, Norway, Canada, Italy, Denmark, USA and Britain.

Following the two days of plenary sessions, there was a two-day field trip led by Professor
Trevor Elliot
to the Westphalian of North Devon, and a two-day field trip led by Professor
John Collinson
to the Namurian of the Pennines. At the weekend following the field trips, there was a one-day core workshop in Edinburgh, organized by the British Geological Survey, looking at the Jurassic Brent cores from the northern North Sea.