bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic studies of the Pendleside Limestone: evidence for remagnetization and late-diagenetic dolomitization during a post-Asbian normal event
Authors: Addison F. T. , Turner P. , Tarling D. H.
Published: December 2007

The Pendleside Formation, a sequence of bioclastic wackestones and grainstones, has been extensively dolomitized and silicified, especially towards the top and near the axis of the Clitheroe Anticline. Undolomitized limestones are characterized by the presence of magnetite and primary-style magnetic fabrics and an exclusively reversed NRM with mean direction of Dec: =204°; Inc: = —21°. The magnetization is considered to be a depositional/postdepositional remanent magnetization, acquired before any significant alteration of the limestones.

Dolomitized and silicified limestones are characterized by hematite; some silicified limestones show the intermediate state of co-existing hematite and magnetite. These rocks have non-primary style magnetic fabrics and a complex NRM with normal components. The best estimate of this component is Dec: = 22°; Inc; = +20° almost antiparallel to the primary remanence. The magnetization is considered to be a chemical remanent magnetization (CRM) generated during the dolomitization of the Pendleside Formation.

The origin of the dolomitization may be associated with mudrock-dewatering as the sequence was buried. The normal CRM indicates that the remagnetization spanned a post-Asbian normal event, possibly in the Westphalian, coincident with the maximum burial of the Pendleside Formation.
Marginal faunal belts and their structural implications, with examples from the Lower Palaeozoic
Authors: FORTEY R. A. , COCKS L. R. M.
Published: December 2007

Fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry, as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms. On a global scale, the identification of exterior, oceanic biofacies may be of use in discriminating the course of former continental margins. The isograptid graptolite biofacies (Early to Middle Ordovician) can be distinguished from contemporary epicratonic graptolite biofacies; its worldwide occurrence corresponds with continent margins reconstructed from other criteria. Hence a new isograptid record from Irian Jaya (E New Guinea), although based on a small sample, suggests that there may have been an Ordovician oceanic site there. On a continental scale, the tectonic juxtaposition of different biofacies, or of different stratigraphical packages, contributes to an understanding of tectonics and can serve to quantify displacement: the accretionary prism hypothesis for the Southern Uplands of Scotland is supported and contrasted with the rearrangement of biofacies in the Cambro–Ordovician Cow Head Group of western Newfoundland which reveals not only the original shelf-margin–slope topography (now vanished), but also provides an estimate of the movement involved in the emplacement of one Taconic allochthon. On a more local scale, faunal evidence is used in assessing the original position of 'suspect' marginal areas, using the simplest possible model. This shows, for example, that Anglesey was not greatly separated from Gondwana in the early Ordovician—but strike-slip movement cannot be disproved. Local changes in relative sea-level are determinable from sediments and faunas; in marginal belts these may differ from the global eustatic curve, and when this happens it is a measure of local tectonic activity. Particular sea-level curves may serve to define structurally coherent units within mobile belts. New sea-level curves are contrasted for a segment of N Wales (north of the Bala fault) with that for central SW Wales (Arenig–Llandovery); the S Welsh area mostly responded passively to the eustatic curve, which can adequately account for shifts in facies and faunas, while N Wales had a curve often at odds with eustasy and reflecting its structural history.
Oceans, island arcs and olistostromes: the use of fossils in distinguishing sutures, terranes and environments around the Iapetus Ocean
Authors: McKERROW W. S. , COCKS L. R. M.
Published: December 2007

The shallow-water benthos of cratonic areas distinguish different continents, and the closure of the Iapetus Ocean during the Ordovician and Silurian can be monitored by the faunas which crossed the ocean at different geological times. Brachiopod and trilobite distributions carry different palaeobiological evidence than, for example, contemporary conodont provinces, which probably reflected a combination of temperature differences and water depths. The Celtic 'Province' is reviewed, and it is concluded that each of the island faunas should be treated separately (since many have links with adjacent continents), rather than together as a province. In Newfoundland, faunas help to locate the site of the main Iapetus closure at the Reach Fault, although a substantial island arc in the Notre Dame Bay area accreted on to America in early Caradoc times. In the late Ordovician and early Silurian of Newfoundland fossils assist in the dating of quite local fault-controlled marginal basins, some of which include large olistostromes; undisturbed assemblages of brachiopods in life position give indications of the depth of water in some basins.
Evidence of displaced terranes from Permian to Jurassic faunas around the Pacific margins
Authors: HALLAM A.
Published: December 2007

For the Permian to Jurassic time interval Tethyan marine invertebrate faunas, which are generally accepted as having lived at low latitude, can be distinguished from less diverse higher latitude faunas. Displacement of these low-latitude faunas to positions of high latitude around the Pacific margins therefore provides key evidence for the movement of so-called suspect or displaced terranes. The fullest story so far has been worked out for the western margin of N America, as far north as southern Alaska, but there is also convincing evidence for the substantial northward movement of continental segments along the NE Asian margin. As regards the Southern Hemisphere the Torlesse Terrane of New Zealand appears to have moved a considerable distance southwards, but there is no fauna1 evidence of comparable far-travelled suspect terranes along the Andean margin of South America. Not only Tethyan and Boreal but E and W Pacific elements are detectable in the faunas, and the distribution of these argues for a Panthalassia studded with islands of various sizes fringing the adjacent continents, rather than for the disintegration of a single continent—Pacifica.
The geology of SW Connemara, Ireland: a fold and thrust Dalradian and metagabbroic-gneiss complex
Authors: LEAKE BERNARD ELGEY
Published: December 2007

Sillimanite grade Dalradian schists composed of pelites, impure psammites, quartzites and calcite marbles, all containing amphibolites, were intruded and hornfelsed (giving hornfels sillimanite, garnet and cordierite) by a plutonic basic to acid igneous rock series now metamorphosed and folded. Important folding (denoted D
2
, D
3
, D
4
, and D
5
) as been recognized with a major southward facing D
2
, anticline, the Cashel antiform, being repeatedly folded by D
3
, which was a very strong phase, and accompanied and followed by D
3
-D
4
, major ductile slides and thrusting. Although the meta-igneous suite includes rare peridotites (olivine Fo
75-87
,) and anorthosites, it is mostly hornblende-augite-labradorite or bytownite-metagabbro and later quartz diorite or trondhjemite gneiss, which has injected the earlier more basic rocks. Variably preserved igneous layering in the basic rocks indicates that the whole intrusive basic sheet is flat-lying and inverted, lying on the inverted limb of the Cashel antiform. About 460 Ma ago the D
3
-D
4
, Mannin thrust carried the igneous complex, including the largely crystallized gneisses and the cover of Dalradian metasediment, over a now largely mylonitized set of acid volcanic rocks (rhyolites or ignimbrites) which enclose a separate suite of massive amphibolites intruded or extruded into the acid volcanic rocks before the thrusting. The base of the overthrust metagabbro sheet, which had cooled to albite-epidote-amphibolite facies conditions, was ground down into a fine-grained NNW lineated amphibolite. The volcanic rocks, the Mannin thrust, and the overlying basic complex, were folded by D
4
, and D
5
, into a domed structure. About 400 Ma the aplopegmatitic facies of the Inish Granite intruded and caused hornfelsing and folding while the Galway Granite was intruded in the south. Lamprophyric sills and dykes and porphyry dykes were followed by the final phase of the Inish Granite. The southward facing folding and thrusting of the Connemara Dalradian block and the gabbro-gneiss emplacement are major elements in the Caledonide history of the British Isles. It is postulated that there was a tectonic and genetic connection between the gabbro-gneiss intrusion into these Dalradian rocks, the unusually rapid decrease in metamorphic pressure already documented for Connemara and the exceptionally southern position of the Connemara block.
A block model of distributed deformation by faulting
Authors: McKENZIE D. , JACKSON J.
Published: December 2007

It is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation. We propose a simple two-dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone. One surprizing feature of this model is that the component of strike-slip motion on the faults within the deforming zone is in the opposite sense to the strike-slip component across the zone as a whole. Thus slip vectors within the zone are not the same as that between the bounding rigid plates: in contrast to deformation at oceanic plate boundaries. Examples of active fault geometries similar to those of our model can be seen in Greece, Iran and the western USA.
Geophysical surveys on the Lizard Complex, Cornwall
Authors: ROLLIN K. E.
Published: December 2007

Bouguer gravity anomalies over the Lizard have been interpreted in terms of a lower tectonic sheet of hornblende schists and metasediments, structurally overlain by a sheet of peridotite and gabbro. The upper tectonic unit shows a lateral variation from harzburgite peridotite, gabbro and a dyke complex in the east to lherzolite peridotite and cumulate complex in the west. This might indicate structural separation into eastern and western units, or primary igneous variation. At Lizard point, the minimum thickness of the lower Landewednack hornblende schists, on the basis of residual gravity anomalies, is about 700 m, while in the eastern ophiolite unit the minimum thickness of the gabbro and hornblende schists is about 1.5 km. The western lherzolite peridotite is generally less than 400 m thick, whereas the eastern harzburgite peridotite is possibly 600 m thick. A strong aeromagnetic anomaly, with a maximum over the peridotite SW of Coverack, extends both offshore and to the NW, across the mapped contact of the Crousa gabbro and western peridotite, and over the Traboe cumulate complex. At ground level, this anomaly appears to be discontinuous. Although the maximum surface magnetic anomalies occur over thin horizons in the Traboe cumulate complex, a zone of discontinuous, high frequency, high amplitude anomalies extends across the mapped Crousa gabbro and indicates a zone of varied gabbroic and associated rocks which mark the real southern boundary of the Crousa gabbro.
Extension tectonics in the Wessex Basin, southern England
Authors: CHADWICK R. A.
Published: December 2007

The Permian to Cretaceous tectonic evolution of the Wessex Basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere. The gross morphologies of its constituent structures were governed by the location of Variscan thrust and wrench faults in the upper and middle crust, which suffered extensional reactivation in tensional stress fields oriented approximately NW-SE. Several episodes of crustal extension can be resolved, in early Permian, early Triassic, early Jurassic and late Jurassic/early Cretaceous times. These were characterized by the rapid subsidence of fault-bounded basins and commonly, by erosion of adjacent upfaulted blocks. Superimposed upon the fault-controlled subsidence, dominant during periods of fault quiescence, and becoming increasingly important with time, a component of regional subsidence is considered to have a thermal origin. This suggests that crustal extension was accompanied by some form of, not necessarily uniform, lithospheric thinning. Subsidence analyses assuming local Airey isostasy give cumulative crustal extension factors of 20–28% beneath the grabens. A more reasonable assumption of regional Airey compensation indicates basinwide crustal extension of 13–17%. which is consistent with BIRPS offshore deep seismic reflection data.
British Geological Survey maps and their availability
Authors: BAIN J. A.
Published: December 2007

In addition to the commonly accepted format of the geological map, displaying lithological, stratigraphical and structural parameters, the British Geological Survey produces a range of thematic maps dealing with geophysical, geochemical and geotechnical data and providing information on mineral deposits, water supply and energy resources. Compilation scale varies with the level of detail to be displayed but only the smaller and intermediate scale maps are printed, in colour, as formal publications. Much of the larger scale work, incorporating more local detail, is produced for reference purposes and may be inspected in the Survey's map collections, although one-off copies can be produced on demand and, in the past, many of the older 'County' series six-inch maps were issued as printed sheets, especially for the coalfield areas. An outline is given of the variety of products that have been prepared by the Survey and of their relative availability as sales stock or reference copies.
Aluminium mobilization in soils and waters
Authors: BACHE B. W.
Published: December 2007

The toxicity of dissolved aluminium to many plant and animal species is one of the major deleterious effects of the acidification of the environment. Al mobilization from insoluble forms in minerals and rocks is governed mainly by the pH of the solution surrounding weathering minerals. To a first approximation, the solubility product of gibbsite gives an indication of Al concentrations expected in solution. Secondary silicate minerals such as kaolinite, imogolite and allophane, and sulphate minerals such as alunite, maintain lower Al concentrations in solution than does gibbsite, particularly at pH 5. The cation exchange system of acid soils provides a large reserve of ionic Al, which can be brought into solution when soluble salts percolate through soils. Ligands such as fluoride and organic anions, which form soluble Al complexes, combine with much of the Al in solution when they are present in suitable concentrations, and therefore maintain higher concentrations of Al than might be expected from mineral solubility equilibria, particularly at pH 5–7.

Slow reactions involving solid phases, and uncertain data for possible Al species present, limit the rigorous application of equilibrium thermodynamics to these systems, but the factors mentioned provide a reasonable understanding of the major features of aluminium mobilization.
River sediment supply, delta formation and adjacent shelf processes: conference report and introduction
Authors: COLLINS M. B.
Published: December 2007

Although an improvement in the exchange of scientific results has taken place between natural scientists and the engineering community over the past decade, there is a need for even more integration between the disciplines. Similarly, there is a need for marine geologists to understand there is a need for marine geologists to understand headwater river processes and
vice versa
. The meeting held at the Geological Society on 17 May, 1984 was organized in an attempt to improve such scientific exchanges, on an international basis. The following review of the presentations at the meeting serves to introduce this thematic set. They are arranged from headwater catchment to continental shelf.

Following an introduction by Collins to some of the processes and controls involved in the transfer of fluviatile sediments to the deep ocean,
Moore & Newson
described 10 years of measurements of sediment yield from semi-natural grassland and commercially afforested catchments in the British Isles. Field investigations using bed load traps were compared with hydrological and transport capacity factors. Channel storage and release of material is identified as a critical control on bedload yields.

Based upon estimates of the solid and solute load passing 13 gauging stations in the Southern Grampian Highlands of Scotland, an apparently anomalous increase in sediment yield with increase in catchment area in a seaward direction was observed by
McManus.
This anomaly is attributed partly to the presence of organic matter in the waters. 50% of the annual total suspended load entering the Tay and Forth estuaries
Land-derived sediment and solute transport to the Forth and Tay estuaries, Scotland
Authors: McMANUS J.
Published: December 2007

Estimates of the solid and solute loads passing 13 gauging stations on rivers draining the southern Grampian Highlands suggest solid yields ranging between 8.9 and 296.1 t/km
2
/yr according to locality. In the Tay basin the estimated sediment yield increases seawards, an anomaly partly attributed to organic matter in the water. Although biogenic suspended matter may originate in river waters, much is shown to be derived from micro-organisms in the lochs which abound in the basin. A direct relationship between the total surface area of the lochs and the sediment yield of the catchment is suggested. Although 1.72 × 10
6
t and 1.9 × 10
5
t of solids enter the Tay and Forth estuaries annually, more than 50% of that may be of organic origin.
Shallow water areas in space and time
Authors: WYATT A. R.
Published: December 2007

Application of modern hypsometric relationships to former continental blocks allows calculation of the shallow sea area around each block for any given sea level. Using Hallam's (1984) sea level curve for the post-Triassic, shallow sea area curves have been drawn for each continental block, and a global curve of shallow sea area with time produced. As the response of a block to sea level change depends upon the size of the block, the cumulative curve does not vary in a straightforward manner with respect to sea level. Predictions of organic diversity change with sea level change must take account of this non-linear relationship.
Sediment exchanges between the Seine estuary and its adjacent shelf
Authors: AVOINE J.
Published: December 2007

The study of sediment dynamics within the Seine estuary and its adjacent shelf permits some conclusions regarding sediment exchanges in this coastal zone. On the shelf, sediment transport is directed toward the Seine estuary and contributes to the infilling of the estuary by marine sands and muds; these were originally derived from land carried to the shelf at times of lower sea level, and subsequently transported shoreward by dominant tidal and wave-induced currents. In the estuarine section, tidal processes form a turbidity maximum both by inducing strong bed resuspension and by trapping fluvial and marine sediments due to flood current predominance. Occasionally this turbid zone extends seaward during periods of river floods, and sediment is redispersed onto the shelf. This phenomenon has been amplified by man-made modifications of the estuarine morphology. However, currents patterns tend to retard the natural seaward escape of fluvial material, mainly due to dredging operations at the present time. Thus, man has changed the natural role of the estuary from a sink to a source of fluvial sediments for the shelf. A tentative sedimentary budget is proposed, taking into account the various sources of material and the complexity of sediment dynamics.
Short and long term changes in estuary capacity
Authors: O'CONNOR B. A.
Published: December 2007

Changes in capacity have been examined in the Lune, Ribble, Mersey and Humber estuaries to assess the role played by land-derived sediments in coastal accretion. The engineering concept of dynamic equilibrium is introduced and shown to imply that land-derived sediments should contribute exclusively to coastal accretion. The various factors responsible for changing estuary capacity are also introduced. Capacity changes over the last 100 years show that all the estuaries considered have suffered large scale siltation, with the majority of the sediment being derived from coastal and offshore sources. In the case of the Lune, Ribble and Mersey estuaries, engineering works have been responsible for large permanent changes in capacity. The situation in the Humber is less clear and siltation is probably a result of natural infilling; the estuary having been over-deepened by glacial and fluvial action in the past. A detailed study of the Mersey suggests that the estuary was also over-deepened and over-widened and has only been tidal for the last 9000 years or so. Calculations suggest that a new equilibrium will be achieved in about 250 years time and that the estuary may then be in a state of dynamic equilibrium. The much smaller Lune estuary may already have achieved this state, although detailed evidence is scarce.
Sedimentation and tectonics in the Welsh Basin
Authors: FITCHES W. R. , WOODCOCK N. H.
Published: December 2007

Report of a joint meeting of the Tectonic Studies Group and the British Sedimentological Research Group of the Geological Society held at the University College of Wales, Aberystwyth on 10–12 April 1986. The organizers were Dr W. R. Fitches and Dr N. H. Woodcock.

Research into the Early Palaeozoic history of Wales is like that history itself; eventful and rarely quiescent. Recent events have been the lively debate on the tectonics of Anglesey provoked by A. J. Barber and M. D. Max, the exemplary volcanological studies in North Wales by the BGS Snowdonia unit, and the definition of Silurian world stratotypes by members of the Ludlow Research Group. The stimulus for this conference was the recently increased activity in structural and sedimentological research in mainland Wales. Twenty-eight papers were given over the first 2 days, followed by a day of field trips to Snowdonia, the Aberystwyth area, and the Wenlock of eastern Mid-Wales.

Precambrian events featured in three papers.
D. S. Wood
concentrated on the evidence for the superficial ‘soft-sediment’ origin of the Gwna melange of Anglesey and postulated a setting predating rather than accompanying the subduction system that produced the Anglesey blueschists. In the later deformation history of Anglesey,
D. Carter
distinguished two main deformations. A Caledonian event was preceded by one of pre-Arenig or probably pre-Arvonian age, with an unconformity present between the Monian and Lower Palaeozoic rocks. Precambrian sedimentation of the Longmyndian of Salop was described by
J. Pauley
in terms of a progradational basin fill.
The British Geological Survey contribution to the exploration of the continental shelf
Authors: WALMSLEY P. J.
Published: December 2007

BGS has provided an invaluable contribution to the successful petroleum exploration of UKCS since exploration commenced in the early 1960s. Legislation provides that all data acquired by industry be lodged with Government who have appointed BGS as custodians. BGS maintains the National Hydrocarbon Core Store in Edinburgh. Their Hydrocarbons Unit prepares for Department of Energy detailed prospectivity reviews which provide the basis for licensing policy and reserves estimates. A systematic programme of sea-bed mapping commenced in 1967 and will be completed in 1990 when 328 geophysical and geological maps will have been published. BGS also monitors seismicity offshore.
Late-Archaean tectonics in the Færingehavn–Tre Brødre area, south of Buksefjorden, southern West Greenland
Authors: FRIEND C. R. L. , NUTMAN A. P. , McGREGOR V. R.
Published: December 2007

The Færingehavn–Tre Brødre area consists of three distinct terranes tectonically jux-taposed by a previously unrecognized event. Contacts between the terranes are mylonitic shear zones truncating lithological units in adjacent terranes. The terrenes are: (1) Færingehavn terrane, largely composed of early-Archaean Amîtsoq gneiss cut by younger Archaean granitic gneiss defined here as the Sätut gneiss; (2) Tre Brødre terrane comprising mid-Archaean Malene supracrustal rocks, anorthosite complex and polyphase Nûk gneisses; (3) Tasiusarsuaq terrane largely comprising mid-Archaean Nûk gneisses affected by
c.
2800 Ma granulite facies metamorphism. The Tasiusarsuaq terrane is structurally above both the Færingehavn and Tre Brødre terranes which at
c.
2800 Ma experienced a lower grade of metamorphism.

Juxtaposition of the terranes took place between 2800 and 2500 Ma and involved thrusting and crustal thickening. Subsequent re-equilibration involved folding, steeply inclined shear belts, intrusion of synkinematic granitoids under amphibolite facies conditions and retrogression of granulite facies assemblages.

This thrusting post-dates the 2800 Ma granulite facies metamorphism. It is younger and distinct from the thrusting postulated to explain the intercalation of the early-Archaean Amîtsoq gneisses and the mid-Archaean Malene supracrustal rocks, associated with intrusion of the Nûk gneiss precursors described from Godthåbsfjord. The tectonic breaks provide, for the first time, marker horizons which can be used to assess the amount and type of late Archaean deformation in the southern Godthåbsfjord region.
Sulphur, low temperature ash and minor elements in humid–temperate peat of the Fraser River Delta, British Columbia
Authors: BUSTIN R. M. , LOWE L. E.
Published: December 2007

Recent peat deposits of the Fraser Delta have accumulated in a variety of depositional settings and from a wide range of vegetation. Studies of these deposits have enabled evaluation of some factors that control the distribution of sulphur, ash and minor elements in coal. Brackish peat of the lower delta plain is characterized by high total sulphur (up to 5.6%), low C/N (12–5), C/S (<11) and total polysaccharide/C ratios and an ash mineralogy dominated by quartz, feldspar and clays. Freshwater peat has lower total sulphur (0.5%), higher C/N and C/S and higher polysaccharide/C ratios and a clay mineralogy enriched in kaolinite. The highest sulphur values occur in brackish sedge peat whereas the lowest values were obtained from
Sphagnum
peat. Organic S is the main S form in all peat (>70% of S): carbon-bonded S comprises 28–88% and ester sulphate 6–40% of total S. Pyritic S, elemental S and soluble sulphate S are minor, whereas hydrogen sulphide occurs in trace amounts. Silicon is the most abundant element (2.8–28%) followed by Al (334 ppm—6.4%) or Fe (357 ppm—5.0%), Na (43 ppm—2.3%), Ca (404 ppm—1.1%), Mg (217 ppm—1.2%), and Ti (40–580 ppm). All the minor elements are correlated with low temperature ash. On an ash basis, brackish and freshwater clay facies have higher Al and K and lower Ca contents than organic facies and brackish facies have twice the Fe and Na content of freshwater facies.

The abundance of total S and the ash content of the peat reflects the depositional environment and the peat-facies. The higher pH of brackish peat has facilitated bacterial reduction of seawater sulphate leading to higher S peat. The higher kaolinite content of freshwater peat reflects the acid conditions (pH 3–4.5) of the peat bogs and the
in situ
formation of kaolinite. There is no evidence for formation of pyrite which reflects the low pH that has inhibited microbial mobilization of organic sulphur. The minor element abundance is a product of the distribution of detrital and authigenic ash. The lower total polysaccharides/C and C/N ratios of brackish facies reflects the greater degree of decomposition in this facies.
Tectonic environment of the Devonian Gramscatho basin, south Cornwall: framework mode and geochemical evidence from turbiditic sandstones
Authors: FLOYD P. A. , LEVERIDGE B. E.
Published: December 2007

The Portscatho Formation, within the allochthonous unit of the Middle and Upper Devonian Gramscatho Group, is a thick sequence of deep-water sandstones and interbedded slates deposited by southerly-derived turbidity currents into the Gramscatho basin of south Cornwall. Throughout an approximately 3.5 km thick sequence, the Portscatho Formation is petrographically and chemically coherent, except that the upper section shows a higher proportion of metamorphic clasts, high, but variable Cr, and low, uniform Zr abundances. Complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition, similar to average upper continental crust, but with an admixture of minor intermediate/basic material. Flysch deposition took place in a fore-arc setting. The presence of an arc to the south of Cornwall during the Devonian implies that there was subduction at the margin of the Gramscatho basin, whose ultimate closure was accommodated by the northward stacking of flysch–ophiolite nappes.
The Silurian of the Southern Uplands and Ireland as a successor basin to the end-Ordovician closure of Iapetus
Authors: HUTTON D. H. W. , MURPHY F. C.
Published: December 2007

A suite of microconglomerates is recognized in Silurian rocks which occur on both sides of the proposed line of the Iapetus suture in Ireland. Clast composition and palaeocurrent data show that these conglomerates, which grade into the typical quartz-rich Silurian turbidites, were derived from two compositionally similar magmatic arc terranes which lay on either side of the present Silurian outcrop. In the Llandovery, derivation was from both the south and the north. In the Wenlock, derivation was from the north and sedimentation prograded southwards across the ‘suture’ and onto the southern margin. The source terrain in the south was probably the Ordovician Wexford–Lake District arc. We identify the northern source as another arc (Cockburnland) which has since been cut out by sinistral strike-slip against the Ordovician Northern Belt. These data imply that arc activity ceased synchronously on either side of Iapetus during the late Ordovician and this leads us to speculate that subduction of oceanic crust ended at that time. Closure was associated with deformation and uplift of the bounding Ordovician terrains. These rocks then contributed detritus to the Silurian infill of a successor basin. Regional sinistral transpression finally deformed and reorganized these units between the end Silurian and the early Devonian and led to the complete closure of the remaining Silurian seaway.
Style, scale and significance of sand bodies in the Northern and Central Belts, southwest Southern Uplands
Authors: KELLING G. , DAVIES P. , HOLROYD J.
Published: December 2007

Sedimentological and biostratigraphical data from the Rhinns of Galloway and adjacent areas in SW Scotland confirm that deep-water depositional systems consistently operated along, and were sourced from, the northwestern margin of an asymmetrical basin during the late Ordovician and early Silurian, while pelagic facies accumulated simultaneously to the SE, providing a scenario analogous to many modern trench systems.

Most of the observed sedimentological anomalies, with regard to this general model, can be explained within the context of the varied styles of trench-filling depositional systems, briefly reviewed here, and the major stratigraphic and sedimentologic features can be best explained in terms of a geotectonically evolving fore-arc region. Two main phases of development are recognized: (a) Llandeilo-late Ashgill: during this time interval the fore-arc trench region was tectonically juxtaposed against an active continental margin arc. Small- to medium-scale, SE-prograding sand-rich fans were formed within a relatively narrow trench, leading to axial diversion of the fans, initially to NE but later mainly to SW. Simultaneously a coarse volcanilithic sediment apron, flanking the arc, migrated gradually northeastwards, probably in response to relative fault displacement of the arc and trench; (b) Llandovery: during this time interval the fore-arc trench region was dominated by a variety of mainly fan-type depositional systems which were exclusively sourced (at least until the uppermost Llandovery) from the northwestern margin. The juxtaposition of coeval depositional systems differing significantly in sedimentological style and composition strongly suggests that the Llandovery sedimentation in this region occurred in several structurally separated sub-basins within the main trench system.
Basaltic replenishment of the Rhum magma chamber: evidence from unit 14
Authors: RENNER R. , PALACZ Z.
Published: December 2007

A detailed geochemical and lithological profile through unit 14 of the Rhum Eastern Layered Series is presented and interpreted to trace the evolution of this cyclic peridotite-troctolite unit. The lower 15.5 m of the unit are peridotite which has an abrupt contact with the upper 35.5 m of troctolite. Numerous thin subsidiary peridotites occur within the troctolite. Variation in the modes, whole rock
87
Sr/
86
Sr ratios, and Ni and Fo in olivine provide most information about the evolution of the unit. Discontinuities in these parameters divide the unit into six subunits: (I) the lower peridotite, (II) the middle main peridotite, (III) the upper main peridotite and lowermost troctolite, (IV) the middle troctolite, (V) the upper troctolite and (VI) the disturbed troctolite. These subunits are interpreted as the result of magma replenishment by picritic and by basaltic magmas. Field evidence suggests that the subsidiary peridotites are later sills intruded into solid or semi-consolidated troctolite. The olivine Fo and Ni values are similar to those of surrounding troctolite suggesting either re-equilibration with, or assimilation of, the troctolite. Comparison with unit 10 shows that the unit 14 resident basaltic liquid was more mafic than that of unit 10. This factor, along with the basaltic replenishment, can explain many of the differences in geochemical and lithological variation between the two units.
Hydrothermal fluid evolution of the Sn-W mineralization in the Parrilla ore deposit (Caceres, Spain)
Authors: Mangas J. , Arribas A.
Published: December 2007

The Parrilla orebody, located on the southern border of the Cáceres province, is a stockwork of quartz veins with scheelite and cassiterite. The Sn-W ore fills fractures in the Greywacke Schist Complex, intruded in this area by Hercynian granites. Most of the veins strike N30°E and dip 45°SE. The mineral association includes scheelite and cassiterite, which are the most important economic minerals, and arsenopyrite, wolframite, sphalerite, chalcopyrite, pyrite, bismuth sulphosalts, pyrrhotite, quartz, muscovite and tourmaline.

The study of the fluid inclusions was undertaken using quartz and scheelite belonging to the different veins. The physicochemical characteristics of the inclusions indicate three stages of fluid circulation. The first stage is characterized by aqueous and complex CO
2
-aqueous inclusions (<7 wt% NaCl equiv.) trapped at temperatures between 350 and 225 °C. The second stage is represented by low-salinity aqueous inclusions (<7wt% NaCl equiv.) trapped at homogenization temperatures between 225 and 150 °C. The third stage is characterized by mixed salt-aqueous inclusions (<31 wt% NaCl equiv.) trapped at homogenization temperatures between 150 and 70°C.
Role of strike-slip faulting in the tectonic evolution of the Antarctic Peninsula
Authors: STOREY B. C. , NELL P. A. R.
Published: December 2007

The Antarctic Peninsula Mesozoic magmatic arc has had a long history of dextral, strike-slip deformation. The deformation was initially associated with the development of a wide accretionary complex, by the migration of fore-arc slivers, and the formation and inversion of a thick fore-arc basin succession. It also formed an important component within major shear zones in the arc, and may have controlled the formation of sedimentary basins in the back-arc region. Although some transcurrent motion within the fore-arc region was related to a component of oblique subduction, the main movement occurred during the breakup of Gondwanaland and the formation of a major transtensional rift system. A new reconstruction for this part of Gondwanaland is presented taking this transcurrent motion into consideration.
Magnetostratigraphy of the Lower Cretaceous Vectis Formation (Wealden Group) on the Isle of Wight, Southern England
Authors: KERTH M. , HAILWOOD E. A.
Published: December 2007

Magnetostratigraphic results are described from two sections within the Lower Cretaceous Vectis Formation (formerly Wealden Shales) of the Isle of Wight, Southern England. The sections are located at Shepherd's Chine and Yaverland, respectively.

In both of these sections a reliably-established reverse polarity magnetozone, herein defined as the Vectis magnetozone, occurs within the Shepherd's Chine Member. This magnetozone has a thickness of some 15 m and its upper boundary is well defined in the Yaverland section but is obscured in the Shepherd's Chine Section due to cliff slumping. The lower boundary is well established in both sections and lies some 15 m above the Barnes High Sandstone Member in the Shepherd's Chine section and 12 m above this unit at Yaverland. This boundary provides a useful chron-stratigraphic datum.

A comparison with established geomagnetic polarity timescales for the Cretaceous indicates that the Vectis magnetozone may be correlated either with Lower Aptian reverse polarity Chron CM-0 or with Lower Barremian Chron CM-1, with the former being the more likely. An important implication of this interpretation is that the base of the Aptian stage, as defined from Tethyan foraminiferal zones, must lie within the Vectis Formation, at least 25-30 m beneath the top of the Shepherd's Chine Member, rather than at the top of this member as hitherto commonly accepted.

Beds characterized by anomalously high intensities of magnetization, which occur at the base of the Vectis Formation and a few metres above the Barnes High Sandstone in the two sections, are tentatively interpreted as having a volcanogenic origin.
Short Paper: Low grade metamorphism of the Welsh Basin Lower Palaeozoic succession: an example of diastathermal metamorphism?
Authors: BEVINS R. E. , ROBINSON D.
Published: December 2007

The Lower Palaeozoic succession of the Welsh Basin has suffered the effects of low grade metamorphism which shows features that do not accord with classical models of regional or burial metamorphism. Textural evidence demonstrates the development of greenschist facies metamorphism
prior
to deformation and cleavage development, while mineralogical characters indicate a low pressure facies series. In order to accommodate these features it is suggested that the area has suffered
diastathermal metamorphism,
in which an enhanced thermal flux develops early in the tectonic cycle in response to an extensional setting. Temperatures remained relatively high during final closure, associated with deformation of the basin sediments and consequent cleavage development. Such a model adequately resolves previously conflicting interpretations of burial- and deformation-related metamorphism.
Depositional models for two Tertiary coal-bearing sequences in the Powder River Basin, Wyoming, USA
Authors: WARWICK P. D. , STANTON R. W.
Published: December 2007

Depositional controls on peat-forming environments which produce thick (>10m) coal beds can be inferred from relationships between coal bed geometry, maceral composition and associated lithologies. Study of these relationships within sedimentary sequences associated with the Wyodak-Anderson (Palaeocene) and the Felix (Eocene) sub-bituminous coal beds in the Powder River Basin, Wyoming, USA suggests two modes of fluvially controlled peat accumulation. The Wyodak-Anderson peat is interpreted to have formed in restricted parts of the floodplain that were separated by deposits of contemporaneous, anastomosed channels. The channels and associated sediments maintained their position through time because they were confined by thick deposits of raised Wyodak-Anderson peat. In contrast, the Felix coal bed is interpreted to have formed as a raised but widespread peat on an abandoned platform of meander-belt sands.

The purpose of this paper is to compare and contrast two different fluvial depositional settings that produced anomalously thick (>10m) coal deposits in the intermontane Powder River Basin of Wyoming, USA. These models may be useful as predictive tools for coal exploration and production.
Polyorogenic
40
Ar/
39
Ar mineral age record within the Kalak Nappe Complex, Northern Scandinavian Caledonides
Authors: DALLMEYER R. D.
Published: December 2007

The Kalak Nappe Complex is composed of variably retrogressed, middle Proterozoic basement and imbricated, polydeformed, metasedimentary cover successions which, at least in part, appear to have originated within the late Proterozoic-early Palaeozoic Baltoscandian miogeocline. Mafic-alkaline plutons (Seiland Igneous Suite) occur within uppermost structural units of the nappe complex.
40
Ar/
39
Ar incremental-release mineral ages suggest local differences in tectonothermal evolution within the Kalak Nappe Complex. Post-metamorphic cooling dates of
c.
490 Ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and/or immediately prior to the Arenig. A distinctly later metamorphic overprint occurred in the Silurian and was of sufficient magnitude to everywhere rejuvenate Ar systems in muscovite and nepheline and locally in hornblende. This was followed by relatively rapid post-metamorphic cooling through hornblende and muscovite Ar closure temperatures between
c.
425 and 415 Ma.

The complex tectonic history suggested for the Kalak Nappe Complex is generally similar to that previously outlined for the central Swedish Caledonides. Together,
40
Ar/
39
Ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the Baltoscandian margin prior to the Silurian. This activity appears, at least in part, to have been associated with formation of a Late Cambrian-Early Ordovician accretionary wedge over a westward-dipping subduction zone during initial closure of the Iapetus Ocean.
Models of convective fluid flow and mineralization in south-west England
Authors: SAMS M. S. , THOMAS-BETTS A.
Published: December 2007

Two notable features of the mineralization in SW England are the asymmetrical pattern of mineral lodes and the mineral zoning within this distribution. Despite the fact that many theories have been advanced to explain the mechanisms of mineralization qualitatively no numerical models have been produced. In this paper, the finite element technique is used to construct a very simple model which helps to explain general features of the pattern of mineralization.

The model describes the steady state convection of fluid in the environment of the Cornubian batholith. Convection is driven by the radiothermal contrast between the granite and the host rocks. Results show that the locations of upward flowing, hot fluids are determined by the three-dimensional shape of the batholith. Initially, upward flow was concentrated along the axis of the batholith and these regions correlate with high temperature mineralization. Erosion of the cover rock above the granites altered the fluid flow pattern such that the upward flow became concentrated outside the outcropping granites. These regions correlate with low temperature mineralization. A correlation also exists between kaolinization and areas of downward flowing fluid for present day levels of erosion.
Is the Welsh Borderland Fault System a terrane boundary?
Authors: WOODCOCK N. H. , GIBBONS W.
Published: December 2007

The Welsh Borderland Fault System forms one of the most prominent tectonic lines in Southern Britain and, along with the Menai Straits and Malverns Fault Systems, is a candidate for a terrane boundry. A review of stratigraphic linkage across the system reveals significant contrasts in pre-Ashgill sequences. These contrasts occur particularly across its north-west edge, the Pontesford and Tywi Lineaments, rather than across the Church Stretton Lineament. The Ashgill event produced strike-slip dominated structure and an unconformity that expands from the Welsh Basin towards the platform. An important linkage sequence was produced by the subsequent late Ashgill to Llandovery marine transgression across the fault system. Silurian facies changes are marked but gradational, and no more than expected across a basin margin from stable to thinned crust.

Devonian (Acadian) sinistral transpression, and later Phanerozoic movements, reactivated the fault system but did not engineer major terrane amalgamation across it. This reactivation has obscured the early history of the fault system. The remaining evidence admits, though does not prove, major Ashgill or earlier transcurrent movements. Broader considerations suggest that the Welsh Borderland Fault System originated either as a Cambro-Ordovician extensional system on the south-eastern margin of the Welsh Basin or during Late Precambrian-Early Cambrian transcurrent movements occurring within Avalonia, inboard from the Menai Strait line.
Geochronology of Late Caledonian magmatism in northern Britain
Authors: THIRLWALL M. F.
Published: December 2007

Rb-Sr, K-Ar, Ar-Ar and Sm-Nd isotopic data are presented for mineral separates and whole rock samples from Old Red Sandstone (ORS) lavas, associated minor intrusions and 'Newer Granite' intrusive complexes from the Cheviot Hills north to Shetland. These data yield 16 internally consistent Rb-Sr mineral ages and one each of Ar-Ar, Sm-Nd and K-Ar ages. When considered with precise and reliable published data, it is clear that there are systematic differences in the age of Late Caledonian magmatism through the geological regions of Scotland. In the Grampian Highlands and the Scottish Midland Valley, magmatism was concentrated during the period 423 to 410 Ma. ORS volcanism in the Highlands occurred around 420 Ma, with plutonism continuing to about 408 Ma. Volcanism and plutonism in the Midland Valley took place between 415 and 410 Ma. In the Southern Uplands, magmatism occurred earlier in the north, with all magmatism close to the Southern Uplands Fault dated around 408 Ma and that close to the Iapetus suture dated at around 394 Ma. As no evidence exists for ocean closure prior to
c
. 400 Ma, the age of igneous activity north of the Southern Uplands Fault is consistent with chemical evidence for a relationship to active NW-directed subduction. The younger magmatism of the S part of the Southern Uplands cannot be subduction-related, and the
c.
408 Ma plutons nearer the Southern Uplands Fault can only be subduction-related if tectonic construction of the Southern Uplands was a two-stage process.