bluuebunny/crossref_metadata_2025 huggingface dataset:
Cretaceous tectonics off mid-Norway: implications for the Rockall and Faeroe-Shetland troughs
Authors: Price I. , Rattey R. P.
Published: December 2007

Between 62° and 68°N on the Norwegian continental margin, the hypothesis of a Cretaceous or Permian ocean extending northwards from the Rockall Trough can be tested with data from commercial reflection seismic profiles. Two major Mesozoic basin systems occur. The Helgeland Basin is a late Triassic and early Jurassic depocentre with a thin Upper Jurassic and Cretaceous cover except in two late Cretaceous sub-basins. The Møre/lnner Vøring Basin system is a middle to late Cretaceous depocentre in which the pre-Cretaceous section is deeply buried and rarely seen on seismic profiles. The two basin systems are separated by a complex zone of faulted 'marginal highs' active in Jurassic times and reactivated during Cretaceous times. Pre-Cenomanian lavas or sills are interpreted within the Møre Basin and a pre-Cretaceous block-faulted sequence can be identified across the inner Vøring Basin except in a narrow axial zone. These features suggest the presence of an extremely narrow zone of oceanic crust of Cretaceous age. Fault patterns confirm a major tectonic episode of mid-Cretaceous age. The geology off mid-Norway supports a mid-Cretaceous age for sea-floor spreading in the Rockall Trough but suggests that the generated oceanic crust narrowed northwards and that plate motion was partially accommodated by dextral transcurrent faulting. Reconstruction of Jurassic tectonic trends in NW Europe must allow for subsequent Cretaceous distortion.
Metamorphic studies: research in progress
Authors: Brown Michael
Published: December 2007

Report of a meeting of the Metamorphic Studies Group held at Burlington House, 7 March 1984. The meeting was organized by Dr M. Brown.

A Metamorphic Studies Group Meeting on ‘Metamorphic studies: research in progress’ and the third Annual General A Metamorphic Studies Group Meeting on ‘Metamorphic studies: research in progress’ and the third Annual General Meeting of the Group were held on March 1984 and more than 80 members participated. Nineteen papers were presented which covered a wide range of interests in metamorphic geology, including for the first time three papers on isotope geology. Six papers were given by research students. Overall, the large number of contributions to the meeting, the lively discussion of these contributions and the substantial attendance at the meeting suggest that the “current research” style of meeting is very worthwhile.

The morning session, chaired by B. Harte, was opened by R. P. Hall who presented an account the inter-relationships between metamorphism and magmatic and tectonic episodes in two contrasted areas within the Archaean craton of southern W Greenland. In Ivisgrtoq the rocks are at amphibolite facies and have never been to granulite facies. In contrast, in the eastern Sukkertoppen region the rocks are partly retrogressed from granulite facies. In such retrogressed granulites, the presence of ‘blebby’ hornblende and biotite after pyroxene is characteristic. Hall presented data on various reactions by which hypersthene has been replaced and concluded that enclosing acid gneisses in which no evidence granulite facies is preserved must have provided a metasomatic influx of elements such as potassium
Conditions of Dalradian metamorphism in the Buchan area, NE Scotland
Authors: Hudson Neil F. C.
Published: December 2007

P–T conditions in the Buchan Dalradian have been estimated using published equilibria. Garnet-biotite (corrected according to
Hodges & Spear (1982)
) and garnethornblende temperatures are in good agreement, recording 430 ± 15°C, 490 ± 15°C and 510 ± 20°C at the cordierite, andalusite and staurolite isograds and 550 ± 40°C in the upper staurolite zone. Garnet-clinopyroxene-plagioclase-quartz and garnet-plagioclase-epidote-quartz-fluid (with aH
2
O = 1) record a consistent minimum pressure of 1.7kbar for the andalusite isograd though the uncertainties in the equilibria indicate this could be 2 kbar higher. In the staurolite zone the latter geobarometer is in agreement with pressures of 2–3.5 kbar derived from garnet-plagioclase-andalusite-quartz. A calcite-dolomite temperature of 537°C from marbles at the Portsoy kyanite/andalusite isograd, implies pressures near 4.5 kbar. The P–T array defined by these data lies at lower pressures and temperatures than that deduced from pelite petrogenetic grids. The possibility of reduced aH
2
O is considered unlikely, as the calc-silicate assemblages are indicative of H
2
O-rich fluids, and it is suggested that the discrepancy may result from inadequate garnet activity formulations.

Inferred overburden estimates are consistent with recent overburden estimates for the Newer Gabbro aureole implying that little or no erosion had occurred by the time of emplacement of the basic intrusions. The overburden estimates are combined with the stratigraphic thickness data of
Sutton & Watson (1955)
to estimate differential erosion/uplift rates in the area.
Geophysical constraints on crustal structure in the Dalradian region of Scotland
Authors: Hall J.
Published: December 2007

The crust in the region of the Dalradian outcrop in Scotland is 25–35 km thick and may be divided into two areas separated by the NW–SE Cruachan Lineament. To the NE the crust is dominated by late Caledonian granites which give rise to surface topography isostatically compensated at shallow depth. To the SW, thick Dalradian sediments formed in an extensional basin later subjected to crustal shortening of 70–100 km achieved by zigzag obduction. Physical parameters of the deep crust are compatible with metamorphic grade increasing downwards except that the basic lower crust may be partly retrogressed and contain free water.
Volcanic and geochemical stratigraphy of the Nussir Group of Arctic Norway—an early Proterozoic greenstone suite
Authors: Pharaoh T.
Published: December 2007

The Nussir Group of West Finnmark is a suite of metabasaltic lavas and tuffs about 1.8 km thick, associated with continental and shallow marine sediments. This assemblage is typical of Karelian (Early Proterozoic) supracrustal sequences throughout northern Norway and northernmost Sweden.

Primary textures are well preserved and permit the establishment of a volcanic stratigraphy for the Nussir Group. The Krokvatn Formation is dominated by mafic aquagene tuffs while the overlying Svartfjell Formation is composed mainly of submarine pillow basalt. Petrographic evidence for the petrogenesis of the metabasalts is poor because of greenschist facies metamorphism during the Svecokarelian Orogeny
c
. 1840 Ma.

The earliest lavas have the most primitive compositions, but subsequent flows exhibit strong enrichment in Fe, Ti and incompatible elements as a consequence of extensive crystal fractionation. The tholeiitic nature of the suite is confirmed by the trace element data. The later lavas are more uniform and less evolved: and are considered to represent steady-state compositions produced by a periodically replenished/tapped open-system magma chamber.

The field relationships, lithological and geochemical evidence suggest that the Nussir Group lavas were erupted in a submarine rift basin within continental crust. They form part of an extensive tholeiitic magmatic province which occupied much of northern Norway, Sweden and Finland in the early Proterozoic. The tectonic environment of this province is poorly constrained by the geochemical data. Continental plateau basalt provinces such as the Columbia River and Karoo provide the closest Phanerozoic geochemical analogues.
Palaeozoic, Mesozoic and contemporaneous megaspores from the Tertiary of southern England: indicators of sedimentary provenance and ancient vegetation
Authors: Collinson M. E. , Batten D. J. , Scott A. C. , Ayonghe S. N.
Published: December 2007

Megaspores are recorded from several localities in the Thanet and Reading Beds (upper Palaeocene) of southern England. Evidence from their taxonomic affinity, colour, compression and state of preservation indicates three separate groups: two reworked from lower Westphalian Coal Measures and Lower Cretaceous sequences, respectively, and one of contemporaneous forms. Mesozoic megaspores redeposited in the British Tertiary have not previously been recorded. Isolated Carboniferous forms have been found before but their possible value in provenance studies has not been fully explored. The new material includes a diverse assemblage of numerous Westphalian and Lower Cretaceous forms from a single horizon in the Thanet Beds. Of possible source areas it seems most likely that these spores were reworked from the Moray Firth Basin, and elsewhere near the present eastern coast of Scotland, by means of longshore drift following a roughly N–S palaeocoastline. Evidence from other studies of heavy mineral assemblages and palaeogeography also indicates derivation of Thanet Beds sediments by this means.

The Cenozoic megaspores include an
Azolla
(water fern) and two distinct lycopsid forms, one probably of selaginellalean and one of isoetalean affinity. These latter provide the first clear evidence of lycopsids in British Tertiary floras and expand our knowledge of freshwater macrophytes of that time. The assemblages of
Minerisporites
show morphological trends which may prove to be of biostratigraphic value.
A theoretical framework for the Pleistocene ice ages
Authors: Imbrie John
Published: December 2007

This paper reviews 150 years of progress towards understanding the succession of Pleistocene ice ages. Emphasis is placed on the process of explaining
forced variations
in climate which occur in the
Milankovitch band
(periods from 10000 to 400 000 years), where astronomical forcing functions are clearly identified and where the amplitudes of climatic change are large. An hierarchy of explanatory models is employed, including a statistical model that uses
gain
and
phase
terms to parameterize the climatic response to orbital forcing in several narrow frequency bands. This type of model accounts for a substantial fraction of the observed temporal variations of δ
18
O over the past 800 000 years. Experiments using the model suggest that a change in the system response occurred about 400 000 years ago. The problem of explaining climatic variations in other frequency bands is briefly reviewed. In the
decadal band
(l0–400 years), there is good evidence of volcanic forcing, solar forcing, and tidal forcing, but much of the observed pattern is presumed to reflect
free variations.
In the
millenium band
(400 to 10 000 years), significant climatic changes occur at periods ranging from 1000 to 3000 years. Their cause remains a challenging problem. Over the
tectonic band
(more than 400 000 years), volcanic fluxes, continental elevation, and continental position are the most likely forcing functions of the observed climatic changes.
Glacial geology and glaciology of the last mid-latitude ice sheets
Authors: Boulton G. S. , Smith G. D. , Jones A. S. , Newsome J.
Published: December 2007

Satellite imagery and data from ground surveys are used to reconstruct the integrated pattern of the principal longitudinal and transverse features produced on a continent-wide scale by the last ice sheets in Europe and North America. From modern analogues, it is argued that most longitudinal features reflect flow in the outer zone of the ice sheet, and that most major transverse features reflect relatively stable ice-sheet margins. These principles are tested and, using them alone, detailed patterns for the decay of the last ice sheets in North America, Europe and the British Isles are produced, and periods during which they attained near steady-states identified. These patterns can be calibrated by dated sequences to yield deglaciation isochrons. Application of glaciological models to these geological reconstructions generates detailed prediction of net ablation for the period of ice-sheet decay and, by using evidence of last glaciation stratigraphy, models of the dynamic behaviour of the ice sheets throughout the last glacial period are constructed. These enable volumetric changes, oceanic isotopic changes and erratic dispersal pathways to be reconstructed. Erratic dispersal patterns give a good indication of the long-term distribution of centres of ice sheet mass. Discrepancies between predicted and empirical oceanic isotopic records indicate ways in which the conventional continental timescale of glacial change must be altered to fit the better-dated deep ocean record. In addition discrepancies between predicted and empirical erratic dispersal patterns suggest that conventional views of ice-sheet behaviour based on high latitude models may be inappropriate to the dynamically more active mid-latitude ice sheets based in large part on deformable sediment beds.
The Plio-Pleistocene climatic record of the tropical Andes
Authors: van der Hammen Thomas
Published: December 2007

Sequences of lake sediments on the high plains of the Colombian Cordillera Oriental (at an altitude of c. 2500 m) represent some 5 or 6 Ma. The last glacial–interglacial cycle is well documented in the sediments of Lake Fuquene; very long sequences (up to 350-m long cores) were collected in the high plain of Bogota, representing more than 3.5 Ma. Pollen diagrams are now available, covering that time and representing the longest known continuous terrestrial record available. They were dated using potassium-argon and fission track methods on material from intercalated volcanic ash layers. The pollen diagrams can be interpreted in terms of shifting vegetation zones, and these in turn enable us to draw approximate temperature and humidity curves. The temperature curve for the last 3.5 Ma can be correlated with deep-sea curves (oxygen isotopes, temperature). An important change in rhythm and intensity seems to take place at approximately 3.1 Ma and a cold period that should correspond in time with the Pre-Tiglian of Western Europe is conspicuous.
Tectonic studies group: 14th annual meeting
Authors: Tanner Geoff
Published: December 2007

Report of a meeting of the Tectonic Studies Group held at the University of Glasgow, 18–21 December 1983. The meeting was organized by Drs P. W. G. Tanner and C. Farrow (Glasgow), I. Allison (Strathclyde) and A. D. Gibbs (Britoil).

After a decade of sustained growth, the Tectonic Studies Group has acquired international status and the 14th Annual Meeting attracted nearly 300 participants, many of whom were from the European continent and North America. Papers on any structural topic were invited and for the first time the number of contributions (92) far exceeded the number of papers (51) which could be given in two days. The organizers were faced with the unwelcome task of selecting speakers and also had to reduce discussion time to less than was desirable. John Underhill was awarded the prize for the best postgraduate contribution.

The meeting began with a 2-day workshop (18 and 19 December) on the interpretation of seismic reflection sections, organized by G . K. Westbrook (Durham) and J. Hall (Glasgow). A basic course in the techniques of reflection seismology was followed by a series of presentations by researchers from the universities and from industry on applications to different tectonic environments.

On 19 December, three field excursions were held. P. R. Thomas (Paisley) led an excursion to look at structures in the Central Highland Moine as exposed in new road cuttings on the A9; W. G. Henderson (BGS) led a party to North Glen Sannox on the Isle of Arran to examine
A gravity traverse across the Coastal Batholith, Peru
Authors: Bussell M. A. , Wilson C. D. V.
Published: December 2007

A 80-km long gravity traverse, with 43 stations, was made across the Lima segment of the Peruvian Coastal Batholith, eastwards from the coast at Huacho (lat. 11°S), through Sayán to Churin. A second traverse, 30 km long, with 14 stations, was made from near Sayán southwards to the coast at Rio Seco. Laboratory measurements of specific gravity were made on 74 samples, taken from all the major units of the batholith and its envelope. A Bouguer anomaly gradient of 5 mGal/km strikes parallel to the axis of the batholith. This gradient fits a model with an upper crust of 2650–2750 kg/m
3
in density, which thickens from 2.5 km at the coast to 25 km at 125 km inland. This wedge of light rock includes the Coastal Batholith and the miogeosynclinal sediments. In addition, the model requires either a buried granitoid beneath Churin, at the eastern end of the traverse, or a lateral change of density in the lower crust. After the regional gradient is removed, the residual anomalies can be correlated well with the distributions and densities of acid and basic rocks in the batholith. Positive residuals over the acid central complex of the Rio Huaura are interpreted quantitatively in terms of bell-jar subsidence of gabbro-diorite blocks.
Shear waves in a seismic survey of Lewisian basement: an extra control on lithological variation and porosity
Authors: Hall Jeremy , Ali Mubarik
Published: December 2007

The study of shear (
S-
) wave velocities in the Lewisian metamorphic complex of Sutherland, NW Scotland, shows their potential value in modelling lithological variation and porosity. The interpretation of a 40-km refraction line across a major lineament separating different rock units produced distinctive lateral and vertical velocity variations due to compositional change and closing of cracks respectively. Analysis of the vertical velocity variation shows water saturation of cracks, except in the top 400 m where cracks may he partially saturated. The lateral velocity variations, which show very good correlation with lithology, have been modelled using effective velocities of essential minerals and by regression analysis of longitudinal (
P-
) and
S-
wave velocity against composition. Adding S-wave data to P-wave data improves the modelling capability here only modestly, but is potentially more useful in identifying separately the proportions of mafic (
v.
felsic) and hydrated (
v.
unhydrated) minerals.
Beach orientation, bar morphology and the concentration of metalliferous placer deposits: a case study, Lake Turkana, N Kenya
Authors: Reid lan. , Frostick Lynne E.
Published: December 2007

The concentration of metalliferous particles in migrating swash bars is shown to depend upon processes controlled by the cross-sectional shape of the bar. A sand-spit provides two shorelines, each with a different pattern of wind-waves and each characterized consistently by bars of different shape. Where the wave period is low the bar is dune-like and its crest is set asymmetrically landward of the centre line. Where the wave period is high the bar is tabular, with a crest set just at the swash limit and on the lakeward side of the centre line. These differences in shape are important to the concentrating process. It is shown that swash-dominated dune-like forms produce concentrations of metalliferous grains that average only 13%. The tabular bar form, on the other hand, effects a significantly higher concentration of 21% through a hydrodynamic sorting process that is governed by limited swash overspill onto the landward slope. Concentrations of 90% are reached at specific positions. Confirmation of the concentrating process is obtained from detailed microstratigraphic interpretation of the contemporary bar, while the ancient bars of abandoned shorelines add supporting evidence. Clear-cut differences in placer concentration allow several diagnostic parameters to be identified for reconnaissance exploration. These include shore-line orientation, wave pattern, and bar cross-sectional morphology which can be combined with the reconstruction of abandoned shorelines using remote sensing imagery to provide a resource evaluation.
Thermal effects and timing of thrusting in the Moine Thrust zone
Authors: Johnson M. R. W. , Kelley S. P. , Oliver G. J. H. , Winter D. A.
Published: December 2007

Illite crystallinity studies in the foreland to the Moine thrust belt show a widespread heating event which is interpreted as a thermal response to thrust sheet emplacement. Temperatures reached ~275°C approximately 24 Ma after the main thrusting events. Based on the relationships between syn-thrusting intrusions and the thrust planes, combined with radiometric dates from the Moine sheet, it is argued that movement on the Moine thrust started between 440 and 430 Ma ago. Contractional slip in the Moine thrust belt ceased at about 425 Ma ago and it is proposed that illite metamorphism attained temperatures of ~275°
C
at about 408 Ma ago.
Computer manipulation of geological exploration data
Authors: Burwell A. D. M.
Published: December 2007

Report of a meeting held by the Geological Information Group at the British Petroleum Research Centre, Sunbury, 24 January 1985

This meeting, concerned mainly with computer manipulation of petroleum exploration data, attracted
c.
95 participants. In addition to eight papers presented, there were two computer demonstrations of log analysis systems and a number of poster displays.

The morning session, concerned with large-scale, integrated hardware and software systems, was chaired by R. Howarth. R. Till of British Petroleum gave the opening paper concerning BP Exploration’s integrated database system. BP Exploration databases fall into three main groups: those containing largely numerical data; databases specifically concerned with text handling; and well-based databases. The ‘numerical’ databases, implemented under the ULTRA database management system (dbms), include a seismic data system, a generalized cartographic database and an earth constants database. Textual databases include a library information system and a Petroconsultants scout data database, both implemented under the BASIS dbms. The well-based systems include a generalized well-data database, a wireline log archive, storage and retrieval system, and a master well index; all three are implemented under the INGRES dbms. Two related BASIS databases contain geochemical and biostratigraphical data.

G. Baxter (co-author M. Hemingway) described the development of Britoil’s well log database which was prompted by the need to have rapid access to digitized wireline log data for
c.
1500 wells on the UKCS. Early work involved both locating log information and digitizing those logs held in sepia form only. Each digitized log occupies approximately 1 Mbyte of
Interpretation of the Minch linear magnetic anomaly and of a similar feature on the shelf north of Lewis by non-linear optimization
Authors: Ofoegbu C. O. , Bott M. H. P.
Published: December 2007

The linear negative magnetic anomaly which stretches continuously for 110 km across the North Minch, extending slightly west of north from Loch Ewe, is interpreted in terms of an unusually wide dyke which does not reach the surface. Fourteen profiles taken from the aeromagnetic map have been interpreted using non-linear optimization, giving an excellent fit to a dyke having an average and fairly constant width of
c
. 1.1km. The depth to the upper surface of the interpreted dyke varies between 0.3 km and over 2 km. It is reversely magnetized in a direction consistent with a Tertiary or possibly earlier origin. The average magnetization is estimated to be 0.51 Am
−1
. A similar magnetic feature on the shelf to the north-west of the Butt of Lewis is also interpreted in terms of a reversely magnetized dyke, having a poorly-resolved width of about 0.8 km, a depth of about 0.7 km and a magnetization of 1.6Am
−1
. On seismic evidence, the Minch dyke appears to be post-Jurassic in age, and an early Tertiary age seems most likely for both dykes. It is suggested that they may be related either to the postulated large igneous pile of early Tertiary age which forms the Wyville-Thomson Ridge, or to the Skye centre. They appear to represent early Tertiary extension of the crust which is taken up by more numerous narrow dykes further south.
The sedimentary facies of a late Bathonian regressive episode: the Kilmaluag and Skudiburgh Formations of the Great Estuarine Group, Inner Hebrides, Scotland
Authors: Andrews Julian E.
Published: December 2007

The Kilmaluag and Skudiburgh Formations of the Bathonian, Great Estuarine Group, represent a unique palaeoenvironment within the British Jurassic. The Kilmaluag Formation is divided into two distinctive facies. The ‘clastic facies’ of N Skye comprises calcareous mudstones and shales, with subordinate sandstones and argillaceous limestones. The depositional setting was one of shallow, ephemeral lagoons, closed from the sea. Sublittoral lagoon, mudflat and channel environments are identified, and fossil faunas indicate low salinity. The ‘argillaceous limestone facies’ of southern Skye, Eigg and Muck, formed in a similar depositional setting, although sandstones are not present. Alternations of carbonate rocks (some dolomitic) and calcareous shales probably reflect palaeoclimatic fluctuations between humid and arid periods. The overlying Skudiburgh Formation is interpreted as being alluvial. Floodplain, channel and overbank deposits are identified by the presence of mottled mudstones, sands and lensoidal silts. Syndepositional carbonate nodules are interpreted as calcrete, which occasionally coalesced to form extensive hardpan calcrete horizons. The vertical facies sequence reflects a late Bathonian regression. The coastal plain, terrestrial environments of the Skudiburgh Formation were transgressed during the Callovian Stage, an event which ended paralic deposition in the Hebridean Jurassic.
Upper Palaeozoic successions and nappe structures in north Cornwall
Authors: SELWOOD E. B. , THOMAS J. M.
Published: December 2007

For many years the geology of north Cornwall has been interpreted in terms of a south-facing overfold model, which predicts a major confrontation at Padstow with the north-facing structures of south Cornwall. New evidence indicates the existence of contrasting successions separated by flat-lying thrusts. In upward succession the Port Isaac, Tredorn and Boscastle nappes are identified; the first appears to have been emplaced by gravity sliding in late Viséan times, followed by the Tredorn and Boscastle nappes in the early Namurïan. Strata represented in the inverted limb of the Port Isaac Nappe, not previously distinguished, are described as the Jacket's Point Slate Formation.

Throughout the nappe pile there is consistent evidence of north-facing and northward transport for distances measured in tens of kilometres. Not more than 3 km of south-facing strata may now exist at the Padstow confrontation, and this feature is unlikely to be of great regional significance. The allochthon extends northwards to the Rusey Fault Zone where the autochthon was locally backfolded over the allochthon in late Westphalian times; this appears to be the only significant confrontation of facing directions in north Cornwall.
Tectonics of the Bude Formation, north Cornwall—the recognition of northerly directed décollement
Authors: WHALLEY J. S. , LLOYD G. E.
Published: December 2007

The Upper Carboniferous Bude Formation of North Cornwall and Devon underwent deformation, beginning shortly after its deposition, which resulted in a complex geometry of folding and thrusting. The deformation initially exploited slumped beds as décollement horizons and resulted in a significant northerly translation of thrust sheets. The development of chevron folds, for which the area is famous, commenced at this stage but continued, causing folding of thrust planes and cleavages. During the deformation the dominant sense of thrust movement switched from a northerly to a southerly direction and this is interpreted as the effect of backthrusting associated with the northwards migration of the deformation front.
The stratigraphy and structure of the Devonian rocks around Liskeard, east Cornwall, with regional implications
Authors: BURTON C. J. , TANNER P. W. G.
Published: December 2007

A formal stratigraphy based on new macrofaunal evidence is proposed for a little-known area of slates, thin limestones, and volcaniclastic rocks of Lower Devonian to early Upper Devonian age around Liskeard, between South Devon and north Cornwall. Open shallow marine shelf conditions persisted from the Emsian until the onset of basinal sedimentation in the Frasnian, with the local development of pillow lavas and pillow fragment breccias during Eifelian and Givetian times. Regional stratigraphic correlations identify a Middle Devonian axial ridge which runs from Tor Bay to Bodmin, and separates a redefined Trevone (north Cornwall) Basin from the south Cornish Basin. A moderate to steeply dipping slaty cleavage (Dl) dips southward throughout the area and is associated with early E–W major folds, inferred to be north- or upward-facing, which plunge gently east. A penetrative, closely spaced crenulation cleavage (D2) is developed in a zone, >0.7 km thick, which trends E–W and dips at 15º to 30º south. This fabric, previously misidentified as the D1 slaty cleavage, is associated with major D2 folds which have near horizontal, east–west trending axes; structures of this age and geometry have not been reported from elsewhere in the region. The Portwrinkle Fault has been traced NW–SE across the area and passes west of Liskeard; it shows a large dextral strike-slip displacement and may have developed early in the history of the thrust belt.
Organic microfossil geothermal alteration and interpretation of regional tectonic provinces
Authors: DORNING K. J.
Published: December 2007

Optical analyses for colour, transparency and reflectance of all organic fossils may be used for palaeotemperature data. Of the organic-walled fossils, acritarchs, chitinozoans, dinoflagellate cysts, graptolites, pollen and spores are of particular value in geothermometry. At increasing temperatures, fossil organic material shows progressive changes in colouration and increasing reflectance. Palaeotemperatures of sedimentary rocks may be derived from the optical characteristics of the main organic fossil groups recorded. Regional palaeotemperature values are associated with variations in overburden thickness and heat flow. Regional tectonic provinces typically record a restricted range of palaeotemperature values that may be related to sediment thickness and phases of igneous and tectonic activity.
Volcanological and petrological evolution of San Pedro volcano, Provincia EI Loa, North Chile
Authors: O'CALLAGHAN L. J. , FRANCIS P. W.
Published: December 2007

The 6163 m high volcano San Pedro in the Western Cordillera of the central Andes of North Chile, is a composite of two cones, each representing a different structural and chemical stage in the evolution of the volcano. Eruption of thin lavas and scoria, dominantly of basaltic andesite composition, built up an older cone, which was subsequently modified by both glacial erosion and a major collapse event, akin to that of Mt. St. Helens in May 1980. A younger cone has subsequently grown within the crater, obscuring much of the detailed structure of the older cone. The younger cone was built up in four distinct phases of eruption which produced andesite and dacite lavas and pyroclastic flow deposits. The latter include both pumice flows and hot avalanche deposits. All of these products from the younger cone are chemically distinct from those of the older cone.

Whilst much of the whole rock geochemistry can be explained by simple crystal-liquid fractionation involving the observed phenocryst phases, this process cannot adequately account for the petrographic textures and mineralogical variations, which show evidence for considerable thermal and chemical disequilibrium. Textural, mineralogical and chemical variations are consistent with models of late stage mixing between magmas of the same fractionation series, with chemical and thermal inputs from hot dense basalt or basaltic andesite injected into the base of the magma chamber.
Neotectonics of the Marmara Sea region of Turkey
Authors: CRAMPIN STUART , EVANS RUSS
Published: December 2007

Seismological investigations in Western Anatolia, NW Turkey have identified linear patterns of earthquake epicentres outlining a wedge-shaped block in the area of the Marmara Sea. This block shows different seismic characteristics from the rest of Western Anatolia and appears to act as a separate tectonic unit. Earthquake fault-plane mechanisms show that the Marmara block is being rotated and sheared in order to accommodate the right-lateral motion of the north Anatolian Fault and the extensional tectonics of the southwestern Anatolia. Investigations of the behaviour of seismic shear-waves suggest that neotectonic stress aligns water-filled microcracks throughout the upper (brittle) 10–20 km of the crust and that
in situ
stress directions can be monitored by analysis of shear waves recorded on three-component instuments.
The British Geological Survey Database
Authors: LUMSDEN G. I. , HAWORTH R. T.
Published: December 2007

The British Geological Survey is a component body of the Natural Environment Research Council, through which it is funded by government to assemble, manage, interpret and communicate the National Geosciences Database for the benefit of the nation. On the 150th Anniversary of the founding of the Geological Survey of Great Britain, set up in 1835, the Geological Society has honoured the Survey by dedicating this issue of its Journal to the reporting of some of the Survey's activities. This issue is not meant to be a compendium of papers covering the full range of BGS activities. That is impossible in an organization currently dominated by a financial need to respond rapidly to the demands of customers (including Government). Instead it represents a snapshot of those activities that reached publication stage during the summer of 1985. Some papers offered for inclusion had to be withdrawn pending their release from confidential status. Others submitted could not be revised in time because of customer demands on the author’s time. They all, however, emanate from a broadly based programme of strategic research responding to the immediate demands of modern industrialized society while contributing to the on-going and long-term assembly of the National Geosciences Database.

The objective of the Survey, 150 years ago, was to assemble and interpret a geological database for the whole country, and initially the only tool available was geological surveying. Geological surveying is carried out by field geologists observing and sampling strata to identify rock type, composition and age, observing topographical features
Geophysical images of the deep crust: the Iapetus suture
Authors: BEAMISH D. , SMYTHE D. K.
Published: December 2007

The Iapetus suture, arguably the most fundamental lineament of British and Irish structure, has been previously identified on the BIRPS WINCH deep seismic reflection profiles offshore as a NW-dipping feature. New depth-migrated interpretations of these and other reflection data show good correlation of structure for 100 km along strike in the northern Irish Sea towards magnetotelluric stations onshore in the north of England and Southern Uplands of Scotland. Three different methods of inverting data from these sites all reveal a thin NW-dipping slab of high conductivity. A contour map of the suture trace, dipping at 15–25°NW, can be constructed down to and through the Moho at 28 km depth. This map suggests crustal stretching below the Solway Basin. The ?mylonitic suture zone is characterized by good seismic reflection layering, high conductivity (presumably fluid-produced), and a steep increase of P-wave velocity over the few kilometres of its width. Crustal refraction experiments LISPB and CSSP provide useful velocities, but locally misleading structure, so that the combination of the seismic reflection and geoelectric methods may be the most powerful means of determining deep crustal structure with a good degree of both vertical and lateral resolution.
The susceptibility of UK groundwaters to acidic deposition
Authors: EDMUNDS W. M. , KINNIBURGH D. G.
Published: December 2007

The weathering of minerals at shallow depths provides much of the sink for acidic atmospheric deposition. The geology of the UK has been divided into four classes according to the extent to which the bedrock is likely to provide buffering and possibly give rise to acidic surface or groundwaters. Other modifying factors including soils, superficial deposits and land use are also considered. The likely sources and sinks of H
+
in shallow groundwater systems are also reviewed.

Most available groundwater data are derived from major aquifers, often in carbonate-bearing lithologies which afford excellent buffering and which are unlikely ever to be adversely affected by acidic deposition. Relatively few data exist for shallow groundwaters widely used for domestic supplies in rural areas, especially in western and northern Britain where groundwaters might be most affected.

Acidic groundwaters and/or surface waters are defined on the basis of their alkalinity and calcite saturation index (SI
c
). Acidic groundwaters are most likely to occur where (1) acid soils are found and glacial drift is thin or absent, (2) the source of acidic inputs is high, (3) carbonate minerals are absent, (4) the residence time of water is short. Low alkalinity groundwater is found in many sandstone lithologies including the Sherwood Sandstone (a major UK aquifer), many Lower Palaeozoic strata and granites. However, existing data for susceptible areas are insufficient to show whether or not there have been significant long-term changes in groundwater acidity or alkalinity.
Fracture zones in the North Atlantic: morphology and a model
Authors: COLLETTE B. J.
Published: December 2007

A morphology is presented for the typical cross-section of an inactive fracture zone in the Atlantic. Inactive fracture zones typically consist of an asymmetric valley to the young side of the fracture zone plane and a high wall or scarp to the old side. Large-offset fracture zones may be accompanied by a marginal valley on the other side of the high wall. This topography is superimposed on the depth-age step due to lithospheric cooling.

A model is developed which accounts for this morphology. The model relates the inactive fracture zone morphology to the topography found at present-day intersections of the spreading axis with transform faults. The asymmetry of the median valley near fracture zones plays an important role in explaining the typical fracture zone morphology. The existence of a median valley is related to the viscous delay of the upwelling mantle material at the spreading axis. Its asymmetry near fracture zones can be accounted for by modelling the viscous drag exerted by the lithosphere on the asthenosphere. If the viscosity is low, as under Reykjanes Ridge and the East Pacific Rise, no median valley develops and a different morphology may be expected. The occurrence of marginal valleys is interpreted as the result of lithospheric warping when the graben walls in the transform domain, which are caused by tension due to horizontal thermal contraction. are excessively high.
Lithosphere age, depth and structural complications resulting from migrating transform faults
Authors: KARSON J. A.
Published: December 2007

If oceanic transform faults migrate back and forth across a finite width of the lithosphere as a consequence of minor ridge propagations and recessions, many structural complications can arise. Patterns of lithosphere age and depth as well as internal structure may be determined by the frequency and magnitude of such migrations. Such processes are expected to be most likely at transforms bounded by relatively young, thin, weak lithosphere, due to either short ridge offsets or fast spreading rates.
The Tydeman: morphology and seismic structure of old fracture zone crust
Authors: POTTS C. G. , WILLIAMS C. A. , CALVERT A. J. , WHITE R. S.
Published: December 2007

The Tydeman Fracture Zone was identified 160 km SE of the Azores in 1977 from a detailed bathymetry and magnetic survey between 22° 30' and 23°40'W, (

Twigt
et al
. 1979

). The fracture zone forms a linear trough here with a width of 20 km, water depth of 4.7 km and orientation of 085°. This study extends the path of this fracture zone between 18° and 30°W though not yet to the ridge crest, using a larger dataset of bathymetric, seismic reflection and magnetic profiles. A discontinuity in the fracture zone valley indicates an interruption in its formation, possibly during the formation of the Azores platform. Two separate wide-angle seismic experiments carried out over old crust in the active section of the Tydeman Fracture Zone show low crustal velocities compared with normal oceanic crust of comparable age, an absence of an identifiable layer 3, and a shallower than normal Moho overlying a region of anomalously low upper mantle velocities. Estimates of Poisson's ratio suggest that hydrothermal circulation may continue for as long as 70 Ma after crustal formation.
Deep-tow seismic profiles from the Vema transform and ridge–transform intersection
Authors: BOWEN A. N. , WHITE R. S.
Published: December 2007

A recently developed near-bottom reflection profiling system has been used to obtain high resolution seismic sections across the Vema transform fault. At the western ridge–transform intersection deep-towed 3.5 kHz echo sounder data show evidence of fresh lava flows at the seabed within the nodal deep.

Over one kilometre of sediment fills the bottom of the ridge–transform intersection deep. Many strong, discontinuous reflectors within the sedimentary section caused by lava layers indicate that the intersection deep has been the site of sustained igneous activity. On the eastern side of the deep is a large, uplifted fault block created as the newly formed crust moved out of the spreading centre. Dipping strata within the fault block document back-tilting as the new crust is extended by normal faulting. Profiles across the active transform fault reveal that the zone of deformation throughout the one kilometre thick sediment column is narrow, suggesting that the location of the fault has remained stable throughout at least the last million years.
Current research in regional geology
Authors: BROWN MICHAEL , COLLEY HOWARD
Published: December 2007

Report of a Society Ordinary General Meeting held at Burlington House on
13
November
1985.
The meeting was organized by Dr M. Brown and Dr H. Colley.

With the success of the Specialist Groups and the decline of the ‘traditional’ OGM, the Society has sponsored several one-day thematic meetings either as OGMs or as SpecialScientific Meetings. Additionally, specialist or thematic meetings have reduced the opportunities for interdisciplinary research on a regional scale to be presented and discussed. These reasons prompted the convenors to propose a meeting on ‘Current research in regional geology’, with papers from academic institutes, the BGS and overseas. Speakers presented recent unpublished research results, and both the substantial attendance at the meeting and the lively discussion after each paper suggest that this style of OGM is very worthwhile. The BGS also displayed a number of poster contributions.

An introduction to the meeting was given by M. Brown, who also shared the chair during the morning session with H. Colley. In the first paper,
R. L. Johnson
presented a general overview of the work undertaken by the BGS overseas, particularly in Africa. The most interesting type of project undertakh by the BGS in Africa under funding from the Overseas Development Administration is that involving research and development in which success is judged in terms of the prospecting licences sought at the end of a project!
P. J. Treloar
followed with a detailed account of recent research’in the Magondi (mid-Proterozoic) and Zambesi (Pan-African) mobile belts of NW and N
Heat flow, heat production and thermo-tectonic setting in mainland UK
Authors: LEE M. K. , BROWN G. C. , WEBB P. C. , WHEILDON J. , ROLLIN K. E.
Published: December 2007

New heat flow data for the United Kingdom, together with additional heat flow and heat production determinations for Caledonian-age granites, have led to a revision of the UK heat flow map and a re-examination of the relationship between heat flow (
q
0
) and heat production (
A
0
) for granites and basement rocks. Previously recognized broad belts of above-average heat flow are now resolved into separate zones which reflect, to a greater extent, the geological structure and tectonic history of the UK. The zones of highest heat flow are spatially associated with voluminous, high heat production granitoid batholiths in SW England, northern England and the Eastern Highlands of Scotland. A single linear correlation between
q
0
and
A
0
is no longer tenable and an analysis in terms of broad heat flow provinces, each with a characteristic upper-crustal heat production distribution and deep heat flow contribution, is also considered to be an oversimplification. On the
q
0
–A
0
plot, the data form four separate clusters; three corresponding to the granite batholiths in SW England, northern England and the Eastern Highlands of Scotland, and the fourth to the basement rocks of central England and Wales. An explanation of the
q
0
–A
0
data is proposed in terms of the crustal structure and thermo-tectonic setting of each area. In the case of the granite batholiths the data reflect the contrasting depth extent and radioelement-depth functions of the intrusions. These parameters in turn are related to the magmatic evolution and emplacement history of each batholith and the nature of the crust into which they were emplaced.
Fine sediment sources and sinks around the East Anglian Coast (UK)
Authors: McCAVE I. N.
Published: December 2007

The cliffs of Norfolk and Suffolk yield an average of 785 000 tonnes (t) of fine sediments to the coastal zone annually. East Anglian rivers yield very little (≈5500 t a
−1
) but those of the Wash produce about 100 000 t a
1
. By contrast the region is dominated by 1.4 × l0
6
ta
−1
input from cliff erosion in Holderness. Accumulation in vertical accretion alone of the coastal marshes of East Anglia, the Wash, north Lincolnshire and the Humber requires 1.12 × 10
6
t a
−1
of fines. Progradation around the Wash probably accounts for another 1.1 × 10
6
t a
−1
. The East Anglian area (including the Wash) is thus sufficient to trap over half the regional mud input from Flamborough Head to the north side of the Thames estuary, and could take it all, depending on assumptions involved in calculation.
Dispersal, concentration and deposition of suspended matter in the North Sea
Authors: EISMA D. , KALF J.
Published: December 2007

Suspended matter comes into the North Sea from the Atlantic Ocean, from the Channel, rivers, seafloor erosion, coastal erosion, the atmosphere, and from primary production. The contribution of the last source is temporarily large when phytoplankton growth is abundant, but is soon decomposed, mineralized or consumed so that over the year the net effect is small. Accumulation and deposition of suspended matter occurs predominantly in only a few areas (the Waddensea, the German Bight, the Skagerrak/Norwegian Channel). The remainder of the North Sea floor consists of Pleistocene and Early Holocene relict deposits and of reworked sands and gravels. The mechanisms resulting in accumulation and deposition are discussed. There are strong indications that the amount of suspended matter flowing out from the North Sea into the Norwegian Sea along the Norwegian coast is only little more, or the same, as the amount coming in from the North Atlantic, although its composition may be different.