bluuebunny/crossref_metadata_2025 huggingface dataset:
Post-subduction alkaline volcanism along the Antarctic Peninsula
Authors: HOLE M. J.
Published: December 2007

Following the cessation of subduction along the Antarctic Peninsula, there was a change in the character of the magmatism from calc-alkaline to alkaline. A Miocene-Pliocene suite of basanites, tephrites and alkali and olivine basalts from Alexander Island, south-west Antarctic Peninsula, was erupted between 18 and 30 Ma after the cessation of subduction. These basalts exhibit incompatible trace element characteristics similar to those reported for continental alkali basalts and OIB. Major and trace element variations are consistent with an origin by low but variable degrees of partial melting of a garnet lherzolite source with residual garnet ± clinopyroxene, followed by limited fractional crystallization of olivine and clinopyroxene. Sr- and Nd-isotope compositions cover a limited range of
87
Sr/
86
Sr 0.70275-0.70343 and
143
Nd/
144
Nd 0.51298–0.51286. These ratios are consistent with the derivation of the basalts from a depleted source region broadly similar to that of MORB and non-Dupal OIB.

Correlated LILE/HFSE-isotope trends demonstrate that the olivine basalts are enriched in the LILE and
87
Sr but depleted in
143
Nd relative to other Alexander Island samples. The LILE-enrichment is attributed to the inheritance of a subduction component from mantle material which previously constituted the mantle wedge during Mesozoic subduction along the Antarctic Peninsula.
Interpretation of aeromagnetic data from the Ellsworth Mountains-Thiel Mountains ridge, West Antarctica
Authors: GARRETT S. W. , MASLANYJ M. P. , DAMASKE D.
Published: December 2007

Over 12000 km of new aeromagnetic data, gathered during periods free from auroral disturbances, are presented for an area of 290 000 km
2
in West Antarctica, including the majority of the Ellsworth-Whitmore Mountain crustal block. Selection of an appropriate line spacing (20 km) and rigorous diurnal control allowed interpretation of isolated magnetic anomalies by two-dimensional modellìng. Anomalies of 50–500 nT amplitude extend for over 100 km, predominantly with an east-west orientation. They attain their greatest amplitudes over scattered exposures of Middle Jurassic granite, but the measured magnetizations of these rocks (
J
<0.1 Am
−1
) are insufficient to match the observed anomalies. It was necessary during modelling to invoke deeper, magnetite-rich, probably mafic plutons (
J
>0.5 Am
−1
) beneath the granites. The intrusions probably form part of a widespread bimodal igneous suite created during early stages of continental fragmentation.
Editorial
Authors: Le Bas M. J.
Published: December 2007

This issue of the
Journal
marks an important event in the history of the Geological Society. It is the first product of the Geological Society Publishing House which was set up by Council last year. The Publishing House will give the Society more control over the production of this
Journal, the Quarterly Journal of Engineering Geology,
the Special Publications, Memoirs, Special Reports and the occasional other publications and it will provide the Society with a greater share of the income from these publications.

To this end, office and warehouse premises have been purchased in the west of England. The address is: Geological Society Publishing House, Unit 7, Brassmill Enterprise Centre, Brassmill Lane, Bath BA1 3JN, and visitors will be welcome. Mr Roger Cooper has been appointed as Publications Manager to be responsible to the Publications Board of the Society for the sales, promotion and technical aspects of publishing and the day-to-day running of the Publishing House. MS Angharad Hills, the Publications Secretary, has moved her office from Burlington House to Bath and all correspondence should be addressed to her there. Now that copy-editing, address- labelling and mailing schedules for the
Journal
are done on Society premises, publication ‘turn round’ time should be speeded up. At present, the interval from acceptance of a paper to its publication is six to seven months. The review and particularly the revision time has been very variable: from two months to a year or more.

Despite all this, we are sad to be reducing our
The Grampian Group: a major Late Proterozoic clastic sequence in the Central Highlands of Scotland
Authors: GLOVER B. W. , WINCHESTER J. A.
Published: December 2007

A stratigraphic framework is proposed for the Late Proterozoic Grampian Group of the Scottish Highlands. The Grampian Group is divided into three subgroups, each defined by distinctive lithofacies associations reflecting different environments of deposition. The thin Ord Ban Subgroup, which is locally developed at the base of the Grampian Group on Speyside and Strath Dearn, consists of shallow marine shelf sediments in association with concordant amphibolite sheets. Elsewhere the Corrieyairack Subgroup, which is thickest around Loch Laggan, forms the lower portion of the Grampian Group and comprises a thick turbiditic clastic sequence laid down in deeper water during rapid basin subsidence. The Glen Spean Subgroup comprises the upper part of the Grampian Group and is thickest in the Atholl District. It is composed of shallow water tidal and deltaic deposits, marking a shallowing of the Grampian Group basin. Lateral facies changes and diachronous contacts are indicative of differential subsidence and the Grampian Group basin apparently developed and filled before the onset of regional subsidence which heralded deposition of the overlying Dalradian sediments. The possibility that the Grampian Group was unconformable on the structurally underly-ing Central Highland Division and Glenshirra Succession is currently unresolved.
Palaeoatmospheres in the Phanerozoic
Authors: HUDSON J. D.
Published: December 2007

Except in the recent geological past, palaeoatmospheric composition cannot be measured but only inferred from palaeontological or geochemical observations. The likely controls on atmospheric composition are reviewed and the role of organisms stressed as monitors, recorders, motors and moderators of palaeoatmospheric changes. Whereas there is a good general case for changes in
PO

2

and
PCO

2

during. Phanerozoic time, proposals for timing and mechanism in the earlier Phanerozoic are speculative at present. It seems probable that the late Palaeozoic spread of land plants raised O
2
, and reduced CO
2
levels in the atmosphere. The end-Cretaceous crisis had a transient impact on the atmosphere, whose general constancy through geological time is one of the most remarkable features of Earth history.
Short paper: The significance of mid-Palaeozoic basement in Graham Land, Antarctic Peninsula
Authors: MILNE A. J. , MILLAR I. L.
Published: December 2007

A mid-Palaeozoic basement to the Antarctic Peninsula is confirmed by a geochronological study of the gneissose country rock of the Mesozoic magmatic arc of eastern Graham Land. Rb–Sr whole-rock ages of 410 ± 15 and 426 ± 12 Ma from samples of orthogneiss indicate a previously unrecognized episode of granitic magmatism in the Antarctic Peninsula during the Silurian. Sm–Nd data on garnet–whole-rock pairs indicate that subsequent amphibolite facies metamorphism occurred in late Carboniferous times, probably as a result of plutonism.
Short Paper: Devonian and later movements on the Great Glen fault system, Scotland
Authors: ROGERS D. A. , MARSHALL J. E. A. , ASTIN T. R.
Published: December 2007

On the Scottish mainland the Great Glen fault (GGF) displaces the Emsian to Frasnian Orcadian Old Red Sandstone (ORS) by only 25–29 km dextrally but net post–ORS dextral offsets in Shetland are much larger (120 km total). Most of the displacement (15–20 km) Permian initiation of the Inner Moray Firth Basin. It probably occurred between Frasnian cessation of Orcadian extension and accompanied transpressional inversion of the Orcadian Basin in the mid-late Carboniferous and/or possibly the late Devonian. Devono-Carboniferous transtension may also have occurred. The earlier history of the GGF includes late Caledonian sinistral motion which must have ceased by the late Emsian.
Short Paper: Timing and regional implications of deformation in the Southern Uplands of Scotland
Authors: BARNES R. P. , LINTERN B. C. , STONE P.
Published: December 2007

The timing of deformation in the Southern Uplands is constrained by tectonostratigraphical and intrusive relationships. Deformation migrated diachronously southwards, affecting the southern part of the Southern Uplands in the mid-Silurian. In contrast deformation in the Lake District cacan be shown by the same criteria to be Early Devonian. Thus, since the possibility of post-Emsian strike-slip along the Iapetus suture is remote, the regional tectonism cannot be related to a climactic episode due simply to closure of the Iapetus Ocean. Instead a southeast migrating deformation front is envisaged linking Silurian closure of Iapetus and the Southern Uplands backarc basin with Early Devonian collision farther south.

The timing and geometry of the main cleavage-producing deformation within the paratectonic Caledonides of northern Britain is generally debated in terms of closure of the Iapetus Ocean. Structures developed are related to accretion of a collage of terranes onto the southern margin of Laurentia, within a sinistral transpressive stress regime, during the collision of the three plates Laurentia, Baltica and Eastern Avalonia (Soper & Hutton 1984). However, within this overall model there is a considerable divergence of opinion as to the chronology and correlation of the main episode of deformation across the Iapetus suture collision zone. In north-west England and Wales, recent regional syntheses propose that the main structures were formed during an end-Silurian/Early Devonian collision and subsequent NW-directed underthrusting. This climaxed with the main cleavage-producing episode in the Emsian (

Soper
et al.
1987

;
McKerrow 1988
) which has been correlated with the Acadian Orogeny of the
The structural history of a transtensional basin: Inner Moray Firth, NE Scotland
Authors: ROBERTS A. M. , BADLEY M. E. , PRICE J. D. , HUCK I. W.
Published: December 2007

The isostatically-uncompensated Moray Firth Basin forms the western arm of the North Sea rift. Unlike other parts of the rift the Moray Firth opened not by dip-slip movements on basin-bounding faults, but as a result of dextral strike-slip motion on the sub-vertical Great Glen Fault Zone, which during basin opening was probably pinned at its intersection with the Wick Fault. Thus the Caithness Ridge and Northern Highland blocks were stable relative to each other, while the Central Highland and Northern Highland blocks accommodated dextral slip.

Previous calculations have shown that a cumulative 8 km of displacement have occurred on the Great Glen Fault Zone since the Permian. Approximately 2 km of this displacement may have formed a small Permian half-graben at the centre of the present basin, the remaining
c.
6 km occurred largely during the Late Jurassic, but Triassic and Early Cretaceous displacement is also inferred.

Although much of the internal structure of the Inner Moray Firth is dominated by tilted-fault-block structures, displacement analysis indicates that the majority of faults within the basin have accommodated significant oblique-slip motion. An understanding of the kinematics of the basin allows structures attributable to oblique-slip movement to be explained, a number of these are illustrated with seismic reflection examples.
Low grade metamorphism of the Manx Group, Isle of Man: a comparative study of white mica ‘crystallinity’ techniques
Authors: ROBERTS B. , MORRISON C. , HIRONS S.
Published: December 2007

Studies have been made in two laboratories on metapelites from the Manx Group, Isle of Man, showing the distribution of white mica ‘crystallinity’, using the Kubler index (Δ°2Θ) and the Weber index
(Hb

rel

).
Two isocryst maps, which show broadly similar distributions of metamorphic grade, are illustrated and a correlation between the laboratories is presented. The mineralogy of the
<2 m
fraction in relation to ‘crystallinity’ has been determined. The distribution of metamorphic grade over central and eastern parts of the Isle of Man, as depicted by the Kubler index isocryst map, is related to subjacent granite plutons, but these contact metamorphic effects overprint an earlier, largely anchizonal, regional metamorphism. Localized, late, retrograde effects are related to low temperature hydrothermal mineralization and to cold re-working in a large fault zone.

Differences between the maps are largely in the degrees of resolution which stem directly from the different sampling intervals employed. Comparisons between the maps suggest a sampling interval of 1-2 km is adequate in regions of simpler geology; but that an interval of <1 km may be necessary in more complex regions. Well resolved maps can be produced only when the sampling interval is linked to geology.

The changes in the mineralogy of the <2 m fraction in relation to grade are closely similar to those described from Lower Palaeozoic metapelites from North Wales, although higher grades have been reached in the Manx Group with the development of biotite.
Aspects of climatic influence on the clay mineralogy and geochemistry of soils, palaeosols and clastic sedimentary rocks
Authors: CURTIS C. D.
Published: December 2007

Climate strongly influences soil clay mineralogy and bulk chemical composition. In humid climates chemical weathering is at its most intense and virtually all ‘primary’ bedrock minerals suffer complete breakdown. They are replaced by authigenic hydrated oxides of Fe and Al together with halloysite and kaolinite in deep profiles. These minerals develop where the residence time of water in the soil is slight. Longer residence times lead to higher solute concentrations and the stabilization of smectite. Authigenic palygorskite and sepiolite may form in highly saline, alkaline soils. The stability of these precipitated minerals is problematic: they may be metastable or even unstable. All other clays found in soils are unstable, being incomplete, solid-state hydrolysis products of substrate minerals. The balance between stable, metastable and unstable minerals and the rate of profile development are both much influenced by temperature, rainfall and activities of soil biota; themselves reflecting climate.

Bedrock influence is greatest under conditions of low to moderate precipitation where unstable minerals persist. Local topography, however, also strongly influences both the rate and products of chemical weathering, quite independently of climate. On the grand scale, tectonic factors may constrain the time available for profiles to develop, hence the extent to which bedrock minerals survive or are altered. Mountain soils reflect local climate and bedrock composition much more than latitude.

The sediments delivered to major basins today do not reflect global soil distribution patterns. The bulk composition of suspended sediment entering the Indian Ocean, for example, is rather similar to that entering the Arctic Ocean. Sediment dispersal patterns can also confuse climatic signals: a problem not encountered with palaeosols. Authigenic clays formed within sedimentary basins and post-depositional (burial) alteration of both sediments and buried soil profiles must lead to interpretational ambiguities. Climatic signals are likely to survive best in bulk compositional data (although diagenetic reactions at depths in excess of about 2 km do not appear to be isochemical) and in the distribution of more stable yet climatically sensitive minerals (kaolinite as opposed to illite, chlorite).
Geomorphology and surface tilting in an active extensional basin, SW Montana, USA
Authors: ALEXANDER J. , LEEDER M. R.
Published: December 2007

The valley and alluvial cone of the antecedent Madison River in the Missouri Flats area of SW Montana lie in a half-graben bounded by a prominent prehistoric fault scarp. Footwall-sourced alluvial fans and fans derived from a major transfer zone have prograded onto the oldest of a prominent suite of three paired terraces of Holocene age which bound the modern braided floodplain of the river. The terraces have been cut into the Pleistocene alluvial cone and are cut by the prehistoric fault scarp. Levelling studies on the terrace surfaces in the hangingwall reveal that movement on the fault has caused surface tilting, erosion and deposition. A suite of terraces present in the footwall of the fault shows backtihing consistent with footwall uplift having occurred.
Estimation of completeness of stratigraphical sections using empirical data and theoretical models
Authors: SADLER PETER M. , STRAUSS DAVID J.
Published: December 2007

The completeness of a stratigraphical section is the fraction of time intervals of some specified length (
t
) that have left a record. A record is left when some sediment is deposited during the interval and is not subsequently eroded. A complete section contains no hiatuses longer than
t
. The completeness of a section varies with
t
and its accumulation rate varies with the length of the time span over which it is measured. Plots of measured accumulation rate against time span are an empirical means of estimating completeness. Simple theoretical models help extrapolate meagre data and identify bias.

Completeness at time scale
t
can depend upon three general properties of the accumulation history: the age of the section, the long term net accumulation rate (drift) and the unsteadiness of the sedimentation rate. The way unsteadiness is measured depends upon the kinds of fluctuations that can be recognized in the accumulation rate. To describe random fluctuations a standard deviation of rates is sufficient. One dimensional Brownian motion is a model of random fluctuations that explains many aspects of stratigraphical completeness. Regular periodic fluctuations in accumulation rate may be described in terms of wavelength and amplitude. Completeness is an increasing function of
t,
drift and, in the periodic case, the wavelength of fluctuations; it decreases with increasing standard deviation of accumulation rate and the amplitude of periodic fluctuations. The completeness and thickness of stratigraphical sections are weakly positively associated.
Arenig biostratigraphy and correlation in the Welsh Basin
Authors: FORTEY R. A. , OWENS R. M.
Published: December 2007

Recent work on the Arenig Series in the Welsh Basin is reviewed; it is now known to be far more complete and richly fossiliferous than has been supposed. Three regional stages, Moridunain, Whitlandian and Fennian, and seven trilobite-based biozones have been defined. Outstanding problems are highlighted, among which remains the definition of a stratotype for a base for the series, for which there appears to be only one feasible candidate in this area, in the Shelve inlier.
The Murchison Symposium
Authors: BASSETT M. G. , SIVETER DEREK J. , COCKS L. R. M.
Published: December 2007

Roderick Impey Murchison's book on The Silurian System was published in January 1839 and immediately established stratigraphical and palaeontological standards for the subsequent classification and correlation of Lower Palaeozoic rocks throughout the world. Over 150 years later this classic work still forms a cornerstone on which studies of the Silurian Period are based. In recognition and celebration of the sesquicentenary of publication, an international conference was held at the University of Keele, Staffordshire from 28 March to 3 April 1989, followed by a field excursion through the Welsh Borderland and Wales from 4 April until 9 April inclusive. Appropriately entitled 'The Murchison Symposium', the conference was the first international meeting devoted specifically to the study of Silurian geology.

The IUGS Subcommission on Silurian Stratigraphy, The Palaeontological Association, The Geological Society of London and The Geologists' Association provided an umbrella of sponsorship, with additional generous support being given by a number of companies and organizations.
M. G. Bassett
and
P. D. Lane
acted as convenors, backed up by an organizing committee comprising
R. J. Aldridge, Lesley Cherns, Dianne Edwards, R. M. Owens, David J. Siveter, Derek J. Siveter,
and
A. T. Thomas.
Over 100 delegates attended from 15 countries. The 49 lectures were organized into thematic sessions covering, respectively, Palaeobiogeography, Geotectonics, Historical Aspects, Sedimentology and Biostratigraphy, Atmosphere and Ocean, and Silurian Life, followed by a Synthesis of the key points to emerge from the meeting. Each theme opened with a global overview, followed by more regional papers.

As a preface to
Rapakivi granites, South Greenland: hydrothermal alteration of igneous layering
Authors: FINCH ADRIAN A. , REAVY R. JOHN , HARRISON TIM N. , BROWN PETER E.
Published: December 2007

Igneous layering is developed in the Proterozoic rapakivi granite suite of South Greenland in an area on the south-easternmost coast of the island of Angnikitsoq. The layering at this locality is unusual in that it is defined by interstitial phases. We suggest that large-scale hydrothermal alteration has converted a fine-grained pyroxene cumulate, in which original cumulate pyroxenes occurred in the interstices between larger feldspars, to interstitial biotite and green amphibole.
Probable tetrapod tracks rediscovered in the Devonian of N Scotland
Authors: ROGERS D. A.
Published: December 2007

The discovery of probable tetrapod tracks in the Upper Old Red Sandstone of Easter Ross, N Scotland, lends credibility to 19th century claims of ‘reptilian’ footprints in these rocks. These are the only probable amphibian fossils known in the west European Devonian and are amongst the oldest anywhere.
Deep-water basins within the Mesozoic carbonate platform of Argolis, Greece
Authors: CLIFT PETER D. , ROBERTSON ALASTAIR H. F.
Published: December 2007

In the past the classic Argolis area of the central southern Hellenides was interpreted as comprised of essentially in situ carbonate platforms and basins, or, alternatively of far-travelled thrust sheets derived from a Mesozoic ocean basin sited well to the east (Vardar ocean). Our fieldwork, however, demonstrates that at two key localities an important unit of Middle Triassic–Early Jurassic deep-water redeposited carbonates (Asklipion Unit) passes laterally into shallow-water platform carbonates (Pantakrator Unit). The deep-water limestones represent basins within the platform, rather than far-travelled thrust sheets, while other slices of deep-water limestone record a platform margin, further east. The basins originated during Middle Triassic (Ladinian) rifting of the Neotethys and are floored by extrusive rocks of intermediate composition. Highly condensed Ammonitico Rosso pelagic limestones accumulated on an inferred volcanic seamount during the Mid–Late Triassic (Anisian–Carnian). The platforms slowly subsided in Early Jurassic time, while the basins partly filled with redeposited carbonates (Adhami Limestone). Shallow-water carbonates locally transgressed the margins of the deeper-water basins. The platforms were submerged in the Mid-Jurassic (Toarcian–Bathonian), with the deposition of pink pelagic Ammonitico Rosso, followed by marked subsidence and ribbon radiolarite deposition below the carbonate compensation depth (e.g. Koliaki Chert). In early Late Jurassic time (Kimmeridgian), the area was regionally compressed (‘Eohellenic’ phase), and the intraplatform basins, founded on thinned continental crust were inverted, and thrust up to several kilometres over the adjacent platform units. The deformed continental margin then flexurally subsided, ahead of emplacing Jurassic ophiolites, largely olistostromes (Migdhalitsa Unit). After taking account of up to 90 degrees clockwise palaeorotation of assumed Neotectonic age, kinematic indicators and facies trends suggest the ophiolite was derived from a Pindos ocean basin originally sited to the west. Early Cretaceous transgression resulted in the deposition of shallow-water limestone and was followed by Late Cretaceous deep-water limestone, then terrigenous flysch accumulation in a foreland basin related to final suturing of the Neotethyan ocean. Later, the area was dissected by a series of mainly E–W trending, high-angle Neotectonic normal faults, related to the Aegean back-arc extensional system.
Pan-African reworked early/middle Proterozoic crust in NE Africa west of the Nile: Sr and Nd isotope evidence
Authors: HARMS U. , SCHANDELMEIER H. , DARBYSHIRE D. P. F.
Published: December 2007

Whole-rock Rb-Sr studies on six suites of highly metamorphosed basement rocks from southern Egypt and northern Sudan, west of the River Nile, yield Pan-African ages (562–918 Ma): these ages are interpreted as reset. Orthogneisses give Nd model ages of 1600 to 2600 Ma for their calc-alkaline plutonic precursors. A gneiss derived from sedimentary precursors gave a mean crustal residence age of 2200 Ma. A series of I-type, late-tectonic, granitoids were intruded during a period of uplift, erosion, and wrench faulting at 560–620 Ma. Geochemical characteristics and Nd model ages (1200–1700 Ma) indicate that these rocks were derived from a mixed source of juvenile Pan-African mantle material and older continental crust of mainly early/middle Proterozoic age. Negative ɛNd
t
, values for granitoid samples (–18.9 to –5.3) show that the Pan-African episode in NE Africa, west of the Nile, involved considerable reworking of pre-existing crust.
A palaeomagnetic study of recumbently folded and thermally metamorphosed Torridon Group sediments, Eishort anticline, Skye, Scotland
Authors: Potts G. J.
Published: December 2007

Two geologically significant palaeomagnetic components have been isolated in samples of Torridon Group sandstones from the Kishorn nappe of NW Scotland. The samples were collected from the Eishort anticline, a large recumbent fold of Caledonian age. The
softer
component (which is demagnetized by low temperatures and weak magnetic fields), when in situ, displays a steep upward direction typical of reversed Tertiary magnetizations. Both polarities of the
harder
component (which is demagnetized by high temperatures only) are present and, when dip corrected, display either northwesterly upward or southeasterly downward directions characteristic of Torridonian remanences. It is suggested that the Tertiary component is of chemical origin and the result of alteration of magnetite (titanomagnetite) grains. The geographical distribution of these grains is irregular and as a result the distribution of the Tertiary overprint is irregular. The Torridonian palaeomagnetic components from both limbs of the fold can be restored by rotation about the fold axis to internally consistent directions which lie close to previously published data from the Caledonian foreland. No correction is necessary for finite strain which suggests that the Eishort anticline formed by a flexural slip mechanism. However, an anticlockwise rotation of 26° is required to reconcile the Torridonian directions from the Kishorn nappe with those of the Caledonian foreland which suggests that, during emplacement, the thrust sheet rotated on the underlying fault surface.
A discussion of Monian Supergroup stratigraphy in northwest Wales
Authors: GIBBONS W. , BALL M. J.
Published: December 2007

New borehole data and trench exposures in northern Anglesey show the Gwna Group melange resting directly upon disrupted sedimentary rocks of the New Harbour Group. Field evidence from Anglesey and the Llŷn peninsula shows that units previously given formal lithostratigraphic status in the higer part of the Monian Sopergroup occur as clasts within the Gwna Group melange. me wbdivision of the Monian Supergroup is therefore simplified to comprise only three groups: the South Stack (lowest), New Har- bour, and Gwna Groups (highest). The disruption of the upper part of the New Harbour Group is interpreted to have been efferied during emplacement of the Gwna Group melange.
Ferrolysis in Arundian alluvial palaeosols: evidence of a shift in the early Carboniferous monsoonal system
Authors: WRIGHT V. P. , VANSTONE S. D. , ROBINSON D.
Published: December 2007

An unusual clay mineral assemblage from early Carboniferous (Arundian) palaeosols in South Wales contains a three component kaolinite/(chlorite-like material)/smectite mixed-layer clay. This is interpreted as the product of ferrolysis, a complex process involving dissolution of clays a d the subsequent production of interlayered varieties from the repetitive reduction and reoxidation of iron compounds in seasonally waterlogged, surface-water grey soils. Support for this interpretation comes from the distribution of iron species, iron concretions and vertic features in the palaeosol profile, which indicate formation under strongly seasonal, dry/hydromorphic conditions. The appearance of the ferrolytic pa- Iaeosol indicates a shi from a ‘dry’ to a ‘wet-type’ monsoonal regime in late Arundian times.
Geochronology of appinitic and related granitic magmatism in the W Highlands of Scotland: constraints on the timing of transcurrent fault movement
Authors: ROGERS GRAEME , DUNNING GREGORY R.
Published: December 2007

The timing of appinitic and related granitic magmatism throughout the W Highlands of Scotland has been investigated using U-Pb geochronological techniques. An appinite from the Garabal Hill/Glen Fyne complex is dated at 429 ±2 Ma (zircon) and 422 ±3 Ma (titanite); appinites from Arrochar and Rubha Mór give titanite ages of 426 ± 3 Ma and 427 ± 3 Ma respectively. The Strontian granodiorite is 425 ±3 Ma (zircon) and 423 ±3 Ma (titanite), and a pyroxene-mica diorite from Rat again gives an age of 425 ± 3 Ma. The data show the value of using titanite to date basic rocks which may lack zircon, and of using inheritance-free phases in rocks which contain mostly inherited zircon.

The narrow range of ages for this magmatism reported here contrasts with a broad smear of previously published ages, and indicates that the middle Silurian was a major period of transcurrent fault movement throughout the W Highlands. Voluminous magmatism of this age is also found in Newfoundland, highlighting the importance of this event in the wider context of the Caledonide orogen.
The deep geology and geophysics of Ireland and its continental margin
Authors: BROCK A. , RYAN P.D. , SHANNON P. M.
Published: December 2007

A two day meeting on 28th and 29rh October 1989 attracted an international audience of over 90 scientists principally from academic institutions and the oil and minerals industries to hear 24 papers on the deep geology and geophysics of Ireland and its continental margin. The aim of the meeting was to present and discuss the results of a number of recent geophysical experiments and to relate them to models of the deep geology

Gravity and magnetic data for Ireland were reviewed by
Murphy
(Dublin Institute for Advanced Studies) whilst
Lowe, Jacob, Prodehl
and
Ruthardt
(Dublin Institute for Advanced Studies and University of Karslruhe gave an account of two land seismic refraction experiments across and parallel to Caledonian trends (COOLE and ICCSP). They demonstrated that the Moho beneath Ireland lies at a depth of about 30 km, and a clear change of velocity structure occurs across the Iapetus suture zone. Two magnetotelluric experiments were described by
Brown & Whelan
(University College Galway) and by
Meju
(University of Leicester). Both indicated zones of anomalously high crustal conductivity, the most prominent of which is associated with the Iapetus suture zone. A petrological model for such zones involving free water in the lower crust was described by
Sanders
(Trinity College Dublin; this volume).
Ford, Brown & Readman
(Plymouth Polytechnic, University College Galway and Dublin Institute for Advanced Studies; this volume) used gravity data from southwest Ireland to elucidate basement structures in the Variscides.

Offshore potential field data were described by
Readman, Gohl, Liebe & Makris
A deep seismic reflection transect across the Irish Caledonides
Authors: KLEMPERER S. L. , RYAN P. D. , SNYDER D. B.
Published: December 2007

New reflection profiles recorded to 18s (
c
.60km) along a 600 km north-south transect West of IREland (WIRE lines) provide a cross-section of the Irish Caledonides from Lewisian basement in the north to the Variscan fold-and-thrust belt in the south, and constrain the offshore extrapolations of major Caledonide structures.

We interpret the profiles as showing the Great Glen fault and associated, NE-trending strike-slip faults as near-vertical structures which cut the whole crust and the uppermost mantle. Beneath the surface trace of the Fair Head-Clew Bay line we image a north-dipping zone which soles into horizontal layers just above the reflection Moho. The north-dipping zone separates south-dipping reflections above and to the north from north-dipping reflections below and to the south. From the Fair Head-Clew Bay line as far south as the Iapetus suture the lower crust contains north-dipping packages of reflectors possibly related to Acadian accretionary underplating. The Iapetus suture zone can be identified as a zone, more than 50 km wide, dipping north at 30° from 5 km depth offshore Dingle peninsula to sole into the Moho at
c
. 30 km depth west of the Shannon Estuary. In the upper crust the shallow part of the Iapetus suture zone appears to be transported to the north by late Caledonian retrocharriage or by Variscan thrusting. The Iapetus suture does not penetrate through the present-day reflection Moho, but there are scattered reflectors in the mantle not continuous with crustal reflectors, perhaps relics of a subducted slab.

We recognize ‘lower-crustal’ reflectivity and the reflection Moho along almost all the WIRE profiles. Regionally the travel-time to the reflection Moho varies from 9
s
(
c
. 28 km?) offshore Donegal (northwest of Ireland) to 12 S (
c
. 35 km?) offshore Kerry and Cork (southwest of Ireland). Apparent Moho offsets (rapid lateral changes in the travel-time to the reflection Moho) north of Donegal and north of Mayo are probably due to the Great Glen fault and associated faults. The ‘lower-crustal’ reflectivity varies considerably in thickness and prevalent dip direction along the WIRE profiles. In Donegal Bay this reflectivity is observed at depths less than 5 km (
c
. 1.5s) whereas west of Kerry prominent reflectivity is only observed beneath 6s (
c
. 17 km). Though the age of crustal reflectors cannot in general be determined, beneath central Ireland from Donegal to Dingle the lower-crustal reflectors mimic in dip direction the structural vergence of the exposed Dalradian and early Palaeozoic rocks, so that the lower-crustal reflectivity patterns, and probably much of the crust, must be Caledonian in age.
The development of Irish offshore sedimentary basins
Authors: SHANNON P. M.
Published: December 2007

A variety of ensialic Mesozoic and Cenozoic sedimentary basins surround Ireland. Three main periods of basin development occurred. The first, in the Permo-Triassic, produced a series of small rift basins which nucleated along reactivated, generally Caledonian, structures. The second, in the Mid- and Late Jurassic, represents a period of crustal extension and rifting. The third phase reflects thermal subsidence of Cretaceous and Tertiary age, and coincides with seafloor spreading in the North Atlantic. The basins developed in response to general east-west extension. Simple extensional structures, accompanied by crustal thinning, dominated in the north-south-trending Porcupine Basin. The NE-SW-oriented basins in the Celtic Sea, Slyne-Erris-Donegal and Rockall areas developed in a transtensional setting until Early Cretaceous times. The Goban Spur basins, at the confluence of regional structural trends, and adjacent to the continent-ocean boundary, are dominated by transtensional structures. The effects of Early Tertiary Alpine compression are seen especially in the Celtic Sea basins. The basins, whilst having some broad geological similarities which reflect eustatic sea-level variations, differ in their detailed evolution. Each basin experienced unique facets of local structural control, tectonic history and facies distribution.
Comparative sequence stratigraphy and structural styles of the Slyne Trough and Hebrides Basin
Authors: TRUEBLOOD S. , MORTON N.
Published: December 2007

The Slyne Trough to the west of Ireland is divided into three sections: North, Central and South. The South and Central sub-basins are separated by a seismic ‘dead zone’ along the line of the Clew Bay disturbance. The Central and North sub-basins are separated by a zone transferring the fault bounding the main basin from the western margin in the Central sub-basin to the eastern margin in the North sub-basin.

Five stratigraphic sequences from the Slyne Trough, which span the Rhaetian to Middle Jurassic, are recognized in the 27/13–1 well, and they are compared to the equivalent sequences in the Hebrides Basin. The Late Jurassic Hebridean sequences are expected in the deeper parts of the Central Slyne Trough. The Slyne Trough and Hebrides Basin sediments are mainly tectonically controlled, although major eustatic events in the Early Toarcian and Late Bathonian are recognized.
Scale of tsunami-generated sedimentary structures in deep water
Authors: PICKERING K. T. , SOH W. , TAIRA A.
Published: December 2007

To date, no attempt has been made to explore possible constraints on maximum water depths for tsunami-generated sedimentary structures of various sediment grain sizes, in terms of estimated wavelength and amplitude of potential bedforms. This paper explores some possible quantitative limits on threshold velocities for sediment movement at specified water depths, assuming Airy wave theory which treats tsunami waves as shallow-water, small- amplitude, long-wavelength waves. Such a treatment suggests that the passage of tsunami waves is unlikely to entrain sediment coarser than line sand to coarse silt in water depths in excess of 200 mm. Although fraught with theoretical difficulties and a lack of observations of modern sedimentary bedforms attributable to known tsunamis, this paper is presented to stimulate debate rather than provide definitive answers.
Sedimentology and depositional setting of the Dartmouth Group, Bigbury Bay, south Devon
Authors: SMITH SIMON A. , HUMPHREYS B.
Published: December 2007

The Lower Devonian Dartmouth Group records some of the earliest stages in the evolution of the Variscan basins of southwest England. This thick, mudstone-dominated group has previously been interpreted as distal fluvial sediments, deposited on a coastal mudplain.

The sequence at Bigbury Bay is made up of two large-scale sedimentary cycles. The base of each cycle consists of pebbly mudstones, graded siltstones and sandstones, massive mudstones, and heterolithic sediments with sporadic phosphatic nodules. These facies were deposited in substantial lakes; they were modified by phases of syn-sedimentary deformation which generated subaqueous debris flows and turbidites. The overlying parts of the cycle, making up the bulk of the succession, consist of mudstone and thin, sheet-like, sandstones. These are fluvial and were probably deposited in mud-dominated terminal fans. Each cycle represents a phase of rapid, probably fault-controlled, subsidence followed by relative tectonic quiescence. This behaviour may reflect pulses of rifting or extension in strike-slip basins, followed by thermal relaxation.
Depth and configuration of the crystalline basement in the Viking Graben area, Northern North Sea
Authors: HOSPERS J. , EDIRIWEERA K. K.
Published: December 2007

The depth of the crystalline basement in the Viking Graben area has been mapped. The dominant structural feature in the study area is a N–S trending zone approximately 150 km wide, containing a variety of structures (graben, basins and structural highs) and named the ‘Northern North Sea Rift Zone’. The Viking Graben is only one structural element, though a major one, in this zone. The following depth ranges appear to apply: (a) on platforms, basement shelves and major structural highs (1–3 km), (b) in basins (7–9 km maximum depth), (c) in graben (8–10 km maximum depth).
The classification of deep-sea depositional systems by sediment caliber and feeder system
Authors: READING H. G.
Published: December 2007

Two methods of portraying a classification of deep-sea elastic depositional systems are shown, based on sediment calibre and the nature of the feeder system, whether single or multiple sourced. Mud-dominated systems, particularly point-sourced submarine fans, are large in area, volume, radius and size of flow, with persistent channel/levee systems that tend to meander and have sheet-like sands in the associated basin plain. With increasing grain size, there is an increase in slope, frequency of flow, impersistence of channel system and channels tend to switch more frequently. As the number of sources increases from a single point source through multiple sources (e.g. submarine ramp) to an almost linear source
slope apron
, so feeder channel stability and organization of the depositional system decreases.
Crustal structure of the central and southern North Sea from BIRPS deep seismic reflection profiling
Authors: BLUNDELL D. J. , HOBBS R. W. , KLEMPERER S. L. , SCOTT-ROBINSON R. , LONG R. E. , WEST T. E. , DUIN E.
Published: December 2007

Through the generous gift of shiptime on M/V Mobil Search in June 1987, BIRPS (British Institutions Reflection Profiling Syndicate) was able to acquire nearly 1500 km of deep seismic profiles recorded to 16s TWT in a regional survey across the central and southern North Sea. Reflective lower crust beneath the southern North Sea basin gives way laterally to a zone of mid-crustal reflections within the London–Brabant platform. These mid-crustal reflectors are interpreted as due to crustal shearing, although whether related to stretching during basin formation or to some earlier event remains enigmatic. Sub-crustal, SW-dipping reflections are observed at the edge of the London–Brabant platform. Across the mid-North Sea High, N–S profiles show distinctive patterns of lower-crustal reflectivity that indicate lateral variability in structure and character on a scale of 30–50 km. These are interpreted as crustal units relating to the Iapetus suture developed during the Caledonian orogeny. They may have been modified, however, during Carboniferous basin development, or subsequently. The absence of any distinctive sub-crustal reflectors associated with the Iapetus Suture, where a Caledonian subduction zone should have existed, tends to suggest that sub-crustal reflections observed elsewhere around Britian are not subduction related but are more likely to be from younger faults or shear zones relating to lithosphere extension and basin formation.

Onshore wide-angle recording in northern England of the marine seismic source produced good quality data. The high resolution obtained has revealed details of mid-crust (PcP) and Moho (PmP) reflections, from around 18 and 30 km depth respectively, not observed before in this area. Both reflectors show events of laterally variable reflectivity that appear as bands of discontinuous reflection segments.
Lithospheric strength and rheological stratification at mid-ocean ridges
Authors: NORRELL GREGORY T.
Published: December 2007

Lithosphere at mid-ocean ridges is rheologically stratified. The extensional failure of rheologically stratified lithosphere can be modelled by integrating the appropriate failure criteria over the appropriate depths to the base of the lithosphere. This integrated lithospheric strength is the force per unit length required for whole lithospheric failure to occur. Oceanic spreading centres are in a nearly constant state of whole lithospheric failure. Lithosphere at a given ridge axis has a characteristic integrated strength which is met for spreading to continue. Variations in integrated strength have important implications for tectonic phenomena such as jumps at spreading centres.
Geochemical and isotopic constraints on the nature and age of basement rocks from Rockall Bank, NE Atlantic
Authors: MORTON A. C. , TAYLOR P. N.
Published: December 2007

An isotopic and geochemical reappraisal of samples from Rockall Bank, NE Atlantic, indicates that the granulites and granites present on the Bank have little anity with the Lewisian of NW Scotland, with which they have been previously associated. New Pb, Rb-Sr and Sm-Nd data, together with existing K-Ar data, indicate that the rocks formed at about 1625 Ma. Although this is contemporaneous with Late Laxfordian events in NW Scotland, the high model p value of 8.03 indicates that the rocks were not derived by metamorphic reworking of ancient Lewisian crust, but largely represent pristine mantle contributions at this time. In this sense, the Rockall terrane is comparable with the Islay terrane, which has a model p value of 7.9 but is apparently somewhat older (c. 1800Ma). The Rockall basement rocks therefore represent a pre- viously unrecognized crust formation event in the North Atlantic region, and reconstructions of Proterozoic geology will need to take into account the presence of this crustal block of predominantly juvenile mantle-derived material. The Rockall area may also be considered a likely source for the Torridonian sediments of NW Scotland.

Our knowledge of the geology of the Rockall Plateau (NE Atlantic, Fig. 1) has not advanced significantly since the review published by
Roberts (1975)
. Subsequent work on the eastern NE Atlantic area has largely concentrated on the development of the Rockall Trough which marks the eastern limit of the Plateau, as summarized by
Smythe (1989)
and on the development of the volcanic passive margin that marks the
Modern and ancient continental hypsometries
Authors: ALGEO T. J. , WILKINSON B. H.
Published: December 2007

Controls on coastal hypsometries of modern continents and oceanic islands may be used to estimate palaeo-continental area-elevation distributions. The most important controls on coastal hypsometry are landmass area and coastal gradient, increases in which result in steeper area-elevation distributions. Thus, any change in sea level will flood or expose a smaller fractional area of continents which are large or have steep coastal gradients than of those which are small or have gentle coastal gradients. Coastal gradients are dictated primarily by the tectonic setting and age of continental margins. While active and transform margins generally have steep coasts, mean coastal gradients for passive margins decrease exponentially with increasing margin age. Consequently, continents comprised mostly of mature passive margins are generally more ‘floodable’.

These observations are applicable to a variety of palaeo-eustatic problems. Hypsometries corrected for changes in landmass area reduce variance in flooding records between different Palaeozoic continents by more than 50%. Assuming minimum-variance superimposition of flooding curves for different Palaeozoic continents permits identification of possible hypsometric anomalies. Calculated Palaeozoic sea level maxima are between +200m and +400m with respect to present sea level, substantially lower than previous estimates to +600 m.

Modelling evolution of coastal hypsometries due to changes in length and age of passive margins suggests that hypsometry varies cyclically in response to continental rifting and collision. Coastal hypsometries are steepest during rifting events and decrease by a factor of two to three as passive margins age. Coastal hypsometries in a ‘sutured’ world are steeper than those of a 'rifted' world due to increased continent size and decreased passive margin length. Thus, sea level highstands associated with times of continent dispersal may result in part from the enhanced ‘floodability’ of rifted continents.