bluuebunny/crossref_metadata_2025 huggingface dataset:
Carboniferous stratigraphy, sedimentation and correlation of well 48/3-3 in the southern North Sea Basin: integrated use of palynology, natural gamma/sonic logs and carbon/sulphur geochemistry
Authors: LEEDER M. , RAISWELL R. , AL-BIATTY H. , McMAHON A. , HARDMAN M.
Published: December 2007

A methodology for the correlation of offshore Silesian (Upper Carboniferous) sequences is developed using an integrative approach based upon biostratigraphy, downhole logging and geochemistry. We develop the combined use of miospore zonation, gamma ray spectrometry, formation velocities and carbon/sulphur ratios to determine the location of marine horizons and other lithofacies in a thick (>1 km) largely uncored Silesian sequence in the Southern North Sea Gas Basin. At least nine major marine horizons are recognized within a basin-fill sequence of Marsdenian, Yeadonian and Langsettian ages (Namurian B/C and Westphalian A) in the well. These horizons help to provide a detailed subdivision of the offshore sequence, although the correlations must remain tentative until further deep wells are drilled in the area. The implications of the correlations for offshore palaeogeography are that the area of northern Quadrant 48 was a deep, periodically anoxic basin until infill by successive submarine fan lobes in late Marsdenian times. Yeadonian delta front and coastal plain deposits pass upwards into fluvio-deltaic/wetland facies of the Langsettian.
Climatic and biotic change in the late Triassic
Authors: SIMMS MICHAEL J. , RUFFELL ALASTAIR H.
Published: December 2007

Generally arid conditions that pervaded much of Europe and North America during the late Triassic were interrupted by a wet monsoonal climatic phase during Middle and Late Carnian times. Extensive fluviatile sandstones deposited at this time throughout the region, occur within a thick sequence of playa-lake mudstones. The sandstones occasionally contain kaolinite, suggesting a humid climate. An extreme δ
13
C depletion in a shallow marine sequence of this age in Israel has been interpreted as evidence for an influx of freshwater. A widespread change from carbonates to clastics in marine sequences at this time may also be climate-related. Water-course cave systems in limestone areas exposed during the late Triassic indicate high levels of runoff during the Middle and Late Carnian.

The marine invertebrate fauna shows a significant turnover at the end of the Early Carnian. The terrestrial fauna and flora were relatively unaffected at this time but subsequently diversified prior to a major biotic turnover at the Carnian-Norian boundary. These periods of biotic change appear to be synchronous with the onset and cessation of a Carnian humid phase.

The change to a monsoonal climate during this interval has been documented over more than 90° of longitude between 5° and 50° north of the Triassic equator. It may have been caused by rising atmospheric CO
2
levels due to volcanism associated with the incipient dispersal of Pangaea.
Palaeocomputing: keyboard to the past
Authors: FUNNELL B. M. , OWEN A. W.
Published: December 2007

The Lyell Meeting ‘Palaeocomputing: Keyboard to the Past’ of
24
February
1988
celebrated the application of computing and, in particular, microcomputers and their associated numerical and graphical methods, to the analysis of problems in palaeontology and stratigraphy. Sir Charles Lyell was one of the earliest geologists to apply numerical and statistical methods deliberately to the resolution of problems in historical geology, so the resurgence of interest in such methods, fuelled by the advent of the new technology of computers, seemed an appropriate topic for a Lyell Meeting. The meeting was also the first to be sponsored by the Joint Committee for Palaeontology (supported jointly by the British Micropalaeonto-logical Society, the Geological Society, the Palaeontographical Society and the Palaeontological Association).

Several speakers contributing to the meeting had recently published or were about to publish the results reported at the meeting, and therefore only two new papers have been contributed to the Journal. This report gives the sources and extended abstracts of the other contributions.

The meeting was organized in three sections: (a) analysis and presentation of data; (b) analysis of shape; (c) reconstructing the past.

(a) Analysis and presentation of data

D. A. T. Harper & P. D. Ryan
commenced the meeting by presenting a paper on ‘The evolution of a statistical system for palaeontologists’ to be published in the
Journal.

They gave an historical review of the increasingly sophisticated use of statistics in palaeontology culminating in modern computer-based approaches. Harper & Ryan emphasized that user-friendly microcomputer software is ideal for
Correlation of the Triassic-Jurassic boundary in England and Austria
Authors: HALLAM A.
Published: December 2007

An attempt is made to fix the Triassic-Jurassic boundary at the classic locality of St Audries Bay, Somerset by reference to biostratigraphy in conjunction with lithostratigraphy, utilizing comparison with the more fully marine sequence of the Kendelbach gorge in Austria. The boundary is placed at the base of the Blue Lias Formation.
The Irish Variscides: a fold belt developed within a major surge zone
Authors: MURPHY FRANCIS X.
Published: December 2007

An arcuate fold belt characterizes the Irish Variscides south of the Dingle-Dungarvan line. The folds are cross-cut by numerous faults which tend to be sinistral in the west and dextral in the east. Clockwise transection of major fold axes by minor folds and by cleavage has been recorded in the east, while anticlockwise transections are common in the west. These and other features suggest that north-south dextral and sinistral shearing occurred in the east and west respectively. This is considered to be a consequence of the morphology of the Munster Basin which allowed the development of a surge zone. In the centre of the fold belt the Variscan sole thrust is believed to lie at the base of, or within, the Old Red Sandstone. However to the east, thinning of the Upper Palaeozoic cover sequence forces the sole thrust to cut down laterally stratigraphic section into Lower Palaeozoic basement. In the depocentre the sole thrust surged ahead by propagating along bedding surfaces or possibly a Devonian-Carboniferous extensional detachment beneath the basin, while to the east and offshore to the west its propagation was inhibited by the absence of easy decollement horizons within the basement. Consequently the tip-line became strongly arcuate and the thrust developed into a surge zone. The sole thrust propagated northwards by stick-slip processes. Much of the deformation within the cover sequence occurred during sticking events, particularly fold tightening and accommodation faulting.
The nature and analysis of the stratigraphic record
Authors: SMITH D. G.
Published: December 2007

Report of an Ordinary General Meeting of the Geological Society, organized by the Stratigraphy Committee and convened by D. G. Smith, held at Burlington House on 28 September 1988.

The purpose of the meeting was to bring together practitioners of as many as possible of the diverse current approaches to stratigraphic analysis, and to present stratigraphy as a dynamic and rapidly developing discipline central to our understanding of global processes. There has been an increasingly open recognition of the role of models as fundamental to progress in stratigraphy, with consequent diminution of emphasis on objective documentation of the stratigraphic record for its own sake. This more analytical approach is underlined by the greater use of numerical methods and by the linking of stratigraphy, through subsidence analysis at the basin-scale, to global-scale tectonic processes. Along with this, there has been a tendency for increasing divergence of approach between those in institutional research and those in exploration, for whom the predictive power of the model-driven approach is essential to their livelihood. The meeting succeeded, through 15 oral presentations and one poster, in giving a good impression of the variety of current approaches to stratigraphic analysis, from highly theoretical to explicitly field based.

The theme of the incompleteness of the stratigraphic record was introduced by
D. V. Ager,
who argued that the record is not even
representative
of the geological past.
E. A. Hailwood
pointed out the danger of circular reasoning in deducing stratigraphic incompleteness from the biostrati-graphic record, as the latter is
Correlation in mosaic environments
Authors: TIPPER JOHN C.
Published: December 2007

A useful theoretical model for studying some aspects of stratigraphical correlation is that of deposition in mosaic environments. The model is readily implemented using computer simulations based on the Voronoi diagram and produces lithosome geometries that are broadly comparable to those commonly seen in the field and on seismic sections. This model is restricted here to two-phase mosaics (e.g. sand/shale) and the lateral persistence of either phase can readily be determined from the computer simulations. This leads directly to measures of the lateral traceability of units of either phase in discontinuous surface outcrop and of reflector persistence in the subsurface. Because these measures are ultimately scaled in terms of the inherent length scale of the mosaic, they can be simply applied to real surface and subsurface data.
A laminated hemipelagic facies from the Wenlock and Ludlow of the Welsh Basin
Authors: DIMBERLINE A. J. , BELL A. , WOODCOCK N. H.
Published: December 2007

A hemipelagic fades from the Silurian succession in Wales consists of finely laminated, dominantly silt-grade sediment. It can be interbedded with sand- or mud-grade turbidites, or can occur as an independent facies. Its occurrence and character was controlled mainly by low bottom water oxicity. The pelagic fauna of the laminated hemipelagite supports this view. Many of the silt-grade particles have an aggregate structure and probably represent the faecal pellets of oceanic zooplankton. The fine lamination is thought to have formed by alternations of planktonic blooms and increased discharges of silt into the basin. By comparison with modern examples this alternation was likely to have been annual or seasonal.
Retiolite nomenclature and relationships
Authors: BATES D. E. B.
Published: December 2007

The retiolite graptolites can be divided into at least two major groups, each derived independently from diplograptid ancestors. The lacinia of some Ordovician forms, and the ancora and ancora sleeve (‘reticulum’) of Silurian retiolites, are both novel structures. Some other retiolite taxa lacking these structures are best grouped within diplograptid families. The nomenclature of retiolite structures is discussed.
Sedimentological response of an alluvial system to Neogene thrust tectonics, Atacama Desert, northern Chile
Authors: JOLLEY E. J. , TURNER P. , WILLIAMS G. D. , HARTLEY A. J. , FLINT S.
Published: December 2007

The Llano de la Paciencia is a thrust sheet top basin in which the sedimentological and topographic evolution can be linked to thrust tip propagation. It is an elongate gravel plain which borders the Salar de Atacama, a major intermontane basin in the Andean forearc of northern Chile. The Llano is bounded to the west by the Cerros de Purilactis a Cretaceous–Paleocene sequence uplifted by the Frontal Domeyko Thrust. The eastern margin of the Llano is formed by the Cordillera de la Sal which was uplifted by a linked back thrust-frontal thrust system. The Salar de Atacama is thus divided into a number of discrete sub-basins: the Llano de la Paciencia, the Pampa Visachita and the western sub-Llano which from east-west are bounded by the Cordillera de la Sal, the northern imbricates and the ignimbrite back thrust. Two phases of sedimentological evolution can be distinguished within the Llano on the basis of Quaternary to Recent sediment dispersal patterns. Initially, Phase 1 alluvial fan lobes prograded eastwards into the main Salar de Atacama basin. Subsequently, uplift of the Cordillera de la Sal deflected drainage systems southwards parallel to the structural strike. These Phase 2 alluvial deposits drain into the Salar de Atacama at the lateral termination of the Cordillera de la Sal frontal thrust. In places where thrust tip ramps are emergent within the Llano, gullies have been incised into the drainage pathways. This has resulted in the reworking of the early Phase 1 gravels and progradation of the Phase 2 fan lobes. The evolution of the Llano de la Paciencia illustrates the close link between topography and syntectonic alluvial drainage patterns in an arid intermontane basin.
The Cenozoic tectonic evolution of Alpine Corsica
Authors: WATERS C. N.
Published: December 2007

During Palaeocene to Early Oligocene times, hinterland and foreland directed thrusts and folds developed in Alpine Corsica in response to the collision of the European continental plate and oceanic crust adjacent to the Adria promontory. The 'Nappes Supérieures' represent fragments of the oceanic lithosphere, emplaced toward the west upon the Eoalpine Schistes lustrés nappes and Hercynian continental basement. The 'Nappes Supérieures' were unaffected by syn-tectonic metamorphism, whilst the underlying Schistes lustrés nappes developed a greenschist facies replacement of blueschist parageneses and the foreland basement of Hercynian Corsica developed prehnite–pumpellyite facies assemblages. Small flexural basins, occupied by continentally derived flysch deposits, developed at the deformation front and were subsequently overridden by ophiolitic and continental nappes. During Oligocene to Early Miocene times there was a change in deformation style with the generation of strike-slip and normal faults. This non-metamorphic deformation event is considered to result from the 30° anticlockwise rotation of Corso–Sardinia relative to the European plate, producing oceanic lithosphere in the Liguro–Provencal back-arc basin and a zone of collision between Corso–Sardinia and Adria. The rotation of Corsica is modelled as resulting from the indentation of the European continental plate by the Adria microplate.
Geohazards: natural and man-made
Authors: McCALL G. J. H. , LAMING D. J. C.
Published: December 2007

Report of a meeting of the Joint Association for Geologists in Development Specialist Group in association with the Joint Association for Geophysics and the Engineering Specialist Groups of the Society, at Burlington House, 18 October 1989. The convenor was G. J. H. McCall.

This meeting was designed to present accounts of a wide variety of Earth science related hazards, both natural and man-made. The theme was particularly topical in view of the commencement of the UN International Decade for Natural Disaster Reduction in 1990. The fact that the San Francisco Earthquake occurred on the night before the meeting added to the topicality of the theme to no small degree! The programme was designed to bring together a number of experts, drawn from both the geological and other related fields such as soil science and geophysics, to cover the scientific investigation of the nature of various hazards and the response to such hazards, both after the event and in the form of prior planning to mitigate the effects of likely future events. The meeting was targeted on the Third World Countries, the Special Interest of the JAGID Specialist Group, but papers of a general nature were included, because of the fact that there is much to be learnt from the experience of developed countries.

G. J. H. McCall
introduced the theme by saying that hazard incidence and scale were increasing because of increased population concentrations (especially the mush-rooming and sprawling of some Third World cities); increased technological development;
Regular and irregular climatic cycles and the Belemnite Marls (Pliensbachian, Lower Jurassic, Wessex Basin)
Authors: WEEDON G. P. , JENKYNS H. C.
Published: December 2007

Time series of carbonate and organic-carbon values are reported for 10.5 m of the Belemnite Marls. The light and dark marl beds form decimetre-scale couplets and metre-scale bundles. Light marls are carbon-poor and carbonate-rich whereas dark marls and laminated shales are carbon-rich and carbonate-poor. Sediment composition appears to have been indirectly controlled by climate; the regular couplets may record orbital-precession cycles (20 ka). However, the bundles cannot be linked to changes in eccentricity; rather they apparently record irregular, large-amplitude climatic variations with periods of a few hundred thousand years. It should not be assumed that 100–400 ka cyclicity in climate-related sedimentary sequences can be explained only by orbital forcing.
Fiamme formed by diagenesis and burial-compaction in soils and subaqeuous sediments
Authors: BRANNEY M. J. , SPARKS R. S. J.
Published: December 2007

Pumice clasts can be diagenetically altered at low temperature and flattened by compaction to form fiamme. Examples are described from trachytic pumice fall layers alternating with palaeosoils on Sao Miguel in the Azores and from Ordovician lacustrine volcaniclastic sedimentary rocks from the English Lake District.
Nd isotopic evidence for exotic detritus in the Kalak Nappe Complex, north Norwegian Caledonides
Authors: AITCHESON SUSAN J.
Published: December 2007

Samples from the Kalak Nappe Complex, north Norwegian Caledonides, have yielded the following ranges of Nd depleted-mantle model ages: orthogneiss 2.8 Ga; paragneisses 1.2-1.8 Ga; and Sørøy Succession metasediments 1.2-2.0 Ga. The presence in the Complex of sedimentary detritus derived from young (<1.3Ga) crust indicates that sedimentation and deformation of these rocks are probably younger than 1.3 Ga. Crust as young as 1.3 Ga seems to be absent from north Baltica, implying that at least some of the Kalak Nappe Complex sediments were derived from sources outside the craton.
Late Caledonian extensional reactivation of a ductile thrust in NW Scotland
Authors: POWELL DEREK , GLENDINNING N. ROBERT W.
Published: December 2007

Evidence is given for ductile extension across a fault zone located on the western seaboard of the Northern Highlands of Scotland. The fault zone lies within the metamorphic Caledonides and extensional movement occurred during the waning stages of Caledonian orogenic activity. An earlier phase of westerly directed overthrusting took place on the same fault zone at higher metamorphic temperatures but after the peak of Caledonian metamorphism. The compression may be broadly coeval with early displacements on the Moine Thrust Zone which probably lies offshore some 10 km to the northwest.

The extensional reactivation could relate to local crustal instability resulting directly from overthrusting; it may have been due to local gravitational collapse following overthickening of the crust. Alternatively the extensional movement may witness the onset of regional gravitational collapse of the orogen during the late Silurian to early Devonian. Reactivation accords with interpretations of the movement histories of similarly eastward dipping offshore faults recognized on seismic reflection profiles.
Late Caledonian dolerite sills from SW Connacht, Ireland
Authors: MOHR PAUL
Published: December 2007

Bimodal Silurian igneous activity in SW Connacht occurred during basin subsidence and sedimentation, and before basin deformation. Mafic sills averaging 3 m thickness were preferentially intruded into and supported by a thin horizon of fine-grained siliceous sediment (Tonalee Fm.). Multiple injection produced the thicker sills. A primary igneous lithology of augite–plagioclase–olivine–phyric dolerite has, in some sills, been obliterated by pervasive hydration and carbonation expressed in a biotite-calcite–quartz–albite mineralogy. This represents volatile influx into magma at a sub-intrusive level, and contrasts with syn-intrusive assimilation and post-intrusive alteration that introduced silica and potassium into, and removed magnesium from marginal dolerite. The SW Connacht magmatism occurred in an extensional tectonic setting, probably in a NNE–SSW structurally controlled basin, and was coeval with bimodal magmatism in other parts of Ireland and Britain on both sides of the Iapetus Sutures.
Major erosion surfaces in the basal Wealden Beds, Lower Cretaceous, south Dorset
Authors: HESSELBO STEPHEN P. , ALLEN PHILIP A.
Published: December 2007

The transition from evaporitic and lagoonal Purbeck Beds into the fluviatile basal Wealden Beds (Ryazanian-Valanginian) has in the past been interpreted as a continuous regressive succession. Mupe Bay and Bacon Hole, in south Dorset, are the only localities in the Wessex Basin of southern England at which the transition strata are well exposed and not extensively faulted. On the basis of facies analysis the lowermost Wealden Beds are interpreted as a regressive-transgressive-regressive package. Environments fluctuated between lagoon, inner-lagoonal shoreline and fluvial flood plain. The overlying succession is remarkable for the presence of two major erosion surfaces which, based on field geometries and facies relationships, are interpreted as unconformities. The lower unconfor­mity is overlain at Mupe Bay by sediments of lagoonal or lacustrine origin. The upper unconformity is expressed as the celebrated Mupe Bay palaeo-oilseep, an oil-cemented conglomeratic sand, overlain by a thick succession of fluvial sediments. A level near the basal sand and the two erosion surfaces are treated as
candidate
sequence boundaries (WBl-WB3), with the thin intervening ?lagoonal deposits representing peaks of transgression. The pattern of one minor (conformable) sequence boundary followed by two major (unconformable) sequence boundaries bears a strong resemblance to the Early Cretaceous sequence stratigraphy suggested in recent ‘global cycle charts’. However, biostratigraphical calibration of the sections is currently inadequate to allow close correlation with candidate sequence boundaries in other areas.
Seismic studies in the North Celtic Sea Basin: implications for basin development
Authors: O’REILLY B. M. , SHANNON P. M. , VOGT U.
Published: December 2007

Modelling of seismic refraction data from the North Celtic Sea Basin offshore Ireland demonstrates the presence of a NNW-trending basement flexure. Mesozoic sediments are 4 km thick on the west and 6 km thick on the east of the feature, which is Interpreted as a transfer fault zone lying along a major reactivated basement fracture. Bulk extension is greater in the lower lithosphere than in the upper crust, with the interface being a rheologically regulated mid-crustal detachment surface. The basin developed in response to the interplay between periodic disengagement along the detachment and selective strain transfer into the upper crust.
Submarine end-moraines as indicators of Pleistocene ice-limits off northwest Britain
Authors: STOKER M. S. , HOLMES R.
Published: December 2007

High-resolution (sparker) seismic profiles reveal evidence for glaciation of the outer part of the northern Hebrides and West Shetland shelves. Submarine end-moraines suggest glacial ice which locally extended out to the shelfbreak. Seismic stratigraphic analysis of the glacial succession suggests that the moraines on the northern Hebrides Shelf are older than those developed on the West Shetland Shelf. Whist the stratigraphic evidence indicates at least two phases of widespread outer shelf glaciation, the timing of these events remains uncertain.
Volatile production during contact metamorphism: the role of organic matter in pelites
Authors: WILKINSON J. J.
Published: December 2007

Elemental analyses of Palaeozoic mudrocks from south Cornwall indicate the presence of 0.04–0.74 wt% carbon primarily in an elemental and/or organic form, in addition to 0.04–0.10 wt% nitrogen as NH
4
+
in micas and in organic material. Both elements are depleted in samples from the lithologically homogeneous Mylor Slate Formation next to the Tregonning Granite, an offshoot of the Cornubian batholith. The depletions are due to an H
2
O-CO
2
-N
2
(-CH
4
) fluid formed during contact metamorphic devolatilization of the pelitic country rocks. Fluids of this type have been reported from a number of Hercynian Sn–W provinces, and may play an important role in mobilizing metals in pelitic rocks during granite-related contact metamorphism and hence in the metallogenic evolution of such regions.
Disequilibrium trace element partitioning in Jurassic sparry calcite cements: implications for crystal growth mechanisms during diagenesis
Authors: HENDRY J. P. , MARSHALL J. D.
Published: December 2007

Sparry calcite cements from Middle Jurassic limestones in Central England contain complex non-concentric zoning patterns produced by a combination of sector zonation and a sector-specific, lamellar or polygonal zonation. Electron microprobe analyses of individual zones within crystals document: (1) a sympathetic covariation of Fe, Mg and Sr between two non-equivalent sectors, and (2) episodic further increase of Sr contents coupled with exclusion of Fe, Mg and Mn within the more enriched sectors. Comparison of results from three different localities demonstrates the regional consistency of this pattern, although the magnitude of the differential trace element partitioning varies.

From combined petrographic and geochemical data the trace element variation in the crystals can be shown to bear no simple relationship with either (1) the chemical evolution of the 'bulk' precipitating porefluid, or (2) the relative overall growth rates of the different crystal faces. Previous sector zoning models based on crystal surface configurations and internal structure are unable to account directly for the geochemical patterns observed in this study. Differences between growth mechanisms on the crystal faces of the studied spars are likely to have exerted a significant influence on trace element partitioning. In particular, they offer a plausible explanation for the geometric and compositional characteristics of the sector-specific episodic zoning on the most enriched crystal faces. In general, crystal morphology and composition will be intimately linked by the growth mechanisms operating on different faces and by their response to changes in the diagenetic environment. The validity of diagenetic interpretations from ‘bulk’ geochemical analysis of sparry calcite cements thus rests upon a detailed analysis of any zonation that they contain.
A polygenetic palaeosol from the Silurian (Wenlock) of southwest Ireland
Authors: WRIGHT V. P. , SLOAN R. J. , GARVIE L. A. J. , RAE J. E.
Published: December 2007

A problematic palaeosol unit caps a thick basalt at the top of the Clogher Head Formation, Dunquin Group (late Wenlock, Silurian) in the Dingle Peninsula, southwest Ireland. The main part of the unit consists of an altered calc-alkaline basalt with a fine clay assemblage of chlorite, corrensite and smectite probably resulting from weathering during Wenlock times. The uppermost part of the unit consists of detrital silicates which were admixed by bioturbation and well-defined burrow-fills are present. The underlying, weathered basalt was possibly truncated before the detrital horizon was deposited, and finally the whole unit underwent a phase of surface-water gleying. A catenary relationship existed locally with the pseudo-gley developed lower in the landscape while contemporaneous basalts in topographically higher, better drained areas, largely escaped the effects of gleying; these now exhibit reddened tops. The complex history and the possiblity of the incompleteness of the profile makes accurate assessment of the soil/climate function difficult. However, the occurrence of calcrete-bearing palaeosols in the overlying Mill Cove Formation supports the view that the basalt was weathered under a sub-humid or semi-arid climate. Considering the alteration of the Dunquin Group to actinolite-prehnite grade, the preservation of the smectite is highly unusual. There is no evidence for its origin due to more recent weathering or interstratal neoformation; it is thus interpreted as a relict product of the original weathering phase.
Tectono-sedimentary development of an extensional basin: the Neogene Megara Basin, Greece
Authors: BENTHAM P. , COLLIER R. E. , GAWTHORPE R. L. , LEEDER R. , STARK C.
Published: December 2007

The ?Miocene/Pliocene to Pleistocene succession exposed in the Megara Basin comprises a grossly coarsening-upwards sequence at least 1 km thick. The oldest strata, exposed in the NW, record the establishment of alluvial fans and axial streams. These drained into a lacustrine environment subject to minor wave and, possibly, tidal action. The lower part of the central basin fill is comprised of marls, siltstones, sandstones and conglomerates. They record the pulsed infill of the predominantly freshwater ‘Lake Megara’ by progradation of a network of shallow multichannel streams, which drained a western hinterland containing ultrabasic rocks, cherts and limestones. Frequent examples of large-scale soft sediment deformation structures and stratigraphic thickening into hangingwall rolloven indicate active fault control of sedimentation. The lake/river interface featured Gilbert deltas, which were subject to periodic transgression by ?climatically-controlled lake expansions. The upper part of the ?Pliocene basin fill largely comprises fluviatile gravels, but with two important marine transgressional horizons and renewed calcareous mar1 deposition, including a basinwide tufa horizon, towards the top. The overlying ?Pleistocene alluvial clastics were deposited by a NW-flowing system and thicken markedly into a major basin-bounding fault. Deposition of these fluvial deposits was interrupted towards the top of the sequence by the rapid deposition of monomict limestone breccias of debris flow origins, which are believed to mark a catastrophic event. At some time in the late Pleistocene (c. 1 Ma), the basin bounding faults became inactive and the entire basin fill was inverted in response to uplift in the footwall of the active major fault strand that bounds the SE margin of the Alkyonides Gulf.
Structural evolution of a subducted continental sliver: the northern Dora Maira massif, Italian Alps
Authors: WHEELER J.
Published: December 2007

Continental crust of the Dora Maira massif was subducted, in part, to pressures of 30 kbar during early stages of the Alpine orogeny. A new investigation in a transect across the north of the massif has shown that much of the dominant foliation in the upper Dora Maira (Pellice) unit was formed at high pressures of the order of 11 kbar, but at lower pressure than the locally preserved relicts of eclogite-facies metamorphism. This dominant deformation phase produced large recumbent isoclinal folds with intensely flattened limbs in the Pellice unit basement and the overlying Permian–Mesozoic cover (now white augen gneisses and calcschists). The rocks were thus part of the upper crust prior to their subduction, unless an unrealistically large thickness of Mesozoic rocks (now removed) is hypothesized. The Pellice unit was later emplaced over the Chisone unit in greenschist facies conditions.

All shear sense indicators are top-to-west, implying a simple but prolonged history in which high-pressure units were emplaced westwards over lower pressure ones whilst being exhumed. The intense horizontal stretching recorded in the basement gneisses may have helped bring them closer to the surface by thinning. Indirect arguments suggest that such tectonic thinning is not, on its own, sufficient to explain the present setting of the eclogite units. One or more sheets of eclogite material may have been extruded from the Eoalpine subduction zone in addition. Such slabs would be bounded below by west-directed, and above by east-directed, shears. As the Dora Maira massif forms the structurally lowest Eoalpine eclogite unit in the Alps, the observed history is not incompatible with this model. East- or southeast-directed structures in the Alps are commonly identified as backthrusts, but an origin for some as the extensional shears predicted by this model should not be excluded.
Campanian–Maastrichtian (Cretaceous) stratigraphy of the James Ross Island area, Antarctica
Authors: CRAME J. A. , PIRRIE D. , RIDING J. B. , THOMSON M. R. A.
Published: December 2007

One of the most important outcrops of uppermost Cretaceous (Campanian–Maastrichtian) sedimentary rocks in the southern high latitudes occurs within the James Ross Island group, northeastern Antarctic Peninsula. These rocks comprise a 1500–2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro-arc basin. They are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas, and a wide range of plant taxa. Campanian–Maastrichtian strata are contained within two component formations of the Upper Cretaceous-lower Tertiary Marambio Group. The lower Santa Marta Formation is approximately 1100m thick and has three constituent members. Ammonites within the Santa Marta Formation indicate an early to late Campanian age assignment. Dinoflagellates suggest that the lower levels of the formation may range into the Santonian Stage. In the northern James Ross Island to Vega Island region there is a conformable transition into the overlying López de Bertodano Formation. Here the basal Cape Lamb Member is unconformably overlain by the Sandwich Bluff Member. Although there are some lithological and fauna1 discrepancies, which are attributed to marked lateral facies changes across the basin, it is believed that the Cape Lamb Member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated López de Bertodano Formation lithologies exposed on Seymour Island. Molluscan data indicate a late Campanian–Palaeocene age range for this upper formation. Dinoflagellates again suggest that the lowest beds may be slightly older. The correlation presented provides the basis for a formal subdivision of the Campanian and Maastrichtian stages in the southern high latitudes. It has also revealed two major basin shallowing events (in the late Campanian–early Maastrichtian and latest Maastrichtian, respectively) and the existence of a major fault/fault zone across southeastern James Ross Island. The improved temporal framework will aid late Cretaceous palaeoclimatic and palaeobiological studies in Antarctica.
Tectonic and climatic control of Triassic sedimentation in the Beryl Basin, northern North Sea
Authors: FROSTICK L. E. , LINSEY T. K. , REID I.
Published: December 2007

The Beryl Basin (Embayment) occupies a central position along the Viking Graben of the northern North Sea and has been a hydrocarbon play since the early 1970s. Detailed analysis reveals a complex half graben that was established during a rift-phase of development that occurred in the Early Triassic (Teist Formation), after which, a long period of thermal subsidence (Lomvi and Lunde Formations) provided accommodation for in excess of 1000 m of sediment. The Teist Formation sediments are complex, they include shales, sands and conglomerates, and their superimposition on Zechstein salts is indicative of both uplift and the development of a moderate relief. They give way to the comparatively clean and occasionally pebbly sands of the Lomvi Formation, for which an analysis of both bedding and texture suggests deposition by a westerly-directed river system draining the hanging-wall ramp. The Lunde Formation records the spreading influence of a bajada/playa complex and its eventual conversion to a more persistent lake. The growing importance and eventual dominance of the succession by lacustrine sediments gives clear indication of a change in climate, and this has been attributed to the rapid northward drift of Pangea during the Triassic period.
Field relations, geochemistry and petrogenesis of the Cretaceous basaltic Jutal dykes, Kohistan, northern Pakistan
Authors: PETTERSON M. G. , WINDLEY B. F.
Published: December 2007

A 75 Ma Cretaceous suite of low-medium-K basalt to basaltic andesite dykes intrudes the Kohistan terrane between Jutal and Chalt, Gilgit area, northern Pakistan. Orientational data suggest they intruded in response to NW–SE to N–S tension. The dykes cut the Albian–Aptian Chalt Volcanic Group and the 102 Ma Matum Das trondhjemite pluton. They cut the fold structures and penetrative fabrics associated with the collision between Kohistan and Eurasia and thus constrain the age of formation of the Northern Suture. The dykes define two groups on the basis of trace element geochemistry and geochemical trends. A depleted D-type group has low concentrations of incompatible elements (2–8 x primordial mantle) and (Ce/Yb)N ratios <1. An enriched E-type group is relatively enriched in both low field strength and light Rare Earth elements and exhibits increasing incompatible element concentrations with increasing Zr. Trace element and field data suggest that the dykes are genetically linked and formed by partial melting of a mantle source which has been metasomatized by subduction-related processes. Models involving (i) different degrees of partial melting (ii) two-stage partial melting and (iii) partial melting of a heterogeneous source are considered.
Timing of post-tectonic Cadomian magmatism on Guernsey, Channel Islands: evidence from
40
Ar/
39
Ar mineral ages
Authors: DALLMEYER R. D. , D’LEMOS R. S. , STRACHAN R. A.
Published: December 2007

The Channel Island of Guernsey exposes pre- and post-tectonic calc-alkaline plutonic rocks attributed to late Precambrian (Cadomian) subduction activity.
40
Ar/
39
Ar mineral cooling ages presented here clarify the age and time-span of post-tectonic intrusions. Amphibole from the Bon Repos meladiorite yields an isotope correlation age of 605.3 ± 4.6 Ma, indicating emplacement during late stages of the tectonothermal event recorded within its host rocks. Igneous hornblendes from the Northern Igneous Complex record consistent isotope correlation ages (St Peter Port gabbro 570.2 ±1.1 Ma, Bordeaux diorite complex 569.0 ± 1.1 and 565.3 ± 2.2 Ma, and a comagmatic enclave within Cobo granite 570.2 ± 1.5 Ma). Hornblende and biotite from contact-metamorphosed host rocks adjacent to the Cobo granite yield isotope correlation ages of 569.6 ±1.1 and 563.8 ± 3.3 Ma respectively. These ages, together with field data, demonstrate that the various members of the Northern Igneous Complex were emplaced contemporaneously at
c.
570 Ma, significantly earlier than a
c.
500 Ma Rb-Sr whole-rock isochron age previously reported for the Cobo granite. The
40
Ar/
39
Ar ages indicate that post-tectonic magmatism on Guernsey was broadly coeval with post-metamorphic cooling around the Baie de St Brieuc on the adjacent French mainland, and occurred
c.
30 Ma prior to peak Cadomian deformation and metamorphism in the St Malo area.
Elemental and O-Sr-Nd isotope geochemistry of the Glen Dessarry syenite, NW Scotland
Authors: FOWLER M. B.
Published: December 2007

Elemental, radiogenic isotope (Sr, Nd) and stable isotope (O) data from samples of the 456 Ma Caledonian Glen Dessarry syenite are all compatible with a two-stage crystal-fractionation model for the evolution of the magmas, locally modified by contamination with a partial melt of the surrounding Moine metasediments. The early-crystallizing phases which controlled melasyenite-leucosyenite evolution were biotite, calcic clinopyroxene plus minor apatite and titanite, whilst in-situ crystal-liquid separation also involved alkali feldspar and amphibole with minor allanite, zirconolite and zircon. The diverse accessory mineral suite controlled significant variations in many of the ‘incompatible’ elements, including inordinate Zr/Hf fractionation. Crustal contamination led to severe disturbance in abundances and inter-element ratios of U, Th; Zr, Hf; Nb, Ta; heavy REEs, Sr and Ba.

The elemental characteristics of the magmas are typical of shoshonitic subduction-related suites, with high LILEs, relatively low HFSEs and pronounced negative Nb-Ta anomalies. Inferred isotopic characteristics of the parent magmas (
87
Sr/
86
Sr ≈ 0.7040, ΣNd = + 2.5 and δ
l8
O ≈ + 7%o) are probably derived from a multicomponent source region involving a substantial input from contemporary depleted mantle.
When is a fault ‘extinct’?
Authors: MUIR WOOD R. , MALLARD D. J.
Published: December 2007

Existing regulatory definitions of time-periods over which evidence should be searched to demonstrate whether a fault is, or is not, active may be unconservative in slowly deforming continental regions where recurrence intervals of surface faulting are in excess of 100 000 years. Self-evidently, no definition of an active fault can be satisfactory when founded on some extrinsic time-period. Instead, it must be derived from the properties of the system itself, preferably through knowledge of fault-movement recurrence intervals, or alternatively and conservatively from an understanding of the time-period over which the present conditions of regional stress and strain (the ‘current tectonic regime’) have prevailed. Borrowing from volcanological terminology, out of the definition of the ‘active’ fault emerges an antithesis: the ‘extinct’ fault. Time-periods by which directly dated faults are designated as active or extinct have to be locally derived.
Dating of Late Quaternary faulting in northern Sweden
Authors: LAGERBÄCK R.
Published: December 2007

Fault scarps, interpreted as post- or late-glacial in age, occur in northern Sweden and adjacent parts of Finland and Norway. In the Lansjärv area in northern Sweden, attempts have been made to date fault displacement relative to the glacial and postglacial stratigraphy by trenching across fault scarps. It is shown that the faulting occurred soon after the local deglaciation some 9000 years ago with no signs of movements since. The faulting appears to have been associated with violent earthquakes, because landslides and soil deformation, interpreted to be seismically induced and dating from the same period as the faulting, are frequently found in the area.
Dependence of active normal fault dips on lower-crustal flow regimes
Authors: WESTAWAY R.O.B.
Published: December 2007

Two key questions are raised by the presence in the Basin and Range Province of subhorizontal normal faults, which were active in and around the Miocene. First, how did they develop, when their existence seems to be precluded by elementary rock-mechanics arguments? Second, if they did slip in the recent geological past, why do normal faults now active in the brittle upper crust have steeper dips, both in the western USA and elsewhere? One may now answer both questions, by considering the stress field in regions where the isostatic response during extension involves horizontal flow in the plastic lower crust. This stress tensor will have inclined principal axes, making it possible for normal faults to form with either very steep or subhorizontal dips depending on the sense of flow. This can be controlled by environmental conditions, which influence rates of hanging-wall sedimentation and footwall erosion and thus determine lateral variations in lithostatic pressure in the lower crust. Regional-scale lateral variations in the geothermal gradient caused by subduction can also influence lower-crustal flow regimes in adjacent zones of continental extension, enabling extension to occur on low-angle normal faults dipping away from the active continental margin.
Crustal evolution and terrane correlation in the eastern Arabian Shield, Yemen: geochronological constraints
Authors: WHITEHOUSE MARTIN J. , WINDLEY BRIAN F. , BA-BTTAT MAHFOOD A. O. , FANNING C. MARK , REX DAVID C.
Published: December 2007

Ion-microprobe U–Pb zircon and
40
Ar–
39
Ar geochronology is presented for two gneiss terranes and an island arc terrane in the Arabian Shield of Yemen. These data confirm the presence of late Archaean (
c.
2.95–2.55 Ga) crust in the Al-Mahfid (eastern) terrane, previously inferred from Nd model age determinations; a minor late Archaean component in the Abas (western) terrane is revealed by a single
c.
2.6 Ga zircon core. No ages have been obtained corresponding to documented
c.
1.8–1.4 Ga events in neighbouring Somalia and Saudi Arabia, but both gneiss terranes are strongly affected by
c.
760 Ma Pan-African reworking which is recorded by Pb loss in zircons of the Al-Mahfid terrane and zircon crystallization ages of granitic gneisses and sheets in both the Al-Mahfid and Abas gneiss terranes.
40
Ar–
39
Ar ages obtained from intrusive rocks in the intervening Al-Bayda arc terrane provide a lower age limit of 615 Ma upon terrane assembly. Correlation of pre-Pan-African events within the Arabian–Nubian Shield remains problematic because of the still limited sampling and available geochronology.
The tectonic significance of pre-Scandian
40
Ar/
39
Ar phengite cooling ages in the Caledonides of western Norway
Authors: ANDERSEN TORGEIR B. , BERRY HENRY N. , LUX DANIEL R. , ANDRESEN ARILD
Published: December 2007

Pre-Silurian continental-margin deposits in western Norway, non-conformably overlying allochthonous continental orthogneisses retain Ordovician
40
Ar/
39
Ar cooling ages for phengites, implying either rapid cooling immediately after a Late Ordovician orogenic event, or less likely, a slow cooling following an Early Ordovician or older orogeny. The Dalsfjord Suite–Høyvik Group basement–cover pair are probably a lateral equivalent to Late Proterozoic sandstones (‘sparagmites’) covering the Jotun Nappe gneisses of the Middle Allochthon in central-south Norway. The Høyvik Group underwent polyphase deformation, greenschist-facies metamorphism (
T

max

<450°C) and exhumation prior to deposition of the unconformably overlying Wenlockian continental-margin deposits of the Herland Group. The Høyvik Group was only weakly metamorphosed during obduction of the Solund–Stavfjord Ophiolite and the Scandian continental collision between Baltica and Laurentia. Phengitic white micas from the Høyvik Group yield cooling ages of 446.1± 3.0, 449.1±2.2 and 447.5±4.0 Ma, respectively, identical within experimental error. One sample gives a plateau over 72% of the gas analysed, whereas the other samples were slightly disturbed after initial cooling, as indicated by systematically lower apparent ages at low experimental extraction temperatures. Minor
40
Ar loss probably occurred during subsequent Scandian deformation and late to post-orogenic extension.The Høyvik Group rocks were unroofed before the Wenlock time (423–428 Ma) and cooled through the temperature for argon retention in phengite at
c
. 447±4 Ma, indicating a maximum cooling rate between 14 and 22C/Ma-
1
through Ashgill and Llandovery times before being subjected to low-grade metamorphism during the Scandian orogeny. Rapid pre-Scandian cooling, combined with peak metamorphic conditions of 450C or less, may indicate that the Dalsfjord–Høyvik basement–cover pair were aVected by an orogenic event during the Late Ordovician (Caradoc) time. The data also suggest that the Caledonian margin of Baltica may have experienced a more protracted tectonism during the Caledonian cycle than previously models focusing on Early Caledonian and Tremadoc (or older) ophiolite obduction and the Scandian continental collision between Baltica and Laurentia.