bluuebunny/crossref_metadata_2025_split huggingface dataset:
Problems interpreting deep crustal reflectors beneath the Moine thrust between Shetland and the Scottish Highlands
Authors: McBride J. H. , England R. W. 
Published: May 2009

AbstractOffshore seismic reflection profiles crossing the Caledonian orogenic front (locally, ?Moine thrust) between Shetland and the Scottish Highlands show a singular coherent east-dipping reflection underlain by a highly reflective dipping zone in the middle crust extending down to the Moho discontinuity. This reflector pattern varies spatially with respect to the eastern edge of the Precambrian Lewisian foreland as well as to previously mapped locations of the Moine thrust. Southwest of Shetland, the reflector pattern coincides with the offshore projection of the Moine thrust, but further south, toward the Highlands, the reflector diverges to the west of the thrust and actually underlies autochthonous Lewisian foreland basement. Where this reflector pattern diverges from the Moine thrust, two interpretations are possible: the prominent reflector is part of a basement imbricate thrust duplex within the footwall (or ‘lower plate’) of the Moine thrust that merges with the thrust zone further north and/or it was originally a Proterozoic normal fault which, further north around Shetland, was reactivated or over-printed by the Moine thrust. The latter interpretation supports the importance of pre-existing crustal structure in controlling Caledonian compressional deformation.
The Siluro-Devonian evolution of the southern Midland Valley of Scotland
Authors: Smith R. A. 
Published: May 2009

AbstractGeological studies along the southern margin of the Midland Valley of Scotland, together with previously published work, suggest a strike-slip model for its evolution during Silurian and Devonian times. The data emphasize the ‘older Caledonian’ influence and persistent, albeit intermittent, transcurrent activity along the Southern Upland Fault which is the boundary between the Midland Valley and Southern Upland terranes. A comparison of the geological characteristics of the Silurian and Devonian rocks in the southern Midland Valley with characteristics from strike-slip basins elsewhere suggests that the Midland Valley rocks were deposited and locally deformed under sinistral strike-slip regimes with two main episodes of transtension — the first acting in Llandovery—Wenlock times and the second in Lower Old Red Sandstone times. A strike-slip model involving transpression may explain why there is a strong unconformity between the Llandovery—Wenlock and the Lower Old Red Sandstone strata in the Pentland Hills and Girvan inliers but only a marked change in sedimentary facies at the equivalent horizon in the inliers of the central Midland Valley. The Lower Old Red Sandstone was probably deposited in a transtensional regime, but the succession is complicated by the widespread Lower Old Red Sandstone calc-alkaline magmatic event. The mid- Devonian deformation is also variable in its effects and the more easterly trend of theen echelonfold axes relative to the Southern Upland Fault trend is indicative of sinistral transpression. Carboniferous and older rocks were affected by smaller dextral movements on the Southern Upland Fault and related faults which started during Namurian times when a change to an overall dextral regime took place.
The Orlock Bridge Fault in the Southern Uplands of southwestern Scotland: a terrane boundary?
Authors: Barnes R. P. , Phillips E. R. , Boland M. P. 
Published: May 2009

AbstractThe Orlock Bridge Fault separates the Ordovician and Silurian turbidite sequences within the Southern Uplands thrust belt. A large biostratigraphical break and the 1 km wide sinistral Slieve Glah Shear Zone associated with the fault in northern Ireland led to previous interpretation as a major regional structure, possibly a terrane boundary. In Scotland, however, the stratigraphical break is much less and an association with inliers of the Moffat Shale Group suggests that the fault is essentially similar to the other tract-bounding faults which originated as syn-D1 thrusts within the imbricate stack. Localized sinistral deformation apparent along the trace of the Orlock Bridge Fault in southwestern Scotland, associated with post-1 reactivation, is comparable to that seen at Slieve Glah. Further east, a broad zone (up to 8 km) of sinistral ductile deformation, the Moniaive Shear Zone, is recognized adjacent to the Orlock Bridge Fault over a strike length of about 100 km. However, this zone differs from the Slieve Glah Shear Zone in its width and its location relative to the fault, suggesting that it is not simply related to the fault but represents a more regional deformation. Sinistral reactivation of the Orlock Bridge Fault was possibly initiated in the Wenlock during the peak of sinistral shear at the thrust front, although it may have developed over a long time contemporaneously with, but locally post-dating, the Moniaive Shear Zone. The latter deforms porphyroblasts with the thermal aureole of the c. 392 Ma Cairnsmore of Fleet granite pluton, which was emplaced into and largely post-dates the shear zone, but is deformed by the Orlock Bridge Fault. Major dip-slip reactivation of the fault post-dates the Moniaive Shear Zone and regional metamorphism and probably occurred in the Carboniferous or Permian. There is some evidence for a deep crustal feature coincident with the Orlock Bridge Fault, possibly the boundary between different crustal blocks in the collage of terrane fragments accreted during the final closure of Iapetus, which may explain the unusual extent of the reactivation of the Orlock Bridge Fault within the allochthonous Southern Uplands thrust stack. However, the situation of the fault within the Southern Uplands terrane and, in Scotland, the biostratigraphical evidence of no major stratigraphical break across the fault and the lack of any clear relationship between the Orlock Bridge Fault and the Moniaive Shear Zone indicate that the fault should not be regarded as a terrane boundary.
Deep resistivity imaging across the Northern and Central belts of the Southern Uplands
Authors: Beamish David 
Published: May 2009

AbstractMagnetotelluric data from 16 soundings have provided a northwest-southeast traverse across the Northern and Central belts of the Southern Uplands. The 34 km profile extends from the Ordovician Portpatrick Formation (northwest of the Thornhill Basin) across the Silurian Gala Group onto the Permian Lochmaben Basin in the southeast. The survey traverses, and has particular relevance to, the Ordovician/Silurian boundary (Orlock Bridge Fault), the associated Moniaive Shear Zone, and the Moffat Valley Lineament. The data obtained have been successfully modelled (inverted) to provide a crustal-scale resistivity cross-section. The two Upper Palaeozoic basins are resolved as relatively conducting features. Basin depths are about 200 m (Thornhill) and 1100 m (Lochmaben). Elsewhere, through the upper crustal interval, resistivities over 500 ohm m are associated with the Lower Palaeozoic greywackes. The Silurian formations appear more resistive (and slightly thicker) than their Ordovician counterparts. Depth to basement (base Lower Palaeozoic) is not a well-resolved characteristic but resistivity gradients observed below 5 km suggest a depth of this order. Concealed beneath the Thornhill Basin lie two narrow, vertical, conductive zones. The more substantial feature lies towards the northwest margin of the basin, and is probably associated with the Orlock Bridge Fault. The second zone lies towards the southeast margin of the basin. The conductivity minima, in both cases, are located in the depth range 2 to 3 km; they are separate and distinct from the overlying basin sediments. If the two anomalies, some 5 to 6 km apart, can be considered an expression of the Moniaive Shear Zone, then the major conductive constituents are concentrated at the margins. Two dipping, resistive features in the upper kilometre are imaged in the vicinity of the Moffat Valley Lineament.
Turbidite geochemistry and provenance studies in the Southern Uplands of Scotland
Authors: Duller P. R. , Floyd J. D. 
Published: May 2009

AbstractRegional lithogeochemical data from the Southern Uplands have been used to characterize a distinctive stratigraphy across this region. A suite of 840 point-counted and petrographically classified greywacke samples were used to establish chemical fingerprints for a series of greywacke-dominated lithostratigraphical units. These fingerprints were then used to evaluate a further 1455 greywacke samples collected throughout the Southern Uplands and Longford Down and enabled a series of strike-parallel geochemical tracts to be defined.Four principal geochemical groups are recognized, relating to cratonic- and volcanic-derived greywacke provenances and both carbonate-rich and hydrothermally altered greywackes. Volcanic-derived units display higher Ti, Fe, Mg, Ca, Na, Mn, Cr, Ga, Ni, Sr, V and Zn values than their cratonic counterparts, which, with the exception of the carbonate-rich Hawick Group, display higher Si, K, La, Nb, Rb, Th and Zr. Volcaniclastic greywackes display REE patterns dissimilar to typical post-Archean upper crust, but similar to their andesitic components, whereas cratonic groups have REE patterns close to that of upper crust. Systematic strike-parallel geochemical variation in the Southern Uplands is controlled by petrographical differences which directly reflect provenance, with individual lithostratigraphical units derived from variable mixtures of ophiolitic, calc-alkaline, acid-igneous, low-grade metamorphic and carbonate-rich detritus.
On the Antarctic Peninsula batholith
Authors: Leat P. T. , Scarrow J. H. , Millar I. L. 
Published: May 2009

AbstractThe plutonic rocks of the Antarctic Peninsula magmatic arc form one of the major batholiths of the circum-Pacific rim. The Antarctic Peninsula batholith is a 1350 km long by < 210 km wide structure which was emplaced over the period ˜240 to 10 Ma, with a Cretaceous peak of activity that started at 142 Ma and waned during the Late Cretaceous. Early Jurassic and Late Jurassic–Early Cretaceous gaps in intrusive activity probably correspond to episodes of arc compression. In a northern zone of the Antarctic Peninsula, the batholith intrudes Palaeozoic–Mesozoic low-grade meta-sedimentary rocks, and in a central zone it intrudes schists and ortho- and paragneisses which have Late Proterozoic Nd model ages and were deformed during Triassic to Early Jurassic compression. In a southern zone the oldest exposed rocks are Permian sedimentary rocks and deformed Jurassic volcanic and sedimentary rocks. All these pre-batholith rocks formed a belt of relatively immature crust along the Gondwana margin. With few exceptions, Jurassic plutons crop out only within the central zone: many are peraluminous, having ‘S-like’ mineralogies and relatively high 87sr/86sri. They are considered to consist largely of partial melts of upper crust schists and gneisses and components of mafic magmas that caused the partial fusion. By contrast, Early Cretaceous plutons crop out along the length of the batholith. Few magma compositions appear to have been affected by upper crust, the bulk being compositionally independent of the type of country rock they intrude. They are dominated by metaluminous, calcic, Si-oversaturated, 1-type granitoid rocks with relatively low 87sr/86sri intermediate-silicic compositions (< 5% MgO). We interpret these to represent partial melts of basic to intermediate, igneous, locally garnet-bearing, lower crust. Contemporaneous mafic magmas (e.g. syn-plutonic dykes) form a more alkaline, Si-saturated series having higher 143Nd/144Nd at the same87sr/86sr than the intermediate-silicic series, to which they are not petrogenetically related. The change from limited partial fusion of upper crust in Jurassic times to widespread partial fusion of lower crust in Early Cretaceous times is considered to be a result of an increasing volume of basaltic intrusion into the crust with time.
Transition from alluvial to coastal deposits (Permian–Triassic) on the Island of Mallorca, western Mediterranean
Authors: Ramos Amparo 
Published: May 2009

AbstractNon-marine redbeds (Permian and Triassic) in the island of Mallorca consist of a 0.4 km-thick alluvial succession that passes upwards into siliciclastic–carbonate coastal deposits. Tectonics and sealevel changes have been the main influences in their evolution. Low in this succession (the ‘Areniscas y lutitas de Port des Canonge’ unit) sandstone sheets with lateral accretion surfaces (macroscale inclined strata) and mudstones with frequent exposure structures are interpreted as the products of a sinuous alluvial system and floodplain. Climatic fluctuations are considered to be responsible for some significant up-section changes in the evolution of the alluvial deposits. Low-angle or horizontally stratified sandy units, interpreted as the result of flash floods, alternate upwards with point-bar deposits in the ‘Areniscas de Asá’. The hydrological response to minor climatic changes was evidently nearly instantaneous due to the lack of significant vegetation cover.During accumulation of mudstones and sandstones of the overlying ‘Lutitas y Areniscas de Son Serralta’ unit, the interpreted environment of deposition changed from a distal braidplain, mainly constructed by superposition of sandy bedforms with straight or linguoid crestlines in low sinuosity river channels, into a coastal plain with evidence of both continental and marine influences. The overlying carbonate platform (Muschelkalk) marks the development of a more homogeneous marine environment resulting from the Tethyan transgressive event that affected the whole peri-Mediterranean realm during the Anisian (middle Triassic).
Some constraints on the form of the Welsh Basin from regional gravity and aeromagnetic data, with particular reference to Central Wales
Authors: Carruthers R. M. , Fletcher C. J. N. , McDonald A. J. W. , Evans R. B. 
Published: May 2009

AbstractGravity and aeromagnetic data sets provide systematic coverage over the whole of the Welsh Basin. Physical property information shows considerable overlap in densities within the Lower Palaeozoic and Precambrian formations, with relatively few units of the exposed succession being strongly magnetic. While the geophysical anomalies cannot be interpreted unambiguously in terms of these sources, the data can still be used to test different geological models and to indicate the range of possible solutions. The major fault zones are seen to influence the anomaly patterns in a variety of ways, reflecting a combination of differing near-surface contrasts and effects within the underlying basement. The general increase in gravity values towards Cardigan Bay may originate from the lower crust, and the large amplitude aeromagnetic low seen over Cardigan Bay indicates that a distinctive change in the character of the crust occurs here. Two-dimensional modelling in central Wales shows that a westward thickening of the Welsh Basin, to a maximum of about 10 km, may also be significant. It is necessary to postulate a separation of the base of denser, Lower Palaeozoic rocks from the underlying, more magnetic basement in order to account for offsets in anomaly source locations. This implies the presence of less dense Cambrian sediments and/or non-magnetic components of the Precambrian basement.
Cambrian and early Tremadoc rocks of the Llangynog Inlier, Dyfed, South Wales
Authors: Cope J. C. W. , Rushton A. W. A. 
Published: May 2009

AbstractUntil recently no Cambrian rocks were known in the Llangynog area. Detailed mapping has now revealed a succession of ?Lower and Upper Cambrian rocks overlain by Tremadoc rocks. The Allt y Shed Sandstones (new) rest unconformably on the Precambrian, but have yielded no diagnostic fossils and are tentatively assigned to the Comley Series. Succeeding with faulted or unconformable contact is an Upper Cambrian Merioneth Series succession which includes in ascending order: conglomerates, sandstones and siltstones with olenid trilobites and resembling the Treffgarne Bridge Beds of the Haverfordwest area; micaceous shales and siltstones referred to the Ffestiniog Flags Formation; and black mudstones with calcareous concretions and a rich olenid fauna referred to the Dolgellau Formation. Succeeding the latter with possible disconformity is a succession belonging to the lower part of the Tremadoc Series and earlier than any rocks of that series hitherto recorded from the area.
Geochemical discrimination of Silurian mudstones according to depositional process and provenance within the Southern Welsh Basin
Authors: Ball T. K. , Davies J. R. , Waters R. A. , Zalasiewicz J. A. 
Published: May 2009

AbstractA preliminary geochemical investigation of Silurian (Llandovery) basinal mudstones (turbidites and hemipelagites) from the Southern Welsh Basin is described. Turbidite mudstones show higher concentrations of Fe2O3, MgO, TiO2, MnO, LOI, Zn and Zr than laminated hemipelagites. This is consistent with the observed higher concentrations of chlorite and Ti-bearing minerals in turbidite mudstones. Laminated hemipelagites show higher values of REEs (Ce and La), concentrated within authigenic monazites, and Ni, As, Cu and Pb within sulphide minerals (pyrite and galena) reflecting the influence of primary organic carbon levels and anoxic bottom waters on early diagenesis. Deposition of hemipelagites under oxidizing conditions is reflected in lower concentrations of authigenic sulphide mineral hosted elements compared with laminated hemipelagic lithologies. There is a distinct geochemical difference between mudstones of easterly and southerly provenance in the Southern Welsh Basin. This is shown for both turbidites and hemipelagites. The differences are due to the increased input of illite and the chemical elements associated with this mineral (K2O, A12O3, Rb and Ba). Turbidite mudstones sourced from the south show increased levels of heavy minerals, especially those associated with Ti-rich minerals. There is also an increase in elements associated with detrital monazites: Th and Y. The hemipelagites show higher values of REE and chalcophile elements consistent with their more reduced nature.
Welsh Basin ‘contourites’ reinterpreted as fine-grained turbidites: the Grogal Sandstones
Authors: Smith R. D. A. , Anketell J. M. 
Published: May 2009

AbstractSince 1976 the Lower Silurian Grogal Sandstones of the Welsh Basin have been interpreted as contourites. Here we show that they are in fact fine-grained turbidites, frequently with pale-coloured oxidized top layers which enable distinction of individual event deposits. As reported previously, palaeocurrent directions derived from ripple cross-lamination are typically at a high angle, often close to perpendicular, to those measured from sole structures. The favoured explanation is that ripples migrated under transverse internal waves generated at an intrabasinal slope to the east. Evidence for the lateral confinement of the overlying Aberystwyth Grits by such a slope provides support for this explanation.
Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland
Authors: Mohr Peter 
Published: May 2009

AbstractRb–Sr isotope whole-rock data from the end-Caledonian Leinster Batholith define an errorchron age of 464±26 Ma, appreciably older than the accepted emplacement age of c. 405 Ma. This anomalously old age is the consequence of a highly variable initial Sr isotopic composition. Initial Nd ratios and TDM model ages also show a wide range of values. However, these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect, in a simple way, geographic position about the axis of the batholith. The isotopic pattern revealed in the Leinster Batholith means that isochron ages obtained from S-type granites may be largely dependent on the sampling scheme adopted. The variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval, dominantly crustal melts.
Sm–Nd isotope characteristics of late Cadomian granite magmatism in northern France and the Channel Islands
Authors: d'Lemos R. S. , Brown M. 
Published: May 2009

AbstractSm–Nd isotopic studies of granites within the late Precambrian, Cadomian, orogenic belt of the North Armorican Massif (northwestern France) and Channel Islands reveal differences between arc-related granite magmatism in outboard terranes and intracrustal granite magmatism in inboard terranes. Late Cadomian (c. 570 Ma), arc-related granitoids exhibit a range of εnd( - 2 to - 6) and Nd model ages (TDM1.0–1.3 Ga) reflecting variable contamination between late Precambrian mantle derived magmas and ancient (c. 2.0 Ga?) continental crust. The contamination did not involve exposed granitic Icartian basement to anygreat degree, a more likely contaminant being unexposed lower crust of intermediate to acidic granulitic composition, or early Cadomian plutons which were themselves contaminated by lower crust. Voluminous granites of the Mancellian region (c. 550–540 Ma) share common isotopic characteristics (εNd-4 to -7, TDM1.5–1.7 Ga) with migmatites and anatectic granites produced by partial melting of metasedimentary sequences within the St Malo region consistent with a common source.
A new discovery of early Cretaceous (Wealden) amber from the Isle of Wight
Authors: Nicholas Christopher J. , Henwood Alison A. , Simpson Martin 
Published: May 2009

AbstractA new discovery ofin situamber is reported from the southwest coast of the Isle of Wight. The productive site is located within the Wealden Marls (Wessex Formation), generally regarded to be of earliest Barremian (early Cretaceous) age; also making this amber amongst some of the oldest known occurrences in the world. Amber globules can be found within two thin, black lignite horizons which form a channel-lag deposit exposed in the cliffssoutheast of Chilton Chine. Examination of plant material above and below this site by other workers, combined with infrared spectra of the amber in this study, implies a coniferous (possibly taxodiaceous) origin for this resin. Palaeoenviron-mental interpretation of the Chilton Chine site suggests that the amber was exuded locally, and in some cases the globules have beenpartly replaced by iron pyrite.
Syn-depositional deformation in a Cretaceous succession, James Ross Island, Antarctica. Evidence from vitrinite reflectivity
Authors: Whitham A. G. , Marshall J. E. A. 
Published: May 2009

AbstractA detailed vitrinite reflectivity study has been made through the Cretaceous sedimentary rocks of northwest James Ross Island, Antarctica. The results show that a progressive increase in reflectivity does not occur with depth and that values (0.45 %) from the base of the succession are lower than expected for the sequence as described by previous authors. Using a synthesis of sedimentological and stratigraphic information, the sequence is reinterpreted as an apparent monoclinal syncline, strongly influenced by syndepositional tectonics, with a thickness appreciably less than previously described.