bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrabasic igneous breccias of the Long Loch area, Isle of Rum
Authors: Wadsworth W. J.
Published: January 2010

Synopsis

Ultrabasic igneous breccias, associated with streakily-laycred and locally slumped allivalites (plagioclase–olivine cumulates) of the Central Series component of the Rum Layered Complex, consist of assorted peridotite and allivalite fragments in a matrix of feldspathic peridotite. The fragments vary considerably in size, shape, texture and concentration, while the matrix is relatively homogeneous. At least three generations of igneous veins have also been identified. The main components of the breccias have been characterized in terms of their olivine compositions. The peridotites (Fo
84.5–89
) are consistently more magnesian than the allivalites (Fo
82–84.5
), while the matrix (Fo
84–85
) is bracketed by both. The field, textural and mineralogical evidence indicates that the fragments have been derived from older parts of the Rum Layered Series as intra-formational debris accumulations, perhaps associated with submagmatic faulting in a central graben, whereas the matrix represents plagioclase–olivine crystal cumulates precipitated directly from the contemporary magma. Away from the breccia zones these cumulates grade into more normal layered allivalites, but even these show abundant evidence of instability associated with steep depositional dips and repeated disturbance.
Ordovician trilobites from the Durness Group, North–West Scotland and their palaeobiogeography
Authors: Fortey R. A.
Published: January 2010

Synopsis

The trilobites of the early Ordovician platform carbonates of the Durness Group comprise two bathyurid species belonging to
Petigurus
and
Jeffersonia,
together with the pliomerid
Cybelopsis
and the asaphid
Isoteloides
(now lost). The species are described and suggest a precise correlation of the Ben Suardal and Croisaphuill formations with trilobite Zone H of the North American zonal scheme and indirect correlation with the early Arenig.
Jeffersonia
and
Cybelopsis
are recorded from the British Isles for the first time. All trilobites are typical of the Ordovician Laurentian plate, and the species in particular compare with inner shelf faunas in western Newfoundland and Greenland. The trilobites are contemporaneous with those from the Dounans Limestone (Highland Border Group), but belong to different genera. Both faunas are equally of Laurentian type.
Reversals of movement sense in Lewisian brittle–ductile shear zones at Gairloch, NW Scotland, in the context of Laxfordian kinematic history
Authors: Shihe Lei , Park R. Graham
Published: January 2010

Synopsis

Narrow (10–100 m wide) brittle–ductile shear zones in the Lewisian high-grade metamorphic complex of Gairloch, occur within broader ductile shear zones tens of kilometres across. The narrow belts contain ductile mylonites showing a sinistral sense of movement, which are cut and disrupted by brittle cataclasites indicating a dextral movement sense. These are in turn affected by sinistral brittle folds, and finally by N–S dextral pre-Torridonian faults.

The ductile mylonites are thought to represent strain concentration during later stages of the high-grade Laxfordian D2 event at
c.
1.7 Ga, associated with north-westwards overthrusting. The reversal to dextral shear shown by the cataclasites is linked with the regional D3 folds, steep shear zones and widespread, retrogression at
c
. 1.5 Ga, and ascribed to a re-orientation of the regional movement direction from NW–SE to N–S. The reversal of shear sense to sinistral during the D4 folding may be explained by clockwise rotation of the shear belts with respect to the regional shear direction as movement continued. The final change to N–S dextral faulting could be related either to late Lewisian strike-slip movements at
c.
1.4 Ga or to Grenvillian movements at
c.
1.1 Ga.
Evidence for Carboniferous thermochemical overprinting in the Cheviot Complex
Authors: Mitchell J. G. , Storetvedt K. M. , Robson D. A. , Abranches M. C. , Ineson P. R.
Published: January 2010

Synopsis

Previous studies of the Lower Devonian lavas of the Cheviot Hills have shown them to contain an unusually complex remanent magnetization, and many lavas have given Carboniferous K-Ar ages which are not compatible with the geological evidence. Furthermore, the Cheviot volcanics display pronounced low temperature alteration, significant jointing and faulting, and a phase of post-volcanic siliceous veining. Further palaeomagnetic and radiometric studies have been carried out in order to establish whether or not the anomalous magnetic and isotopic results are related to the tectono-thermochemical processes and mineral alteration. K-Ar analyses of clay mineral concentrates of lava and vein material from eight sites all give Carboniferous ages; the lava-derived clay ages cluster around 325 Ma, while the clays from veins have ages close to 300 Ma. Palaeomagnetic studies of the intrusive rocks also show extensive low temperature oxidation of the Fe–Ti oxides, even in the compact and subglassy varieties. Magnetization is typically multicomponent (dual-polarity) and is no less complex than that observed in the lavas. Inferred single-component directions are consistent with those recognized in the extensive Permo-Carboniferous intrusive sheets of the region (the ‘Whin Sill’). It is concluded that Hercynian tectonic reactivation in the Cheviot region led to chemical and mineralogical modification of all of the rock units examined, finding explicit expression in low temperature oxidation, remagnetization, isotopic setting (or resetting) of the K-Ar system in clay minerals from the lavas, and the development (or rejuvenation) of siliceous veining in the SE of the Cheviot massif.
Glossary of Scottish mineral species—an update
Authors: Livingstone A.
Published: January 2010

Synopsis

A literature survey over the period January 1981 to December 1990 reveals that about 132 mineral species new to Scotland have been discovered. This is a 32% increase over the previous decade and results mainly from electron probe-microanalyses. Silicates, oxides, hydroxides, sulphides and sulphosalts form the bulk of the compilation. Highlights of the decade include the discovery of platinum group minerals in Shetland, work on manganese oxides and hydroxides and clay minerals, tellurium and selenium minerals and the discovery and description of five new mineral species.
Mafic dykes within the Lewisian Complex on Tiree and Coll, Inner Hebrides
Authors: Muir R. J. , Evans J. A. , Fitches W. R.
Published: January 2010

Synopsis

Mafic dykes within the Lewisian Complex on Tiree and Coll were emplaced after a granulite-facies metamorphic event in the host gneisses. They were subsequently deformed and metamorphosed under amphibolite-facies conditions and cut by quartzofeldspathic pegmatites. The dykes are quartz-tholeiites and have a typical ‘continental’ trace element signature; showing enrichment in large ion lithophile and light rare earth elements and depletion in the high field strength elements. The intrusions are indistinguishable from Proterozoic (2.4–2.0 Ga) quartz-dolerite Scourie dykes of mainland Scotland, in terms of their field relationships, petrography, geochemistry and Sm-Nd isotope systematics. The occurrence of Scourie dyke-like bodies enables pre-and post-dyke events within the Lewisian on Tiree and Coll to be tentatively assigned to Scourian (2.9–2.5 Ga) and Laxfordian (1.9–1.5 Ga) events respectively. Sm-Nd whole-rock-mineral ages of
c.
1.75 Ga are interpreted as dating garnet growth during the Laxfordian event and provide a minimum emplacement age for the dykes.
The structure of the Sea of the Hebrides Basin: an integrated gravity and seismic model
Authors: O'Neill P. S. , England R. W.
Published: January 2010

Synopsis

By combining seismic and gravity data for the Sea of the Hebrides Basin it has been possible to overcome problems of sea bed multiples and poor energy transmission in seismic data where a sediment starved sea floor and extensive igneous intrusions and volcanic rocks close to the sea bed have previously inhibited detailed interpretation of the basin structure. Models for the basin structure, partly constrained by the seismic data, parallel to the dip and strike of the basin show a good correlation between calculated and observed gravity anomalies and are consistent with the onshore geology. The basin has a half graben geometry with late-Triassic syn-rift sediments thickening toward the eastward dipping Minch Fault, overlain by post-rift Jurassic sediments. Early Tertiary volcanism was followed by Oligocene extensional faulting.
A new vertebrate trackway from the Permian of Dumfries and Galloway
Authors: McKeever Patrick J.
Published: January 2010

Synopsis

Formal diagnosis of a recently discovered vertebrate trackway from the Locharbriggs Sandstone Formation of southern Scotland is given. It belongs to a new ichnospecies,
Chelichnus locharbriggsensis.
The tracks were made by a small, wide-bodied pelycosaurian reptile with a distinct sprawling gait. Calculations suggest that the animal was moving very slowly at the time of trackway formation. The trackway was formed and preserved after the substrate had been subjected to wetting and detrital clay infiltration, thereby imparting to the sand the degree of cohesion necessary for trackway formation and preservation.
Sedimentology of the upper Dinantian Charlestown Main Limestone: implications for the controls on cyclothem deposition, eastern Midland Valley of Scotland
Authors: Pickard Neil A. H.
Published: January 2010

Synopsis

The Charlestown Main Limestone of the upper Dinantian (Brigantian) Lower Limestone Group was deposited in an intracratonic basin undergoing differential subsidence. In the eastern Midland Valley two areas of increased susidence are recognized, the Fife-Midlothian Low and the Central Low, separated by an area of reduced subsidence, the Burntisland High, centred on West Lothian and Central Fife. The Charlestown Main Limestone forms the base of a typical Yoredale cyclothem and the area of deposition was flanked to the NW and NE by fluvio-deltaic systems.

Five distinct lithofacies are recognized within the Charlestown Main Limestone (CML); bioclastic wackestones, argillaceous lime mudstones, mottled limestones, bioclastic grain-stone/packstones and carbonate buildups. Bioclastic wackestones are present at the base of the CML throughout the eastern Midland Valley. However, distinct regional differentiation of lithologies followed: buildups and bioclastic grainstones and packstones developed on, or near, the Burntisland High whereas fine terrigenous material (introduced from the flanking fluvio-deltaic systems) preferentially accumulated in the bounding lows where the CML is dominated by more argillaceous lithologies (the argillaceous lime mudstone and mottled limestone lithofacies). Progradation of prodeltaic muds from the NE curtailed carbonate deposition earlier in East Fife and accounts for the thinning of the CML towards this area. In distal areas, such as Midlothian, this progradation was heralded by an influx of fine terrigeneous sediment reflected in an increasingly argillaceous upper part of the limestone.

Eustasy appears to have been the primary control on the deposition of the Charlestown Main Cyclothem: sea level rise resulted in transgression and initiation of carbonate sedimentation while delta progradation, which curtailed carbonate production, was probably triggered by a sea-level fall. Differential subsidence and autocyclic processes (such as major channel avulsion) were secondary factors and controlled the distribution and thickness of lithofacies within the limestone and the nature of the overlying deltaic sediments.
The structure of the Skye lava field
Authors: England Richard W.
Published: January 2010

Synopsis

A new map and interpretation of the structure of the Skye lava field and its offshore continuation are presented. Onshore the base of the lavas is synclinal with a NW–SE axis resulting from loading-induced subsidence. The development of later N–S- to NE–SW-trending folds, including the offshore Canna Basin, is consistent with movement, during the Oligocene, on N–S- to NE–SW-trending faults controlling the structure of the Sea of the Hebrides Basin. Deposition of Oligocene sediments within the Canna Basin resulted in burial of potential hydrocarbon source rocks to depths of
c.
2.3 km.
The derivation and definition of the ‘Southern Upland Fault’: a review of the Midland Valley – Southern Uplands terrane boundary
Authors: Floyd J. D.
Published: January 2010

Synopsis

Although the Southern Upland Fault (SUF) is widely recognized as a major Caledonoid crustal structure in south Scotland, the derivation of the term ‘SUF’ has never been definitively established. The historical background to the naming of the fault is discussed and a definition proposed for the Southern Upland Fault (
sensu strictu
). Traced towards both the SW and NE, the SUF (
ss
) is represented by multiple fault traces, each the locus of a particular phase of 102ement. The evidence for the correlation of each fault is reviewed and recommendations for future fault nomenclature proposed. It is concluded that the Stinchar Valley Fault (Pyet Thrust) – SUF (
ss
) – Firth of Forth Fault line represents the original terrane boundary between the Southern Uplands and the Midland Valley of Scotland.
A sulphur isotope study of iron sulphides in the late Precambrian Dalradian Ardrishaig Phyllite Formation, Knapdale, Argyll
Authors: Hall A. J. , Boyce A. J. , Fallick A. E.
Published: January 2010

Synopsis

The origin of sulphur in iron sulphides occurring in siliceous and chloritic metasediments of the Ardrishaig Phyllite Formation of Knapdale, Argyllshire, was assessed using sulphur isotope analysis. The formation lies within the Argyll Group of the late Precambrian Dalradian Supergroup. Iron sulphide textures indicate an early metamorphic generation of pyrrhotite, while pyrite porphyroblasts grew at a late stage of regional metamorphism. Preferential association of iron sulphides with certain lithologies indicates that the sulphide accumulations are of original synsedimentary origin, even though there have been several stages of remobilization.
δ
34
S values range from − 14.8 to − 6.3‰ (
n
= 18;
x
= − 11.7‰). The values are rather low for the sulphur to be of magmatic or hydrothermal origin which is also unlikely from geological considerations. Since the sulphur isotopic ratio of seawater sulphate during Ardrishaig Phyllite times would have been between + 30 and +40‰, the isotopic fractionation of about 40–50‰ is too large to be explained by abiogenic reduction of original evaporitic sulphates on metamorphism. This isotopic fractionation is consistent with the sulphides originating by bacterial reduction of sulphate within marine sediments of general high permeability with ample replenishment of seawater.
The Ordovician genus
Thamnograptus
Hall 1859 (Graptolithina)
Authors: Strachan Isles
Published: January 2010

Synopsis

The description of thecal dimorphism in the graptolite
Thamnograptus
Hall by Finney (1980) has led to the rehabilitation of the genus which Bulman at one time regarded as possibly non-graptolitic. The genus was widely recorded from the south of Scotland at the end of the last century but there is no modern account. The Scottish specimens were referred to two different species by Lapworth (1876) but no formal description was ever provided and a re-examination of old collections does not show any consistent differences which could be taken as specific. The stratigraphical range of the genus appears to be quite short, mainly
Nemagraptus gracilis
Zone, so it may be of use in correlation when found.
Taphonomy of fish beds from the Upper Flagstone Group of the Middle Old Red Sandstone, Caithness
Authors: Hamilton R. F. M. , Trewin N. H.
Published: January 2010

Synopsis

The taphonomy of Devonian lacustrine fish-beds from The Upper Flagstone Group of the Middle Old Red Sandstone of Caithness has been studied at Holborn Head and Lythmore near Thurso. The beds of carbonate/organic laminites are dominated by
Osteolepis panderi
and contain less common
Thursius, Dipterus, Mesacanthus
and
?Diplacanthus.
The abundance of
O. panderi
may reflect opportunistic expansion of a species in the absence of a large predator. Mass mortality horizons within the fish beds are associated with bundles of dolomitic laminae. Articulation of preserved carcasses of
Osteolepis
is best in the central parts of the beds, deposited in low energy conditions in the deepest lake phase. A preferred orientation of carcasses between 150° and 180° is ascribed to weak currents caused by seiches or lake overturn. The similarity of the fish beds at the two localities is such that they are probably lateral equivalents.
Pseudomorphs after ikaite in a glaciomarine sequence in the Dalradian of Donegal, Ireland
Authors: Johnston J. D.
Published: January 2010

Synopsis

Ikaite, calcium carbonate hexahydrate (CaCO
3
.6H
2
O) has been reported from several localities world-wide in periglacial and glaciomarine settings. The mineral has been documented forming in seawater and lakewater at temperatures close to 0°C, but inverts to calcite at higher temperatures. Widespread occurrences of pseudomorphs after ikaite have been described from the geological record in glacial sequences. An isolated occurrence of similar pseudomorphs in Precambrian Dalradian rocks on the Garvellach Islands has been noted. A newly discovered occurrence in the Skelpoonagh Bay Limestone of the Appin Group Dalradian in south Donegal is reported here. This is in exactly the same part of the stratigraphy as the Garvellach example, suggesting that there may have been widespread development of pseudomorphs after ikaite within the Dalradian basin. The Donegal examples are preserved as slightly ferroan dolomite pseudomorphs up to 40 mm in length in a matrix of calcite. The occurrence of these structures immediately beneath the Dalradian Boulder Bed is consistent with its widely accepted glacial origin.
The geochemistry of Llandovery and Wenlock age K-bentonites in the Southern Uplands
Authors: Pearce R. B.
Published: January 2010

Synopsis

A stratigraphical and geochemical investigation of Silurian age K-bentonites from the Central and Southern belts of the Southern Uplands of Scotland indicates temporal differences in both the prevalent type of magmatism and possible tectonic settings. The data support current evidence of peralkaline to high-K subalkaline within-plate volcanicity during Llandovery times. However, new analyses of Wenlock age K-bentonites from the Raeberry Castle Formation in the Southern Belt indicate a predominantly calc-alkaline volcanic arc source for these ash deposits. This Wenlock age volcanism coincides with a pause, or slowing down, in subduction prior to closure of the Iapetus Ocean during the Late Silurian times.
The structure and affinities of
Lapworthograptus grayae
(Lapworth, 1876)
Authors: Zalasiewicz Jan
Published: January 2010

Synopsis

The graptolite
Lapworthograptus
(formerly
Cyrtograptus
)
grayae
is redescribed. Evidence for branching is reassessed: two specimens (one the type) show somewhat equivocal evidence for the development of secondary branching, and in both instances the secondary ‘cladia’ appear to come from the upper part of the protheca, rather than from the thecal aperture as is normal. The distal thecae are folded back on themselves, with everted apertures which face proximally to proximo-dorsally; they are unlike those of the other branched monograptid genera
Cyrtograptus, Diversograptus, Sinodiversograptus
or
Barrandeograptus.
They resemble rather those of the monograptid species
singularis
and
knockensis,
and these graptolites are here assigned to the genus
Lapworthograptus
Bouček and Přibyl, 1952 (type species
L. grayae
). The genus
Prochnygraptus
Přibyl and Štorch, 1985 (type species
P. singularis
) therefore becomes a junior synonym of
Lapworthograptus. L. grayae, knockensis
and
singularis
occupy a shorter, and younger stratigraphic interval than previously thought, the
crenulata
to
spiralis
Biozones of the upper Telychian. Thus derivation of these species from previously postulated upper Aeronian ancestors seems unlikely.
Lapwortho-graptus
may have a streptograptid origin or, alternatively, could have originated via a
Monograptus crispus–Monograptus wimani
lineage late in the Telychian; this is suggested by an indication that
grayae
has biform thecae, as some isolated proximal ends bearing enrolled thecae, associated with the type and other material, may belong to this species.
Depositional setting of Permian and Upper Carboniferous strata of the Thornhill Basin, Dumfriesshire
Authors: McMillan A. A. , Brand P. J.
Published: January 2010

Synopsis

Data from the field and Survey boreholes show the Coal Measures (Westphalian) in the Thornhill Basin to comprise an attentuated sequence of paralic strata in which restricted marine faunal assemblages, including representatives of the Vanderbeckei and Aegiranum Marine Bands, have been recognized at four horizons. The Thornhill Basin developed under an extensional regime as a result of dextral displacement on structures of Caledonoid (NE–SW) trend. However, intermittent normal dip-slip displacement on these faults caused uplift of the Southern Uplands, relative to the Midland Valley and Northumberland Basin, resulting in limited Dinantian sedimentation and only intermittent marine access during the Namurian. More sustained subsidence occurred during Westphalian time. Late Carboniferous to early Permian rifts along re-activated NW–SE-trending faults acted as foci for basaltic volcanicity prior to the deposition of sheetflood breccias and accumulation of desert dune sands. Oxidation beneath the late Carboniferous to early Permian land surface was responsible for reddening of the Coal Measures and replacement of coal.
A multiple till sequence near Ellon, Grampian Region: T. F. Jamieson’s ‘indigo boulder clay’ re-examined
Authors: Hall A. M. , Jarvis J.
Published: January 2010

Synopsis

Jamieson in 1906 described an ‘indigo boulder clay’ lying beneath younger glacial deposits in the Ellon area, Grampian Region. A pitting survey has revealed that this unit (the Pitlurg Till) lies beneath Late Devensian glacial and glacifluvial deposits (the Hatton Till and the Kippet Hills Gravels and Sands) and rests on a basal till (the Bellscamphie Till). The Pitlurg Till contains palynomorphs of Kimmeridge Clay age and shows weak northerly fabrics, suggesting ice transport from the Moray Firth. Amino acid ratios for sparse included shells indicate that the Pitlurg Till is younger than Oxygen Isotope Stage 7 and may post-date Stage 5e. The Bellscaphie Till lies beneath weathered gravels at Tillybrex and probably predates Stage 5.
Late Devensian meltwater movement and storage within the Ochil Hills, central Scotland
Authors: Russell Andrew J.
Published: January 2010

Synopsis

This study examines the origin and significance of spectacular bedrock channel forms and sedimentary sequences in the Ochil Hills, central Scotland. Channels and terraces form a discontinuous system extending 4 km from the main Forth valley into central Glen Devon via Glen Quey. It is suggested that as the Ochil Hills emerged above the Late Devensian ice sheet, large amounts of glacial meltwater flowed into the ice free area mainly from the margins of the Forth valley glacier. Meltwater entered Glen Devon via a series of deeply incised meltwater channels passing into a large ice-dammed lake with an overflow into Glen Eagles. Boulder-sized sediment forming a large delta confirms the tremendous erosional and transport capacity of flows entering the former ice-dammed lake. Glaciofluvial and glaciolacustrine sedimentation within the Ochil Hills was very sensitive to changes in ice-margin position and ice thickness due to the configuration of outlet spillways and cols. The Ochil Hills therefore acted as a major storage area for meltwater during deglaciation. The release of such stored meltwater may have taken place suddenly resulting in high magnitude floods or jökulhlaups whose erosional and depositional effects may have extended beyond the immediate area.
Mineral magnetic analyses of glacial diamicts from the Midland Valley of Scotland
Authors: Walden J. , Smith J. P. , Dackombe R. V. , Rose J.
Published: January 2010

Synopsis

Mineral magnetic measurements are applied to samples from Late Devensian glacial diamicts from the Midland Valley of Scotland to assess the effectiveness of the mineral magnetic approach as a tool for sediment provenance indication. The results indicate that the magnetic mineral assemblages within the diamict sediments are strongly related to the underlying and up-ice lithologies and suggest ice-flow directions from west to east. Such inferences are consistent with published data on ice-flow patterns based upon other evidence (clast lithology, diamict matrix colour, drumlin orientations, striations, etc.). These data also stress the need for measurements of mineralogical or chemical components to be made on a particle size specific base.
Palaeomagnetic investigation of organic-rich lacustrine deposits, Middle Old Red Sandstone, Scotland
Authors: Plaster-Kirk Lisa E. , Elmore R. D. , Engel M. H. , Imbus S. W.
Published: January 2010

Synopsis

Organic-rich lacustrine carbonate laminites and mudstones in the Old Red Sandstone (middle Devonian) from the Orcadian Basin, Scotland, contain a magnetization that resides primarily in magnetite. After removal of a modern viscous magnetization at low demagnetization temperatures, a southerly and shallow Late Carboniferous component (before tilt: decl = 184°, incl = −5°,
k
= 36, α
95
= 7.3,
n
= 12 sites) is removed between 100 and 450°C in most specimens. A regional fold test on the shallowly dipping rocks is inconclusive, but suggests a post-folding time of remanence acquisition. A few specimens also contain a northerly and shallow component interpreted as the antipodal equivalent of the southerly and shallow direction. Rock-magnetic studies performed on representative specimens suggest that the remanent magnetic carrier is single domain, non-interacting magnetite. Partial anhysteretic remanent magnetization measurements indicate a wide range of grain sizes. The southerly component is interpreted as a Late Palaeozoic chemical remanent magnetization (CRM). The association between the CRM and the organic-rich source rocks suggests a remagnetization mechanism related to diagenesis of the hydrocarbons.
Photographic evidence for slope-current activity, Hebrides Slope, NE Atlantic Ocean
Authors: Howe J. A. , Humphery J. D.
Published: January 2010

Synopsis

Evidence from sea-bed photographs and current-meter data from the Hebrides Slope, indicates that there is a slope-current flowing northward along the bathymetric contours in water depths of 500–1100 m. Structures identified from photographs include: asymmetric linguoid ripples, scours, crag-and-tail structures and current-induced smoothing of the seabed in fine- to medium-grained contourite sands. Bioturbated hemipelagite muds are characterized by populations of the brittle-star
Ophiocten.
The densities of these decrease with increased current activity, suggesting that the organism is sensitive to stronger flows. Current-meter data reveal peak flows of 15–25 cm s
−1
at depths of 1035 m and 457 m, in a north-north-easterly direction, with little depth stratification through the water column, but with fluctuations in velocity and possible tidal oscillation. The current is probably of Eastern North Atlantic Water origin, flowing northwards along the eastern margins of the Rockall Trough.
Regional implications of micropalaeontological and palaeo-environmental investigations of the early Eocene interval in BGS borehole 90/3, offshore NW Scotland
Authors: Hitchen K. , Jolley D. W. , Harland R. , Jones J. M.
Published: January 2010

Synopsis

In BGS borehole 90/3, drilled 110 km NNW of Cape Wrath, the lowermost interval (96.00–187.50 m below sea bed) consists mainly of claystone, with subordinate sandstone and silt-stone. Lignite is present in thin
in situ
bands and as derived clasts. Other organic debris is also common. The sandstone is predominantly volcaniclastic. Some local reworking is evident. Preliminary dinoflagellate cyst analysis suggested a Late Cretaceous age for this interval, but this was incompatible with the sediment characteristics and known palaeogeography. Low vitrinite reflectance values obtained from the organic matter (average 0.25) were also inconsistent with some of the dark spore colours observed. Further palynology has confirmed an early Eocene age (Balder Formation/Beauly Member equivalent). The older marine dinoflagellate cysts (of McIntyre Suite affinities) have been reworked into a younger deltaic environment which was receiving eroded Late Cretaceous material as well as locally and contemporaneously derived organic, plant and volcanic debris.
The Colonsay Group and basement–cover relationships on the Rhinns of Islay, Inner Hebrides
Authors: Muir R. J. , Fitches W. R. , Maltman A. J.
Published: January 2010

Synopsis

Detailed mapping on the Rhinns of Islay has prompted a revision of the stratigraphy of the lower part of the Colonsay Group (Neoproterozoic). Previously unrecorded metasedimentary rocks exposed along the SE coast rest upon and are intersliced with the Rhinns Complex (Palaeo-proterozoic basement). These metasedimentary rocks, here termed the Octofad Sandstone Formation, are considered to represent the lowest preserved part of the Colonsay Group. On the central-west side of the Rhinns, the Colonsay Group comprises four formations (Eilean Liath Grit, Kilchiaran Phyllite, Rubha Gaidhealach Grit and Rubha na h-Airde Moire Phyllite) with a total stratigraphical thickness of
c.
550 m. The stratigraphy is repeated by large-scale NE–SW-trending upright folds. The basement-cover contact in central-west Islay is a major tectonic dislocation, here termed the Kilchiaran Shear Zone. An unknown thickness of stratigraphy has been excised along this contact. There has also been extensive basement–cover interslicing along the SE coast of the Rhinns.
The Moniaive Shear Zone: a major zone of sinistral strike-slip deformation in the Southern Uplands of Scotland
Authors: Phillips E. R. , Barnes R. P. , Boland M. P. , Fortey N. J. , McMillan A. A.
Published: January 2010

Synopsis

The Moniaive Shear Zone is a recently delineated major zone of enhanced ductile deformation (up to 5 km wide) within the Southern Uplands of Scotland. The northern margin of the zone coincides with the Orlock Bridge Fault at the boundary between Ordovician and Silurian grey-wackes. Outwith the shear zone, the greywackes are typically weakly deformed, with the regional S1 fabric being developed within mudstone interbeds. Within the shear zone, Silurian Gala Group greywackes are deformed by locally pervasive linear and planar fabrics which yield a consistent sinistral sense of shear. The shear-zone fabric, in general, dips steeply towards the NW with its strike being sub-parallel to that of the regional S1 cleavage. Detailed petrological and micro-structural studies have demonstrated that the Moniaive Shear Zone comprises several zones of high strain enclosing lenticular domains of relatively low strain. The relationship between the Moniaive Shear Zone and the Cairnsmore of Fleet Granite indicates that the main phase of ductile movement on the zone occurred prior to 392 Ma although the exact age of ductile deformation on the shear zone is uncertain.
Rare earth element geochemistry of Lower Palaeozoic turbidites in the British trans-Iapetus zone: provenance patterns and basin evolution
Authors: Williams T. M. , Henney P. J. , Stone P. , Lintern B. C.
Published: January 2010

Synopsis

Rare earth element (REE) signatures provide a potentially powerful tool for evaluating the provenance and tectonic setting of turbidites throughout the geological record. The acquisition of REE data for the Southern Uplands of Scotland may thus assist in resolving uncertainties regarding the depositional regime and evolution of this important Lower Palaeozoic turbidite sequence. In this paper REE spectra for a comprehensive stratigraphic suite of Southern Uplands greywackes are presented. These highlight a juvenile volcanogenic component (probably derived from a southerly source and deposited in a back-arc environment) in the Leadhills Group and northern part of the Gala Group, conspicuous by the lack of a Eu/Eu* anomaly. A more evolved ‘granitic’ REE signature, showing distinct affinities to the Lake District Windermere Supergroup, is evident in the southern sector of the Gala Group and the Hawick Group. These results are compatible with structural models which indicate a transition from a back-arc basin to a foreland basin during the mid–late Llandovery closure of the Iapetus Ocean. Comparisons between the Southern Uplands data and the REE signatures of modern turbidites from a variety of tectonic settings are of some value for determining the nature of the Lower Palaeozoic depositional environment. However, the approach must be used with caution in view of the clear temporal adjustments of sedimentary REE signatures resulting from changing crustal evolution processes on timescales ranging from 10
6
to 10
9
years.
The Glas Bheinn Appinitic Complex, Glen Roy: a model for foliation development during emplacement
Authors: Phillips E. R. , May F.
Published: January 2010

Synopsis

The Glas Bheinn Appinitic Complex forms part of a suite of Silurian calc-alkaline igneous intrusions exposed in the Glen Roy area. The complex comprises three main components: (1) horn-felsed schist and schist breccia; (2) quartzite and quartzite breccia; and (3) a suite of mafic and ultra-mafic, variably foliated and/or lineated appinitic intrusive igneous rocks. Emplacement of the complex post-dated the main tectonothermal history of the country rock, which is entirely of Leven Schist (Appin Group), and predated the intrusion of the Ben Nevis Dyke Swarm. A four stage model for the emplacement of the Glas Bheinn Complex has been erected: (1) development of a breccia pipe with minor amounts of ultramafic material; (2) compaction and consolidation of the breccia; (3) intrusion of the dioritic (appinitic) magma; and (4) crystallization and foliation development within the appinitic diorites. A detailed petrological study indicates that fabric development within the appinitic igneous rocks occurred in response to the heterogeneous collapse of a primocryst framework prior to full crystallization, probably in response to deformation associated with continued forceful intrusion. The residual melt expelled during this process migrated into regions of low strain and crystallized as leucocratic domains within the appinitic diorite. Initial results suggest that final equilibration of the plagioclase–K-feldspar–amphibole assemblage occurred at temperatures of
c.
500°C (±60°C).
The faunas of the Albany Group in the Girvan area, and their palaeogeographical implications
Authors: Rushton A. W. A. , Tunnicliff S. P. , Tripp R. P.
Published: January 2010

Synopsis

The Albany Group, off-shelf equivalent to the Barr Group of the Girvan cover-sequence, yields mid-Ordovician faunas from its constituent Doularg and Craigmalloch formations. The Doularg faunas have been largely described; they are shelly assemblages typical of the Laurentian margin and are correlated with the North American Whiterock Series. Some new trilobite discoveries are reported. The fauna of the Craigmalloch Formation is described here, and consists mainly of pandemic graptolites of the
Nemagraptus gracilis
Biozone, but includes two trilobites known principally from peri-Gondwanan sites; their occurrence on the Laurentian margin confirms that deep-water trilobites make poor indicators of faunal provinces.
The geology of the Succoth–Brown Hill mafic–ultramafic intrusive complex, near Huntly, Aberdeeenshire
Authors: Gunn A. G. , Styles M. T. , Rollin K. E. , Stephenson D.
Published: January 2010

Synopsis

The Succoth–Brown Hill Intrusion is a deformed mafic-ultramafic body exhibiting multiple phases of recrystallization and alteration as a result of regional metamorphism and shearing deformation associated with the Portsoy Lineament. It comprises dominantly metagabbro within marginal belts of ultramafic rocks, the latter commonly rich in clinopyroxene. The effects of late brittle faulting and attendant hydrothermal alteration are superimposed locally on the sheared lithologies. Primary magmatic features are rarely preserved.

The gross structure of the complex, deduced from field mapping, ground magnetic surveys and diamond drilling, has been modelled as a series of sheets steeply dipping to the SE. New gravity observations have revealed a local residual anomaly of about 7 mGal which indicates that the intrusion could extend to a depth of 2.5 km.

A comparison of lithological, mineralogical and structural features with those of the nearby Huntly Intrusion reveals many contrasts. It is suggested that the two intrusions are not related, having been derived from magmas of different compositions. A structural separation of the two bodies is indicated by the geophysical data. Furthermore, the much simpler history of alteration and deformation in the Huntly Intrusion suggests that the Succoth–Brown Hill Intrusion may be an earlier body.
Landform–sediment distributions within the northern part of the Younger Dryas Highland ice-field, Scotland
Authors: Bennett Matthew R.
Published: January 2010

Synopsis

The aim of this paper is to describe the landform–sediment distribution within the northern part of the Highland ice-field, which existed in the Scottish Highlands during the Loch Lomond Stadial or Younger Dryas. Strong spatial variations in the distribution of both subglacial and ice-marginal landforms are described. The role of geology and variations in the dynamics of this former ice-field are discussed as possible explanations for the observed patterns.
The thermal aureole of the Lochnagar Complex: mineral reactions and implications from thermal modelling
Authors: Goodman S. , Lappin M. A.
Published: January 2010

Synopsis

The Caledonian Lochnagar Complex in the NE Highlands of Scotland comprises a central granite and earlier marginal quartz diorites. Contact metamorphism of the Dalradian country rocks has caused a thermal overprint on upper amphibolite facies regional metamorphic assemblages. Distinctive assemblages in metapelites and amphibolites can be mapped across the aureole, showing that the thermal effects are greatest where the marginal quartz diorites occur. Mineral chemistry in the metapelites can be related to contact metamorphic reactions and to a change in bulk rock chemistry due to partial melting of the metasediments in the high-grade parts of the aureole. Amphibolites within the aureole show no evidence of partial melting; their mineral chemistry is controlled by contact metamorphic reactions.

The form of the aureole is a function of the different phases of intrusion, and mathematical modelling has been applied to distinguish between different intrusive scenarios. It is likely that two phases of contact metamorphism, related to early quartz diorite and later granite intrusion, were necessary to produce the highest grades of metamorphism. Mismatch between the modelled aureole shape and that observed in some areas is probably due to enhanced local heat flow and the lateral extension of the intrusion below the present erosion level.
The geology and evolution of the Ballachulish Igneous Complex and Aureole
Authors: Pattison David R. M. , Harte Ben
Published: January 2010

Synopsis

The Ballachulish Igneous Complex and Aureole is one of the world’s most intensively studied plutonic-metamorphic complexes. The 412 ± 28 Ma igneous complex was emplaced at a depth of about 10 km in regionally deformed and metamorphosed mica schists, quartzites and siliceous carbonates belonging to the Dalradian Supergroup. The intrusion is exposed over an area of
c.
7.5 × 4.5 km
2
and is roughly cylinder-shaped to about 4 km beneath the surface, with the exception of two areas where the intrusion lies shallowly beneath the country rocks. The intrusion consists of an outer orthopyroxene-bearing diorite shell (emplacement temperature
c.
1100°C) surrounding a central body of granite (emplacement temperature
c.
850°C), the latter emplaced when the central portion of the diorite was still partially molten. A small, late leucocratic body in the centre of the granite is associated with weak Cu–Mo mineralization. The different intrusive phases represent separate magma batches which underwent little physical or chemical interaction during emplacement. A well-developed contact aureole surrounds the intrusive complex. Isograds in pelitic rocks, the most abundant rock type in the aureole, can be mapped around the intrusion and range from development of cordierite ‘spots’ (c. 550°C) up to anatectic migmatization (700–800°C). Isograds in siliceous carbonates rocks range from development of talc (< 480°C) up to periclase formation (c. 750°C). In the quartzites, recrystallization and coarsening of clastic quartz occurs, and clastic feldspar grains develop a high-temperature structural state, as the contact is approached. The agreement of the sequence and spacing of isograds in pelites, siliceous carbonates and quartzites with equilibrium phase diagrams indicates no significant kinetic control on the positioning of isograds, although some metamorphic processes appear to have been kinetically controlled. The contact metamorphism was mainly caused by intrusion of the diorite phase, with the later granite having little effect. Variations in width of the aureole are mainly due to variations in shape of the intrusion, temperature of the different intrusive phases, and the relative proportions of quartzite and pelite in the country rocks. The duration of the contact metamorphic event, for temperatures above conditions of the cordierite isograd (c. 550°C), was about 500 ka, whereas rocks were hot enough to be partially molten (temperatures above ca. 660°C) for about 270 ka. With the exception of some extensively fluid-fluxed partial melting on the west flank of the complex (Chaotic Zone), fluid communication between the intrusion and aureole was generally limited. Fluid fluxes in siliceous carbonates from the inner aureole on the east flank ranged from 100–1000 moles fluid cm
−2
. There is no evidence for the development of a large-scale hydrothermal circulation system.
The Sigmundur Complex, a ?Tertiary igneous centre in the northern Rockall Trough
Authors: Ritchie J. D. , Hitchen K. , Edwards J. W. F.
Published: January 2010

Synopsis

Seismic reflection data have revealed the presence of a large dome-like volcanic structure in the northern Rockall Trough, known as the Sigmundur Complex. The complex comprises a single, nearly circular platform marked by scarp edges, with some evidence for intra-basalt sequence reflectors, representing the original depositional attitude of former lava flows, dipping away from an eroded central volcano. The complex is mostly buried beneath Lower Eocene–Recent sediments although the culmination of the structure does crop out at sea bed. A free-air gravity anomaly over the complex reaches a peak value of +600 gu. Gravity modelling suggests the presence of a large mafic plutonic mass immediately underlying the volcanic pile. The intrusion possesses an asymmetric shape with a sloping top and base at depths of 2.4–3.0 km and 24.8–25.4 km respectively. The diameter increases downwards from 3.6–7.2 km at the top to 14.5–21.1 km at the base.
Mineralogy, geochemistry, provenance and sodium metasomatism of Torridonian rift basin clastic rocks, NW Scotland
Authors: van de Kamp P. C. , Leake B. E.
Published: January 2010

Synopsis

Closed-basin
deposits of the Stoer Group and Diabaig Formation were locally derived from Lewisian felsic and mafic rocks in semi-arid to temperate climates. For
open-basin
deposits of the Applecross and Aultbea Formations, provenance was Grenville-age rocks and older Pro-terozoic and Archaean rocks in Laurentia, west of the rift basin.

Petrography shows that detrital Ca-plagioclase, K-feldspar, and matrix clays were albitized during diagenesis. Evaluation of geochemical data for Stoer and Torridonian Group sedimentary rocks indicates widespread sodium metasomatism in these rocks. For the very sodic Stoer Group sandstones and siltstones, containing as much as 6% Na
2
O, up to 2–3% Na
2
O was added, during diagenesis, to the detrital sediments. Similar Na-metasomatism occurred in the Diabaig and Cailleach Head sandstones. The meta-somatic process involved evaporative concentration of salts in closed basin groundwaters yielding Na-rich brines which reacted with detrital silicates to develop authigenic albite. Calcium, released from detrital plagioclase during diagenesis, is resident in authigenic epidote or calcite, depending on local
p

CO
2

. During metasomatism, potassium minerals were replaced by albite and the liberated K was incorporated into illite-mica in shales. Granulite facies provenance is indicated for some of the clastics by K/Rb of 465–1295, much higher than common crustal K/Rb values.

In
open-basin
deposits of the Applecross and Aultbea Formations, low abundances of Fe, Mg, Co, Cr, and Ni indicate little mafic and/or ultramafic rock in the source area. Petrography indicates that these immature sediments include some recycled sedimentary or metasedimentary rocks and were developed in a temperate-humid climate where moderate weathering removed considerable plagioclase from the source rocks prior to transport and deposition.
The origin and significance of sheet joints in the Cairngorm granite
Authors: Glasser Neil F.
Published: January 2010

Synopsis

The development of sheet joints parallel to topographic surfaces is a characteristic of granitic rocks. These sheet joints are well developed in the granite of the Cairngorm Mountains. Both preglacial and glacial origins have been proposed for these joints and their genesis i s an area of considerable uncertainty. In this study, a quantitative analysis of joint characteristics of the granite sheets in the Cairngorm Mountains was undertaken. Sheet joints can be divided into two distinct categories: a first set of near-horizontal sheets parallel to the upper plateau surfaces of the area and a second, steeply dipping set developed parallel to the walls of glacial troughs. Both the near-horizontal and the steeply dipping sheet joint s contain the same set of primary structural joints. In all localities the sheet joints lie parallel to the surrounding topography, suggesting that they represent unloading surfaces. The near-horizontal sheets are interpreted as the result of gradual surface lowering through the Quaternary, whilst the steeply dipping sheets exposed in trough walls may be the result of more rapid erosion during Quaternary glaciations.
The Ben Nevis Intrusive Ring Tuff, Scotland: re-interpretation of the ‘Flinty Crush Rock’ as part of an ignimbrite conduit in the roots of an ancient caldera
Authors: Burt R. M. , Brown P. E.
Published: January 2010

Synopsis

Intermittently exposed around the margins of the Ben Nevis volcanic pile is a thin (< 5m) rhyolite with a well developed magmatic flow foliation that includes rock previously described as ‘flinty crush rock’. Previous models for the development of this ‘flinty crush rock’ suggested that it developed as a result of intense mechanical shearing during subsidence of the volcanic pile into the underlying Inner Granite. New field, petrographic and geochemical evidence presented here, indicate that the ‘flinty crush rock’ is magmatic and part of a larger body of flow-foliated rhyolite that represents the remains of an ignimbrite conduit formed during caldera collapse. Post-eruption closure of the conduit imposed a well developed flow-foliation on the rhyolite destroying any primary pyroclastic textures. The rhyolite is compositionally identical to a small outcrop of amphibole-biotite Inner Granite, suggesting an intimate and probably co-genetic relationship between flow-foliated rhyolite and Inner Granite magmas. It is recommended that the term ‘flinty crush rock’ be abandoned and replaced by ‘Ben Nevis Intrusive Ring Tuff. This unit affords a rare opportunity to examine a ring fracture conduit associated with a caldera-forming eruption.