bluuebunny/crossref_metadata_2025 huggingface dataset:
Geological remote sensing of rocky coasts
Authors: Wadge G. , Quarmby N.
Published: May 2009

From remotely sensed images of rock surfaces at coasts it is possible to map some characteristics of different rock types. To do this a selection must be made of those parts of the image that correspond to the rock surfaces prior to interrogation of their geological information content. A comparative study of satellite-acquired multispectral Thematic Mapper data and aircraft-acquired multispectral scanner data at four test sites on the Pembrokeshire coast was made. The spatial resolution of the Thematic Mapper data (30 m) proved to be too coarse to provide any continuity of mapping over several kilometres of rock exposures, whereas the 10 m resolution of the aircraft data was adequate to do this. Using the aircraft scanner data, neighbouring Old Red Sandstone and Carboniferous (mainly carbonate) rocks could be discriminated in both three-band and principal components images. Furthermore, it proved possible to distinguish between limestone and dolomite lithologies in the Carboniferous succession and between some of the mudstones and sandstones in the Old Red Sandstone. Airborne multispectral scanning of rocky coasts is a new potential tool for geological mapping in exploration projects in which it would be best integrated with the acquisition of airborne geophysical and field geological data.
Geochemistry of bimodal amphibolitic—felsic gneiss complexes from eastern Massif Central, France
Authors: Briand Bernard , Bouchardon Jean-Luc , Ouali Houssa , Piboule Michel , Capiez Paul
Published: May 2009

High-grade basic and acidic meta-igneous rocks are widespread in the bimodal amphibolitic—felsic gneiss complexes, which are characteristic formations of the ‘Middle Allochthonous Unit’ from eastern and southern French Massif Central. The metabasites from the Lyonnais and Doux complexes are chemically diverse and range from N-MORB type tholeiitic to transitional types. The two populations are not related by fractional crystallization or crustal contamination processes and their chemical characteristics reflect differences in their mantle sources. An ensialic setting is supported by the crustally-derived character of some of the associated felsic rocks, but the presence of N-MORB-type metabasites argues for an extensional environment. This bimodal association compares well with the magmatism of rifted continental margins and may reflect a transitional stage between continental rifting and oceanic crust formation during the Cambro-Ordovician spreading event.
The age and correlation of Skiddaw Group (early Ordovician) sediments in the Cross Fell inlier (northern England)
Authors: Cooper A. H. , Molyneux S. G.
Published: May 2009

The Skiddaw Group in the Cross Fell inlier comprises the Catterpallot Formation of latest Tremadoc or earliest Arenig age, the Murton Formation of Arenig age, and the Kirkland Formation of early Llanvirn age. Each of these formations can be correlated with formations in the Skiddaw Group of the Lake District. The faulted contact of the Catterpallot and Kirkland formations is the probable extension of the Causey Pike Fault (CPF), which separates two distinct sequences in the Skiddaw inlier of the northern Lake District. Contrasts across the CPF in the Cross Fell inlier reflect those seen in the Skiddaw inlier. The CPF is a major basement structure, separating markedly different successions in the Ordovician strata of northern England.
Chemical and stable isotope fractionation in manganese oxide—phosphorite mineralization, Timna Valley, Israel
Authors: Bar-Matthews Miryam , Matthews Alan
Published: May 2009

Element, carbon and oxygen isotope fractionations have been studied in laminated deposits, manganese nodules and phosphorite lenses in clastic sediments of the Cambrian Timna Formation, southern Israel. Comparisons of element abundances show that only manganese, phosphorus and uranium were mobilized and concentrated during diagenesis: element fractionations among the diagenetic manganese components particularly resemble those observed in present-day suboxic pelagic marine sediments. Epigenetic processes involving reducing solutions reversed the diagenetic geochemical trends, with the redox-sensitive elements manganese and uranium showing considerable depletions in nodules, and iron and lead showing corresponding enrichments. The manganese oxides of nodules have calculated δ18O compositions varying from –1.6 to 3.1 ‰. These compositions are significantly lower than a δ18O value of 7.9 ‰ obtained for the manganese oxides of an ocean floor nodule and are taken to largely represent temperature differences between the ocean floor and the shallow marine Timna conditions. Slight decreases in δ18O accompany the transformation from diagenetic type A to epigenetic type B manganese nodules; corresponding shifts to lower δ18O are also inferred for the structural carbonate of apatites. Such shifts are compatible with re-equilibration accompanying a slight temperature increase and/or low temperature meteoric-water alteration. δ13C values of –7 to –12‰ obtained for the apatites of laminated deposits and phosphorite lenses are consistent with phosphorite diagenesis in suboxic to anoxic pore-waters. Early diagenetic redox conditions are indicated to be major controls governing the development of the assemblages.
Arenig sedimentation and basin tectonics in the Harlech Dome area (Dolgellau Basin), North Wales
Authors: John-Joe Traynor
Published: May 2009

Arenig (Ordovician) clastic sediments crop out in the Harlech Dome region (North Wales), and are placed in a single stratigraphic unit: the Allt Lwyd Formation. This unit records a marine transgression onto an erosion surface produced during late Tremadoc arc volcanicity. Four discrete petrofacies are denned, and reflect differing proportions of detritus derived from Tremadoc-type basic-intermediate igneous rocks, and the local sedimentary basement. Initial shallow marine siliciclastic sandstones and conglomerates are overlain by extensive deep water mud-rich units. These generally shallow up into a complex arc-apron deposit, with sediments derived from the eroding Tremadoc arc, as well as from similar, synchronous volcanics. Predominantly epiclastic sandstones and conglomerates were deposited in deltaic and tidal environments in an arc-apron complex, and capped by condensed mudstones and an ironstone, deposited as sea level rose across these systems. Sediments were ponded in north–south orientated troughs and derived from uplifted blocks. Facies and petrofacies distribution were controlled by syn-sedimentary north-south and northeast–southwest faults. The Allt Lwyd Formation was ponded in a fault-controlled basin (theDolgellau Basin), one of a series of interconnected sub-basins flooded by the Arenig transgression. The sediments preserved reflect deposition during the transgression of a volcanic arc, prior to the extrusion of marginal basin-type volcanics.
Silurian collision and sediment dispersal patterns in southern Britain
Authors: Soper N. J. , Woodcock N. H.
Published: May 2009

The evidence is reviewed for the timing of collision between the microcontinent of Eastern Avalonia (southern Britain and adjacent areas) and the Laurentian continent. Recent palaeomagnetic results placing Eastern Avalonia in a high (50°) southern latitude in mid Ordovician time are now consistent with faunal evidence for the first time. The resulting apparent polar wander path is evaluated and suggests that Eastern Avalonia detached itself from a southern peri-Gondwanan latitude in the early Ordovician, moved northwards, and approached Laurentia by the late Ordovician. Its western corner probably impinged on Laurentia in the early Silurian and it docked against the Laurentian margin during Silurian and early Devonian time with a component of anticlockwise rotation.

This kinematic history is supported by a compilation of sediment dispersal patterns on Eastern Avalonia. A low-volume Ordovician and earliest Silurian supply from within the microcontinent was overwhelmed in late Llandovery time by a large volume of southwest-derived turbidites, probably from the uplifting impact zone to the west. This source was later augmented by a high-volume clastic supply to the north margin of the microcontinent. Eastward migration of this source through Wenlock and Ludlow time reflects the progressive anticlockwise docking of Eastern Avalonia against the Laurentian margin. The earliest sign of a large-volume supply from Baltica is in the late Wenlock, arguing against any earlier hard collision.
The ammonium content of granites in the English Lake District
Authors: Cooper D. C. , Bradley A. D.
Published: May 2009

Granitic rocks from all the exposed components of the Lake District batholith have been analysed for ammonium to look for evidence of an ammonium-rich sedimentaryprotolith. The results indicate that the ammonium content of Lake District granites is related to the type and degree of alteration experienced by the rocks. Fresh, little-altered granites from all parts of the batholith have low ammonium contents (< 30 ppm), whereas highly altered rocks contain up to 250 ppm ammonium. The most ammonium-rich rocks are highly altered specimens of Skiddaw Granite containing appreciable secondary muscovite, sericite and clay. The degree of ammonium enrichment is related to the style of alteration and host-rock lithology. Evidence for the source of ammonium is provided by strong depletion (< × 0.3) of ammonium in silty mudstones within the cordierite andgarnet hornfels zones of the Skiddaw Granite aureole. In view of the low ammonium content of some sediments and the losses known to accompany high-grade metamorphism and associated dehydration, the low primary ammonium contents of the granites are not considered to be evidence either for or against a sedimentary protolith.
Syntectonic alluvial fan sedimentation, southern Pyrenees
Authors: Nichols G. J.
Published: May 2009

The Aguero fanglomerate body developed in late Oligocene to early Miocene time at the northern margin of the Ebro Basin where the emergent southern Pyrenean thrust front created a topographic high. Tectonic activity in the thrust belt strongly influenced the sequences and structures within the fan deposits. The fan deposits display an initial coarsening-up sequence. Intraformational unconformities subdivide the proximal sediments into a series of wedges. These result from a continued uplift along the thrust front during the initial stages of fan development. A major intraformational unconformity marks the top of this sequence and the start of a fining-up sequence. Further tectonic activity in the thrust front is indicated by a syn-depositional synclinal fold which decreases in amplitude up sequence. Rejuvenation of fan sedimentation to form a second coarsening-up sequence reflects renewed activity in the thrust front. This second sedimentation event resulted in a plus 200 m thickness of massive conglomerates. The geographical limits of fan sedimentation can be determined because the fan deposits are lithologically distinct from the other Ebro Basin molasse in the area. The area of the drainage basin of the fan can also be estimated by consideration of the clast types present in the fan deposits. The fan and drainage basin areas are estimated to be 6 km2 and 10 km2 respectively.
Palaeoenvironmental setting of the Kangdian area, southwest China, in Proterozoic Datian–Meidang time
Authors: Fuxing Wang
Published: May 2009

Numerous acritarchs and stromatolites have been discovered and studied from the Proterozoic Datian Formation of the Kunyang Group and the Meidang Formation of the Dongchuan Group in Sichuan–Yunnan area, southwestern China, and more than 80 oxygen isotope data have been obtained from the sediments. Based on size-range and variation of non-filamentous acritarchs, the development of columnar stromatolites and the 18O/16O values of stromatolitic and nonstromatolitic carbonate rocks, the author proposes, for the first time, a palaeoenvironmental framework of the Kangdian area during Datian–Meidang time.

Although the usefulness of Precambrian acritarchs and oxygen isotope values in palaeoenvironmental analysis of a sedimentary basin is just beginning to be understood, it is evident that these data are an important basis for palaeoenvironmental studies.
Supposed Precambrian trace fossils from Jersey, Channel Islands
Authors: Bland B. H. , Evans G. , Goldring R. , F.R.S A. E. Mourant , Renouf J. T. , Squire A. D.
Published: May 2009

abstract

SIR - Squire (1973) described and figured fossil burrows, ascribed to Sabellarites, from the Upper Proterozoic Brioverian Jersey Shale Formation of Jersey, Channel Islands. The meander-like structures are from calcisiltite beds within a turbiditic sequence and were collected from low intertidal reefs. Re-examination by all of us of one of Squire's specimens (Jersey Museum, La Hougue Bie, SJM C 2026; Squire, 1973, plate 1 a) and more decisive material (SJM C 1002, 5 specimens), collected later from the same reefs by Stéphane Rault, confirms that the structures are attributable to modern polychaetous annelids, almost certainly to Polydora sp., an attribution with which Dr J. D. George (Head, Polychaeta Section, British Museum (Natural History)) concurs. Polydora is associated with a wide range of substrate preference, constructing borings in hard calcareous substrates, pseudoborings on the inside of shells and true burrows in loose sediment. In the Jersey material the irregular, but quite typical, U-form tubes have been formed along open joint planes with slight dissolution of the rock, or along thin calcite-filled veins, also with dissolution of the rock. The joints occur at all angles to the bedding. Very pertinent is the attitude of the tubes, which is principally normal to the rock surface rather than to the bedding. No tubes have been seen on freshly broken surfaces and in no instance has a tube been seen to enter the rock, though there are numerous moulds of pyritic concretions which happen to be of about the same diameter as the width of the tubes. Lithothamnium sp. is patchily distributed over the rock surface and locally penetrates into the joints, showing that they were open.
The Tarskavaig Nappe of Skye, northwest Scotland: a re-examination of the fabrics and their kinematic significance
Authors: Law R. D. , Potts G. J.
Published: May 2009

Early petrofabric studies of quartz c axis preferred orientation within the Tarskavaig Nappe, located at the southern end of the Moine thrust zone, have been interpreted as indicating that structures within the nappe have been produced by tectonic movements acting at right angles to those responsible for formation of structures within the overlying, but immediately adjacent, Moine Nappe. Such a dramatic contrast in inferred transport direction has not been recognized within the rest of the thrust zone.

Re-examination of the microstructures and c axis fabrics within mylonitic metasediments from the western part of the Tarskavaig Nappe has revealed that these tectonites are characterized by maximum principal extension axes which trend sub-parallel to the WNW-trending Moine thrust zone transport direction. Later folding has reorientated and modified these structures within the eastern part of the nappe producing fabrics which have erroneously been taken to indicate a transport direction orientated sub-perpendicular to that of the rest of the Moine thrust zone.

WNW-trending maximum principal extension axes and WNW-directed overthrust senses are indicated by microstructures within schists from the adjacent Moine Nappe, suggesting that structures within both the Tarskavaig and Moine nappes may be associated with a common west-northwest transport direction.

Essentially coaxial (pure shear) strain paths (indicated by symmetrical c axis fabrics) dominate the internal parts of the Tarskavaig Nappe. Close to the base of the nappe, non-coaxial strain paths, originally associated with WNW-directed overthrusting, are indicated by asymmetrical c axis fabrics and oblique grain shape alignments. Strain compatibility considerations indicate that the lower kinematic domain (which must either be contemporaneous with, or later than, formation of the upper domain) must be characterized by a combination of pure and simple shear deformation.
Fans and fan deltas – precursors to the Armorican Quartzite (Ordovician) in western Iberia
Authors: McDougall N. , Brenchley P. J. , Rebelo J. A. , Romano M.
Published: May 2009

The Armorican Quartzite (Lower Ordovician) is a very extensive sandstone body found throughout a large part of Iberia and Brittany; similar quartzites are present in north Africa and elsewhere. In Iberia it generally lies unconformably on a thick, folded, late Precambrian to Cambrian turbidite sequence (the Complexo Xisto-Grauváquico (CXG)), but there are some places where the quartzite has a conformable relationship with the underlying CXG. Where conformable the whole succession shows varied facies sequences including: (i) a regressive mud–sand sequence as a precursor to the main quartzite development, (ii) submarine fan sediments of the CXG passing up into slope and then shallow marine facies, or (iii) fluvially influenced breccio-conglomerates of a marginal fan delta passing up into shallow marine sediments.

The inferred development of alluvial fans associated with fan deltas prograding into shallow marine environments implies steep slopes and the likelihood that faulting controlled some of the uplift. The mozaic pattern of differential uplift and subsidence throughout the region suggests that the CXG was affected by local block movements rather than by regional folding.

The presence of upstanding blocks during the initial sedimentation of the Armorican Quartzite suggests that the quartz sand might have been derived from multiple sources dispersed throughout the area rather than from sources along a single shoreline at the margin of the depositional area.
A trepostome bryozoan from the Lower Arenig of south Wales: implications of the oldest described bryozoan
Authors: Taylor Paul D. , Cope John C. W.
Published: May 2009

A specimen of the trepostome bryozoan Orbipora from the Lower Arenig of south Wales is described and figured. This is currently the oldest unequivocal bryozoan recorded in the literature. Although mostly decalcified, the colony preserves clear remnants of the large styles which characteristically indent the zooecial apertures in Orbipora. The wide palaeogeographical distribution of Orbipora in the early Ordovician is consistent with the hypothesized planktotrophic larval phase. Theoretical considerations and evidence from the occurrence of Orbipora in south Wales suggest that nearshore clastic environments would be fruitful settings in which to search for further early bryozoans, although quality of preservation may be poorer than in offshore carbonates.
A model for stratigraphic and metamorphic inversions at Sulitjelma, central Scandes
Authors: Boyle A. P.
Published: May 2009

The relationship between disposition of metamorphic isograds and early strain history is examined for the Sulitjelma Fold Nappe of the central Scandes. Evidence for stratigraphic inversion and the widespread inversion of the garnet isograd is reviewed, and new evidence for the nature of early Scandian deformation is presented. A two-stage model is presented which explains the inversions by (i) an initial phase of horizontal compression resulting in crustal thickening by vertical stretching during closure of a marginal basin, followed by (ii) continued horizontal compression and crustal thickening by eastward-directed nappe emplacement. The emplacement of the Sulitjelma Fold Nappe during the latter phase of progressive simple-shear-dominated deformation was accompanied by the development of sheath fold geometries and the overturning of isotherms to produce the widespread inversion of the garnet isograd.
A trilobite fauna from the highest Shineton Shales in Shropshire, and the correlation of the latest Tremadoc
Authors: Fortey R. A. , Owens R. M.
Published: May 2009

A rich fauna dominated by trilobites and calcified chordates has been collected in Shropshire from the Arenaceous Beds, the highest member of the Tremadoc Shineton Shale Formation, and hitherto regarded as poorly fossiliferous. This fauna shows that shelf conditions persisted longer in Shropshire than has been supposed. It is likely that even younger Tremadoc is cut out at the unconformity below the Caradoc in the Shineton Inlier. The correlation of the later Tremadoc is reviewed, and the nomenclature of British Tremadoc biozones is revised. The trilobites described here are a mixture of previously known and new forms. The nameShumardia (Conophrys) salopiensisCallaway is revived for British material traditionally assigned to the Scandinavian speciesShumardia pusilla(Sars), from which it is distinct. The new taxaLitagnostus meniscussp.nov.,Apatokephalus sarculumsp.nov. andSkljarella cracenssp.nov. are described. The type species ofAsaphellus, A. homfrayiandLeptoplastides, L. salteri, are redescribed, andGeragnostus callavei, Pseudokainella impar, andParapilekiasp. are recorded. New information on the ontogeny ofS. (C.) salopiensisandA. homfrayiis given.LitagnostusandSkljarellaare recorded from the British Isles for the first time.
A ‘reg’ palaeosol from the Lower Triassic of south Devon: stratigraphic and palaeoclimatic implications
Authors: Wright V. P. , Marriott S. B. , Vanstone S. D.
Published: May 2009

A ‘reg’-type palaeosol occurs at the top of the Lower Triassic Budleigh Salterton Pebble Beds at Budleigh Salterton, south Devon. Its morphology supports the idea that such soils form by the introduction of wind blown fines below a surface stone layer by a process of wetting–drying and crack formation. The degree of profile development indicates a prolonged period of pedogenesis, corresponding to a major stratigraphic break. The palaeosol formed under arid conditions, and represents a change in climate during Scythian times from a semi-arid to arid regime.
The middle Lanna/Volkhov Stage (middle Arenig) of Sweden and its conodont fauna
Authors: Löfgren A.
Published: May 2009

In the established European conodont zonation theParoistodus originalisZone represents an interval in the upper middle Arenig or middle Lanna/Volkhov Stage. I have so far found it at 14 Swedish localities, represented in my collections by more than 116 000 conodont elements from 79 limestone samples. Presence/absence data together with major frequency shifts among conodont taxa allow the recognition of five successive phases within theP. originalisZone and the corresponding chron. Phase 1 occurs in the basal part of the zone, where an increase in frequency ofTriangulodus brevibasisandP. originalisdistinguishes it from immediately subjacent beds. Phase 2 corresponds to the (transgressive) lower middle part of the zone with an influx ofPeriodon, andDrepanoistodus basiovalisreplacingD. forceps. Phase 3 is equivalent to the upper middle part of the zone with generally more than 30% of the zonal denominator and withMicrozarkodina parvareplacingM. flabellum. Phase 4 is a short (regressive) event where the frequency ofParoistodusis drastically lowered, and phase 5 corresponds to the upper part whereParoistodusagain increases. The zone is particularly well represented at Lanna, Province of Närke, in south-central Sweden, where it also seems possible to connect the conodont succession with the standard trilobite zonation. Thus, at Lanna as well as at Finngrundet in the Bothnian Bay,Megistaspis (M.) simonfirst appears in the basal lower middle part of theP. originalisZone.
A late ultramafic suite in the Kap Edvard Holm layered gabbro complex, East Greenland
Authors: Tegner Christian , Richard Wilson J.
Published: May 2009

The Kap Edvard Holm Complex is an early Tertiary layered gabbro situated on the western side of the Kangerdlugssuaq fjord. Layered olivine gabbros in the Taco Point area are cut by several wehrlitic sill-like bodies which comprise a late ultramafic suite. An intrusive wehrlitic facies in the inner part of the bodies consists of olivine (+minor chrome-spinel) orthocumulate with clinopyroxene oikocrysts and interstitial plagioclase, kaersutite and phlogopite. A replacive facies which occurs in the marginal zones is texturally similar to the intrusive facies but contains no chromespinel and is more feldspathic, varying from a melanocratic olivine gabbro to a feldspathic wehrlite. It occurs where the sills wedge out laterally, in the lower contact zones where finger structures are widely developed, and in the upper contact zones where wehrlitic pipes feed melanocratic sheets, called parasol structures, which preferentially follow mafic layers in the host olivine gabbro. The wehrlites formed by the intrusion of hot, hydrous, ultrabasic magma into consolidated layered olivine gabbro. The replacive facies was formed by the volume for volume metasomatic replacement of olivine gabbro; dissolution of plagioclase was accompanied by crystallization of olivine. Some clinopyroxene was initially resorbed and later reprecipitated during this process. The relatively dense pore magma migrating upwards was restricted to pipes and spread out laterally when it encountered readily replaced mafic layers, while below the sills gabbro was replaced en masse and finger structures were formed. Similar late ultramafic suites occur in ophiolites, and their presence in the Kap Edvard Holm Complex supports suggestions that it acted as an ocean ridge type magma chamber during the initiation of early Tertiary sea floor spreading in the North Atlantic.
A new geological map of the Brabant Massif, Belgium
Authors: De Vos W. , Verniers J. , Herbosch A. , Vanguestaine M.
Published: May 2009

A new geological map, mostly subcrop, of the Brabant Massif is presented, based on a revised lithostratigraphy of the outcrop area and on recently acquired palaeontological and lithological data from boreholes in the concealed area. New interpretations of magnetic and gravity data are used to extend the lithostratigraphical units into areas with few or no boreholes. A structural model of the western, northern and southern parts of the Brabant Massif is presented. The main anticlinal axis plunges towards the west-northwest, its core comprising Upper Precambrian (?) to Lower Cambrian terrigenous rocks which outcrop in the southeast. To the north of the main axis, younger rocks appear in regular succession, but to the southwest this picture is complicated by the occurrence of a second anticlinal structure and by a subparallel magmatic arc.
Subduction-related magmatism of late Ordovician age in eastern England
Authors: Pharaoh T. C. , Brewer T. S. , Webb P. C.
Published: May 2009

Deep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.
Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain
Authors: Thorpe R. S. , Gaskarth J. W. , Henney P. J.
Published: May 2009

Lamprophyre sills and dykes of Ordovician age were emplaced within Cambrian–Lower Ordovician sedimentary rocks around the northern margins of the Midlands Microcraton. The intrusions show internal mineralogical and chemical variations indicating emplacement as multiple intrusions of co-magmatic pulses. The chemical characteristics of the lamprophyre magmas indicate formation by small-degree volatile-rich partial melting of lithospheric mantle enriched and modified by Lower Palaeozoic subduction (Th/Ta 5.3–11.6, La/Ta 29–82.3), together with a contribution from within-plate mantle source (Zr/Yc. 6) and/or mineralogically heterogeneous lithosphere, followed by varying degrees of fractional crystallization during uprise.
Silurian fades beneath East Anglia
Authors: Woodcock N. H. , Pharaoh T. C.
Published: May 2009

Core material from proven or probable Silurian sedimentary rocks beneath East Anglia has been re-examined. Four recognizable facies probably represent an environmental transition from anoxic basin slope or outer shelf through oxygenated outer shelf to storm-dominated inner shelf. This transition could have occurred laterally, from east to west across the Anglian Basin, or in time, from Llandovery (early Silurian) up to Př (late Silurian). Partial biostratigraphical constraints allow either interpretation, but the regional setting favours a marked facies transition through time as the Anglian Basin shallowed prior to the Acadian Orogeny. Reddening of the Silurian is mostly secondary beneath the sub-Triassic unconformity.
The early Palaeozoic evolution of northwest England
Authors: Cooper A. H. , Millward D. , Johnson E. W. , Soper N. J.
Published: May 2009

The Lake District and smaller Craven inliers of northwest England contain a Lower Palaeozoic sequence deposited on the Gondwanan side of the Iapetus Ocean, close to the junction with the Tornquist Sea. The Tremadoc to Llanvirn Skiddaw and Ingleton groups are deep water assemblages of turbidite, olistostrome and slump deposits, formed at a continental margin. They experienced uplift and erosion as a precursor to the eruption of two largely subaerial Llandeilo-Caradoc volcanic sequences: the tholeiitic Eycott Volcanic Group in the north and the calc–alkaline Borrowdale Volcanic Group in the central Lake District. The volcanic episodes are the earliest part of a major episode of magmatism, extending through to the early Devonian and responsible for a major batholith underpinning the Lake District. Subsidence in an intra-arc rift zone preserved the subaerial volcanic sequences. A marine transgression marks the base of the Windermere Group, which comprises a mixed carbonate–clastic shelf sequence of Ashgill age, passing upwards through the Silurian into a thick, prograding foreland basin sequence of Ludlow turbidites. Deformation of the Lower Palaeozoic sequences was possibly diachronous from north to south. It is attributed to the late Caledonian (Acadian) Orogeny and resulted in folding, cleavage and thrust development. Granitic intrusions, including those at Shap, Skiddaw and beneath the hydrothermal Crummock Water Aureole, are partly syntectonic and were therefore penecontemporaneous with this deformation event. Some thrust faulting post-dates the intrusive phase. Post-deformation Devonian conglomerates are also present locally.
Preliminary report on the geochemistry and mineralogy of the Nod Glas and related sediments (Ordovician) of Wales
Authors: Temple J. T. , Cave R.
Published: May 2009

Preliminary results are reported of geochemical and mineralogical studies on the Nod Glas sediments of Caradoc age (clingani-linearis biozones) in Wales. Results are based on sampling at three localities in North Wales, together with a coeval section in South Wales. Data have been obtained for 21 elements by ICPAES, and for organic C, S and ignition loss. XRD analysis has provided semi-quantitative data on abundances of muscovite 2M1, quartz, albite and chlorite. Mean values of K2O, organic C, S, Cu, Zr and Ba are higher in the Nod Glas than in adjacent strata, while Fe203, MnO, MgO, CaO and P205 are lower. Analogy with the chemical composition of modern sediments reinforces the interpretation of the Nod Glas as being deposited under dysaerobic to anaerobic bottom conditions. There is considerable variation in composition between different Nod Glas sections. Analysis of mineral/chemical relationships shows some consistencies: for example, chlorite shows significant positive correlations with the heavier transition elements Mn to Zn, as well as with Li and Mg, presumably due to enrichment by adsorption of these elements onto subsequently recrystallized smectites. Other relationships are less consistent: organic C is correlated with muscovite (where it is probably held in interlayer sites as a relic from a smectite precursor) and sometimes also with albite. Inconsistencies between the sections in mineral/element interrelations may be due to diagenetic/metamorphic changes.
The use of kink bands to constrain fault displacements: an example from the Bala Lineament, Wales
Authors: Pratt W. T.
Published: May 2009

The Bala Lineament is a major NE-SW-striking fault zone that crosses the Lower Palaeozoic Welsh Basin. The southwest segment of it, the Tal-y-llyn Fault, mostly lies within a tract of Ordovician mudstones with few marker bands. Consequently, post-Caledonian (early Devonian) displacements are poorly understood. However, there is a close link between the distribution of kink bands and the fault zone. The kink bands provide information about the contemporary stress conditions and, in combination with slickensided fractures, give qualitative information about the various fault displacements. Matching of major folds across the fault suggests approximately 3–4 km of dextral strike-slip, probably of Lower Carboniferous age. A younger episode of normal faulting, perhaps related to Mesozoic extension, was accompanied by kink bands with more brittle characteristics.
The Nod Glas décollement of the Welsh Basin
Authors: Pratt W. T.
Published: May 2009

Structural, petrographic and metamorphic evidence is presented for localized end-Caledonian (Acadian) décollement within a ‘black shale’ formation in the central Welsh Basin, close to the Caradoc–Ashgill boundary. Similar detachments are probably widespread in other parts of the, paratectonic Caledonides with upright folds and cleavage, particularly in sequences with strong viscosity contrasts.
The post-Devonian tectonic evolution of southern Spitsbergen illustrated by structural cross-sections through Bellsund and Hornsund
Authors: Mann A. , Townsend C.
Published: May 2009

Construction of cross-sections in Bellsund and Hornsund, southern Spitsbergen, using offshore and onshore structural data illustrate the main tectonic units of the region. From west to east these are: a wedge of late Cenozoic clastic sediments; a series of late Palaeozoic to early Mesozoic grabens controlled by basement faults along the west Spitsbergen margin; the Basement Horst, comprising late Precambrian to early Palaeozoic rocks deformed and metamorphosed during a mid-Palaeozoic orogeny; the Fold Belt, which forms a narrow NNW–SSE striking zone of eastward verging folds and thrusts attributed to Eocene inversion of a pre-Cenozoic basin; the Palaeogene Central Basin, deformed into a broad synclinorium and bound to the east by the Billefjorden Fault Zone. This basement lineament shows evidence of Palaeogene reactivation and may be linked to the Fold Belt by a detachment zone beneath the Central Basin. East of Spitsbergen, there is an offshore basin of possible Carboniferous age controlled by the Storfjorden Fault Zone which shows evidence of later inversion to form a positive flower structure.
Partial thermal resetting of 40Ar/39Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism
Authors: Dallmeyer R. D.
Published: May 2009

Hornblende and muscovite within high-grade Caledonian metamorphic rocks exposed in Albert I Land (northwest Spitsbergen) display internally concordant 40Ar/39Ar age spectra providing no record of any post-Silurian thermal history. Both minerals record 420−425 Ma plateau ages indicating that relatively rapid cooling followed Silurian metamorphism. Muscovite within some metamorphic sequences exposed within the Tertiary tectonic zone of Oscar II Land (west-central Spitsbergen) displays a low-temperature 40Ar/39Ar age spectra discordance suggestive of a slight, post-Caledonian thermal disturbance. This is consistent with a post-Palaeozoic thermal overprint documented elsewhere in Oscar II Land and indicates that, at least locally, metamorphism may have accompanied the Tertiary orogeny.
Mesozoic extension versus Tertiary compression along the Billefjorden Fault Zone south of Isfjorden, central Spitsbergen
Authors: Haremo Pål , Andresen Arild , Dypvik Henning
Published: May 2009

The Billefjorden Fault Zone displays a complex tectonic history going back into Precambrian times. Observed thickness variations within Mesozoic sequences across the fault zone have previously been related to Mesozoic extensional movements along the fault zone. Recent structural, stratigraphical and sedimentological investigations suggest that the thicknessvariation observed across the fault zone is due to Tertiary compressional tectonics, and that Mesozoic extensional movements are minor or nonexistent.Tertiary deformation is characterized by a combined thin-skinned/thick-skinned structural style. Thin-skinned thrusting is due to the development of décollement zones in the Jurassic/Cretaceous Janusfjellet Subgroup and in the Triassic Sassendalen Group. Thick-skinned faulting is related to reverse faulting along a steep, east-dipping fault rooted in the pre-Mesozoic basement. Interacting thin-skinned thrusting and thick-skinned faulting has resulted in out-of-sequence thrusting, and is responsible for the thinning of Mesozoic sequences across the fault zone.
The Lower—Middle Cambrian stages and stratotypes from the Iberian Peninsula: a revision
Authors: Liñán E. , Perejón A. , Sdzuy K.
Published: May 2009

Lower-Middle Cambrian regional stages of the Iberian Peninsula (Cordubian, Ovetian, Marianian, Bilbilian, Acadoparadoxides and Solenopleuropsidae stages) are now reconsidered in the light of new stratigraphic and palaeontological (trace fossils, trilobites and archaeocyaths) studies. These stages are re-described with selected stratotypes and chronostratigraphic boundaries. The names Leonian and Caesaraugustian are formally proposed to replace the provisional stages of Acadoparadoxides and Solenopleuropsidae, respectively. A correlation chart of the Lower-Middle Cambrian lithostratigraphic units from the Iberian Peninsula is also presented. Two regessive-transgressive cycles are proposed to explain the lithological and palaeontological peculiarities through the Lower-Middle Cambrian sequence in the Iberian Peninsula.
Distribution and tectonic setting of Ordovician K-bentonites in the United Kingdom
Authors: Huff W. D. , Merriman R. J. , Morgan D. J. , Roberts B.
Published: May 2009

Twenty-five Ordovician K-bentonite samples ranging in age from Llanvirn to Ashgill and representing both sides of the lapetus suture were analysed by INAA and XRF and compared on magmatic and tectonic discrimination diagrams. The proportional distribution of Nb, Y, Ti, Zr, Hf, Ta, Th and REE indicates that source volcanics were erupted in a setting that changed from subduction-related in the Llanvirn/Llandeilo to marginal basin extensional volcanism in the Caradoc/Ashgill. Welsh K-bentonites appear to be derived from volcanoes within the Welsh Basin, but K-bentonites from the Southern Uplands to not have characteristics consistent with a fore-arc setting, further suggesting a source related to ensialic marginal basin extensional volcanism.
The internal tectonic fabric of minor intrusions and their potential as regional palaeostress indicators
Authors: Borradaile Graham J.
Published: May 2009

A suite of late-tectonic minor intrusive rocks in the Inner Hebrides of Scotland show a well developed internal tectonic fabric. This fabric has a similar orientation in adjacent intrusions and it is usually not seen in the wall rock. It is suggested that the intrusions' tectonic fabric records the effects of palaeostress over the cooling period of the intrusions and thus provides palaeostress trajectories over a geologically short period of time over the area occupied by the swarm of intrusions.
Field evidence for turbulence during flow of basalt magma through conduits from southwest Mull
Authors: Kille I. C. , Thompson R. N. , Morrison M. A. , Thompson R. F.
Published: May 2009

The swarm of Palaeocene inclined sheets around Loch Scridain in southwest Mull includes basaltic sheets which contain abundant metasedimentary xenoliths that show evidence for having been partially molten. In contrast with the majority of dyke-like conduits worldwide, which have essentially planar margins, the contact of one of these xenolithic sheets with Moine metasediments is irregular along a segment where it crosses interbedded psammites and pelites. Relatively fusible mica schists have been excavated by the magma, on either side of a massive refractory quartzite horizon. Furthermore, the dolerite of the sheet shows only a slight reduction of grain size, through a zone 0.5 m wide, adjacent to its margin, in contrast with the pronounced marginal chilling which characterizes most intrusions of the Loch Scridain swarm. These field relationships are interpreted as evidence that the basic magma which formed this sheet flowed with local turbulence during its emplacement. The estimated liquidus of the magma (1130 °C at 1 atm) is approximately 200 °C above the solidus of pelitic horizons in the country rock, but far below the solidus of the quartzites.
The geological significance of some Triassic microfossils from the South Orkney Islands, Scotia Ridge
Authors: Dalziel I. W. D. , Elliot D. H. , Jones D. L. , Thomson J. W. , Thomson M. R. A. , Wells N. A. , Zinsmeister W. J.
Published: May 2009

Late Triassic Radiolaria have been recovered from a bedded chert collected early in 1977 in the South Orkney islands. This is the first reliable palaeontological evidence for the age of the so-called basement complex that forms most of the exposed rock of a microcontinent on the southern limb of the Scotia Ridge. The fossils place a lower limit on the age of deformation of at least part of the complex as post-Karnian or Norian. The basement is overlain by undeformed Jurassic to Cretaceous conglomerates, which suggests this event took place during the early Mesozoic Gondwanian orogeny.

The new data are consistent with the interpretation that the basement complex of the South Orkney Islands represents part of a subduction complex and was accreted to the Pacific margin of Gondwanaland during the late Triassic or early Jurassic time.
The application of trend surface analysis to directional data
Authors: Shakesby R. A.
Published: May 2009

Trend surface analysis has been used widely in geology and geomorphology but only rarely has it been applied to directional data. This neglect stems from the inapplicability of normal trend surface procedures to such data. An adaptation of normal trend surface procedures specifically designed for use with directional data is, however, available as a FORTRAN IV computer program. This technique is described and its usefulness in generalizing regional patterns of flow is illustrated by applying it to data representing ice flow direction in Central Scotland.
Quartz-albite rocks of ash-fall origin
Authors: Leitch Evan C.
Published: May 2009

Thin beds composed mainly of quartz and albite occur interstratified with epiclastic rocks in a thick marine Early Permian sequence in the eastern part of the New England Fold Belt, eastern Australia. The sequence has suffered very low grade regional metamorphism and the quartz-albite rocks retain few primary textural features. A pyroclastic origin for these rocks is argued on the basis of inherited sedimentary characters and their distinctive mineralogical and chemical composition, and it is suggested that they accumulated as glass-rich ash-fall tuffs. The present chemical composition of the quartz-albite rocks suggests the tuffs may have initially altered to zeolitic assemblages. Similar quartz-albite rocks, perhaps misidentified as chert or siliceous siltstone, probably occur in other low-grade metamorphic sequences, the progenitors of which accumulated adjacent to active magmatic arcs.
The Ordovician proetacean trilobiteRorringtonia
Authors: Owens R. M.
Published: May 2009

New, well-preserved material of the Ordovician proetacean trilobiteRorringtonia, hitherto of uncertain taxonomic position, indicates that it belongs to the aulacopleurid subfamily Scharyiinae. It also elucidates the position of another problematic proetacean,Analocaspis, which is now considered to be congeneric withRorringtonia.
Irumide and post-Mozambiquian plutonism in Malawi
Authors: Haslam H. W. , Brewer M. S. , Darbyshire D. P. F. , Davis A. E.
Published: May 2009

Rb-Sr whole-rock isochron ages of 443 ± 30 Ma, 449 ± 42 Ma and 489 ± 14 Ma with initial 87Sr/86Sr ratios of 0.70669 ± 0.00068, 0.70599 ± 0.00035 and 0.70658 ± 0.00025 were obtained, respectively, for the Cape Maclear granite, the surrounding Cape Maclear syenite and the Senga Bay granitic body. The results confirm previous estimates of the age of the post-Mozambiquian Lake Malawi Granitic Province, of which these plutons are part. Data from the Dzalanyama granite have excess scatter, but indicate an Irumide age of about 1000 Ma. This batholith is therefore much older than the Lake Malawi Granitic Province but much younger than the Nyika granite of northern Malawi, contrary to earlier suggestions. The porphyritic foliated granite of Mcezi Hill gave an age of 1016 ± 55 Ma and an initial ratio of 0.70522 ± 0.00084. Irumide plutonism in the region includes several dissimilar groups of intrusions, all with low initial87Sr/86Sr ratios. The Irumide age of the Dzalanyama granite makes it possible that the metasediments of the Mchinji Group are wholly post-Ubendian.
Partial melting of semipelite and the development of marginal breccias around a late Caledonian minor intrusion in the Grampian Highlands of Scotland
Authors: Platten I. M.
Published: May 2009

A water saturated melt was developed in the semipelitic Leven Schist in contact with the kentallenitic basic rocks of the Barnamuc intrusion. The partly melted rock consisted of a small volume of granitic melt with relict refractory quartz grains and layers of aluminosilicates. This material could be mobilized and mixed with phenocryst-bearing magma. Sheets of country rock breccia are associated with the mobilization and veins of breccia and mobilized hornfels invade the intrusion. Sheets of igneous rock occur along the contact zone and their emplacement is related to the mobilization of the hornfels. Loss of cohesion between solid country rock and crystallized outer parts of the plug leads to collapse and removal of early formed igneous rocks, accounting for the lack of chilled margins in some intrusions.
Obtaining English translations of Russian publications in the Earth Sciences - an English view
Authors: Miles P. J. S.
Published: May 2009

A course of action is described for obtaining an English translation of a Russian geological text. It is suggested that the Russian ‘language barrier’ in this field is largely psychological.
The double cone fracture in flint
Authors: Williams D. J.
Published: May 2009

This work proposes a mechanism for the formation of the characteristic ‘double cone’ cracking and ‘bulb of percussion with bulbar scar’ cracking caused by the artificial fracture of flint. The double cone fracture is observed as a large, small apex angle, cone that is truncated by a smaller cone of increased apex angle. The author considers that the large narrow apex angle truncated cone of the fracture is caused by Hertzian loading of the flint on impact and the upper complete cone is formed as a result of the unloading of the stressed flint. This mechanism has been deduced from work carried out in the fractography of glass by others and from some restricted laboratory experiments.