bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformational behaviour of migmatites and problems of structural analysis in migmatite terrains
Authors: McLellan Eileen
Published: May 2009

An understanding of the response of migmatites to deformation is crucial to an interpretation of their structures, and in anatectic and intrusive migmatite terrains due consideration must be given to the modification of deformation processes imposed by melts. In partially molten systems containing more than 30% melt the classical theories of fold formation are inapplicable; the folds produced are of the ‘viscous fold’ type. Their geometry is unpredictable and may mimic structures due to refolding; this is particularly true at very high degrees of melting where flow of melt carrying rafts of solids begins. Failure to distinguish ‘viscous folds’ from the products of refolding will lead to errors in interpreting the structural and metamorphic history of an area, and to consequent misinterpretation of the true structural relations between geometrically complex high-grade and more regularly deformed low-grade areas.
Thermal metamorphism of the Silurian strata of the Oslo region, assessed by conodont colour
Authors: Aldridge R. J.
Published: May 2009

The colours of conodont elements recovered from Silurian limestones in the Oslo region, Norway, range from brown to grey. Samples from the south of the region contain black and grey conodonts, indicative of high palaeotemperatures. There is a general decrease in thermal metamorphism towards the north, with the lowest palaeotemperatures recorded from Toten, Ringsaker and parts of the Ringerike district. There is a close correlation between thermal metamorphism and the proximity of Permian intrusions.
Two new Ordovician graptolites from Bolivia
Authors: Finney S. C. , Branisa L.
Published: May 2009

Two new graptolite species from the Ordovician of Bolivia are described. These species, Maeandrograptus bolivianus n.sp. and Gymnograptus floweri n.sp., were probably contemporaneous with congeners from the Didymograptus hirundo Zone (Lower Ordovician) of Sweden and the lower half of the Glyptograptus teretiusculus Zone (Middle Ordovician) of Baltoscandia, respectively. This is the first report of these genera in the Western Hemisphere.

The assignment of a new species to Maeandrograptus necessitated a review and revision of that genus. As revised, it consists of M. schmalenseei Moberg, Didymograptus mobergi Törnquist, and M. bolivianus n.sp. Cymatograptus undulatus is a possible ancestor for this group of species, and an assignment of Maeandrograptus to the Sinograptidae is favoured.
The role of silica and iron oxide mobility in the formation of gold-bearing fluvial sediments in the Proterozoic Mporokoso Basin, northern Zambia
Authors: Andrews-Speed C. P.
Published: May 2009

Gold-bearing sandstone and conglomerate near the base of the Proterozoic Mporokoso Group were deposited in a braided river system. The detrital sand grade material is mainly of quartz, sericite and haematite, and the pebbles are of vein-quartz, chert, silicic volcanics, quartzose metasediment and jaspilite. The basement rocks presently exposed in the basement are silicic igneous rocks and quartzose metasediments.

The petrography of the fluvial sediments suggests that silica and, to a lesser extent, iron oxide were mobile both in the source-area and in the braided river system. Evidence for silica-mobility includes jaspilite pebbles with spherulites and glaebules of chalcedony, abundant vein-quartz pebbles, intra-basinal sandstone pebbles, and the silicification of volcanic pebbles. The detrital haematite in the fluvial sandstone forms pseudomorphs after magmatic magnetite. Authigenic iron oxide occurs in several forms which suggest that iron oxide was mobile in the source-area and in the fluvial sediments. Uranium is locally abundant in basement and sedimentary rocks, cassiterite is a common heavy mineral in the fluvial sediments, and fluorite has been found in the basement.

These features may be explained by intense weathering which mobilized both silica and iron. The silica was concentrated near the surface to form silcretes in the basement and later in the overlying fluvial sediments. Hydrothermal convection cells driven by the granites may have carried silica, iron, tin, fluorine and uranium towards the surface before and during the erosion of the igneous basement.
The sedimentology of the South Connemara Group, western Ireland – a possible Ordovician trench-fill sequence
Authors: Ffrench G. D. , Williams D. Michael
Published: May 2009

The stratigraphy of the ?Ordovician South Connemara Group is described. The group is approximately 3 km thick and includes sedimentary and volcanic rocks. The sedimentary elements of the succession include conglomerates, sandstones, shales, cherts and minor limestone breccias. The Lettermullen Formation exhibits the thickest continuous sedimentary sequence in the group. It is divided into five facies: a conglomerate facies, thick sandstone facies, medium sandstone facies, sandstone/siltstone facies, and chert facies. The sedimentary features of these rocks include channelling and grading and are described in terms of Bouma units where applicable. The coarse elements of the formation are thought to represent deposition in, or proximal to, submarine channels feeding a more distal depositional site represented by the finer elements. Igneous rocks of the group include pillowed and non-pillowed lavas, massive amphibolites and minor tuffs often in conformable contact with the sediments. Petrography of conglomerate clasts and sandstones indicates derivation from a continental source area. Palaeocurrent analysis reveals a primary easterly mode with a subsidiary northerly mode. It is suggested that the group exhibits some characteristics of trench-fill sequences and the succession may be related to similar environments within the Southern Uplands accretionary wedge.
Systematic fissuring of a matrix-dominated lodgement till at Church Wilne, Derbyshire, England
Authors: Derbyshire E. , Jones P. F.
Published: May 2009

A set of sub-vertical curving fissures in a Pennine-derived lodgement till of Wolstonian age is described from Church Wilne near Derby. The fissures are at least 5 m long and curved (radius of curvature c. 3 m) in both vertical and horizontal planes, the concavity facing SE in the direction of regional ice movement. The origin of the structures is considered in the light of a review of modes of formation of structural discontinuities in till. Origins due to stress relief following excavation, desiccation, frost action, direct ice push, ice-core meltout, compaction of the substrate and shear failure are rejected. It is proposed that the fissures were produced by point loading of a frozen till surface by englacial (basal) boulders which provided periodically high compressive stresses and induced tensional failure. Analogous fissures occur in a Devensian lodgement till in the Wirral peninsula in Cheshire. It is concluded that curved fissure sets are localized features of lodgement tills but that they may be quite widely distributed.
Primary bone and dinosaurian physiology
Authors: Reid R. E. H.
Published: May 2009

Primary compact bone is ignored in some recent discussions of claims that dinosaurs were endotherms, but forms the basis of one of the arguments from bone, and part of the basis of another. This paper explains its histology and discusses its possible significance. In dinosaurs the primary compact bone was commonly fibre-lamellar bone, resembling bone seen in many large mammals, and implying a capacity to sustain rapid growth to large sizes. This probably indicates some physiological difference between dinosaurs and modern types of reptiles; but similar bone is present in early therapsids, which were probably not endotherms, and bone with typical reptilian ‘growth rings’ was sometimes formed. Endothermy is also unlikely in most kinds of dinosaurs, if its evolution requires a trend to small sizes; but perhaps they were ‘failed endotherms’.
Kinetics of pyrope megacryst reactions in ascending basaltic magma – relevance to high-pressure magmatic crystallization at Elie Ness, East Fife
Authors: Donaldson Colin H.
Published: May 2009

The rates of resorption of pyrope in basaltic melt and of pyrope decomposition to pyroxene + melt at pressures below the stability of garnet are used to examine the proposition (Chapman, 1976) that pyrope megacrysts in the Elie Ness neck began ascent from the mantle at 1300–1450°C. Both reactions are extremely rapid at these temperatures and yet the petrographic evidence is that neither occurred. Either the transporting magma cooled extremely rapidly during ascent (> 30000 °/h) or, more likely, was considerably cooler than previously proposed. Water was a significant constituent of the magma, and a crystallization temperature for the garnet of as little as 1000 °C is possible, based on existing phase–equilibria data.
Facies variations in peralkaline ash-flow tuffs from the Kenya Rift Valley
Authors: Leat P. T.
Published: May 2009

Two late Quaternary ash-flow tuffs erupted as single flow units from the Menengai caldera volcano, Kenya, show marked facies variations. Dense welding of the tuffs close to source may have been promoted by their peralkaline trachyte compositions. Coarse, near-vent breccias are partly welded and were emplaced as lithic-rich parts of the body of pyroclastic flows. Non-welded tuff forms the bulk of the outflow sheets which include valley-fill deposits up to 520 m above the present caldera rim, indicating ash-flow generation by collapse of moderately high eruption columns. The flows overran varied topography which controlled development of ash-flow tuff facies. On hilly terrain, the flows became turbulent and separated into a lithic-rich, rapidly deposited part and a fine-grained lithic-and crystal-poor part which was subsequently deposited farther from source. Caldera walls belonging to an earlier caldera probably formed a major barrier to the spread of the second ash-flow from its site of collapse. There are many similarities in the facies variations in these peralkaline tuffs and subalkaline tuffs. Differences in welding characteristics and the shape of ash particles reflect the lower viscosity of peralkaline magma.
Morne Patates volcano, southern Dominica, Lesser Antilles
Authors: Wadge G.
Published: May 2009

Mornes Patates is the youngest volcano in Dominica occupying a depression on the southwestern flank of a larger stratovolcano, Morne Plat Pays. Within the depression an arcuate ridge, apparently of acid andesite lavas, has been cored and largely buried by the explosive emplacement of two acid andesite domes and their associated pyroclastic deposits, mainly block-and-ash flow deposits. A basaltic scoria horizon, exposed on the northern side of the depression, has a14C age of 28450 ± 1500 years B.P. and is not seen on the volcano itself, which suggests that the domes and pyroclastic rocks are younger than this. A14C age of 450 ± 90 years B.P. from a block-and-ash flow deposit from the Morne Patates dome apparently confirms this and the youthful morphology also suggests a young age. The angular shape of the depression and the steep submarine slopes are consistent with an origin as a lateral gravity slide rather than a caldera collapse. Vigorous fumarolic activity and swarms of local earthquakes suggest that magma exists at depth (several kilometres) beneath the Morne Patates–Morne Plat Pays area.
The Ordovician–Silurian boundary at Keisley, northern England
Authors: Wright A. D.
Published: May 2009

The relationships of the Keisley Limestone, an isolated carbonate mudmound in the Cross Fell Inlier of northern England, have long been problematical with respect both to the other upper Ordovician as well as the Silurian strata of the inlier. Bedded limestones, separated by gaps from the Keisley mudmound below and fromatavusBiozone graptolite shales above, yielded a prolific shelly fauna to Temple in 1968 which he regarded as being of lower Llandovery age. This age is controversial. To try to establish the precise ages of the rock units, the position of the Ordovician–Silurian boundary, and the detailed nature of the changes which took place at this boundary, a critical section was excavated. Bed by bed lithological and faunal collections reveal from beneath the knownatavusoutcrop (a) five bentonite bands, unexpected in the context of northern England, (b) graptolites of bothacuminatusandpersculptusBiozonesabovethe bedded limestones and (c) a similar but distinct assemblage from siltstones associated with these limestones which containsHirnantiaelements. From the palaeontological evidence there is little doubt that the topmost part of the carbonate sequence is of Hirnantian age.
Silurian trench sedimentation in the Southern Uplands, Scotland: implications of new age data
Authors: Kemp A. E. S. , White D. E.
Published: May 2009

Results of detailed remapping of the Kirkcudbright area in the Southern Belt of the Southern Uplands of Scotland, together with new palaeontological data, necessitate revision of the regional structure, and re-interpretation of the sedimentary history of the northwest margin of the Lower Palaeozoic lapetus Ocean. On the east side of Kirkcudbright Bay, at least six sediment-ologically and structurally distinct, subvertical tectonic blocks can be distinguished. Recognition of the Raeberry Castle Formation as a Wenlock turbidite sequence, rather than mid- to late Llandovery as previously interpreted, removes the need to postulate the existence of an axial rise and a distinct basin adjacent to the south, in mid- to late Llandovery times.
Microstructure, geochemistry and differentiation of a primary layered teschenite sill
Authors: Martin D.J.
Published: May 2009

A 22 m thick primitive, basanitoid sill comprises homogeneous olivine teschenite, overlain by picrite and a rhythmically layered sequence of olivine teschenite, salitic teschenite and syenite. Differentiation occurred in two stages by fractional crystallization, in part from melt residual from formation of picrite. Syenitic blebs and hydrated globules, occurring through the layered sequence, formed by the same mechanism rather than by immiscibility. Endothermic cindering of a small coal seam below the intrusion absorbed heat and steam from the sill, removing volatiles from the lower part and establishing a strong downward heat flux. The picrite was restricted to the upper part of the sill by more rapid cooling of the lower half.
Palaeomagnetism of the Lower Carboniferous Billefjorden Group, Spitsbergen
Authors: Watts D. R.
Published: May 2009

Palaeomagnetic data from mid to late Palaeozoic rocks are potentially valuable for testing models of the assembly of Spitsbergen and for determining the palaeo-position of parts of Spitsbergen relative to the major tectonic elements that comprised the Old Red Continent. Fine-grained red sandstones from the Tournaisian to Namurian Billefjorden Group, collected by members of Cambridge Spitsbergen expeditions, were subjected to stepwise chemical and thermal demagnetization. The characteristic magnetization is found in normal and reverse polarities and corresponds to a pole position at 23° S, 332 °E, dp = 5.7°, dm = 10.5°, which is near an early Carboniferous pole computed for the Baltic Shield-Russian Platform (Baltica). When compared to Laurentia (North America) in the context of the revised Mauch Chunk palaeomagnetic study, Spitsbergen falls a few degrees south of the Bullard reconstruction but the error of the determination of the palaeolatitude overlaps with this position. Therefore relative motion between any part of Spitsbergen and Laurentia and Baltica during the Carboniferous is not resolved.
A seismic refraction line across Norfolk
Authors: Chroston P. N.
Published: May 2009

A simple seismic refraction line some 115 km long has been made across Norfolk to provide constraints on the depth to the ‘igneous/metamorphic’ basement. Shots were fired in the Wash and off the coast near Lowestoft and attempts were made to record at approximately 2 km intervals along the line. Recording quality was only fair, resulting in incomplete coverage of the line, and this restricts the quality of interpretation. The results show a refractor of about 6.05 km s−1 revealed over the whole line with no first-arrival evidence of the 4.5–5.5 km s−1 velocity expected from Palaeozoic sediments. Using estimated velocities of 2.4 km s−1 for the post-Palaeozoic succession, 4.5–5.5 km s−1 for the Palaeozoic succession and an estimated sub-crop position of the basement on the sub-Mesozoic floor, models are produced which suggest that the Palaeozoic sediments are no more than 600–1500 m thick at the eastern end of the line, depending on the Palaeozoic velocity assumed.
Landsat MSS imagery applied to geological investigation of the Norseman area granitoid–greenstone terrain, southeast Yilgarn Block, Western Australia
Authors: Spray John G. , Burgess Lyle A.
Published: May 2009

Interactively processed Landsat MSS imagery has been used as an aid to studying the regional geology of approximately 10 800 km2 of terrain at the southeast margin of the Archaean Yilgarn Block in Western Australia. The technique proved successful in extending positions of known lithological contacts and lineaments into poorly exposed, inaccessible areas and in revealing new geological features, especially faults, previously unrecognized at ground level. During this investigation the distribution of granitoids and greenstones was more precisely defined, internal greenstone structures highlighted and three main fault trends were identified: (1) NW–NNW and (2) ENE, both within Archaean shield, and (3) NE–NNE within the transition to adjacent Proterozoic mobile belt. In order for the most information to be extracted from Landsat MSS images it is recommended that, whenever possible, image processing should follow ground-based studies as well as precede them, and that field geologist and Landsat specialist should work at the image processing system together.
Correlation of Old Red Sandstone (Devonian) outliers in the Northern Highlands of Scotland
Authors: Blackbourn G. A.
Published: May 2009

A summary has been made of the distinguishing lithological features of four sedimentary groups long recognized from the Lower and Middle Old Red Sandstone (Devonian) of the Northern Highlands of Scotland. This has led to recognition of the groups in unfossiliferous outliers to the W, permitting the correlation of these outliers with the main outcrop.
The chalky till at Barrington, near Cambridge, and its connection with other Quaternary deposits in southern Cambridgeshire and adjoining areas
Authors: Hoare P. G. , Connell E. R.
Published: May 2009

The current belief in a single chalky till glaciation of eastern England is upheld by a detailed examination of a section at Barrington which had been said to reveal two such tills. An attempt is made to arrange the glacial, periglacical and interglacial beds of southern Cambridgeshire into stratigraphic order and to place them within Quaternary stages. The study concludes with a consideration of the fabric data that were used to support the claim that two major chalk-rich tills occur in East Anglia. Till mineralization is reported in the area for the first time.
The erosion factor in the emplacement of the Keystone thrust sheet (South East Nevada) across a land surface
Authors: Johnson M. R. W.
Published: May 2009

The Keystone/Muddy Mountain thrust of South East Nevada provides a spectacular example of a thrust sheet that has travelled across the earth's surface for a distance of at least 25 km, probably as much as 50 km. Along the thrust a Palaeozoic to early Mesozoic succession (> 4 km thick) has moved over a channelled erosion surface cut into Jurassic aeolian sandstone. Clasts in the channels are stratified, with those in upper layers being easily matched with the rocks in the thrust sheet – thus the clasts ‘herald’ the approach of the sheet. The clasts are only weakly deformed by the thrusting which belongs to the Sevier-Laramide orogeny.

Erosion appears to be a significant if not crucial factor in the emplacement of the Keystone thrust sheet. Adopting an erosion rate of 1 mm/a (in accord with Alpine and Himalayan estimates) and a rate of thrusting of 5 mm/a (in accord with estimates from the Canadian Rockies) it follows that the thrust sheet was ‘half-eroded’ after travelling about 25 km.

It is concluded that large displacement (i.e. > 25 km) may be impossible without erosion and one of two ‘erosion models’ would greatly facilitate transport up to 50 km, which is the likely maximum displacement.
Deep-rooted overthrusting and blueschistic metamorphism in compressive continental margins. An example from Calabria (Southern Italy)
Authors: Piccarreta Giuseppe
Published: May 2009

At the base of austroalpine nappes in Calabria alpine greenschist dynamometamorphism is overprinted by blueschist metamorphism. Tectonic overpressures and deep-rooted movements of upthrusting type in compressive regime are the key to generation of blueschistic conditions and to greenschist-bluecschist evolution of metamorphism. The tectonic overpressures are generated because the rocks at higher confining pressures and lower pore pressures have relatively higher resistance to deformation. The evolution from greenschist to blueschist conditions results from cooling during upward motion with overpressures remaining concentrated along the thrust zones.
Petroleum Basins of the Soviet Arctic
Authors: Meyerhoff A. A.
Published: May 2009

The Soviet Arctic extends 6700 km from the border with Norway, on the west, to the border with the United States, on the east. The region contains the largest unexplored shelf area on earth – approximately 3917000 km2. Of the several onshore petroleum-bearing basins, at least two extend into the offshore – the Timano-Pechora basin, which passes beneath the Barents Sea, and the West Siberian basin, which includes much of the Kara Sea. The Laptev and East Siberian Seas seem to be underlain by separate offshore basins, possibly unrelated to any onshore. The Chukchi Sea is geologically a part of the Alaskan North Slope. The Vilyuy basin, along the Vilyuy and Lena Rivers, does not extend offshore. Only small basins are present along the Pacific shore; of these, two have petroleum potential – the Khatyrka basin which passes eastwards into the Navarin basin of the Bering Sea, and the Anadyr' basin which joins the St Lawrence basin. Peripheral to the Arctic, but of great importance relative to several Canadian Arctic basins, is the Irkutsk amphitheatre in which the main hydrocarbon accumulations are Proterozoic.

Of the three largest onshore basins, the West Siberian is the greatest, with major production from Lower and Middle Cretaceous, and smaller production from Upper Jurassic and Upper Palaeozoic rocks. The major production from the Timano-Pechora basin is from the Middle Devonian and Upper Carboniferous–Lower Permian; minor production is from the Silurian, Lower Devonian, Upper Devonian, Lower Carboniferous, Upper Permian and Triassic. Production in the Vilyuy basin – all of it gas – is from Lower and Middle Jurassic, Triassic and Permian. Although non-commercial, known potential production from the Nordvik area is from Triassic and Permian sandstones; that from the Khatyrka basin is Oligocene and that from the Anadyr' basin is Miocene. The potential of the Soviet Arctic is huge, with major oil reserves and the largest known gas reserves on the earth.
The Northern Suture, Pakistan: margin of a Cretaceous island arc
Authors: Pudsey Carol J.
Published: May 2009

The Northern Suture is a fault separating the Cretaceous Kohistan island arc terrain (northwest Himalayas) from Palaeozoic sediments of the Asian Plate to the north. The Kohistan arc includes volcanic and sedimentary rocks (andesitic lavas, tuffs, volcaniclastics, slates and limestones), metamorphosed to greenschist facies and intruded by the two-phase Kohistan Batholith. Asian continental margin sediments are mainly of shelf type, are variably metamorphosed and intruded by the Karakoram Batholith. The Northern Suture is a zone of melange from 150 m to 4 km wide, and contains blocks of volcanic greenstone, limestone, red shale, conglomerate, quartzite and serpentinite in a slate matrix. It has a strong planar fabric; but in many places bedding is preserved in blocks and matrix, and depositional rather than tectonic contacts are seen between the two. The melange is inferred to be an olistostrome largely derived from the Kohistan arc, formed in a small back-arc basin between Kohistan and Asia. Limestone blocks in the melange are dated as Aptian–Albian; post-tectonic intrusions yield radiometric ages from 111 to 62 Ma. The Northern Suture therefore probably formed in the early Late Cretaceous during closure of the back-arc basin. The Tethys ocean lay south of Kohistan, where the Main Mantle Thrust represents the westward continuation of the Indus–Tsangpo Suture.
New evidence on the South African Lower Palaeozoic: age and fossils reviewed
Authors: Cocks L. R. M. , Fortey R. A.
Published: May 2009

Trilobites from the Soom Shale, Cedarberg Formation, of the Table Mountain Group, South Africa, have been identified asMucronaspis oliniTemple, indicating a latest Ordovician (Rawtheyan–Hirnantian) age. This new data is taken as an opportunity to present new records of some non age-diagnostic brachiopods and molluscs from the area, and also to review the substantial shelly fauna from the overlying Disa Member of the Cedarberg Formation. It is concluded that that fauna is of Hirnantian age and not early Llandovery as stated by some previous authors.
Paedomorphosis and cryptogenesis in trilobites
Authors: Whittington H. B.
Published: May 2009

Stubblefield suggested that proparian trilobites may have arisen by paedomorphosis. Examples of the role of paedomorphosis in the evolution of species and of particular organs are reviewed. The cryptogenetic renewal of trilobites after the Cambrian resulted in distinctive major taxa, but their relationships to each other and to older groups remain unsolved. Similarities between early developmental stages should be re-assessed as a possible guide to relationships. The early Upper Cambrian, type species of the proparianSchmalenseeiais re-described. It was small, possibly world-wide in distribution, the exoskeleton thin, the parts not articulated, apparently forming a more or less rigid shield. It may have been a paedomorphic, planktic species, but its origin and relationships are obscure.
Marine faunas from concealed Devonian rocks of southern England and their reflection of the Frasnian transgression
Authors: Butler D. E.
Published: May 2009

Successive early Upper Devonian deposits penetrated in the Willesden No. 1 Borehole, along with their associated fossils, bear testimony to changing environments attributed to movements of the shoreline. The inferences drawn from these, and from marine-influenced deposits and faunas of similar age encountered elsewhere in the concealed strata, reinforce and refine the concept of a discrete Frasnian marine transgression. The event was probably linked with a similar, mid-Frasnian, movement in northern France.

Marine fossils have been recovered from the Downtonian–Devonian sequences of nineteen boreholes in southern England, most of which include strata referable to the Frasnian or early Famennian. A revised, Frasnian, age is suggested for deposits encountered in the Brightling Borehole and part of the Bolney succession. Upper Devonian strata with marine faunas are recognized in the Ashwell, Little Chishill and Northbrook boreholes, and late Silurian or very early Devonian at Lakenheath.
The phosphatic chalks and hardgrounds of Boxford and Winterbourne, Berkshire – two tectonically controlled facies in the late Coniacian to early Campanian (Cretaceous) of southern England
Authors: Jarvis I. , Woodroof P.
Published: May 2009

The litho-and biostratigraphy of Boxford quarry and Winterbourne pit are described in detail. Boxford quarry displays a section through parallel bedded soft white chalks and hardgrounds which dip at 25° SSE, overlain by a chalk mélange composed of displaced and deformed blocks of hardground surrounded by calcarenitic chalk. The succession is of late Coniacian to mid Santonian age and is interpreted as being the result of intra-Upper Cretaceous tectonic activity. Winterbourne pit exposes a late Santonian to early Campanian sequence of poorly phosphatic chalks and hardgrounds containing an abundant macrofauna. This deposit is the same age as, and in part similar to, the classic phosphatic chalks of northern France, to which it is compared. However, it is best explained as resulting from a continuation of the abnormal tectonic and bottom-current conditions indicated by the older, atypical chalks of the Boxford area.
Electron microscope and microprobe analysis of chlorite–mica stacks in the Wenlock turbidites, mid Wales, U.K.
Authors: Dimberline Andrew J.
Published: May 2009

Chlorite–mica stacks in the Wenlock turbidites have been studied using backscattered electron microscopy and electron microprobe analysis, combined with thin-section work and bulk rock chemical analysis. The stacks occur in fine sandstones and silt–mud turbidites and range in length from < 30 μm to 1.5 mm. They consist of interlayered packets of Fe-rich chlorite and mica.

Combined textural and chemical data suggest that many of the stacks represent altered detrital biotite micas. A four-stage alteration sequence is proposed:

(1) Subaerial alteration of biotite, in the source area, to interlayered biotite–hydrobiotite/vermiculite.

(2) Post-depositional collapse of vermiculite to form a mica phase under conditions of high K+/H+in the sediment pore waters.

(3) Decrease in K+/H+ratio, possibly due to H+ build up in the fermentation zone, causing alteration of biotite layers to chlorite.

(4) Kinking of the stacks and pressure solution of chlorite early in the development of cleavage.
Variations in platinum group element concentrations in the Alexo mine komatiite, Abitibi greenstone belt, northern Ontario
Authors: Barnes Sarah-Jane , Naldrett A. J.
Published: May 2009

The noble element (Os, Ir, Ru, Rh, Pt, Pd, Au) patterns from sulphides associated with the komatiites at the Alexo mine show variable degrees of fractionation. Massive sulphides at the contact between underlying intermediate volcanics and overlying komatiites have the least fractionated patterns (Pd/Ir = 44). Net-textured sulphides which immediately overlie the massive sulphides have extremely fractionated noble element patterns (Pd/Ir = 171). The disseminated sulphides in the overlying komatiite exhibit an intermediate degree of fractionation (Pd/Ir = 110). The variations in noble element patterns are complemented by variations in the Ni, Cu and Co concentrations. The massive sulphides are depleted in all three of these elements relative to the net-textured sulphide ore. The disseminated sulphides have intermediate values of Ni and Co, but are enriched in Cu relative to the other two sulphides.

Processes that could have affected the composition of the sulphides include: (a) fractionation of monosulphide solid solution (Mss) from a sulphide liquid during initial cooling of the komatiite, and (b) mobilization of Pt, Pd, Au, Cu, Ni and Co from the massive sulphide into footwall veins. A mass balance calculation indicates that the sum of the massive and net-textured sulphide agrees with the disseminated sulphide for all elements except Au. Thus the massive sulphide cannot have lost significant amounts of Pt, Pd, Ni and Co to footwall veins and significant mobilization of these elements does not appear to have occurred. The crystallization of Mss from a sulphide liquid will account for the enrichment of Ir, Os, Ru and Rh in the massive sulphide relative to the net-textured sulphide, and enrichment of Pd, Pt, Au, Co and Ni in the net-textured sulphide relative to the disseminated sulphide.
The age and structural setting of limestones and basalts on the Main Ring Fault in southeast Rhum
Authors: Smith N. J.
Published: May 2009

In southeast Rhum, a Mesozoic/Tertiary sequence is preserved as a fault-bounded and rotated wedge. This is juxtaposed between Precambrian rocks (Torridonian sediments and Lewisian gneiss) and caught up in the complex structure of the Tertiary Main Ring Fault (MRF), which shows three distinct phases of movement. The Mesozoic rocks comprise fossiliferous limestone, sandstone and shale, which show differing degrees of thermal metamorphism depending on their relationships to the Layered Complex. On the basis of faunal and lithological evidence the Mesozoic sediments have been correlated with the Lower Liassic Broadford Beds. The Rhum sediments are overlain by sheared Tertiary basalts, the contact between them probably representing the original landscape unconformity. The presence of these younger strata caught up along the MRF provides crucial evidence for a major phase of central subsidence in the early history of the Rhum Tertiary volcanic centre.
Isotopic and geochemical investigation of unit 10 from the Eastern Layered Series of the Rhum Intrusion, Northwest Scotland
Authors: Palacz Z. A. , Tait S. R.
Published: May 2009

Sr and Nd isotopic compositions together with whole rock Sr and Nd abundances and olivine compositions are presented for cumulates from unit 10 of the Eastern Layered Series of the Rhum intrusion, Northwest Scotland.

The results show an Nd–Sr isotopic correlation consistent with contamination by high 87Sr/86Sr, low 143Nd/144Nd crust. There is a strong correlation between the degree of contamination, Sr and Nd whole rock abundance and Fe enrichment in cumulus olivine. The allivalites are the most contaminated, while the basal peridotites are uncontaminated. This suggests that the cumulates crystallized from a primitive uncontaminated magma and the allivalites from an evolved contaminated magma. Subsequently, movement of contaminated feldspathic intercumulus liquid has perturbed the isotopic, trace element and olivine composition of the upper peridotites.
Finger structures in the Rhum Complex
Authors: Butcher Alan R. , Young Iain M. , Faithfull John W.
Published: May 2009

Finger-like protrusions of peridotite are developed on Rhum where peridotite is overlain by allivalite. These structures, which were described by Brown as ‘upward-growing pyroxene structures’, are found in the following environments: at the main intra-unit junctions; along the upper surface of subsidiary peridotites in certain allivalites; and along the lower surface of allivalite blocks in some peridotites.

The structures generally take the form of parallel-sided or tapering protrusions with circular cross-sections. The tops of fingers are conical or hemispherical in shape. Typical dimensions are: finger amplitude, 2–5 cm; finger diameter, up to 3 cm; and finger wavelength, 5–10 cm. Peridotite in the finger is modally and texturally similar to the underlying layer, varieties range from feldspathic peridotite to dunitic peridotite. In the field the fingers apparently cut through layering, laminae and lamination without any associated disruption of the planar structures.

Two contrasting mechanisms of formation are discussed: vertical deformation of crystal mushes, and metasomatic replacement. On balance, we prefer to interpret the fingers as evidence for the replacement of pre-existing allivalite by secondary peridotite. Replacement was achieved by pore magma from the underlying peridotite migrating upwards into the overlying allivalite, in response to compaction. This pore magma was able to resorb plagioclase but crystallize olivine and pyroxene in its place.
Formation of granular-textured layers and laminae within the Rhum crystal pile
Authors: Young I. M. , Donaldson C. H.
Published: May 2009

In the allivalite of cyclic unit 9 in the Eastern Layered Series of the Rhum intrusion there is an undulatory contact between a relatively dense pyroxene-rich rock and a less dense pyroxene-poor rock. The three-dimensional form of this contact resembles that developed between two fluids deforming under the influence of gravity. Minor layers, laminae and lamination in these rocks in places cut across the contact between the pyroxene-rich and pyroxene-poor rock types. They are, therefore, inferred to post-date the formation of the contact and hence to have formed within a porous crystal pile on the chamber floor. Possible mechanisms of formation are discussed but their origin remains unclear. These observations cast doubt on the common assumption that the combination of granular (cumulus) textures and layering structures is sufficient evidence on which to infer equilibrium of granular crystals with a contemporary magma.
Sulphide droplets-and the Unit 11/12 chromite band, Rhum: a mineralogical study
Authors: Dunham A. C. , Wilkinson F. C. F.
Published: May 2009

A microscopic and electron microprobe investigation has been made of six samples of the allivalite–chromitite–peridotite band at the junction of Units 11 and 12, Eastern Layered Series, Rhum. Analyses are presented of olivine, plagioclase and pyroxene, the plagioclase showing reverse zoning in the chromitite. Sulphide droplets occur within and above the chromitite, and contain pyrrhotite, pentlandite, cubanite, bornite, digenite, chalcocite, native copper and electrum, as well as chromite zoned to magnetite, spinel and ilmenite. The variation from aluminous chromite to chromite in the chromitite is confirmed by analyses of five new traverses. The rocks formed during and just after the time when new magma entered the magma chamber. The variation in the chromite compositions is ascribed mainly to magmatic variation in composition due to the mixing process.
Terminology of postcumulus processes and products in the Rhum layered intrusion
Authors: Wadsworth W. J.
Published: May 2009

The terminology of cumulates is discussed with particular reference to postcumulus processes as exemplified by the Rhum layered intrusion. The history of the terms orthocumulate, adcumulate, heteradcumulate and harrisitic cumulate is reviewed, and some modifications to the classification scheme proposed by Irvine (1982) are suggested. Possible mechanisms of adcumulus growth are considered and, on balance, the Rhum evidence confirms the view that postcumulus cementation occurred at a relatively early stage, while the intercumulus melt was in effective contact with the main body of magma.
Postcumulus processes in layered intrusions
Authors: Sparks R. S. J. , Huppert H. E. , Kerr R. C. , McKenzie D. P. , Tait S. R.
Published: May 2009

During the postcumulus stage of solidification in layered intrusions, fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks. One mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir. Convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma. Another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir. This process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile. Calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions, but could not form pure monomineralic rocks. Intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment. Dense magma, emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers. Reactions between melt and matrix may lead to changes in mineral compositions, mineral textures and whole rock isotope compositions. Another important mechanism for forming adcumulate rocks is compaction, in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled. For cumulate layers from 10 to 1000 metres in thickness, compaction can reduce porosities to very low values (< 1%) and form monomineralic rocks. The characteristic time-scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion. During compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix. Both compaction and compositional convection can be interrupted by solidification in the pore spaces. Compositional convection will only occur if the Rayleigh number is larger than 40, if the residual melt becomes lower in density, and the convective velocity exceeds the solidification velocity (measured by the rate of crystal accumulation in the chamber). Orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection.
Metamorphic rocks of an intermediate facies series juxtaposed at the Start boundary, southwest England
Authors: Robinson D.
Published: May 2009

X-ray diffraction analysis of metamorphic rocks from the Start peninsula shows that the dominant mineral assemblage in the Start schists is quartz-muscovite-chlorite ± paragonite ± albite. The assemblage in the Devonian phyllites to the north of the Start boundary is quartz-muscovite-chlorite and the crystallinity of the white mica there is indicative of greenschist fades. Theb0parameter of white micas indicates that the metamorphism was of an intermediate facies series (Barrovian type), but of a lower pressure variety to the north of the Start boundary juxtaposed against a higher pressure variety to the south. No evidence exists of the high pressure metamorphism needed to support tectonic models in which the Start boundary is identified as a suture representing a Variscan subduction margin.
Some geochronological observations on the Precambrians of Chotanagpur, Bihar, India
Authors: Ghose N. C. , Shmakin B. M. , Smirnov V. N.
Published: May 2009

K–Ar measurements of the Chotanagpur granite and associated intrusive rocks are found to be younger than the geological events in the Singhbhum region of Bihar. The history of metamorphism, granitic activities and igneous intrusions in the Chotanagpur area continued for a period from over 1000 Ma to 185 Ma. The relevant geological sequences and correlations are briefly discussed.
Late Cretaceous climatic trends, faunas, and hydrography in Britain and Ireland
Authors: Reid R. E. H.
Published: May 2009

Changes in the Upper Cretaceous faunas of northeastern Ireland point to rising Cenomanian temperatures, and to progressive falls in temperatures from early Santonian to Maastrichtian times. At first sight, these changes fit the Cretaceous climatic trends claimed from isotopic data; but comparison with faunas seen in England suggests that this fit is illusory. It is suggested that faunas were more directly controlled by the influence of contrasting Atlanto-West Tethyan and Russo-Germanic water masses, and by changes in their relative distribution. Changes seen through the Irish Senonian may reflect the progressive submergence of a Scotland—Pennines barrier, permitting an increasing westward spread of the Russo—Germanic (‘boreal’) water and fauna.
Evidence of co-genesis of the Troodos Lavas, Cyprus
Authors: Desmet A. P.
Published: May 2009

Petrological and geochemical features of recently discovered basalts of the Troodos Massif, Cyprus — a dyke in the Basal Group and altered pillow lavas in the Lower Pillow Lavas — suggest that all the lavas are part of a single volcanic suite.
Clastic dykes from the Precambrian Porsangerfjord Group, North Norway
Authors: Williams D. M.
Published: May 2009

Clastic dykes are described from a late Precambrian sequence of shallow water sediments — the Porsangerfjord Group of Finnmark, North Norway. The dykes are from one stratigraphic member of the Group and only occur where this member outcrops in a zone where sedimentation was thought to have been affected by recurrent earthquake shock. The dykes consist of poorly defined sandstone clasts in a muddy matrix. They exhibit no significant internal sedimentary structures. It is suggested that the dykes were intruded due to remobilization of sediment affected by a combination of tectonic shock and hydrostatic load. The dykes bear no genetic relationship to tectonic structures (cleavage and jointing) and evidence suggests that dewatering was virtually complete before the formation of the first cleavage.
Phengite spherules from the Dalradian Bonahaven Formation, Islay, Scotland: glauconitized microfossils?
Authors: Fairchild I. J.
Published: May 2009

Abundant spherules of phengite, 50—150 μm in diameter and with a radial texture, occur in mudstones at the top of the lowest member of the Bonahaven Formation. They have smooth, sharp boundaries, show flattening next to desiccation cracks and exhibit a restricted, bi-or tri-modal size distribution. It is inferred that the spherules represent infilled voids in a sediment which was deposited entirely from suspension. Accordingly, it is considered likely that the spherules are microfossils, although characteristic morphological features are lacking. They were probably infihled by glauconite, which was transformed to phengite during diagenesis and low-grade metamorphism.
Dating of adularia and the relationship of hydrothermal events in the Lizard complex, Cornwall
Authors: Seager A. F. , Fitch F. J. , Miller J. A.
Published: May 2009

A new total degassing argon-40/argon-39 age determination is given for crystals of fresh adularia from hydrothermal veins within the amphibolites near Porthkerris Point, the Lizard, Cornwall. The apparent age of 211±2 Ma obtained is regarded as a close minimum age for crystallization of the adularia. There appears to have been only one phase of crystallization of primary hydrothermal adularia, about 210–220 Ma, in the granulites and amphibolites in the vicinity of Porthkerris Point and in the gabbro of Dean quarry. Another hydrothermal event occurred c. 160–170 Ma. Younger apparent ages have been attributed to hydrothermal activity at one or more subsequent periods.
The Origin of the Dwyka Conglomerate of South Africa and other “Glacial” Deposits.
Authors: Sandberg C. G. S.
Published: May 2009

To reopen a question which has seemed definitely settled ever since 1898, and which has accordingly become an accepted opinion in geological circles, is neither a pleasant nor an enviable task. Yet, as the question is one of universal interest geologically, it has to be tackled and settled. In the following I intend to discuss the problem in a manner as objective and concise as possible, in order to concentrate the argument on the points which fundamentally govern the problem. As, from personal observations on the spot I am only familiar with the South African occurrence, I intend discussing that one only, however likely it be that the arguments brought forward may fundamentally affect the appreciation of other similar occurrences in South America and Asia.