bluuebunny/crossref_metadata_2025 huggingface dataset:
The Ballantrae ophiolite
Authors: Church W. R. , Gayer R. A.
Published: May 2009

The Ballantrae complex, variously interpreted in the light of plate tectonics, is reappraised on the basis of comparisons with ophiolites of the Newfoundland Appalachians and the southwestern Pacific. All the main components of a typical ophiolite sequence can be recognized although the sequence has been greatly disturbed by post-emplacement Caledonian deformation. The presence of a garnet granulite-amphibolite ‘aureole’ beneath the peridotite member of the complex is confirmed, thus establishing the affinity of the complex to other ophiolite-amphibolite associations of the Appalachian and Alpine systems. Rock units previously described as agglomerates are re-interpreted as olistostromes, and the important Pinbain Beach ‘shaly group’ containing fragments of ophiolitic debris, garnet-ariegite, and glaucophane schist, is considered to be a Wildflysch unit of Middle Arenig age. The olistostromes were deposited following obduction of oceanic lithosphere represented by the ultramafic and mafic rocks of the Ballantrae complex. Recognition of the complex as overthrust ophiolite removes certain constraints on the position of a Lower Paleozoic subduction zone within the Southern Uplands.
Ultramafic and mafic protoclastic intrusions in the Dahomeyan gneiss of Ghana
Authors: Holm R. F.
Published: May 2009

Characteristics of mineralogy and texture, together with systematic changes in the enstatite content of orthopyroxene and in the anorthite content of plagioclase, indicate that intrusions of pyroxenite, norite and gabbro, and diorite and leucocratic diorite in the Dahomeyan gneiss of Ghana are genetically related, and that they belong to a subalkaline comagmatic series derived from a parental mafic magma. Partial recrystallization (deuteric) of the igneous rocks during and after intrusion and protoclasis produced minerals characteristic of temperatures higher than those that existed during the medium-grade regional metamorphism of the Dahomeyan gneiss, thus indicating that emplacement of the igneous rocks occurred late during, or perhaps after, the metamorphism. Contact metamorphism appears to have resulted in higher than normal anorthite contents of the plagioclase in the surrounding Dahomeyan gneiss.
Controls of mylonitic compositional layering during non-cataclastic ductile deformation
Authors: Vernon R. H.
Published: May 2009

Lenticular compositional layering and/or rodding in blastomylonitic rocks, in the simplest situations, can be controlled by (i) the presence of more than one mineral in the parent rock and (ii) relative large grain-size of the parent rock. Deformation and recrystallization during non-cataclastic ductile deformation can produce compositional layering, without chemical segregation.
Fine-scale layering in igneous intrusions: a possible mechanism for a non-depositional origin
Authors: Kanaris-Sotiriou R.
Published: May 2009

Examination of layered rocks from the Currywongaun-Doughruagh Intrusion, Connemara, Eire, has suggested a possible connexion between adcumulate crystallization and the formation of thin, yet very persistent igneous layering. It is thought that as a result of adcumulate crystallization proceeding under undisturbed conditions near the top of a pile of cumulus crystals, a zone of liquid, supersaturated in those components not required for adcumulate growth, could be generated in the magma just above the cumulate pile. Crystallization from such a supersaturated zone would result in the cumulate phases, inter-directly beneath. The rhythmic deposition is lacking, could by this mechanism build up a sequence of cumulate layers interbedded with fine-scale layers of a non-depositional origin.
Pleistocene gravels of the River Axe in south-western England, and their bearing on the southern limit of glaciation in Britain
Authors: Green C. P.
Published: May 2009

The source of far-travelled pebbles in the Pleistocene gravels of the lower Axe is investigated. Reference is made to the possible introduction of far-travelled material by glacial meltwater, flowing into the basin of the Axe through a ‘gap’ in the present watershed at Chard. Gravels of the lower Axe are described and compared with gravels of the upper Axe and of neighbouring streams. Far-travelled material is found in almost all of the gravels examined. The source of the material is identified in early Tertiary gravels which occur within the present basins of the rivers in question. A glacial origin for the far-travelled material is rejected.
Geochemistry of post-Dharwar basic dikes and the Precambrian crustal evolution of peninsular India
Authors: Naqvi S. M. , Rao V. Divakara , Satyanarayana K. , Hussain S. M.
Published: May 2009

The post-Dharwar basic dikes from Chitaldrug and Shimoga schist belts have been analysed to determine their major, minor and trace-element composition. The comparison of the results from these formations (1.4–0.95 b.y.) with those of the early Precambrian metabasalts (2.4 b.y.), which are indicative of a thin crust at the time of their extrusion shows significant differences between them. Utilizing this and results of similar studies on corresponding formations it is suggested that the present thickness of this part of the crust might have been obtained after the extrusion of the early Precambrian basalts and before the intrusion of the middle Precambrian dolerites.
Calcareous nannoplankton and the age of the Globigerina silts of the western approaches of the English Channel
Authors: Martini E.
Published: May 2009

Calcareous nannoplankton from the Globigerina silts of the western approaches of the English Channel indicate the presence of standard nannoplankton zones NN2, NN 4 and NN 5, part of which can be correlated with Neogene beds in Belgium and Northern Germany. The calcareous nannoplankton support the possibility of a connexion between the North Sea Basin and the Atlantic Ocean through the English Channel during part of the Lower Miocene.
Tectonic control of graphite mineralization in Sri Lanka
Authors: Silva K. K. M. W.
Published: May 2009

The localization of graphite veins in well-defined regions within anticlinal structures of the SW sector of the island, where the rocks have been migmatitized partially by a reactivation, is very significant. The graphite mineralization seems to have taken place during the above mentioned reactivation and has followed regions of structural weakness developed during the folding of the metasedimentary rocks.
Jointing along the Swansea Valley Disturbance between Clydach and Hay-on-Wye, South Wales
Authors: Weaver J. D.
Published: May 2009

Along the length of the Swansea Valley Disturbance, from Clydach (near Swansea) to Hay-on-Wye (Herefordshire), 4 main joint sets are developed. They are NE—SW, NW—SE, N—S and E—W in trend. On the NW and SE sides of the main fault zone only the N—S and E—W sets tend to be developed, whereas within this fault zone only the NE—SW and NW—SE sets are found. It is suggested that the NE—SW and NW—SE sets are shear joints developed at the same time as the main fault zone and the N—S and E—W sets have been developed in response to the release of residual strain energy after the end of the Variscan orogeny.
An essexitic sill at Mbalevuto, Viti Levu, Fiji
Authors: Colley H.
Published: May 2009

The Mbalevuto sill intrudes sedimentary rocks on the SW flank of Tavua volcano, Viti Levu, Fiji. It appears to have been intruded at shallow depth in a semi-molten state. The sill is of essexitic composition and petrochemical evidence suggests that magmas forming the sill and lavas of the Tavua volcano are consanguineous.
Regulaecystis devonica, a new Devonian pleurocystitid cystoid from Devon
Authors: Paul C. R. C.
Published: May 2009

Regulaecystis devonica, which is probably from the Meadfoot Beds (Siegeman— Emsian) near Torquay, Devon, is characterized by smooth thick thecal plates and a deeply sunken pectinirhomb. Coopericystis Parsley from the Middle Ordovician of Tennessee is considered a junior synonym of Regulaecystis from the Lower Devonian of Europe.
Syndepositional tectonism in the Kvamshesten district (Old Red Sandstone), western Norway
Authors: Bryhni I. , Skjerlie F. J.
Published: May 2009

Continental Middle Devonian sediments of the Kvamshesten district have recently been interpreted as a thrusted block. However, although basal contacts in the E of the district are mylonitized, contacts in the W can be interpreted as depositional unconformities. Coarse alluvial-fan breccias (Markavatn Formation) in the district's northern margins interdigitate with fluviatile sandstones (Heilefjell Formation) towards the basin's centre. Syndepositional tectonism is demonstrated by the geometry of the coarse marginal deposits.
Concise description of fold orientations
Authors: Chaudhuri A. K.
Published: May 2009

A new structural diagram derived from the equal-area net is proposed that helps in conversion of pitch data of folds into amount and direction of plunge, and in precise classification of the fold orientations. A new convention for indexing of folds and the use of subscripts for concise description of inclined folds are suggested.
Zircon U–Pb ages of granulites from the Central Region of the Lewisian, northwestern Scotland
Authors: Pidgeon R. T. , Bowes D. R.
Published: May 2009

The overprinting of the high grade rocks of the Scourian episode, during the Inverian and Laxfordian episodes, has so far prevented a reliable estimate being made of the age of the Scourian granulite–facies metamorphism in the Central Region of the Lewisian of northwestern Scotland. In an attempt to solve this problem the U–Pb isotopic systems of zircons from two samples of hypersthene granulite from the Kylesku group have been examined. These zircons have discordant apparent ages complicating the interpretation of the results. However, by measuring a number of size fractions from each of the two zircon suites it has been possible to demonstrate that a major isotopic event or events took place approximately 2700 m.y. ago in these granulite–facies rocks. It has also been shown that the two discordance trends found for the two zircon populations can be explained in terms of episodic disturbances of the U–Pb isotopic systems at times which correspond to the known ages of ‘Laxfordian’ and ‘Caledonian’ events.
Size-graded, igneous layering in an Icelandic intrusion
Authors: Roobol M. J.
Published: May 2009

The Vesturhorn Intrusion of SE Iceland contains a tilted block consisting largely of size-graded, igneous-layered, eucritic gabbro, which is described in some detail. Size-graded, igneous layering is remarkably uncommon and at present there appear to be only two known occurrences. The physical properties of basalt magma suggest that most igneous layering is likely to form from currents moving by laminar flow. Considerations of flow in such a simple system do not satisfactorily account for the scarcity of this structure. It is suggested that size-graded, igneous layering may reflect the availability of convecting magmas containing crystals with appreciable proportions of different grain sizes of each mineral species. Such a grain size distribution, together with other features considered here, may indicate primocryst growth outside the chamber of deposition.
The significance of toolmarks on a Silurian erosional furrow
Authors: Bridges P. H.
Published: May 2009

The toolmark pattern on an erosional furrow from the Llandovery shelf sequence in the Welsh Borderland indicates that there was:— (i) local helical flow within the furrow similar to that found in sinuous alluvial streams and (ii) a moderately powerful current which moved towards the shore. Erosion by a shallow water turbidity current or storm surge tidal ebb flow therefore seems unlikely. A flood tidal current super-imposed on storm wave oscillatory disturbance of the sea-floor provides a possible mechanism.
The tectonic evolution of the the southern portion of the Benue Trough, Nigeria
Authors: Nwachukwu S. O.
Published: May 2009

A reconstruction of the tectonic history of part of the Benue Trough is made from a study of the marine transgressions and regressions in SE Nigeria. Two periods of deformation involving essentially the interaction of continental plates are suggested. The oceanic crust produced by crustal attenuation in the Benue rift is very minimal. Unstable tectonic conditions in the Benue Trough may have created conditions for the development of an evaporite sequence.
Potassium–argon ages from the Cheviot Hills, northern England
Authors: Mitchell J. G.
Published: May 2009

Potassium–argon ages of a variety of rocks and minerals from the Cheviot Hills, northern England, lie in the range 390 m.y. to 370 m.y. The Cheviot granite, dated at 380 m.y., has an age similar to that of many of the younger members of the British late Caledonian granites.
The origin of cordierite—anthophllite rocks in the Land's End aureole
Authors: Chinner G. A. , Fox J. S.
Published: May 2009

The prevalence of low-variance assemblages, the frequency of the buffered association anthophyllite—cordierite—cummingtonite—plagioclase, and the ubiquity of aluminium-rich clots of diaspore incompatible with the ortho-amphibole of the rock suggest that the cordierite—anthophyllite rocks of the Land's End aureole are not the product of metasomatism, but resulted from the thermal metamorphism of pre-existing rock-compositions. The origin of many kyanite-, amphibole- and cordierite-rich bodies by pre-metamorphic alteration is of economic significance in regions where such curious silicate assemblages accompany sulphide deposits.
Basaltic volcanism in south-east Terceira, Azores
Authors: Rosenbaum M. S.
Published: May 2009

The Terceira Rift is a subsidiary zone of crustal generation in the Azores to the E of the Mid-Atlantic Ridge. The geology of the island of Terceira, which straddles the rift, is thought to give an indication of the nature of the volcanic activity along this zone of crustal separation. Terceira is composed of 4 large strato-volcanoes associated with trachytic or trachybasaltic activity which have since been intruded by basaltic magmas to form monogenic cinder cones and lava flows on the flanks of these large volcanoes. There is little direct evidence of eruptions along fissures although lines of cinder cones may indicate zones of weakness in the crust.
Hornblende-Granulite Subfacies Mineral Assemblages from Areas in Ceylon
Authors: Hapuarachchi D. J. A. C.
Published: May 2009

Hornblende and biotite occur very commonly in the granulite facies rocks of the areas mapped, and both appear to occur as stable phases. Thus, these hornblende- and biotite-bearing rocks find accommodation only in the hornblende-granulite subfacies. It appears that most of the rocks in the areas mapped would fall into this subfacies and the mineral assemblages of these rocks are recorded in this paper under the different chemical classes. Hornblende and biotite are very commonly present in the pelitic, quartzo-felspathic, basic and magnesian rocks; phlogopite and sphene are commonly present in the calcareous rocks. A tentative ACFK tetrahedral phase diagram has been constructed for these rocks.
An Outline of the Geology of the Juan Fernandez Archipelago
Authors: Baker P. E.
Published: May 2009

The Juan Fernandez Archipelago, located off the coast of Chile, comprises a group of three small, considerably eroded volcanic islands, probably of late Tertiary age. Traces of old craters or calderas have been recognized on Robinson Crusoe Island which is built mainly of basaltic lava flows, many of them picrite-basalts. Coarse-grained ejected blocks, in which olivine predominates, are fairly common on Robinson Crusoe and there are also a number of exposures of dolerite showing pronounced banding. The only acid rock reported from the group is a soda-trachyte from Alexander Selkirk Island. Pumice washed ashore on the islands during the past year is possibly from a submarine eruption near the South Sandwich Islands in 1962.
Preliminary Account of Recent Geological Investigations on Easter Island
Authors: Baker P. E.
Published: May 2009

Easter Island comprises three major volcanoes, Poike a simple strato-volcano, Rano Kau which is of similar size but with a caldera at its summit, and Terevaka which is the largest and most complex of the three. In addition there are about seventy minor eruptive centres. The lavas constitute an alkali-basalt-trachyte-soda-rhyolite series but the acid members are of very restricted development. There is evidence that the parasitic tuff cone of Rano Raraku has had a more complicated history than previous reports have suggested. Although no volcanic activity has ever been reported, some of the lava flows appear to be of very recent origin.
Dolomitization of Siliceous Microfossils in Namurian Concretionary Limestones
Authors: Holdsworth B. K.
Published: May 2009

Early diagenetic, micritic, carbonate concretions from Namurian goniatite bands in Staffordshire and Derbyshire contain Radiolaria and sponges excellently preserved owing to replacement by ankeritic dolomite anhedra. The microfossils are detectable only by acid etching of limestone surfaces and thin sections. Preservation by the dolomite is believed to occur under restricted conditions in which silica solution and dolomite crystallization post-date a phase of rapid calcite crystallization.
Bittnerula Hall and Clarke, and the Evolution of Cementation in the Brachiopoda
Authors: Cowen R. , Rudwick M. J. S.
Published: May 2009

A new specimen of the rare spiriferide brachiopod Bittnerula zitteli (Bittner), from the St. Cassian beds (Triassic) of the Italian Alps, has a well-preserved ventral umbo with a small sub-apical pedicle foramen and no cicatrix of attachment. Bittner's interpretation of the genus, as attached by cementation, is therefore rejected. There is now no authenticated case of cementation attachment in any spiriferide brachiopod, or in any articulate brachiopod outside the Strophomenida. The evolutionary history of cementation, and the affinities of the problematical Thecideacea, are discussed briefly in the light of this discovery.
On the Late Precambrian–Early Cambrian Hartshill Formation of Warwickshire
Authors: Brasier M. D. , Hewitt R. A. , Brasier C. J.
Published: May 2009

The Hartshill Formation (c. 270 m) consists largely of shallow-water feldspathic sandstones and greywackes lying unconformably on Precambrian (Vendian?) volcanic rocks and below shales with the first olenellid trilobites. Five members are recognized. The Park Hill Member is conglomeratic and arkosic near the base, passing up into green-grey megarippled quartzites with some thick shale bands. The Tuttle Hill Member is more shaly and glauconitic with conspicuous bioturbation. The Jee's Member is of distinctly cross-laminated glauconitic, feldspathic greywackes and shales with numerous trace fossils. Conglomerates, shales, sandstones, phosphorites and limestones comprise the Home Farm Member, withadiverse Tommotiantype shelly fauna and stromatolites near the top. Massive arkoses and greywackes of the Woodlands Member yield similar shelly fossils in calcareous beds at the base and top while the overlying Purley Shale yields the first Lower Cambrian trilobites.
Folding and pressure solution in a laminated calcite-quartz vein from the Silurian slates of the Llangollen region of N Wales
Authors: Nicholson R.
Published: May 2009

Folds of a 12 mm thick calcite-rich vein, embedded in slate and with a primary planar fabric of parallel, thin and plate-like calcite crystals, or laminae, have a vein thickness/arc length ratio near 1. Folds were first entirely dependent for development on intra-laminar strain and inter-laminar sliding. As limb dips increased, however, pressure solution began to thin laminae in limb regions only. As adjacent inter-laminar surfaces met at fold inflexion points, where laminae were first cut through, loss on fabric-cutting surfaces began to replace inter-laminar pressure solution. The resulting stylolites grew across the vein in fold limbs, at the limit eliminating them. In contrast, in folded equigranular calcite rocks stylolites are widely developed in both limbs and hinges, and eventual fold collapse through late stage concentration of pressure solution takes place in fold hinges and not limbs.
I.U.G.S./I.G.C.P. Project 29 Precambrian–Cambrian Boundary Working Group in Cambridge, 1978
Authors: Cowie J. W.
Published: May 2009

Nineteen members of the Working Group attended the meeting and constituted a good representation in experience, variety of specialist knowledge of disciplines within geology, and first-hand knowledge of appropriate global stratigraphy. The following resolutions as a whole were accepted, as an account of the meeting by those present, with a large majority. The minority of four who did not accept Resolution I requested that the Minority View (see below) should be recorded but it was decided not to include it in the Resolutions.
Source ages of zircons in an Archaean quartzite, Rona, Inner Hebrides, Scotland
Authors: Bowes D. R. , Hopgood A. M , Pidgeon R. T.
Published: May 2009

The internal variations in the discordance of an inhomogenous zircon population from a bedded quartzite within a c. 2700 Ma old gneiss have been studied. Varying degrees of response to events in a common multi-episodic, post-depositional history are reflected in the uranium and lead isotopic systems of size and magnetic fractions.

A minimum 207Pb/206Pb age for non-magnetic zircons is 2840 Ma with 206Pb/238U and 207Pb/235U data for the three size fractions raising the possibility of an age of at least 3250 Ma. This is interpreted as a minimum age for crustal material that was in existence in the region before the formation of the Lewisian complex. Some of the slightly magnetic zircons also have a pre-2700 Ma radiogenic lead component.
Quartz replaced anhydrite nodules (‘Bristol Diamonds’) from the Triassic of the Bristol District
Authors: Tucker Maurice E.
Published: May 2009

Quartz nodules and geodes, known as Bristol Diamonds, occur in the Triassic Dolomitic Conglomerate of the Bristol district of England. They are composed of either, megaquartz, milky in the outer part and clear towards the centre, or fibrous quartz, chalcedony and lutecite. Much of the quartz, particularly in the outer parts, is full of anhydrite inclusions which are relics of larger lath-shaped anhydrite crystals. The Bristol Diamonds formed by silica replacement of anhydrite nodules, with replacement proceeding from the outside inwards. In many cases anhydrite solution was faster than silica replacement, so that a central void developed into which grew crystals with fine terminations. The anhydrite formed by precipitation of sulphate from hypersaline sediment-porewaters, probably in a marginal playa situation.
K—Ar isotopic age determinations from some Lake District mineral localities
Authors: Ineson P. R. , Mitchell J. G.
Published: May 2009

Forty-seven new K—Ar analyses are reported from 15 mines in the Lake District. Analyses of clay mineral concentrates from vein gouges and altered wallrock support a hypothesis of at least 3 distinct isotopic events. Caledonian ages (388 Ma) are reported from the Coniston Copper deposits, while the extensive mineralization in and around the Vale of Newlands indicates a metasomatic event occurring at around 360 Ma. The ages of the sporadic mineral localities to the E of the area (i.e. Greenside, Threlkeld, etc.) are grouped around 325 Ma while those of the Caldbeck Fell deposits are close to 230 Ma. An epidosic model may be advanced for the Carrock Fell Tungsten deposits with a range from 197 to 282 Ma. The geochronological significance of these and other previously published results is considered.
Geochemistry and geotectonic implication of basic volcanic rocks in the Lower Gondwana sequence (Upper Palaeozoic) of the Sikkim Himalayas
Authors: Roy S. Sinha , Furnes H.
Published: May 2009

As in Kashmir and Arunachal Pradesh (NEFA) Himalayas, the Upper Palaeozoic (Lower Gondwana) sequence in Sikkim Himalayas contains basic lavas. These are interbedded with boulder bed/pebble slate, sandstone andshale, exposed in a tectonic window. Geochemically the basic lavas are characterized by high contents of TiO2, K2O, P2O5and ‘incompatible’ trace elements. The chemistryis compatible with a small degree of partial melting under high pressure ofa titan-phlogopite-bearing peridotite mantle. The only primary quench phases are frequent apatite, magnetite and profuse ilmenite, the latter accounting for the high FeO/Fe2O3ratio of the rock, and demonstrating rapid crystallization. The geochemistry of the lavas appears to be consistent with basic volcanism associated with the initiation of continental rifting. From this study and from a consideration of the geochemistry of the volcanic rocks of similar age in Kashmir area, it is suggested that rifting of the northern continental margin of the Indian plate and formation of a transitional crust during Upper Palaeozoic times are important geotectonic features in the Himalayan region.
Silurian trilobites from arctic Canada
Authors: Thomas A. T. , Narbonne G. M.
Published: May 2009

Trilobites of upper Ludlow age are described from Member A of the Read Bay Formation on Cornwallis Island. Four new species are represented:Helokybe spiogen. et sp.nov. (Dechenellinae),Encrinurus hyperboreussp. nov.,Kailia? caprasp.nov. (Encrinurinae) andHemiarges echinatussp.nov. Other taxa present are: an effaced scutelluid;Cyphaspissp.; a warburgelline; two more encrinurids; two other forms ofHemiarges. The trilobites occur in sediments indicative of a shallow subtidal environment, with the exception of the warburgelline which occurs in sediments deposited under deeper subtidal conditions below storm wave-base.
Some international agreement on essentials of stratigraphy
Authors: Laffitte R. , Harland W. B. , Erben H. K. , Blow W. H. , Haas W. , Hughes N. F. , Ramsbottom W. H. C , Rat P. , Tintant H. , Ziegler W.
Published: May 2009

An agreed short text in English, French and German, presents a unified statement on those aspects of stratigraphy that require formal international acceptance. The statement is designed to avoid philosophical hazards and misunderstandings between the three language communities; it also harmonizes differences of three national traditions as far as is yet possible.

Stratigraphy is presented as an indivisible science dependent for its successful pursuit and synthesis on the application of numerous widely different methods.

The argument is presented in successive numbered steps to facilitate its critical discussion.
The junction between the Skiddaw Slates and Borrowdale Volcanics in Newlands Beck, Cumberland
Authors: Jeans Peter J. F.
Published: May 2009

The junction in Newlands Beck between the steeply dipping Skiddaw Slates striking N–S, and Borrowdale Volcanic rocks dipping gently to the SE is interpreted as an angular unconformity, and indicates the existence of pre-Borrowdale Volcanic folding. There is no cleavage associated with this folding, however, the ENE–WSW Caledonoid cleavage being the only one present, and this is common to both Skiddaw Slates and Borrowdale Volcanics.
Rb-Sr age determinations on shales associated with the Varanger Ice Age
Authors: Pringle I. R.
Published: May 2009

Rb–Sr whole-rock isochron ages from shale horizons in the Late Pre-Cambrian tillite succession in Varangerfjord, Northern Norway, are presented. Although data from the Stappogiedde Formation, which overlies the tillite horizons, give a Caledonian, metamorphic age of 530±50 m.y., ages obtained from shales occurring between and below the tillites are believed to represent the approximate times of deposition of the sediments. An age of 810±90 m.y. for the Tanafjord Group enables this group to be correlated with the Upper Torridonian and the age of 668±23 m.y. for the Nyborg Formation, which is taken as the age of the Varanger Ice Age, allows a tentative correlation to be made with the Egan and Marinoan Glaciation in Australia.
A mammalian fauna from the Stretton Sand at Stretton-on-Fosse, South Warwickshire
Authors: Shotton F. W.
Published: May 2009

A small fauna of mammals, which includes Elephas antiquus, has been obtained from the Stretton Sand. This, the oldest member of the Pleistocene succession north of Moreton-in-Marsh, has previously been interpreted as glacial outwash from a Severn Valley source and usually ascribed to an early phase of the Wolstonian Glaciation. It is now ascribed to the Hoxnian interglacial, with its rare erratics of presumed Welsh provenance derived from erosion of an earlier Anglian glaciation.
Modes of turbidite deposition deduced from grain-size analyses
Authors: Buller A. T. , McManus J.
Published: May 2009

Values of quartile deviations (QDa) and medians (Mdmm) have been calculated from over 400 grain-size distributions of modern and ancient turbidites. Each QDa–Md pair is plotted on double-log paper to establish any distinctive trends. The QDa–Md analysis of modern turbidites reveals a steep gradient trend derived from the grain-size distributions of submarine canyon and delta fan sediments, and a shallow gradient trend derived from the grain-size distributions of samples from oceanic bottoms and nepheloid water layers. The QDa–Md analysis of ancient turbidites reveals two trends, but these do not coincide with their modern counterparts. The steeper gradient trend is related to distal and proximal turbidites, while the shallow trend is related to fluxoturbidites. The disparity between the ancient and modern QDa–Md analyses is caused by textural modifications of turbidites by diagenetic disintegration of unstable minerals. The alteration products are incorporated subsequently in the matrix. The diagenetic effects on the positions of the QDa–Md plots are demonstrated theoretically by computing the textural alteration of six modern turbidites by assuming that they will lose 20%, and then 40%, of their sand-sized particles to the matrix. By working in reverse the QDa–Md plots of ancient turbidites can be ‘restored’ to their diagenetically unaltered positions. Their restored positions correspond to the QDa–Md trends of modern turbidites.
Spilites, keratophyres, and the igneous spectrum
Authors: Hughes C. J.
Published: May 2009

Although the structures and textures of spilites and keratophyres are comparable to those of fresh lavas, recent work has established that they did not acquire their present mineralogy at the time of extrusion. Furthermore, the compositions of many analyzed samples of spilites and keratophyres are shown to lie outside a ‘spectrum’ of compositions of all comparable fresh igneous rocks. A later metamorphism has therefore been responsible for their formation and has commonly been accompanied by metasomatism. This possibility of later metasomatism must be appreciated before conclusions are drawn that are based upon analysis of rocks of a spilitic or keratophyric mineralogy. This applies to age-dating and to analytically based petrographic and petrogenetic conclusions.
An exhumed Jurassic meander belt from Yorkshire, England
Authors: Nami M.
Published: May 2009

Three-dimensional coastal exposures of the Middle Jurassic (Bathonian) Scalby Formation in Yorkshire, England, exhibit a complex, exhumed meander belt. The lateral accretion surfaces (epsilon-cross stratification) of individual meander loops are described. Field and aerial photograph measurements of accretion-surface dimensions have enabled direct determination of channel bankful depths and widths and meander wavelengths. Values for mean annual discharge of the channel system are derived using existing empirical equations. Palaeocurrents measured in the meander belt sandstones show a wide dispersal due to many periods of meander migration and cut off.
Unusual morphological features in the blastoid genus Pentremites
Authors: Strimple H. L.
Published: May 2009

Although a root system has been discussed for the blastoid Pentremites, no cirri have been reported and no photographic illustrations have heretofore been given of the complete animal. Two specimens with complete stems with sporadic cirri along the entire length and distal attachment cirri, and one specimen with a long portion of stem, a few cirri and spiracle covering plates preserved in place, are reported herein. All three specimens are from the Fraileys Formation, Hombergian Stage, Chesterian Series, Upper Mississippian of southern Illinois, U.S.A. (Zone E1, Pendelian Stage, Namurian Series [A], Upper Carboniferous). An eleutherozoic or free life style is postulated.
Timing of events in an Early Cretaceous island arc–marginal basin system on South Georgia
Authors: Tanner P. W. G. , Rex D. C.
Published: May 2009

19 new K–Ar mineral ages of 78-201 Ma and 3 Rb–Sr whole rock isochron ages of 81 ± 10, 127±4 and 181±30 Ma are presented from units of continental crust, mafic complex and island arc assemblage on South Georgia. The Drygalski Fjord Complex, part of the possible floor of the marginal basin in the southern part of the island, includes granodiorite and gabbro plutons of minimum age 180–200 Ma. Together with older metasediments they have been affected by a major thermal event at about 140 Ma, thought to have resulted from the emplacement of a mafic complex (Larsen Harbour Formation) during the initial opening of the marginal basin. Rocks of the Larsen Harbour Formation are cut by the Smaaland Cove intrusion dated by Rb–Sr whole rock isochron at 127±4 Ma. An island arc assemblage exposed to the SW of South Georgia consists of pyroclastic rocks cut by monzodiorite and andesite intrusions, which give radiometric ages of 81–103 Ma. These data suggest that the marginal basin opened during the late Jurassic (pre-140 Ma); that part of an earlier (early Mesozoic) magmatic arc is preserved in continental crust making up part of the floor of the basin; and that subduction continued beneath the island arc until at least the Senonian time. The younger plutons in the arc were emplaced at roughly the same time as turbidite facies rocks at deep levels in the marginal basin were being affected by penetrative deformation and metamorphism. The timing of events on South Georgia agrees closely with that deduced for the continuation of the same island arc–marginal basin system in South America. The 180–200 Ma plutons correlate with an older suite of plutonic rocks reported from the Antarctic Peninsula and southern Andes; they are part of a once-continuous magmatic arc related to subduction of the Pacific plate beneath Gondwanaland during the early Mesozoic.
A Late Mesozoic island arc in the southern Andes, Chile
Authors: Suárez M.
Published: May 2009

The Hardy Formation, a sequence of Upper Mesozoic volcanic rocks exposed in Peninsula Hardy (Isla Hoste) in the southernmost archipelago of Chile represents, at least in part, the island-arc assemblage of an island-arc-marginal-basin system related to an eastward dipping subduction zone. This island arc was founded on South American continental crust and is also represented in the island of South Georgia 2000 km to the E. The island-arc assemblage includes pyroclastic rocks, characterized by a high proportion of vitric material, and lava intercalations ranging in composition from rhyolite to basalt. These rocks underwent zeolite and prehnite-pumpellyite facies metamorphism and are gently folded, in contrast with the intense folding exhibited by the rocks exposed to the north of Peninsula Hardy. Silicic volcanics assigned to this assemblage underlie pillow lavas, and are intruded by dolerites and gabbros probably related to a Late Jurassic-Early Cretaceous ophiolite magmatism associated with the generation of a quasioceanic marginal basin. Volcanic turbidites (Yahgan Formation) were deposited into the marginal basin.

It is suggested that in pre-marginal basin times the Hardy Formation interfingered towards the Atlantic with the silicic volcanics of the Tobifera Formation. However, recent geochemical work on the Tobifera Formation suggest an origin by continental crust anatexis in a volcano-tectonic rift zone related to upper mantle diapirism, whereas an island arc origin is favoured for at least the andesitic and basaltic components of the Hardy Formation. Therefore, the geology of Peninsula Hardy as presented here, confirms early assumptions of the splitting apart of a Middle–Upper Jurassic volcanic terrain along the Pacific margin of South America during the generation of a marginal basin. The spreading axis of the latter seems to have been located at the boundary of two somewhat overlapping petrotectonic assemblages: and island arc on the Pacific side and a silicic volcano-tectonic rift zone towards the Atlantic. A probably Cenozoic volcanic complex discordantly overlies the Yahgan and Hardy formations.
A re-evaluation of the blueschist facies
Authors: Wood R. M.
Published: May 2009

Within blueschist facies rocks it is common to find that mineral assemblages represent a series of attempts to arrive at changing states of equilibrium. To interpret such rocks it is necessary to study how the mineral constrains and determines chemical interaction. The gradual process of chemical exchange between minerals, during changes in conditions, is interrupted by the nucleation of a new mineral species. Mineral reactions are instigated by the nucleation of one new mineral species, though when a reaction is seen at an equilibrated completion the reaction path cannot be traced. In low temperature metamorphism the preservation of partial mineral reactions is very widespread. The growth, adaptation and resorption of a mineral are considered in order to demonstrate: (1) how and why a mineral should zone during growth: (2) the competitive reaction paths that may allow a mineral to change composition, even across and internal solvus; and, (3) through the consideration of a few simple parameters, the prediction of a variety of resorption textures. It is proposed that through an understanding of the way in which the mineral can store information on the chemical history of the rock it is possible to obtain a metamorphic analysis without recourse to the conventional phase equilibrium metamorphic model - a frequent misapplication in the blueschist facies.
The palaeomagnetic evolution of continental red beds
Authors: Turner P.
Published: May 2009

The palaeomagnetism of continental red beds is considered in the light of evidence concerning the diagenetic origin of various textural phases of hematite. The relative roles of pigmentary hematite and specularite as magnetization carriers is discussed and it is concluded that all magnetizations are post-depositional: the magnetization of continental red beds is therefore of diagenetic origin.

Three types of non-viscous magnetization, A, B and C, are recognized in continental red beds. Type-A magnetizations retain some features of the original magnetization and are most closely coincident with the depositional age of the rocks. Type-B are composite magnetizations acquired over a long period (more than 108 yr) of time and after substantial changes in the ambient geomagnetic field. Type-C magnetizations bear no relationship to the depositional age of the rocks and represent the ultimate end-product of the diagenetic processes which affect continental red beds. Thus, these magnetizations represent stages in the diagenetic evolution of red beds. The rate of diagenetic evolution, and hence of the modification of the magnetization, is variable and depends on a variety of local geological variables.

The study enables some assessment of the reliability of palaeomagnetic data from red beds. Type-A magnetizations, although of diagenetic origin, are considered to be palaeomagnetically reliable, but only within certain limits. Red beds with Type-B and Type-C magnetizations are not considered to be generally suitable for palaeomagnetic study. Palaeomagnetic studies are, however, considered to have great potential value for dating specific diagenetic processes in continental red beds.
Experimental investigation of etch pit formation on quartz sand grains
Authors: Wilson P.
Published: May 2009

An experimental investigation into the formation of crystallographically orientated etch pits on quartz sand grains was undertaken. The methods and materials used in the experiments differ considerably from those of other workers in this field. Using natural as opposed to artificial solutions, V-shaped or triangular etch pits as well as rectangular pits have been produced on the quartz grains after time periods of 4 hours and 20 hours. Features of intense surface disintegration have also been recorded. The etch pits are compared to those of natural occurrence on grains from the Millstone Grit (Namurian) sediments and the differences discussed.
Apatite in South Wales anthracite
Authors: Baqri R. , Hodson F.
Published: May 2009

Carbonaceous dirt bands containing some 40% hydroxyapatite and 10% kaolinite are recorded from the Hornlo seam of the Brynammon district of the South Wales coalfield with an appreciable areal extension. X.R.D. and some chemical data are recorded. The origin of the deposits is ultimately biogenic, possibly located by the porous environment provided by fusinite; but the immediate cause remains uncertain.
Facies variations in the Devonian limestones of eastern South Devon
Authors: Scrutton Colin T.
Published: May 2009

The Middle and Upper Devonian limestone successions at Torquay and in the Lemon Valley SW of Newton Abbot are described. Lithostratigraphic units are proposed for the Torquay succession. The compositions of the coral faunas in both successions are outlined and contribute, together with the other available faunal evidence, towards a broad internal dating of these limestone sequences. Successions elsewhere in the limestones of eastern South Devon are briefly outlined. On the basis of this evidence facies variations from the margin towards the centre of the carbonate platform in eastern South Devon are demonstrated and interpreted as reflecting the development of barrier reefs along parts at least of the platform margin in Givetian times. The character of the reef-complex, named the Tor Bay Reef-Complex, is briefly compared with Devonian reefs elsewhere.
Controls of copper mineralization at Coniston, English Lake District
Authors: Dagger G. W.
Published: May 2009

Analysis of the fracture pattern in the Coniston area of the Lake District indicates that copper mineralization is localized in a series of fractures produced during the main phase of deformation affecting the Borrowdale Volcanic Series. Three events are recognized on the basis of field and textural evidence obtained from polished sections: an early haematite mineralization, correlated with the low grade regional metamorphism affecting the rocks; the main phase of sulphide mineralization, with zoning, which is correlated with a granite intrusion at depth; and a late renewed movement on the veins, with carbonate mineralization, believed to be related to uplift of the granite.
Mylonitic microstructures and their bearing on the development of mylonites – an example from deformed trondhjemites of the Bergen Arc region, SW Norway
Authors: Sinha Roy S.
Published: May 2009

Thrust-bound bodies of trondhjemite, showing variable intensity of deformation, contain micro-structural evidences which suggest that the mylonitic fabric in them had developed in stages. An initial shearing stage was followed by a flattening one when the characteristic mylonitic microstructures and banding developed. These stages were punctuated and overlapped by phases of recovery and recrystallization. Mineral parageneses and microstructures indicate that prograde metamorphism and ductile deformation characterize the flattening stage. The origin of mylonite is explained in a scheme of progressive deformation during which planes of maximum shear strain and flattening became almost parallel, so that brittle microstructures were either modified or obliterated by ductile ones. The sequence of microstructural development and mineral redistribution suggest that in mylonite formation mechanical process is accompanied with chemical mobility.
A nomogram to estimate the size for a random sample from a normal population for mean
Authors: Awasthi A. K. , Kumar Surendar
Published: May 2009

A method is presented using a nomogram to estimate the size of a random sample from a normal population.
Trilobite traces from the Lower Tremadoc of Tortworth
Authors: Crimes T. P.
Published: May 2009

The ichnogeneric status of trilobite furrows (Cruziana) and resting excavations (Rusophycus) is discussed and the suggestion (Seilacher, 1970) that these two distinct types of trace should be united under the genusCruzianais rejected.
A Palaeocene Foraminiferal assemblage from Halesworth, Suffolk
Authors: Fisher M. J. , Williams G. M.
Published: May 2009

An assemblage of benthonic Foraminiferida of late Palaeocene age is described from subsurface material from Halesworth, Suffolk. Twenty-two species are listed, and are compared with microfaunas which were described by Haynes (1954–8) from the type Thanetian.
The stratigraphical relationships of the earliest monograptidae, and the dimorphograptidae
Authors: Toghill P.
Published: May 2009

The earliest monograptids are shown to appear at exactly the same time (base of the vesiculosus Zone in Scotland) as Dimorphograptus and Rhaphidograptus, and the earliest species of these two genera are those with long uniserial portions, the forms wiht shorter uniserial portions appearing in the overlying cyphus Zone. Akidograptus is entirely restricted to the premonograptid beds. One of the earliest monograptids is described as Monograptus cyphus var. praematurus var. nov., which has a distinct and earlier range than M. cyphus s.s. Lapworth.
The Neogene calcalkaline volcanism of Central Anatolia: geochronological data on Kayseri—Nigde area
Authors: Innocenti F. , Mazzuoli R. , Pasquarè G. , Radicati Di Brozolo F. , Villari L.
Published: May 2009

The evolution of Neogene volcanic activity in the Central Taurus is investigated; stratigraphical and radiometric age data from the Ürgüp (Kayseri) basin idicate that volcanism in the area began at least as early as Upper Miocene, lasting up to prehistoric times. The volcanism maintained throughout this time interval a calcalkaline character. The diachronous end of calcalkaline volcanism along the Taurus margin is tentatively related to the differential collision between the Afro-Arabian and the Anatolian plates, probably due to an original irregular shape of the Anatolian continental margin.
Coral patch reefs in the Bajocian (Middle Jurassic) of Lorraine
Authors: Hallam A.
Published: May 2009

An account is given of coral patch reefs in the Bajocian of Lorraine, France, and a distinctive ecological association in the other invertebrate fauna recognized, which compares closely with that present in the late Oxfordian reef facies of southern England. The inference is made of a series of low mounds on the original sea bed, composed of coralline sheet structures interfingering with calcareous sediment which locally and periodically enveloped the coral colonies. Compared with Recent patch reefs in the Bahamas and around Bermuda, important differences can be inferred for the Jurassic structures, principally the lack of significant topographic relief, major internal cavities, erosion and algal incrustation.
Structures in the lawsonite—glaucophane schists of New Caledonia
Authors: Lillie A. R.
Published: May 2009

The regional strike of the bedding and foliation is NW but most of the folds and lineations plunge roughly SW. Lineations that resemble grain (longrain) seem to be usually parallel to the steeply plunging fold axes. This structural pattern occupies more than 2,000 km2. The formation of this pattern of folds was preceded and succeeded by regional folding along horizontal axes.