bluuebunny/crossref_metadata_2025_split huggingface dataset:
A seismic refraction line across Norfolk
Authors: Chroston P. N. 
Published: May 2009

AbstractA 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

AbstractInteractively 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

SummaryA 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

SummaryThe 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

SummaryThe 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

SummaryAt 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

SummaryThe 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

AbstractThe 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

AbstractTrilobites 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

SummaryStubblefield 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

SummarySuccessive 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

SummaryThe 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

AbstractChlorite–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

AbstractThe 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

AbstractIn 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

AbstractSr 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

AbstractFinger-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

AbstractIn 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

AbstractA 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

AbstractThe 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.