bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geophysical investigation of the Beinn an Dubhaich Granite, Skye
Authors: Goulty N. R. , Darton C. E. , Dent A. E. , Richardson K. R. 
Published: May 2009

AbstractThere has been a long-standing controversy concerning the form of the Beinn an Dubhaich Granite, which intrudes Cambro-Ordovician limestones and contains enclosures of limestone at outcrop. We have undertaken a three-part geophysical investigation with the aim of resolving some issues raised by previous workers. Our most significant finding results from the measurement of a gravity profile across Beinn an Dubhaich. It reveals a negative anomaly of more than 2 mGal over the granite outcrop. Our preferred model to fit this anomaly is a steep-sided granite stock extending down to about 1 km depth, which implies that the limestone enclosures are roof pendants. In a supplementary study, we measured magnetic profiles across dykes in some of the limestone enclosures in order to determine the depth to the contact with the underlying granite. However, in the most clear-cut cases we could only determine a minimum depth of 20 m, and were unable to constrain the maximum depth. In hindsight, we suggest that microgravity surveying would be a better method for determining the thicknesses of the limestone roof pendants. In the third part of the investigation, we measured a tight grid of magnetic profiles to the northeast of the granite outcrop to test a previous suggestion that dyke-like lobes of granite intrude pre-existing fractures in the overlying limestones. We located several large magnetic anomalies associated with outcropping doleritic dykes and concluded that these had not been correctly identified in the earlier work. Consequently, the ground magnetic profiles acquired to date provide no valid evidence to support the idea of an interfingering contact between the limestones and the underlying granite.
Age and significance of Upper Cretaceous siliciclastic turbidites in the central Pindos Mountains, Greece
Authors: Wagreich M. , Pavlopoulos A. , Faupl P. , Migiros G. 
Published: May 2009

AbstractA significant 5- to 30-metre-thick interval of siliciclastic turbidites forming the First Flysch is present in the deep-water succession of the Pindos Zone. Nannofossil investigations in the central parts of the Pindos Mountains of mainland Greece indicate an assemblage of theMarthasterites furcatuszone (CC13). The presence ofM. furcatus, together with commonQuadrum gartnerisuggests that the turbidites were deposited mainly during the middle to upper part of the late Turonian. The siliciclastic turbidites are interpreted as deposits of a lowstand fan as a result of a pronounced short-time eustatic sea-level drop in the late Turonian.
Single zircon evaporation ages constraining the growth of the Archaean Aravalli craton, northwestern Indian shield
Authors: Roy A. B. , Kröner A. 
Published: May 2009

AbstractSingle grain 207Pb/206Pb zircon ages were determined for granitoids and gneisses which constitute the Archaean basement rocks of the Aravalli craton of Rajasthan, northwestern Indian Shield. The protolith ages for two gneisses, collected from east of Udaipur, are ˜3230 Ma and 2887 Ma respectively. The granitoids display an intrusive relationship with the gneisses and yielded ages ranging between 2666 Ma and 2620 Ma. These ages provide the basis for a geochronological model of evolution of the oldest basement of the Aravalli craton.
The graptolite nema: problem to all our solutions
Authors: Rickards R. B. 
Published: May 2009

AbstractLack of understanding of the graptolite nema and virgula is probably the main cause of the general failure to arrive at a general mode of life theory for planktonic species. The nema and virgula are shown to be different structures. The nema may have had a rhabdosome rotational function at early growth stages; the primary function of the virgula may have been rhabdosomal rotation, whilst a secondary function was as a stipe growth guide. Rotational function would be inapplicable for pseudovirgulae and in synrhabdosomes.
Albitized microcline grains of post-depositional and probable detrital origins in Brøttum Formation sandstones (Upper Proterozoic), Sparagmite Region of southern Norway
Authors: Morad S. 
Published: May 2009

AbstractUntwinned albite (Ab99.4An0.4Or0.2) grains, forming during diagenesis and very low-grade metamorphism, are common in sandstones of the Brøttum Formation (Upper Proterozoic) in the Sparagmite Region of southern Norway. These untwinned albite grains are usually clouded by vacuoles and tiny inclusions which are mostly made of carbonaceous material (although some albite grains also contain some combination of carbonates, quartz, phengite, chlorite, pyrite, halite and anatase). The presence of microcline grains replaced partly by albite indicates that the albite grains are pseudomorphs after microcline. Chessboard albite which occurs in the Brøttum Formation is suggested to be detrital in origin.
Determining the representative composition of a set of sandstone samples
Authors: Philip G. M. , Watson D. F. 
Published: May 2009

AbstractThe description of sandstone samples, defined by three components, is introduced through non-parametric sample density description. The composition of a particular sample defines a direction from the origin of the Cartesian reference frame. Radial difference between individual samples then provides the measure of their similarity. A sample set can be viewed as a bundle of compositional axes with a corresponding density distribution on both the ternary diagram (or unit constant sum plane) and the positive octant of the unit sphere. Because radial differences are disproportionately displayed on the ternary diagram, radial density calculations on the sphere are to be preferred. The mode of the sample set, the implied centre of greatest data concentration, is considered to be the most meaningful representative value, as the component joint mean can lie outside the data field with certain data configurations. In addition, the component joint mean cannot provide a useful representative composition for samples drawn from a bimodal distribution. Sample density distribution not only provides a data defined approach to describe sample dispersion, but also furnishes an indication of sample sufficiency in displaying the degree to which modes are supported by surrounding observations.
Structural evolution of a frontal ramp section of the West Spitsbergen, Tertiary fold and thrust belt, north of Isfjorden, Spitsbergen
Authors: Wennberg Ole Petter , Andresen Arild , Hansen Sigurd , Bergh Steffen G. 
Published: May 2009

AbstractThe geometry and kinematic evolution of a frontal ramp section associated with the Tertiary West Spitsbergen Orogenic Belt has been investigated in a small area (Lappdalen) north of Isfjorden. The previously recognized thrust front corresponds to a complex step or ramp in the position of the sole-thrust in the area. The sole-thrust is localized to the evaporites of the Permian Gipshuken Formation to the west of the footwall ramp, whereas to the east it continues as a bedding-parallel thrust in Triassic shales (Sassendalen Group). The area to the west of the footwall ramp is characterized by large scale thrusts and folds involving the Permian Gipshuken and Kapp Starostin formations and the lower part of the Triassic Sassendalen Group. East of the footwall ramp both Permian and Triassic strata are sub-horizontal and apparently undeformed. Three major thrust sheets are recognized. Based on the geometric relationship between folds and faults in the area, both fault-bend and fault-propogation mechanisms of folding are inferred. Restoration of the Kapp Starostin Formation to its pre-deformational state indicates a minimum of 35% shortening. Structural observations within the Sassendalen Group in the study area and on Dickson Land suggest that some of this shortening is transmitted eastwards along one or more bedding parallel thrusts in the Sassendalen Group.
Post-impact deposits in Tvären, a marine Middle Ordovician crater south of Stockholm, Sweden
Authors: Lindström M. , Flodén T. , Grahn Y. , Kathol B. 
Published: May 2009

AbstractThe well-preserved Tvären crater is noteworthy for being one of a small number of Early and Middle Ordovician impact structures formed in a marine environment. It is demonstrated to be an impact structure by the presence of a breccia lens, consisting of crystalline basement rocks, and shocked quartz. The breccia lens formed under dry-hot conditions after expulsion of sea-water by the impact. Resurging sea-water thereupon deposited a positively graded, 60 m thick turbidite-like unit. This graded resurge deposit is a previously unknown feature, to be expected in open-sea impacts. Breccia in the lower part of this graded deposit contains fragments of a remarkably complete orthoceratite limestone succession that existed at the site of impact, resting on non-lithified sand of probably Early to earliest Middle Cambrian age. A sedimentary succession was deposited inside the crater at depths decreasing from more than 200 m in the initial stages to some 100 m at the time of deposition of the youngest preserved beds. The environment within the crater thus favoured deposition of an essentially complete stratigraphic succession with depth-controlled palaeoecology for a significant time interval after the impact. Whereas planktonic members, like graptolites and chitinozoa, are present throughout the post-impact succession, and asaphids, almost as persistent, became established at an early date, burrowers were somewhat reluctant to enter and remopleuridids and small strophomenids came in at a late stage. We suggest as a result of this study that structures formed by impact may offer unique information about the palaeogeology and palaeoenvironment of the region hit by the impact.
Geochemistry of the Sunnfjord Melange: sediment mixing from different sources during obduction of the Solund–Stavfjord Ophiolite Complex, Norwegian Caledonides
Authors: Alsaker Einar , Furnes Harald 
Published: May 2009

AbstractThe Sunnfjord Melange is a strongly tectonized sedimentary assemblage occurring tectonostratigraphically below the Solund–Stavfjord Ophiolite Complex of Ashgill age, and upon continental margin deposits of Wenlock or older age. The Sunnfjord Melange, which probably started to form within an oceanic transform fault, developed further during obduction of the Solund–Stavfjord Ophiolite Complex. The Sunnfjord Melange is divided into two units, the lower Øyravatn Unit of predominantly fine grained calcareous quartz-bearing chlorite–muscovite schists, and the upper Markavatn Unit, mainly metagreywackes. Both units contain blocks of metabasalts, marble and meta-arkose. Serpentinite blocks are restricted to the Markavatn Unit. The appearance of serpentinite detritus is marked by much higher contents of Cr and Ni in the metasediments of the Markavatn Unit than in those of the Øyravatn Unit. The geochemistry of the metasediments from the Øyravatn Unit and the Markavatn Unit is compatible with mixing of detritus from continental and ophiolitic sources. Despite the strong and pervasive deformation of the Sunnfjord Melange, its geochemical composition from the lowest to the highest tectonostratigraphic levels reflects that of the inverse pseudostratigraphy of the Solund–Stavfjord Ophiolite Complex. Thus, only metabasalts of the Solund–Stavfjord Complex and continental meta-arkoses yielded detritus to the schists of the Øyravatn Unit. The compositions of the schists and metagreywackes of the Markavatn Unit, on the other hand, show that a multicomponent detritus derived from metabasalt and serpentinite of the Solund–Stavfjord Ophiolite Complex, mixed with the detritus from continental meta-arkoses.
Geology and geochemistry of the volcanic rocks of the Pioneer Formation, Bridge River area, southwestern British Columbia (Canada)
Authors: Dostal J. , Church B. N. 
Published: May 2009

AbstractThe Pioneer Formation of southwestern British Columbia (Canada) is composed predominantly of middle to late Triassic pillow basalts. These rocks are an integral part of the Cadwallader and the Bridge River terranes that were delaminated from the oceanic lithosphere and stacked against the continental margin of the North American craton by middle Jurassic time. The basalts are underlain and locally intercalated with ribbon cherts and argillites that range in age from Mississippian to Triassic. The Triassic basalts are conformably overlain by clastic sediments containing late Carnian–Norian conodont fauna. The tholeiitic basalts have enriched and depleted REE patterns, and have been emplaced in an oceanic environment. The compositional variations of the basalts are attributed to dynamic partial melting of source rocks that are believed to have been part of the rising mantle diapir. According to our model, after initial melting in the garnet stability field, the mantle diapir rose up to the spinel stability field where it underwent subsequent melting. The reconstructed stratigraphy of the Bridge River area may be interpreted in terms of an oceanic plate moving over a mantle plume and into a trench where offscraping preserved tectonic lenses of the subducting plate in an accretionary prism.
First record of the Devonian lycophyte Leclercqia from South America
Authors: Berry Christopher M. 
Published: May 2009

AbstractA single leafy stem from the Middle or lowermost Upper Devonian Campo Chico Formation, Sierra de Perijá, western Venezuela, is the first record of the important Devonian herbaceous lycophyte Leclercqia from South America, usually considered as part of western Gondwana. The seemingly cosmopolitan distribution of this genus is discussed in relation to coeval assemblages and palaeo-continental reconstructions.
Nd isotope chemistry of Tertiary igneous rocks from Arran, Scotland: implications for magma evolution and crustal structure
Authors: Dickin A. P. 
Published: May 2009

AbstractThe geochemistry of Tertiary igneous rocks from Arran, western Scotland, provides a probe for the structure of the crust in the region of the Highland Boundary Fault (HBF). New Nd isotope data, coupled with other geochemical evidence, point to variable contamination of primitive mantle-derived magmas during magmatic differentiation in the crust. Two different isotopic contamination trends are seen. The northern granite was generated by contamination of basic differentiates by crust resembling exposed Dalradian units. Data for the central granite, and several other minor intrusions from south of the HBF, trend towards the reported isotopic signatures of granulite-facies xenoliths from the Midland Valley. However, quartz porphyry intrusions in the south of the island are compositionally similar to the nothern granite, and were probably intruded southwards across the HBF in dykes. Hence the isotopic signatures of the Tertiary intrusions reflect the different character of the crustal units on either side of the fault.
Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica
Authors: Carson C. J. , Dirks P. G. H. M. , Hand M. , Sims J. P. , Wilson C. J. L. 
Published: May 2009

AbstractMeta-sediments in the Larsemann Hills that preserve a coherent stratigraphy, form a cover sequence deposited upon basement of mafic–felsic granulite. Their outcrop pattern defines a 10 kilometre wide east–west trending synclinal trough structure in which basement–cover contacts differ in the north and the south, suggesting tectonic interleaving during a prograde, D1 thickening event. Subsequent conditions reached low-medium pressure granulite grade, and structures can be divided into two groups, D2 and D3, each defined by a unique lineation direction and shear sense. D2 structures which are associated with the dominant gneissic foliation in much of the Larsemann Hills, contain a moderately east-plunging lineation indicative of west-directed thrusting. D2 comprises a colinear fold sequence that evolved from early intrafolial folds to late upright folds. D3 structures are associated with a high-strain zone, to the south of the Larsemann Hills, where S3 is the dominant gneissic layering and folds sequences resemble D2 folding. Outside the D3 high-strain zone occurs a low-strain D3 window, preserving low-strain D3 structures (minor shear bands and upright folds) that partly re-orient D2 structures. All structures are truncated by a series of planar pegmatites and parallel D4 mylonite zones, recording extensional dextral displacements.D2 assemblages include coexisting garnet–orthopyroxene pairs recording peak conditions of ∼ 7 kbar and ∼ 780°C. Subsequent retrograde decompression textures partly evolved during both D2 and D3 when conditions of ∼ 4–5 kbar and ∼ 750°C were attained. This is followed by D4 shear zones which formed around 3 kbar and ∼ 550°C.It is tempting to combine D2–4 structures in one tectonic cycle involving prograde thrusting and thickening followed by retrograde extension and uplift. The available geochronological data, however, present a number of interpretations. For example, D2 was possibly associated with a clockwise P–T path at medium pressures around ∼ 1000 Ma, by correlation with similar structures developed in the Rauer Group, whilst D3 and D4 events occurred in response to extension and heating at low pressures at ∼ 550 Ma, associated with the emplacement of numerous granitoid bodies. Thus, decompression textures typical for the Larsemann Hills granulites maybe the combined effect of two separate events.
The Holocene lithostratigraphy of Fenland, eastern England: a review and suggestions for redefinition
Authors: Wheeler A. J. , Waller M. P. 
Published: May 2009

AbstractThe Fenland basin is filled with unconsolidated Holocene marine and freshwater deposits. Stratigraphic studies of the basin date back to 1877. This paper reviews the various lithostratigraphic schemes which have been proposed. Particular attention is paid to the presently accepted lithostratigraphy. Examples and a case study of a newly surveyed area are used to highlight its failings. Many of the difficulties experienced in Fenland are common to problems of lithostratigraphic classification in coastal lowland environments, as is demonstrated by reference to recent debate in the southeastern North Sea. In Fenland, as a result of the shortcomings of the various schemes, it is proposed that a new lithostratigraphy with formal stratotypes is devised. Suggestions are made as to the form this new stratigraphy could take. In the meantime, an informal lithostratigraphy should be adopted which has no regional or chronostratigraphic connotations.
The Variscan thermal history of west Clare, Ireland
Authors: Fitzgerald E. , Feely M. , Johnston J. D. , Clayton G. , Fitzgerald L. J. , Sevastopulo G. D. 
Published: May 2009

AbstractVitrinite reflectance data from Namurian rocks in west Clare suggest that high maturation levels, corresponding to palaeotemperatures of 340–370 °C, were attained prior to Variscan deformation. Fluid inclusions in syntectonic quartz veins homogenize between 330 °C and 50 °C with an accompanying decrease in salinity from 27 to 5 eq. wt % NaCl. Maximum fluid inclusion entrapment temperatures ranged from more than 300 °C to 250 °C during Variscan folding in County Clare. The observed maturation levels (c. 7.5% Rmax) far exceed values for simple burial maturation based on the estimated burial history and ‘normal’ geothermal gradients, and do not increase with depth in the Doonbeg No. 1 exploration well. Fluid advective heating is suggested as the most likely mechanism consistent with the Clare reflectance and thermometric data. Vein and shear zone dimensions preclude rapid vertical movements of hot fluids through the section, and extensive lateral fluid migration from sedimentary basins undergoing tectonically driven dewatering to the south or west is therefore proposed.
Palynology of the ‘Lower Old Red Sandstone’ at Glen Coe, Scotland
Authors: Wellman Charles H. 
Published: May 2009

Abstract‘Lower Old Red Sandstone’ deposits preserved by cauldron subsidence at Glen Coe, Scotland have hitherto lacked secure biostratigraphical age constraint. A sporomorph assemblage recovered from basal sediments of these deposits permits age determination, despite being highly carbonized. The sporomorph assemblage is correlated with the micrornatus-newportensis Sporomorph Assemblage Biozone, indicating a late early-early late Lochkovian age (early Devonian). Sporomorph assemblages from basal sediments of the ‘Lower Old Red Sandstone’ sequence at nearby Lorne, a suggested correlative of the Glen Coe deposits, are older (latest Pridoli-earliest Lochkovian age). However, the new biostratigraphical data do not preclude the possibility that the Glen Coe and Lorne deposits are lithological correlatives and the basal sediments are diachronous.
Cambrian–Ordovician Boundary beds at Tônismägi, Tallinn, North Estonia
Authors: Kaljo D. , Heinsalu H. , Mens K. , Puura I. , Viira V. 
Published: May 2009

AbstractThe Cambrian–Ordovician Boundary beds at the Tônismägi section in Tallinn, North Estonia, are represented by siltstones and sandstones with interlayers of clay and kerogenous argillites. In this section, three conodont zones –Cordylodus proavus, C. intermediusandC. rotundatus-angulatus– were established. Graptolites of theRhabdinopora flabelliformegroup were found in the upper part of theC. proavusZone. This section demonstrates that in suitable facies, species ofRhabdinoporamay appear earlier than usually considered.
Litophragmatoceras incomptum gen. et sp.nov. (Cretaceous Ammonoidea), a cryptic micromorph from the Upper Cenomanian of Arizona
Authors: Kennedy W. J. , Cobban W. A. 
Published: May 2009

AbstractLitophragmatoceras incomptum gen. et sp.nov. is a small dimorphic planulate ammonite from the Upper Cenomanian Metoicoceras mosbyense Zone of Arizona in which microconchs are adult at as little as 5 mm diameter and macroconchs at 23 mm diameter or less. The quinquelobate suture is very simple, with entire lobes and saddles. It is distinct from all contemporaneous ammonites and is referred, with no great certainty, to the otherwise exclusively Upper Albian and Lower Cenomanian Flickiinae Adkins, 1928.