bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regional geothermobarometry in the granulite facies terrane of South India
Authors: Raith M. , Raase P. , Ackermand D. , Lal R. K. 
Published: November 2011

ABSTRACTIn the southern part of the Archaean craton of South India, an approximately 3.4–2.9 b.y. old migmatite–gneiss terrane (Peninsular gneiss complex) has been subjected to granulite facies metamorphism about 2.6 b.y. ago. During this event, the extensive charnockite-khondalite zone of southern India developed. A younger metamorphism (Proterozoic?) led to retrogression of the charnockites and khondalites, mainly under the conditions of the amphibolite facies.The physical conditions of metamorphism have been evaluated by applying methods of geothermobarometry to the widespread charnockitic assemblages with garnet, orthopyroxene, clinopyroxene, plagioclase, and quartz. The interpretation of the P–T estimates includes a critical discussion of potential error sources, e.g. errors of the analytical data and the calibrations of the models, and takes into account the complex metamorphic history of the rocks and the kinetics of the mineral equilibria.P-T estimates were obtained for seven subareas from the rim compositions of the coexisting minerals: Shevaroy Hills 680±55°C—7·4±1 kb; Kollaimalai area 680±40°C—8·6± 1 kb; Nilgiri Hills 680±90°C—6·6±0.8kb (upland massif) and 705±60°C—9·3±0.8 kb (northern margin); Bhavani Sagar area 650±50°C—7·2± 1 kb; Sargur-Mysore area 690±60°C—7·6 kb; Bangalore-Kunigal-Satnur area 760±50°C—6 kb. Except for the last subarea, the P-T model data reflect the conditions of a late annealing stage probably related to the retrogressive metamorphism. Conditions near the peak of granulite facies metamorphism (730–800°C—6·5–9·5 kb) are recorded by the core compositions of the minerals. Although a rather uniform cooling history of the main part of the charnockite-khondalite terrane is suggested from the temperature data, differential uplift of smaller blocks is indicated by the regional variation of the pressure data.
K–Ar ages of clay concentrates from Irish orebodies and their bearing on the timing of mineralisation
Authors: Halliday A. N. , Mitchell J. G. 
Published: November 2011

ABSTRACTThe K–Ar ages of 117 clay concentrates from samples associated with mineral deposits in Ireland indicate that most, if not all of the major ore deposits were formed during Carboniferous times or earlier. The Avoca orebodies are pre-400 Ma in age. Many of the vein deposits traversing Palaeozoic rocks were either formed or rejuvenated during the Hercynian orogeny c. 300 Ma ago. The SW Ireland Cu–Ba ores are 290 Ma old, and the major, frequently stratiform, base metal deposits stratabound in the Lower Carboniferous were, at least largely, formed during the Carboniferous period. In the case of the Navan orebody, an early Carboniferous age is indicated. Previous models invoking major mineralisations during Mesozoic or Tertiary times are rendered invalid. However, in some areas there appears to have been hydrothermal activity during the Triassic and possibly the Permian. The Triassic event is thought to be genetically related to coeval hydrothermal avtivity found throughout the N Atlantic regions. The data suggest that probably <10 km of cover has been removed from the majority of Ireland since Lower Carboniferous times. K–Ar dating of clays is shown to be a powerful method for constraining the ages of oredeposits.
Development of lichenometric dating curves for Highland Scotland
Authors: Innes John L. 
Published: November 2011

ABSTRACTThe lichens growing on gravestones in 142 Scottish graveyards have been examined. Measurements were restricted to SectionRhizocarponthalii. These data permit the development of lichenometric growth curves on acidic igneous, basic igneous, sandstone and slate substrates in most areas of Highland Scotland. The colonisation of gravestones, which is extremely erratic, takes place after a minimum of eight years. The ‘great period’ of growth lasts for approximately 20 years after the erection of the gravestone. The lichen factor (growth after 100 years) is correlated with the growth after 25 and 250 years indicating that it is a representative index of the growth rates. Growth rates are non-linear, decreasing with time. Calculated lichen factors for acidic igneous substrates range from 33 to 104 mm. The distributions of different types of gravestones are non-uniform in both time and space, making the comparison of growth rates on different rock types impractical. The results indicate that there may be a gradual decrease in the growth rates from W to E, reflecting the decreasing maritime influence towards the E.
Structural evolution of an early Proterozoic strata-bound Cu-Co-Zn deposit, Outokumpu, Finland
Authors: Koistinen T. J. 
Published: November 2011

ABSTRACTThe massive pyrite-pyrrhotite-chalcopyrite-sphalerite deposit of Outokumpu, comprising the Keretti and Vuonos orebodies, is a deformed and metamorphosed strata-bound mass associated with mineralised stockworks. Mobilisation of much of the ore followed formation of large recumbent isoclinal folds that are the major structures of the surrounding rocks and associated with the modification of originally flat saucer-shaped ore lenses into elongate ruler-shaped masses. Further modification of shape took place at the mobilisation stage with much of the pyrrhotitic ore, particularly, now occupying the thickest parts of the orebodies in the form of breccia or microbreccia. In many parts gross original characters still exist and the pyritic and pyrrhotitic constituents of the ore have survived as separate entities while locally the pyritic ore retains pre-deformational characteristics and consistent stratigraphic position within a thin horizon.Both ore and country rocks show evidence of extensive polyphase deformation with the effects of six fold phases shown in the ore. Mineral assemblages in the country rocks indicate a middle amphibolite facies peak of metamorphism. The serpentinite-black schist-carbonate-quartzite rock assemblage, with which the ore is associated, was tectonically incorporated within the regionally extensive mica schist by even earlier subhorizontal thrusting. This is related to the movement of a thrust nappe with the interdigitation of an ocean-floor ophiolite assemblage and flysch deposited during ocean closure associated with Svecokarelian tectonism.The original formation of the Keretti and Vuonos sulphide masses took place in a marine exhalative environment with a pyritic layer overlying a pyrrhotitic layer in each of the two c. 4 km diameter irregularly oval-shaped depressions whose centres were c. 8 km apart. The mineralised stockwork below each mass represents the upper parts of the conduit for metalbearing fluids in a convective system.
Carbonate, silicate and fluid relationships in eclogites, Selje district and environs, SW Norway
Authors: Lappin M. A. , Smith D. C. 
Published: November 2011

ABSTRACTOrthopyroxene- and kyanite-lineage eclogites are distinguished on the basis of silicate and carbonate petrography and chemistry. Different textural and chemical types of magnesite, dolomite and calcite can be satisfactorily attributed to one of the three sequential metamorphic stages of eclogite history at anhydrous eclogite facies, hydrous eclogite facies and amphibolite facies. The chronological sequence of development of magnesite, dolomite and calcite matches the carbonate sequence found experimentally in synthetic peridotite-CO2-H2O systems during decompression. Magnesite and dolomite show reasonably regular Fe/Mg distribution relationships with silicates.A new geothermobarometer based upon is provisionally calibrated. It yields T estimates for given P very similar to those given by the geothermobarometer, e.g. 759–829°C at 20 kb and 803–894°C at 40 kb. P is tentatively estimated at 30±10, 23±6 and 10 ± 3 kb respectively for the three metamorphic stages.Fluid conditions after equilibration during each stage were either low or fluid-absent, but not low . A unique quartz-magnesite-dolomite vein represents an influx of CO2 in the P-T regime of instability of CO2 + pyroxene. Tectonic emplacement by deep-level obduction of diverse foreign source materials remains the petrogenetic model which best fits the data for these eclogites.
Upper Ordovician graptolites from the top Lower Hartfell Shale Formation (D. clinganiandP. lineariszones) near Moffat, southern Scotland
Authors: Williams S. Henry 
Published: November 2011

ABSTRACTThe top 9 m of Lower Hartfell Shale has been collected in 10 cm samples through a continuous sequence on the North Cliff at Dob's Linn. The boundary between theDicranograptus clinganiandPleurograptus lineariszones is denned for the first time in a measured section, 5.0 m below the top of the Lower Hartfell Shale, with the excavation of the North Cliff proposed as stratotype. The lateD. clinganiZone is characterised byDicranograptus ramosus?, Dicellograptus moffatensis, D. flexuosus[=D. forchhammeri], Climacograptus dorotheus, Glyptograptus daviesisp. nov.,Diplograptus? pilatussp. nov.,Neurograptus margaritatusandCorynoides calicularis. TheP. linearisZone is characterised byPleurograptus linearis linearis, Amphigraptus divergens divergens, Leptograptus capillaris, Dicellograptus elegans elegans, D. pumilis, D. carruthersiandClimacograptus tubuliferus. A range chart is provided and an attempt is made at a revised correlation of the Scottish succession with coeval zonal sequences in North America and Australia. Twenty-one taxa are described including the two new species noted above.
Lower Cambrian acritarchs from Scotland, Norway, Greenland and Canada
Authors: Downie C. 
Published: November 2011

ABSTRACTAssemblages of acritarchs are described from the Fucoid Beds of Skiag Bridge, Knockan Cliff and Skye in NW Scotland, and Holmia Shales of the Mjøsen area of Norway, the Bastion Formation of Ella Ø in East Greenland, the Lower Cambrian of the Burin Peninsula in Newfoundland and from the Gog Formation of the Rocky Mountains of Banff National Park, Alberta. These are shown to be correctable on the basis of acritarchs and with the Lower Cambrian successions of the Russian Platform. Twenty-one genera and fifty-three species of acritarchs and one tasmanitid are described. These include the new genera Skiagia and Volkovia, and thirteen new species, Acrum cylindiferum, Micrhystridium coniferum, M. ellaensis, M. ellipticum, M. flexispinosum, M. gogensis, M. minutum, M. ordensis, Multiplicisphaeridium ? waltoni, Skiagia brevispinosa, S. scottica, Revinotesta ordensis and Evittia irregulare. A number of recombinations have also been made.
Deformational history of an area with well-developed tectonic slides: Dalradian rocks of Horn Head, NW Irish Caledonides
Authors: Hutton Donald H. W. 
Published: November 2011

ABSTRACTA structural reinterpretation of Appin Group metasediments of the Dalradian Supergroup in part of the northwestern marginal zone of the Irish Caledonides is presented. No major F1 folds have been recorded although bedding occasionally faces upwards NW in S1. The structure is dominated by a series of NW-facing F2 recumbent folds and associated D2 tectonic slides. The slides, which have thrust the overlying rocks to the NW, are generally oblique to the fold axial planes and commonly cut out major F2 fold hinges. Rotation of the hinges towards the NW-SE (Caledonian) stretching direction in areas adjacent to the slides may have contributed to fold excision: an example of a major dislocated sheath fold is described. DM3 produces major SE-verging inclined folds. Although D4, D5 and D6 are of minor importance in the area D6 intensifies towards the SE to become the principal fabric in a major NE–SW-trending sinistrai shear zone that contains the c. 400 Ma Main Donegal granite. The early major structures of this area are compared with those in Dalradian Supergroup of adjacent parts of Scotland. It is suggested that the absence of a major F1 fold (analagous to the Islay anticline) and the occurrence of D2 recumbent folds and low angle thrusts in NW Ireland reflect the close proximity of the foreland, composed of the Lewisian complex, to the NW; such a situation is analagous to the Moine thrust zone in Scotland. The progressive development of low angle structures and thrusts to the W of the Scottish mainland is attributed to a westward shallowing of the Lewisian basement between the SW Highlands of Scotland and NW Ireland.
Sedimentology of the Dinantian of Foulden, Berwickshire, Scotland
Authors: Anderton R. 
Published: November 2011

ABSTRACTThe Berwickshire Cementstone Group was deposited on a coastal plain crossed by meandering rivers flowing S into a marine gulf, the Northumberland basin. Sedimentation was mainly by overbank flooding onto an alluvial plain which largely dried out between floods. The resulting sediments include poorly-stratified mudstones and siltstones and crevasse splay sheet sandstones. The depositional environment of the cementstones is not clear. Lacustrine and tidal flat origins are considered. Semi-permanent floodplain lakes were very rare, but in one the uniquely fossiliferous Foulden Fish Bed was deposited. This lake was shallow and filled by repeated influxes of sediment carried from rivers by sheetfloods. On entering the lake, these sheetfloods may have become density underflows from which thin, graded siltstones or sandstones were deposited. These floods carried plant debris into the lake and rapidly buried the remains of the lake fauna. The salinity of the lake cannot be determined, but the input of both fresh and saline waters can be envisaged. There is no evidence that the lake was permanently eutrophic. The mortality of the animals may have been due to changes in water chemistry produced by hot dry spells of weather followed by storms and floods.
Plants from the Dinantian of Foulden, Berwickshire, Scotland
Authors: Scott Andrew C. , Meyer-Berthaud Brigitte 
Published: November 2011

ABSTRACTAnatomically preserved plants are recorded from calcareous nodules and include Lepidodendron calamopsoides Long which demonstrate for the first time the presence of anisotomous branching, in addition to the normal isotomous branching and details of the stele and the cortex seen in longitudinal section. The nodules also contain Setispora subpaleocristatus (Alvin) Spinner and Lagenicula crassiaculeata Zerndt megaspores. There is an abundant compression flora. Compressions and petrifactions of Tristichia ovensi Long may not represent the same plant and may not be connected to Stamnostoma huttonense Long. We suggest that the compressions of T. ovensi were of a pteridospermous plant with unlaminated fronds bearing small uncupulate seeds and lateral clusters of microsporangiate organs of a new type.
A remarkable arthropod fauna from the Upper Cambrian “Orsten” of Sweden
Authors: Müller Klaus J. , Walossek Dieter 
Published: November 2011

ABSTRACTExtensive preparation since 1975 has yielded thousands of specimens of various minute arthropods, mainly phosphatocopid ostracods and other crustaceans. The whole exoskeleton is exceedingly well preserved in three dimensions, showing even delicate mo1 phological details. The material permits not only the description of the morphology and systematic status of the animals but also interpretation, with a high degree of confidence, of the function, life habit, and ontogeny of these early arthropods.
The Lower Carboniferous shrimpTealliocarisfrom Gullane, East Lothian, Scotland
Authors: Briggs D. E. G. , Clarkson E. N. K. 
Published: November 2011

ABSTRACTTealliocarisis probably one of the best preserved of all Carboniferous crustaceans. It occurs scattered through the 12 cm thick laminated Gullane ‘shrimp-bed’. The cuticle is exceptionally well preserved and the specimens, which are normally complete, are infilled with fluorapatite. The carapace has an elongate rostrum, a defined frontal area, a median ridge and paired gastric and inner and outer lateral ridges. The eyes are borne on a stout peduncle. The first antenna bears a pair of flagella, the second an antennal scale and long flagellum. The mandible is large and heavily sclerotised with molar and incisor process. The maxillae and anterior thoracopods are poorly preserved. The posterior six thoracopods each have a long segmented endopod and annulated setose exopod. More than half the specimens preserve lamellae which may represent branchial epipods, or floor a brood chamber beneath the carapace on either side of the thorax. The pleopods are biramous. The telson and uropods form a tail fan. In the absence of oostegitesTealliocariscannot be assigned to the order Mysidacea but its affinities lie close to these Eumalacostraca.Tealliocariswalked on the thoracic endopods, but could also swim using the pleopods and thoracic exopods. The mode of feeding is uncertain.Tealliocarisprobably inhabited a brackish lake or lagoon, but its distribution elsewhere suggests that it may have been tolerant of a range of salinities.
Isopodichnus, related arthropod trace fossils and notostracans from Triassic fluvial sediments
Authors: Pollard J. E. 
Published: November 2011

ABSTRACTThe commonest arthropod trace fossils from Triassic aquatic red beds are the bilobate tracesIsopodichnusand trackways known as‘Merostomichnites’ triassicus. These trace fossils were probably produced by notostracan branchiopods, similar toTriops.Four arthropod ichnocoenoses from Lower Triassic fluvial sandstones have been analysed in terms of size frequency distribution, behavioural variation and relationship to sedimentary structures and depositional environment. OneIsopodichnusichnofauna associated with flute moulds (Dumfries-shire, Scotland) shows a normal age-structured population of arthropods responding with strong rheotaxis within shallow fluvial channels. The secondIsopodichnusassemblage associated with ripple marks (Worcestershire, England) also shows strong rheotaxis but is bimodal in size and morphotype, possibly suggesting change in arthropod behaviour with age. Two ichnocoenoses of trackways with less pronounced rheotaxis associated with ripples (Cheshire, England) and flute moulds (Württemberg, Germany) were produced by larger arthropods than the resting traces. These arthropods probably possessed 6 to 9 pairs of walking limbs.The conclusions derived from these notostracan trace fossils are compared with data on palaeoecology, population size-frequency, morphology and behaviour ofTriops cancriformisderived from the analysis of three Triassic body fossil faunas and literature on living populations. Taxonomic consideration favours retention of the nameIsopodichnusbut the trackways should be included inAcripesMatthew. Brief review of late PalaeozoicIsopodichnusassemblages which appear to predate known notostracan fossils is inconclusive as regards both identifying producers or infallible means of separation fromCruzianaassemblages.
Form and function in Thylacocephala, Conchyliocarida and Concavicarida (?Crustacea): a problem of interpretation
Authors: Rolfe W. D. Ian 
Published: November 2011

ABSTRACTDifferences in the preservation of Jurassic thylacocephalans and conchyliocarids have given rise to different interpretations of the form of these fossils, and thus their mode of life. When evidence from these two groups is combined with that derived from Palaeozoic concavicarids, it becomes possible to unify the several interpretations of this one group of organisms, the Thylacocephala. The group ranges from at least the Silurian to the Cretaceous.A review is given of how these differences of interpretation have arisen, and some resolution is attempted. If the thylacocephalan “anterior structure” is reinterpreted by analogy with hyperiid amphipods as a paired compound eye occupying most of the surface of the head, it explains its bilobed nature and the position of the stomach within the structure, but it raises the difficulty of a post-cephalic origin for the carapace. The simpler solution is preferred of regarding this structure as discrete paired eyes with a smooth cornea and subjacent crystal cones.The raptorial appendages are post-oral and post-adductor in insertion. They are therefore tentatively identified as the maxillae and maxilliped, but verification of the mandible's position is needed to test this. The postero-ventral battery of “body somites” is reinterpreted as paired protopods of abdominal limbs. A respiratory current is deduced to have entered a branchiostegal chamber ventrally, and left it posterodorsally. It is speculated that the looped linear pattern of intra-cuticular spheres in Paraostenia are photophores. The large eyes with small interommatidial angles were probably used to discern low contrast prey or carrion against a dim background. By analogy with hyperiid amphipods, it is suggested that at least some thylacocephalans were mesopelagic predators. They may have attained neutral buoyancy from their food substrate of shark and coleoids.
Petrography and geochemistry of feldspathic and mafic sediments of the northeastern Pacific margin
Authors: van de Kamp Peter C. , Leake Bernard Elgey 
Published: November 2011

ABSTRACTThis study attempts to ascertain whether the differing provenance sources and plate tectonic settings of deposition of clastic sediments and rocks can be identified by chemical means, thus opening the increased use of these rocks and their metamorphosed derivatives in plate tectonic modelling. Mineralogically immature feldspathic and mafic sands, muds, sandstones and shales from Mesozoic, Cenozoic and Holocene clastic deposits in California, Oregon, Alaska and Colorado have been both modally and chemically analysed providing a valuable data base (217 samples; 216 samples chemically analysed, many for 28 elements).There is significant upward chemical variation in the Great Valley sequence of California which mimics previously described petrographic variation and in turn reflects provenance changes with igneous episodes and erosional stripping of the Sierra Nevada in late Mesozoic time. Differing sandstone petrofacies result in varying chemical signatures and while the provenances of monomict sediments are easiest to identify, polymict sources involving granitoid or ophiolitic material can often be identified by potassium feldspar or Cr contents. The distinction of K which is derived from detrital potassium feldspar from K derived from detrital illite, micas or other sheet minerals, is best made by a Niggli al–alk plot against k. Mafic sandstones derived from mafic volcanic or plutonic rocks preserve essentially mafic igneous chemistry and could be possible parent sources of some amphibolites which grade into metasediments. The lithified erosion products of the Sierra Nevada calc-alkaline igneous rocks have higher Niggli al–alk and higher average Niggli si at any given mg value than the fresh igneous rocks enabling meta-arkoses to be distinguished from meta-igneous rocks.Applying previously published chemical criteria gives the actual plate tectonic setting of deposition of most of the sandstones studied. This suggests that the chemical composition of sandstones can yield much more information about the provenance and plate tectonic setting than hitherto recognised.
Value of chemostratigraphical correlation in metamorphic terranes: an illustration from the Colonsay Limestone, Inner Hebrides, Scotland
Authors: Rock N. M. S. 
Published: November 2011

ABSTRACTChemostratigraphical correlation provides valuable insights into the status of the Colonsay Group, which field and structural studies have left unresolved. Using published discriminant functions, major and trace element data support previously proposed correlations of the Colonsay Limestone with Appin Group (Lower Dalradian) limestones, and particularly with the Ballachulish Limestone Formation. They also tend to preclude correlations with other nearby Dalradian carbonate formations, with marbles of the early Precambrian Lewisian complex, and with miscellaneous unassigned limestones in a similar structural position to the Colonsay Limestone, astride the Great Glen fault.