bluuebunny/crossref_metadata_2025 huggingface dataset:
Granulites in and around the Bengal anorthosite, eastern India; genesis of coronal garnet, and evolution of the granulite-anorthosite complex
Authors: Bhattacharyya P. K. , Mukherjee Subimal
Published: May 2009

Granulites occur in and around an anorthosite massif (commonly referred to as the Bengal anorthosite) in eastern India. The central part of the anorthosite is massive in nature with locally developed ‘fluxion structure’ in isolated blocks. Banding in the peripheral part is typical of that of the massif anorthosites of Anderson & Morin. The granulites bear imprints of polyphase deformation, and the xenoliths of granulites within the anorthositic massif maintain their regional structural alignment. The Anorthosite, syntectonic with the second fold movement in the terrane, has developed second generation structures.

Hornblende, orthopyroxene, clinopyroxene, plagioclase and quartz with or without garnet and other minor phases consitute the granulites. In the anorthosites, orthopyroxene, clinopyroxene, hornblende, and magnetite with or without garnet may constitute more than 15% of the mode. Garnet, when present in the rocks, is a late overprint. Symplectitic growth of garnet with one or more of the phases such as ilmenite, quartz, clinopyroxene and sodic plagioclase indicates genesis of garnet through decomposition of orthopyroxene and/or prograde hornblende in the presence of calcic plagioclase. The garnet formed during prograde dehydration reactions, rather than cooling of the complex.

Chemical characteristics of the mafic phases in the rocks indicate attainment of exchange equilibrium with respect to the major cations in closely associated hornblende, clinopyroxene, orthopyroxene and garnet. Estimated physical conditions of metamorphism from contrasted assemblages suggest a final equilibration of different granulitic assemblages as well as of the anorthositic assemblages under similar conditions. There was, however, belated building up of water pressure in the anorthositic domains stabilizing a late hornblende during cooling of the complex. Absence of chilled margins in the anorthosite as well as absence of contact aureoles in the enveloping and enclosed granulites indicate emplacement of the anorthosite in a hot environment, prior to cooling of the complex.
Late Caledonian granitoids and timing of deformation in the Iapetus suture zone of eastern Ireland
Authors: Murphy Finbarr C.
Published: May 2009

Late Caledonian granitoids, (c. 400 Ma) in the zone of the Iapetus suture provide a datum against which current models for the relative timing of deformation can be tested. One such granitoid adjacent to the proposed suture ‘line’ in eastern Ireland is now buried by an Upper Palaeozoic cover. It is identified geophysically by a negative Bouguer anomaly with no magnetic signature, and geologically by a hypabyssal dyke swarm and hornfels metamorphism. The timing of intrusion of the granitoid is shown to have occurred during the continuing end-Silurian/early-Devonian deformation. Other members of this widespread suite in Ireland show features consistent with diapiric intrusion during the later stages of the deformation. This evidence brackets the age of regional deformation as continuing during granite emplacement and cooling (c. 400 Ma). The unifying characteristics of the straddling granitoid suite, coupled with a sinistrally transpressive deformation, in this broad suture zone are interpreted in terms of a continental collision which climaxed in late-Silurian/early-Devonian time.
On the directional nature of stratigraphic correlation
Authors: Tipper John C.
Published: May 2009

In every correlation exercise the diachroneity of the lithostratigraphic boundaries determines the discrepancy between lithostratigraphic correlation and time-correlation. Here it is shown that diachroneity varies in degree as a simple function of the direction in which correlation is made, and hence that stratigraphic correlation must take that direction into account. When the direction of correlation is not known, a sound strategy for time-correlation of lithostratigraphic boundaries is to assume that each is at its most diachronous.
Burial of trees by eruptions of Mount St Helens, Washington:implications for the interpretation of fossil forests
Authors: Karowe Amy L. , Jefferson Timothy H.
Published: May 2009

Lahars and fluvial sediments which buried trees following the 18 May 1980 eruption of Mount St Helens were investigated during August of 1982. Trees buried in older mudflows, dated at a.d. 1885, a.d. 1450–1550, and 36000 years b.p., also were examined. Although many logs clearly were transported, large numbers of trees were buried in growth position. Burial by lahars generally resulted in the death of trees, whereas some trees survived burial by fluvial sediments. Scanning electron microscope studies show that trees buried in lahars are well preserved. Pre-1885 buried woods show incipient silicification, and woods buried 36000 years b.p. show silica impregnation of cell walls.

Features ofin situand allochthonous burial very similar to those seen in southern Washington are found also in Eocene silicified forests in Yellowstone National Park, Wyoming, U.S.A., and in Cretaceous fossil forests in southeastern Alexander Island, Antarctica. Observations of Recent wood from volcaniclastic deposits of Mount St Helens provide valuable insights into processes of burial and silicification of fossil forests of various ages around the world.
Origin of finger structures in the Rhum Complex: phase equilibrium and heat effects
Authors: Morse S. A. , Owens Brent E. , Butcher Alan R.
Published: May 2009

The finger structures described earlier by Brown and later by Butcher, Young & Faithfull involve dissolution of troctolite during crystallization of olivine, followed by crystallization of pyroxene around olivine grains in the fingers. However, the ingestion of troctolite takes the liquid away from pyroxene saturation rather than toward it. The pyroxene field can be encountered metastably, and pyroxene caused to crystallize, by supercooling the olivine-rich liquid against the troctolite. The melt corrosion represented by the fingers, and other field relations, suggest that the mafic layers were emplaced as sills of mafic magma into nearly solid troctolites. Melting at the base of mafic liquid layers was impeded by a bed of olivine crystals releasing light solute upward, causing compositional convention and rapid heat transfer to the top of the layer, where melting demonstrably occurred. Recognition of this process introduces the novel concept of a magmatic heat pump driven by compositional convection. The crystallization path ol–px–pl(–sp) is also found next to xenoliths in the Kiglapait Intrusion where the magma was normally saturated only in ol+pl, directly demonstrating the effect of supercooling on the crystallization sequence.
Continuous out-of-sequence ductile thrusting in the Norwegian Caledonides
Authors: Rice A. H. N.
Published: May 2009

Peak metamorphic conditions (up to sillimanite grade) in a unit of rocks beneath the evolving Kalak Nappe Complex (Finnmarkian Caledonides) developed prior to its incorporation as a nappe within the complex. The presence of displacement textures in peak metamorphic por-phyroblasts indicates that they grew in a hydrostatic stress regime and thus that the emplacement of tectonically higher units caused little or no deviatoric stress in the footwall rocks except close to the thrust plane.

The developing geotherm in the incipient nappe was disrupted by the onset of thrusting (D2 deformation), which placed hot rocks on colder rocks. This led to the cessation of prograde metamorphism and accounts for the ubiquitous association of nappe emplacement and the meta morphic peak. Later deformation (D3/D4) occurred at lower grades (biotite/chlorite). Consideration of nappe translation rates and the likely erosion/cooling rates indicates that nappe movements must have occurred ‘continuously out-of-sequence’ within the Kalak Nappe Complex.
Jurassic clay mineral assemblages and their post-depositional alteration: upper Great Estuarine Group, Scotland
Authors: Andrews Julian E.
Published: May 2009

Clay minerals from Middle Jurassic lagoonal mudrocks, siltstones and silty fine-grained sandstones of the upper Great Estuarine Group (Bathonian) are divided into four assemblages. Assemblage 1, the most common assemblage, is rich in mixed-layer illite–smectite with attendant illite and kaolinite. Assemblage 2 is dominated by smectitic clay. These assemblages are indicative of primary Jurassic deposition. Illite and kaolinite were probably derived from the weathering of older rocks and soils in the basin hinterland and were deposited in the lagoons as river-borne detritus. The majority of smectite and mixed-layer illite–smectite is interpreted as the argillization product of Jurassic volcanic dust, also deposited in the lagoons by rivers. Near major Tertiary igneous intrusions these depositional clay mineral assemblages have been altered. Assemblage 3 contains smectite-poor mixed-layer illite–smectite, whilst Assemblage 4 contains no smectitic clay at all. Destruction of smectite interlayers occurred at relatively shallow burial depths (< 2500 m) due to enhanced geothermal gradients and local convective hot-water circulation cells associated with the major Tertiary igneous intrusions.
Enriched komatiitic basalts from Newton Township, Ontario: their genesis by crustal contamination of depleted komatiite magma
Authors: Cattell Alan
Published: May 2009

LREE-enriched komatiitic basalts are commonly found in association with LREE-depleted komatiites. This association is found in a sequence of late Archaean lavas from Newton Township, Ontario. The komatiitic lavas at Newton Township differ from most late Archaean examples in that both the komatiites and the komatiitic basalts are depleted in Al and in the HREE. The close association and distinctive Al and HREE depletions of the two lava types strongly suggest a common origin, despite their contrasting LREE patterns.

A model is proposed whereby the LREE-depleted komatiites represent the parental magma to the LREE-enriched komatiitic basalts, the two being linked by a combination of crystal fractionation and crustal assimilation. The composition of the contaminant is estimated by comparing the LREE-enriched komatiitic basalts with the evolved part of a thick layered komatiite flow that has similar major element chemistry. The contaminant composition coincides closely with Taylor & McLennan's estimate of the composition of the Archaean upper crust. It is concluded that LREE-enriched komatiitic basalts can be produced from LREE-depleted komatiite parent magmas by combined assimilation and fractionation, and that such a process best explains the geochemistry and Nd isotopic features of most komatiitic basalts.
Asymmetric extensional structures and their implications for the generation of melanges
Authors: Needham D. T.
Published: May 2009

Studies of melanges in the Shimanto Belt of southwest Japan have shown that many of the included blocks exhibit asymmetric geometries, similar to boudins and inclusions in medium grade metamorphic rocks which have been subjected to markedly non-coaxial strains. Deformation is accomplished by mesoscopically ductile processes such as pore-pressure-controlled or diffusionally-controlled grain boundary sliding, although localized fracture and cataclasis also occurs. It is suggested that the melanges developed by the propagation of extensional displacement zones, analogous to shear bands, through sandstone beds, so progressively dismembering them. Studies of the detailed internal geometries of melanges along with the deformation mechanisms active during their formation may help resolve the mode of formation of these problematic units.
The significance of large-scale sedimentary structures in the Silurian succession of western Ireland
Authors: Williams D. Michael , Nealon T.
Published: May 2009

Large-scale sedimentary structures are described from the Lough Muck Formation (Wenlock) of north Galway, Ireland. They consist of bed packages separated by truncation surfaces of varying orientations. They had previously been interpreted as rotational slumps generated on a shelf–slope interface. It is shown that the structures formed in a tidally influenced environment far removed from a slope. They bear strong similarities to structures described from other tidal channel environments and it is proposed that they represent deposition on aggradational margins of such channels. The supposed slope–shelf transition is therefore not present at this level in the Silurian succession and much of the Lough Muck Formation may be of a dominantly shallow-marine origin.
Strike-slip terranes and a model for the evolution of the British and Irish Caledonides
Authors: Hutton Donald H. W.
Published: May 2009

Evidence is presented that many of the major strike faults in the British and Irish Caledonides were active as sinistral strike-slip zones in the end-Silurian to pre-mid-Devonian period. Some, such as the Highland Boundary Fault, moved in this way at an earlier stage in the Ordovician. These data allow the Caledonian rocks lying between the Laurentian miogeocline (whose basement is represented by the Lewisian, Moine and possibly the Dalradian) and the Gondwanaland miogeocline (Midland Platform and Welsh Basin) to be re-analysed as a group of disorganized terranes which originated to the southwest in North America and southwest Europe/Africa prior to the Silurian.The Highland Border TerraneandNorthern Belt Terraneare interpreted as duplicated pieces of a mid-Ordovician sequence which was a back are to northwest subduction. TheMidland Valley Terraneis interpreted as a slice of Laurentian foreland onto which ophiolites were obducted in the lower Ordovician but which became the basement of a continental margin arc to northwest subduction in the mid-Ordovician. TheCockburnland Terraneis inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip. TheConnemara Terraneis regarded as an allochthonous piece of the Dalradian miogeocline and theSouth Mayo Terraneas a remnant of an early Ordovician arc and fore arc which in mid-Ordovician times became a back arc/marginal basin to northwest subduction. TheLake District-Wexford Terraneis part of an arc to southeast subduction under Gondwanaland whose activity climaxed in the mid-Ordovician. TheCentral Terraneis interpreted as a Silurian overstep assemblage which blankets the junction between Laurentian- and Gondwanaland-derived oceanic terranes, and therefore Iapetus is regarded as an Ordovician ocean which closed prior to the Silurian. The model suggests that at the end of the Silurian, a clockwise-rotating Gondwanaland, having carried Laurentia into collision with Baltica, broke free and created a major sinistral strike-slip zone which disrupted the Ordovician palaeogeography in the British Isles/North American sector of Iapetus.
A shallow detachment beneath the North Greenland fold belt: implications for sedimentation and tectonics
Authors: Soper N. J , Higgins A. K.
Published: May 2009

In northern Greenland in early Palaeozoic time a turbidite trough (the eastward extension of the Hazen trough of Arctic Canada) was flanked to the south by a carbonate platform. The trough was deformed during the mid-Palaeozoic Ellesmerian orogeny to form the E–W trending North Greenland fold belt. This fold belt was deformed further by Eurekan (Tertiary) structures, important among which is a major fault complex, the Harder Fjord fault zone (HFFZ). The suggestion has been made that this fault zone controlled early Cambrian sedimentation, even though the fault trace does not coincide with the trough–platform facies transition in sediments of that age; this has led to some controversy.

We report new information from a mapping programme by the Geological Survey of Greenland which has established the thin-skinned nature of Ellesmerian deformation at the trough-platform transition and implies that much of the fold belt is underlain by a shallow detachment. This in turn implies that the HFFZ exists in the hanging-wall of the detachment while the early Cambrian trough-platform transition is located autochthonously in the foot-wall. We adduce evidence to show that the latter was probably controlled by syndepositional faulting with actively eroding fault scarps and suggest that these basement structures were reactivated in a dextral strike-slip mode in early Tertiary time to form the HFFZ as now observed.
The emplacement of geochemically distinct groups of rhyolites during the evolution of the Lower Rhyolitic Tuff Formation caldera (Ordovician), North Wales, U.K.
Authors: Campbell S. D. G. , Reedman A. J. , Howells M. F. , Mann A. C.
Published: May 2009

Rhyolites in the vicinity of Snowdon (North Wales) are intimately associated with the evolution of the Lower Rhyolitic Tuff Formation (LRTF) caldera of Ordovician (Caradoc) age. They occur as deep-seated dykes, sills and small stocks, shallow-level intrusive domes, and domes extruded within a predominantly shallow-marine environment. Extrusion occurred during three main phases, indicating the episodic availability of rhyolite magma. The rhyolites can be divided on their trace element ratios (e.g. Nb/Zr) into five main groups. Extrusive representatives indicate that each group correlates strongly with a single phase of rhyolite extrusion. Within each group, the distribution and variation of intrusive form with stratigraphic level suggests that geochemically similar rocks were emplaced at approximately the same time. Consequently, the groups represent discrete magma compositions tapped from the evolving Snowdon subvolcanic magma system. Differences in distribution of the groups reflect changes in structural controls of emplacement before and after development of the LRTF caldera.
Cretaceous diapiric plutonism in the southern cordillera, Chile
Authors: Suarez M. , Herve M. , Puig A.
Published: May 2009

The Castores and probably the Santa Rosa plutons of north-west Isla Navarino, southern Chile, have been emplaced by in situ diapirism into metasedimentary rocks of the Upper Jurassic (?)–Lower Cretaceous Yaghan Formation. For the former, this model is consistent with the concentric foliation paralleling the margin of the pluton and the foliation and stratification planes in the metamorphic aureole. Only the southern part of the Santa Rosa Pluton is preserved, and it has some structures similar to those of the Castores Pluton, which can also be interpreted as produced by an inflating diapir. The main intrusive rocks of these plutons are quartz-monzodiorites and quartz-diorites with synmagmatic foliation. They were preceded by minor bodies of hornblende gabbros, and followed by dykes and small bodies of non-foliated granodiorites. Non-foliated to weakly foliated granodiorites, forming the centre of the Castores Pluton, probably represent a younger intrusive pulse.

Twelve K–Ar mineral dates from 10 specimens of plutonic rocks, interpreted as near crystallization ages, span the period 80–90 Ma. These dates do not show the sequence of intrusion of the different rock-types, which may suggest that all of them were intruded and cooled in a short period of time. The timing of emplacement of these plutons in relation to tectonism is difficult to determine; however, a post-tectonic emplacement for at least the Castores Pluton, is proposed.
Stratigraphy and morphotectonics of Karoo deposits of the northern Selous Basin, Tanzania
Authors: Wopfner H. , Kaaya C. Z.
Published: May 2009

Late Permian Karoo deposits of the northern Selous Basin in south-central Tanzania comprise conglomerates and diamictitic boulder beds of alluvial and scarp-foot fan origin. These merge with grey to greenish sandstones, siltstones and black shales of deltaic and lacustrine environments. Microflora assemblages indicate a late Permian age. Lateral changes and interfingering of various lithofacies units are common. Depositional development was controlled by syndepositional faulting and variations of gradients resulting from fault movements. The position of the fault scarp separating the basin area from the elevated basement horst to the west roughly corresponded with the present boundary between the Selous Basin and the Precambrian metamorphics of the Uluguru Mountains.

The late Permian Karoo succession of this part of the Selous Basin apparently overlaps older Karoo deposits contained in the north-northeast trending narrow graben structures. It is therefore regarded as a new depositional event which was initiated by renewed tensional tectonism in late Permian time. During this tectonic episode the narrow early Karoo graben structures were expanded into much broader rift basins. Material eroded from the rift shoulders and associated highlands was literally dumped across the fault scarps, forming debris aprons and scarp-foot fans. Rivers emanating from the highlands formed large alluvial fans and, further afield, deltas issued into freshwater lakes.

Some of these late Permian faults were rejuvenated by late Cretaceous to early Tertiary tectonism. Thermal waters circulating along fractures converted feldspars, biotites and hornblendes to prehnite. Further tectonic adjustments in mid Tertiary time led to the present-day morphology.
Cathodoluminescence of Recent biogenic carbonates: environmental and ontogenetic fingerprint
Authors: Barbin V. , Ramseyer K. , Debenay J. P. , Schein E. , Roux M. , Decrouez D.
Published: May 2009

Cathodoluminescence (CL) examination of Recent biogenic carbonates shows that they are often luminescent regardless of their mineralogical composition (calcite v. aragonite), habitat (marine v. fresh water), way of life (sessile v. vagile) or environment (hyper- v. hyposaline water). Thus, the presence of luminescence in biogenic particles is not a reliable indicator of diagenetic alteration as some authors have suggested. In addition, CL can reveal variations in the mineralogy of shell material (e.g. regenerated calcitic v. primary aragonitic) and can highlight growth-related structures. Manganese (Mn2+) is the most likely activator of this luminescence, and its content in the shells of benthic organisms seems to be linked to growth rate, ontogeny, open sea conditions, bathymetry and salinity. In neritic environments the Mn2+content and the CL of molluscs and foraminifera appear to increase with decreasing salinity. This study indicates that CL may be an important tool for the determination of environmental and ontogenetic parameters in biogenic carbonates in addition to its current use indiagenetic studies.
Modelling of chalk diagenesis (Eldfisk Field, Norwegian North Sea) using whole rock and laser ablation stable isotopic data
Authors: Maliva R. G. , Dickson J. A. D. , Råheim A.
Published: May 2009

Laser ablation techniques permit the determination of the stable isotopic ratios of finely crystalline calcite cements in chalks for the first time. Modelling of fluid–rock interaction using whole rock and laser ablation stable isotopic data indicates that carbonate mineral diagenesis in the Eldfisk Field consisted largely of the dissolution and reprecipitation of calcite with little associated loss of porosity. Cementation by calcite derived from stylolites apparently occurred throughout the Eldfisk Field chalk, but had only a subsidiary effect on whole rock isotopic ratios. Oxygen isotopic data indicates a pore water temperature of 50–80 °C during the bulk of chalk recrystallization. Increases in whole rock δ13C values with depth are likely the result of bacterial methanogenesis during chalk recrystallization.
Late Cenozoic crustal extension and basin formation in west Turkey
Authors: Seyitoǧlu Gürol , Scott Barry
Published: May 2009

It is proposed that north–south crustal extension and related sedimentary basin formation commenced in the early Miocene. This extension is believed to be related to a spreading of a thickened crust as a result of Palaeogene compression. That such spreading commenced virtually immediately after the cessation of this compression is considered to be due to the high thermal profile of the crust in that area at the end of the Palaeogene.
Superimposed extensional tectonics in the Argana Triassic formations (Morocco), related to the early rifting of the Central Atlantic
Authors: Medina Fida
Published: May 2009

The first Mesozoic beds in the western Atlas (Morocco) are the Triassic redformations of the Argana valley. The present study was carried out in order to determine the tectonic pattern, especially in the lowermost formations, related to the rifting of the Central Atlantic and to the creation of the Atlas trough. The main results are: (1) from the stratigraphic point of view, the lowermost formation (the Ikakern Formation) is probably of early Triassic age; (2) the sediments of this formation were deposited in an ENE–WSW trending basin affected by northward-tilted blocks delimited by almost pure normal faults; (3) this basin, whose trend was oblique to the younger Atlantic rift, represents a failed branch of the Atlas trough; (4) the “Atlantic stage” corresponds to the creation of a NNE-SSW trending basin superimposed on the first, and the sediments were, in this area, tilted to the west by a major end-Triassic extensional event, just before the extrusion of the basalts.
A newWorthoceras(Ammonoidea, Cretaceous) from Hungary, and remarks on the distribution ofWorthocerasspecies
Authors: Bujtor L.
Published: May 2009

A new species of the genusWorthocerashas been recognized in material from a borehole (Bóly-1) in southern Hungary.Worthoceras pygmaeumsp. nov. co-occurs with typical Upper Albian (Stoliczkaia disparZone) ammonites. It seems likely that the genusWorthocerasarose in early late Albian times in North America and migrated eastward (Europe). During the Cenomanian it reached the southern margin of Tethys (Madagascar, India). It reached its most widespread distribution in Turonian times (from North America to New Zealand) and then became extinct. Beside the increasing area and growing dimensions, the strengthened sculpture is characteristic of theWorthocerasevolution.
Rift formation in the Gökova region, southwest Anatolia: implications for the opening of the Aegean Sea
Authors: Görür N. , Sengör A. M. C. , Sakinü M. , Akkök R. , Yiğitbaş E. , Oktay F. Y. , Barka A. , Sarica N. , Ecevitoğlu B. , Demirbağ E. , Ersoy Ş. , Algan O. , Güneysu C. , Aykol A.
Published: May 2009

The time of the onset and the nature of the extension in the Aegean area have been problematic owing to the confusion of neotectonic replacement structures with neotectonic revolutionary structures. This paper concerns two rift systems of different ages and orientations in the Gökova region of southwestern Anatolia. The first system has a northwest—southeast trend with a Middle to Upper Miocene infill, whereas the second system is orientated in an east—west direction and filled with Plio-Quaternary rocks. Structural and palaeomagnetic data indicate that the first system originally had a north—south trend, and then bodily rotated anticlockwise to its present orientation before the end of the Miocene. Both the orientations and the structural patterns of these cross-cutting rift systems suggest that they resulted from two different and successive tectonic régimes. Regional geology suggests that the generative régime of the older system was characterized by north—south compression and related to the palaeotectonic evolution of southwestern Anatolia, whereas that of the younger system is characterized by north-south extension and relates to the neotectonic evolution of this region. This inference contradicts, at least in southwestern Anatolia, some recent claims that the extensional tectonics and the related rift formation in the Aegean region began in the early Miocene, with the alleged demise of the compressional palaeotectonics during the late Oligocene, but is consistent with older views that placed the onset of north—south extension into the later middle Miocene. The formation of the Aegean Sea seems to be the result of these two complicated and contrasting, succesive tectonic regimes that have affected this region since middle Miocene times.
A global Chitinozoa biozonation for the Silurian
Authors: Verniers J. , Nestor V. , Paris F. , Dufka P. , Sutherland S. , Van Grootel G.
Published: May 2009

A global Chitinozoan biozonation for the Silurian Period is proposed. Each biozone is an interval range defined by the first occurrence of an index species, selected from well-defined species with a relatively short biostratigraphic range. To be included in the scheme, index species must have been recorded from at least two major Silurian palaeocontinents where usable Chitinozoa assemblages have been studied, that is, Avalonia—Baltica (which had already undergone collision by the Silurian), Laurentia, Gondwana and Southern China. Seventeen biozones are identified with seven in the Llandovery: thefragilis, postrobusta, electa, maennili, alargada, dolioliformisandlongicollisbiozones; four in the Wenlock: themargaritana, cingulata, pachycephalaandlycoperdoidesbiozones; three in the Ludlow: theelongata, philipiandbarrandeibiozones; and three in the Přídolí: thekosovensis, elegansandsuperbabiozones. Chronostratigraphic calibration is partly provided by reference to the range of the appropriate Chitinozoa index species in the global stratotype sections and points (GSSP) of the Silurian series, e.g. in Bohemia (Czech Republic) for the Přídolí and the Welsh Borderland in England for the Ludlow and part of the Wenlock. When this information was not available, independent biostratigraphic control was provided by calibration with graptolite biozones or in a few cases, conodont or trilobite biozonal schemes. The index and most characteristic species of each biozone are illustrated and their total stratigraphie range provided.
Pan-African charnockite formation in Kerala, South India
Authors: Choudhary A. K. , Harris N. B. W. , van Calsteren P. , Hawkesworth C. J.
Published: May 2009

Sm-Nd mineral ages of gneisses and associated granulites from the Ponmudi incipient charnockite locality (South India) indicate that granulite metamorphism occurred at, or shortly after, 558 Ma. Proterozoic ages recorded by garnet separates reflect a detrital age or an earlier metamorphic event preserved by inclusions within garnet. The age of post-metamorphic uplift (440–460 Ma) is constrained by Sr isotope equilibration between biotite and plagioclase. Since charnockite formation and subsequent uplift north of the Palghat-Cauvery shear zone had terminated by earliest Proterozoic time, these results confirm two distinct periods of granulite formation in South India and suggest that the Palghat-Cauvery shear zone represents the boundary between two blocks of strongly contrasting geological histories. Both incipient charnockite formation and subsequent uplift at Ponmudi may be correlated with the tectonothermal evolution of the Highlands Group in Sri Lanka. The similarity between Nd and Sr model ages for charnockites and gneisses from Ponmudi indicates that no significant Rb-Sr fractionation has occurred during the crustal history of these incipient charnockites. Pb isotopic ratios suggest that Th-U ratios were fractionated during charnockite formation at about 500 Ma. In contrast to charnockites found north of the Palghat-Cauvery shear zone, fractionation of U-Pb during the Archaean did not occur in the Ponmudi granulites.
Oxygen and carbon isotope stratigraphy of early Cambrian carbonates in southeastern Newfoundland and England
Authors: Brasier M. D. , Anderson M. M. , Corfield R. M.
Published: May 2009

Carbonate rocks have been sampled through predominantly siliciclastic sediments above the Precambrian-Cambrian global stratotype level in southeastern Newfoundland to assess their potential for oxygen and carbon isotope stratigraphy. Comparable successions were sampled at Nuneaton and Comley in England. Greatly depleted δ18O signals are attributed to widespread thermal alteration during deep burial and granitic intrusion, including within the stratotype region. Carbon isotope ratios appear to have been less affected and these are described from nine sections. A provisional, composite δ13C curve is based on non-ferroan, pink nodular and bedded micrites. Several δ13C excursions occur in the fossiliferous Bonavista Group and allow the position of the Tommotian-Atdabanian boundary to be identified. Chemostratigraphic correlation of the new Precambrian-Cambrian boundary stratotype may, however, prove difficult because of the lack of suitable, well-preserved carbonates. The search must begin for a comparable reference section allowing global correlation of the boundary level using chemostratigraphy as well as biostratigraphy.
The numerical age of the Devonian-Carboniferous boundary
Authors: Claoué-Long J. C. , Jones P. J. , Roberts J. , Maxwell S.
Published: May 2009

The SHRIMP ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the Hasselbachtal auxiliary global stratotype section through the Devonian-Carboniferous boundary in Germany, and a tuff located at a similar biostratigraphic level in Australia. Multiple replicate analyses have yielded indistinguishable ages, and indicate 353.2±4.0 Ma (2σ) as the age of the boundary. Obtaining an age for the boundary in the German reference section depended on the ability of SHRIMP to date a small sample and to target small areas of structurally complex zircons. Future refinements of the age of this boundary may depend on re-analysis of this uniquely placed bentonite, and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons.
Recent and ancient fluvial deposition systems in the Amazonian foreland basin, Peru
Authors: Räsänen Matti , Neller Ron , Salo Jukka , Jungner Högne
Published: May 2009

Still active Sub-Andean foreland deformation is suggested to have syndepositionally modified the fluvial depositional environments in the Peruvian Amazonian foreland basin throughout Neogene-Quaternary time. Modern fluvial aggradation continues to proceed on a large scale (c. 120 000 km2) in two differing depositional systems. Firstly, various multistoried floodbasin deposits are derived from the meandering and anastomosing rivers within the subsiding intraforeland basins. Secondly, in the northern part of the Pastaza-Marañon basin the largest known Holocene alluvial fan-like formation (c. 60 000 km2) composed of reworked, volcaniclastic debris derived from active Ecuadorian volcanoes, has been identified.

The widespread, poorly known, dissected surface alluvium (terra firme) which covers the main part of the Peruvian Amazonian foreland basin shows further evidence of long-term foreland deformation, and terraces indicate both the effects of tectonism and Pleistocene climatic oscillations. In northern Peru, the surface alluvium was deposited by a Tertiary fluvial system with palaeocurrents to the west and northwest into the Andean foreland basin. In southern Peru, the respective surficial alluvium was part of a post-Miocene fluvial system flowing northeast into the main Amazon basin. Both systems were gradually abandoned when the eastward migrating Andean foreland deformation led to the more distinctive partitioning of the intraforeland basins, and the modern drainage system was created.
Primitive olivine melanephelinite dykes from the Orkney Islands, Scotland
Authors: Upton B. G. J. , Mitchell R. H. , Longs A. , Aspen P.
Published: May 2009

Two suites of Permian dykes in the Orkney Islands consist of a predominantly ENE trending camptonite suite and a mainly N-to NE-trending suite formerly referred to as monchiquitic. Some of the silica-poor and more magnesium dykes in the latter suite can be more precisely defined as olivine melanephelinites. Within the parochial context of the British Isles, such compositions appear to be unique. The magmas are deduced to have been primitive, small-scale (? < 0.2%) partial melt products of the asthenospheric mantle that have experienced relatively little modification in transit through the lithosphere.
Recycled acritarchs as provenance indicators: implications for Caledonian terrane reconstruction
Authors: Mccaffrey W. D. , Barron H. F. , Molyneux S. G. , Kneller B. C.
Published: May 2009

Silurian successions deposited on the margins of the Iapetus Ocean in the English Lake District, Southern Uplands of Scotland and Ireland contain recycled Ordovician acritarchs. These include taxa known only from Avalonia and Gondwana, with other recycled acritarchs possibly derived from Baltica. There is no palynological evidence to indicate that Laurentiaconstituted a source area. The data presented herein suggest that provinciality in derived microfossils may be profitably exploited in provenance studies.
A new post-early Cambrian archaeocyath from Antarctica
Authors: Wood Rachel A. , Evans Kevin R. , Zhuravlev Andrey Yu.
Published: May 2009

A new species of archaeocyath sponge, Dictyocyathus neptunensis, is described from the lower third of the Nelson Limestone of the Neptune Range, Antarctica. Based on the presence of the trilobites Nelsonia schesis and Amphoton oatesi, these strata are interpreted to be mid- to late middle Cambrian in age. D. neptunensis shows a branching, low integration modular form and a very simple skeletal type. Such an organization is predicted from known morphological trends within the early Cambrian Archaeocyatha. Specimens are not in life position, and probably form part of a storm deposit. The absence of Dictyocyathus from latest early Cambrian (Toyonian) strata worldwide suggests a convergent nature for this highly simplified skeletal type in archaeocyaths.
Possible forced folding in the Taurus–Zagros Belt of northern Iraq
Authors: Ameen M. S.
Published: May 2009

The folds in the Taurus–Zagros Belt of northern Iraq have generally been considered to be decollement buckle folds. This implies the presence of a decollement horizon at or near the base of the sedimentary cover, the ‘Infra-Cambrian Hormuz Salt’ and a passive role of the Precambrian basement in the tectonic evolution of the folded belt. Structural, stratigraphic, geophysical and remote sensing evidence suggests that forced folding, due to faulting in the basement, has played a significant role in the development of many of the folds in this region. This is clear from the substantial evidence of basement faulting, the lack of any convincing evidence for the presence of an extensive and regional decollement horizon (i.e. the Hormuz Salt) between the basement and the cover rocks, and the geometries of the folds and related mesostructures. The study shows that in the Taurus Foothills Zone, the folds are short, oval in plan shape, and arranged in an en echelon pattern along two sets of dislocation zones in the basement. However, the folds in the Zagros Foothills Zone are longer, linear and arcuate in plan shape. Many of the studied folds show similar features to those observed in the Rocky Mountains, U.S.A.
Magnesian andesites from the island of Skyros, Greece: geochemistry and regional significance
Authors: Pe-Piper G.
Published: May 2009

High-magnesian andesites outcrop in a subvolcanic complex in the island of Skyros in the central Aegean Sea. Mineralogical indicators of this high-Mg content include bronzite and clinopyroxene phenocrysts, the former with high Cr2O3, and some phlogopite. Plagioclase (oligoclase–andesine) and Fe–Ti oxides were late phases to appear at the liquidus. Whole-rock geochemistry shows trace element features similar to those of subduction-related rocks. Radiometric dating indicates an early Serravallian (middle Miocene) age, approximately synchronous with the onset of post-orogenic rifting and extension of the Aegean Sea. This tectonic setting is consistent with an origin by adiabatic decompression of mantle peridotite previously modified by subduction-related fluids.
A reinterpretation of Scottish ‘hummocky moraine’ and its significance for the deglaciation of the Scottish Highlands during the Younger Dryas or Loch Lomond Stadial
Authors: Bennett Matthew R. , Boulton Geoffrey S.
Published: May 2009

The aim of this paper is to demonstrate that much of the ‘hummocky moraine’ present within the northern part of the LochLomond Readvance ice cap formerly situated in the North West Scottish Highlands may be interpreted as suites of ice-front moraines deposited during active decay. These landforms can be used to reconstruct ice cap decay, whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions. Evidence has been collected from 10803 airphotographs and from detailed field survey. It is presented at three spatial scales.
Graphite geothermometry in low and high temperature regimes: two case studies
Authors: Luque F. J. , Barrenechea J. F. , Rodas M.
Published: May 2009

This paper examines the potential use of the variation of the co parameter of graphite with temperature for geothermometric estimations. Two examples are presented in which graphite geothermometry, at low-and high-temperature conditions, is tested against other widely used geothermometers. The results obtained indicate that, at low-grade metamorphic conditions, the co parameter of graphite is affected by other factors besides the temperature, so graphite geothermometry (based on co) can only be used in such rocks for qualitative estimations. For temperatures above 500 °C, when the fully ordered graphite appears, there is a close correlation between the temperature estimations based on the structural ordering of graphite and from mineral-exchange geothermometry. The temperature calculations based on the co parameter of graphite are not influenced by factors (such as pressure or retrometamorphism) that clearly affect the exchange equilibria. Thus, graphite thermometry is a useful tool, for temperatures above 500 °C.
Geology and petrogenesis of the Straumsvola nepheline syenite complex, Dronning Maud Land, Antarctica
Authors: Harris Chris , Grantham Geoffrey H.
Published: May 2009

The 170 Ma Straumsvola nepheline syenite complex in western Dronning Maud Land, Antarctica, is located on the eastern edge of the Penck-Jutul Trough, a major tectonic feature which may be a Palaeozoic-Mesozoic rift system. The 5 km diameter pluton consists entirely of nepheline syenite and can be divided into two volumetrically important units: a relatively structureless outer zone which is overlain by a layered zone. The latter exhibits continuous rhythmic alternations of layers containing different proportions of alkali feldspar to amphibole+Na-rich pyroxene+biotite+nepheline throughout its 350 m thickness. The mafic zone is a volumetrically minor unit which unconformably overlies the layered zone and consists almost entirely of mafic minerals and nepheline. The layered zone shows no systematic stratigraphic variation in major or trace composition or mineral chemistry which is interpreted as being due to a combination of migration of intercumulus liquid and action of deuteric fluids. The remarkably constant thickness of successive layers throughout the layered zone suggests that layering resulted from an internally self-regulating process(es). The layering is defined by changing proportions of alkali feldspar to mafic minerals+nepheline which is consistent with layering being caused by differences in nucleation rate during eutectic crystallization. Dykes associated with the complex show wide-ranging compositions and include both over-and undersaturated types. Low σ18O values of the nepheline syenites (mean 5.9%, n = 9) suggest that the magma from which the nepheline syenites crystallized was mantlederived. Peralkaline microgranite dykes have higher σ18O values (mean 7.3%, n = 4) and it is suggested that they are either undersaturated liquids contaminated by siliceous crust, or derived by partial melting of partly fenitized gneiss. Oxygen isotope ratios of the surrounding gneiss indicate that the intrusion of the nepheline syenite did not cause extensive circulation of meteoric or magmatic hydrothermal fluids.
Deep structure of the Anglo–Brabant massif revealed by seismic profiling
Authors: Blundell D. J.
Published: May 2009

Deep seismic reflection profiles over the Anglo–Brabant massif in the southern North Sea reveal reflection patterns throughout the crust that are distinctive and which differ significantly from those observed beneath adjacent areas with Mesozoic basins. Comparisons with reflection profiles from other platform areas suggest that the reflection patterns indicate large-scale structural features associated with compressional tectonics. If so, they may represent thrust structures associated with continental accretion of preferred Caledonian age.
The metamorphic history of the concealed Caledonides of eastern England and their foreland
Authors: Merriman R. J. , Pharaoh T. C. , Woodcock N. H. , Daly P.
Published: May 2009

White mica (illite) crystallinity data, derived mostly from borehole samples, have been used to generate a contoured metamorphic map of the concealed Caledonide fold belt of eastern England and the foreland formed by the Midlands Microcraton. The northern subcrop of the fold belt is characterized by epizonal phyllites and quartzites of possible Cambrian age, whereas anchizonal grades characterize Silurian to Lower Devonian strata of the Anglian Basin in the southern subcrop of the fold belt. Regional metamorphism in the Anglian Basin resulted from deep burial and Acadian deformation beneath a possible overburden of 7 km, assuming a metamorphic field gradient of 36 °C km-1. Late Proterozoic volcaniclastic rocks forming the basement of the microcraton show anchizonal to epizonal grades that probably developed during late Avalonian metamorphism. Cambrian to Tremadoc strata, showing late diagenetic alteration, rest on the basement with varying degrees of metamorphic discordance. During early Palaeozoic times, much of the microcraton was a region of slow subsidence with overburden thicknesses of 3.3–5.5 km. However, concealed Tremadoc strata in the northeast of the microcraton reach anchizonal grades and may have been buried to depths of 7 km beneath an overburden of uncertain age.
Relationship between metamorphism and structure in the Skiddaw Group, English Lake District
Authors: Fortey N. J. , Roberts B. , Hirons S. R.
Published: May 2009

Regional variation of white mica (illite) crystallinity in the Skiddaw Group is set against the structural interpretation of Hughes, Cooper & Stone (1993, this issue) in which early- or pre-Ludlow deformation and slaty cleavage development (S1) were succeeded by southward thrusting and an associated development of S1 and S1 crenulation cleavages, possibly during early Devonian times. Kubier index (KI) values are plotted in relation to geological structure for a major part of the Skiddaw Group, and cross-sections constructed. The pattern is interpreted in terms of three processes: (1) diagenetic to low anchizonal burial metamorphism under a relatively high geothermal gradient during the late-arc stage (early to mid-Silurian) which preceded the orogenic phase and formation of S1; (2) upper anchizonal to epizonal metamorphism due to tectonic thickening and slaty cleavage development during the early to pre-Ludlow orogenic phase following closure of Iapetus; (3) late-tectonic uplift of already metamorphosed rocks by southward-directed movement on the Loweswater, Gasgale Gill and Causey Pike Thrusts possibly during early Devonian time. An analogous interpretation is made for the Skiddaw area, though with the addition of major post-S1 contact metamorphism.