bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recrystallization in microfossiliferous limestones
Authors: Banner F. T. , Wood G. V. 
Published: February 2007

AbstractThe microfauna and microflora of the Lower Miocene limestones of the Darai Complex of Papua have been found to recrystallize in a constant order related to the biological affinities of the fossil genera. This recrystallization is independent of the sparry or micritic nature of the interstitial material.Dolomitisation also destroys the fossil skeletons in a comparable order except that the coralline algae appear to be relatively more resistant to replacement by dolomite.Only when the skeletons of the most resistant fossil groups have been recrystallized can the occurrence of interstitial sparry calcite be suspected to have originated from recrystallization of an original micritic matrix. Obliteration of fossil remains by recrystallization presents an additional hazard in the interpretation of biofacies in limestones of this type.
The geology and geomorphology of Los Ajaches, Lanzarote
Authors: Driscoll E. M. , Tinkler K. J. , Hendry G. L. 
Published: February 2007

AbstractThe Los Ajaches area, Lanzarote, Canary Islands consists of a Tertiary volcanic series overlain by Quaternary lava areas. A trachyte outcrop, the only acid volcanic rock on the island, was relocated and mapped during a survey in 1963. Erosion stages at heights of 460, 400, 300, 190 and 100 m, occur in the eastern highlands. The coastal plain has a remarkable raised beach succession at heights of 55,35,25,15,6. and 1 m. This chronological sequence enables a new dating of the Quaternary vulcanism. Certain observations are also made on landform development and correlation with other areas.
The flandrian sequence of north Wirral (N. W. England)
Authors: Kenna R. J. B. 
Published: February 2007

AbstractThe correlation of borehole logs, together with evidence from temporary exposures, shows the relationship between glacial deposits and the overlying Flandrian strata. The courses of buried channels in‐filled with Flandrian strata have been plotted. Radiocarbon assays and pollen and diatom analyses have mainly been confined to samples taken from near the main lithological boundaries, but some radiocarbon assays have been undertaken on in situ tree stumps and on bone. New thick buried channel sequences are described, and an outline chronology from c. 6420 years BP is proposed for the Flandrian coastal sequence of the North Wirral. The data can be applied to the interpretation of sea‐level change and coastal archaeology.
Depositional history of a muddy sabkha complex in the Sokoto Basin of Nigeria, West Africa
Authors: Alam Mahmood 
Published: February 2007

AbstractSedimentological and stratigraphical analysis of the Sokoto Basin has resulted in recognition of four lithostratigraphic units. They are Unit A—siltstone and fine‐grained sandstone; Unit B—shale and marl; Unit C—limestone and calcareous shale; and Unit D—red sandstone. Unit A represents a wadi plain system composed of desert‐alluvial beds; Unit B, a mud‐rich sabkha system; and Unit C, an inner‐shelf carbonate system. A marine transgression from the northwest began in the Maastrichtian and reached its peak in the Palaeocene. After regression in the late Palaeocene, the area was subjected to erosion, followed by fluvial sedimentation of Unit D. Wadi plain beds and mud‐rich sabkha facies of Sokoto Basin are similar to alluvial and coastal mud‐flat deposits in the northwestern Gulf of California and ephemeral stream and tidal‐flat sediments in Gladstone Embayment, Australia.
Depositional environments of the Triassic system in central Saudi Arabia
Authors: Sharief Farooq A. 
Published: February 2007

AbstractFacies analysis of Triassic rocks in central Saudi Arabia indicates a wide expanse of interfingering siliciclastic and carbonate rocks with some evaporites. Eight distinctive sedimentary facies have been recognized. The distribution of these facies show a systematic gradual change in their presumed depositional environments, laterally as well as vertically.The Lower Triassic Sudair facies represents a widespread regressive condition where the Upper Permian marine conditions gave way to the Lower Triassic with predominantly fine clastic deposits representing a restricted shallow marine shelf. This fine‐grained clastic facies consists mainly of unfossiliferous, laminated or massive, varicoloured shale with some silty shale, siltstone and very fine‐to fine‐grained sandstone. The facies is highly calcareous and gypsiferous in the northern area.A belt of Middle Triassic rocks of mostly non‐marine sandstone with some shale is present in the southern area passing into mixed siliciclastic‐carbonate facies of continental aspect with some intermittent emergence and nearshore conditions in the central area. This facies grades in the northern area into carbonate‐evaporite facies of restricted to more open marine shelf conditions.Thick siliciclastic deposits characterize the Upper Triassic Minjur facies, where a uniform repeated fining‐upward sequence of mainly sandstone and some shale developed in a non‐marine environment with some intermittent emergence in the northern area.
The fenestrate bryozoan Septopora carbonaria (Etheridge Jun. 1873a) from the Carboniferous of Great Britain
Authors: Bancroft Adrian J. 
Published: February 2007

AbstractThe Carboniferous fenestrate bryozoan Synocladia carbonaria Etheridge Jun. (1873a) is redescribed. Originally assigned to Synocladia and subsequently diagnosed as a variety of Synocladia biserialis Swallow by Etheridge Jun. (1873b), S. carbonaria is here considered to be a distinct species. Synocladia(?) scotica Young and Young (1878) is conspecific with S. carbonaria, as suggested by Graham (1975). Graham (1975) established the new genus Lanarkopora, naming S. carbonaria and S.(?) scotica in synonomy, with S. carbonaria, the senior synonym, being selected as the type species. Re‐examination of the type material of S. carbonaria and S.(?) scotica has shown that they are referable to the genus Septopora Meek, and Lanarkopora is herein designated a junior synonym of Septopora.
Mohr circles for strain, simplified
Authors: Treagus Susan H. 
Published: February 2007

AbstractThe Mohr circle is a well known representation of two‐dimensional strain. It is commonly used to illustrate strain algebra, or derive a strain ellipse from particular strain data. The established sign convention is positive (anticlockwise) shear strain on the upward ordinate, after Brace. However, in practice, confusion may easily arise from inconsistent conventions in standard text books.A Mohr‐circle convention is proposed here which represents clockwise shear strain on the upward γ ordinate (i.e. upside‐down). It simplifies the Mohr circle by representing both single and double angles in their natural sense. Single angles may be traced from rock to Mohr circle directly which is not the case for the Brace circle. Deformed brachiopods and stretched belemnites are used to illustrate this simplified Mohr circle.The pole to the Mohr circle is a useful addition which allows strain data to be represented in their true orientation. The pole method only works on the γ clockwise‐up Mohr circle.The Mohr circle is useful to demonstrate simple‐shear geometry and algebra. Successive Mohr circles with poles may be used to map strain across a heterogeneous simple‐shear zone.
Lower delta plain interdistributary deposits — An example from the Westphalian of the Lancashire Coalfield, northwest England
Authors: Fielding C. R. 
Published: February 2007

AbstractA large quarry at Billinge Beacon in Lancashire, northwest England, has provided an excellent exposure of part of the Lower Westphalian A (Upper Carboniferous) Coal Measures sequence which was deposited in a lower delta plain setting. The main horizon exposed, known as the Dyneley Knoll Flags, is interpreted as the proximal reaches of two crevasse‐initiated minor delta complexes, into the lower of which has been incised a sinuous minor distributary channel.The channel, which was approximately 120 m wide, built a 160 m wide channel belt by limited lateral accretion with time; vertical accretion appears to have been the dominant infilling mechanism. This produced a stacked series of epsilon cross‐strata, made up of rhythmically interbedded sandstone and silty claystone. The peculiar style of infilling of the channel is ascribed to deep incision of the channel into minor delta deposits, and possibly the influence of a seasonal climate.
Mud‐Dominated Storm Deposits From A Lower Carboniferous Ramp
Authors: Simpson John 
Published: February 2007

AbstractThe Lower Carboniferous Pen‐y‐Holt Limestone of South Wales comprises about 300m of interbedded wackestones and lime mudstones.The wackestones are interpreted as relatively distal ‘turbidite‐like’ storm‐generated deposits and the lime mudstones as background deposits. The storms had a periodicity of about one per 9000–18000 years. They were deposited in a deep‐ramp carbonate environment at least 20–30km from the ancient shoreline and in about 100m water depth, and therefore probably below wave base. The ramp is estimated to have had an average slope angle of 0·5–1·0 degree.Unlike other previously described carbonate or siliciclastic storm deposits, the Pen‐y‐Holt Limestone storm deposits are totaly mud‐supported and generally lack internal sedimentary structures, yet contain large bioclasts such as crinoid ossicles. The simultaneous deposition of lime mud and crinoid ossicles from a storm‐generated turbidity current is hydrodynamically untenable. Thin‐section evidence however, suggests that the lime mud may have originally been deposited as peloids which have since been largely destroyed during diagenesis. Peloids and crinoid ossicles, it is suggested, could have been transported by the same current.
Punctuated equilibria between rival concepts of granite genesis in the late 18th, 19th, and early 20th centuries
Authors: Tex E. Den 
Published: February 2007

AbstractA concise review of concepts dealing with the genesis of granite in the late 18th, 19th, and early 20th centuries is given. Arguments are provided for the repeated recurrence of genetic concepts in an altered form which were separated by periods in which a rival concept was dominant. This type of development may be likened to Eldredge and Gould's (1972) punctuations of biological equilibrium. On the other hand phases of development may be recognized in which rival concepts tend to converge towards a unified content, thus conforming to the ‘tree of knowledge’ hypothesis of Popper (1972). In this context the two metaphors do not appear to be mutually exclusive.
The Coastal Batholith of Peru: The product of rapid recycling of ‘new’ crust formed within rifted continental margin
Authors: Atherton Michael P. 
Published: February 2007

AbstractThe Coastal Batholith of Peru was intruded into ‘new’ Albian crust of the marginal basin, which formed on major continental rifting. The ‘magic switch’ from basalt dominated volcanogenic basinal filling to tonalitic Cordilleran type magmatism is part of a magmatic scenario in which the ‘new crust’ melts on major decompression along megafractures defining the batholith structural lineament. Quantitative modelling of the Icelandic rifting system, which is similar in many respects, indicates basalt melting is likely to produce large amounts of tonalitic to granitic magma. The whole sequence of events leading to batholith formation i.e. extension → subsidence with basin formation → spreading → dyking → splitting → basin filling → gabbro intrusion → compression with partial inversion → cratonization → fracturing and batholith intrusion along the axis of the basin relates to a major cycle of crustal growth.
Magmatic mafic enclaves in granitoids of northern Sierra de Paimán, Argentina
Authors: Lorenc Marek W. 
Published: February 2007

AbstractField relationships of three types of granitoids with basic rocks, with different mineralogy and structure are described. Zones of mixed‐type character exist between the several types of granitoids as well as between the granitoids and basic rocks. The distribution of magmatic mafic enclaves (MME) in the granitoids varies widely but the largest concentrations occur in the mixed zones between the granites and basic bodies. The origin of such enclaves is closely related to processes of hybridization and mingling of acid and basic magmas. One of the possible variants of such interaction is the fragmentation and partial hybridization of synplutonic basic dykes.
Intrusion sequences within ore‐bearing granitoid plutons
Authors: Štemprok Miroslav 
Published: February 2007

AbstractA new database of some 200 granitic bodies throughout the world associated with Sn, W and Mo deposits is analysed with respect to size and petrological characteristics. Most Sn, W and Mo deposits relate to small stocks not exceeding 25 km2. Biotite granites are the most common type of ore‐bearing plutons, while two mica granites are subordinate. There seems to be an upward grading in grain size such that the later, higher members of a suite are the finest grained. Ore‐bearing processes relate to deep evolving differentiation of specialized magmas modified by mantle fluids.
Textural variation and tin mineralization in granites from the main range province of the Southeast Asian Tin Belt
Authors: Pitfield P. E. J. , Teoh L. H. , Cobbing E. J. 
Published: February 2007

AbstractTextural evolution from coarse K‐feldspar megacrystic granite, through heterogeneous granite porphyry to microgranite corresponds to a sequence of geochemical evolution. It was probably triggered by a sudden loss of pressure, resulting in quenching, fluidization, and disruptive emplacement of the residual melt into the partially or wholly crystalline host granite. It was accompanied by alkali metasomatism, volatile‐fluxing, and hydrothermal alteration, culminating in the formation of greisen bordered vein swarms and massive greisens mineralized with tin and other metals.
Rhaxellid sponge microscleres from the Portlandian of Dorset, UK
Authors: Haslett Simon K. 
Published: February 2007

AbstractThree previously described species and two new species of rhaxellid microscleres, Rhaxella winspitensis sp. nov. and R. elongata sp. nov., are described from cherts collected from the Cherty Series of the Portlandian of Dorset. The classification of Rhaxella is reviewed, retaining the genus within the family Geodiidae Gray. The results of this study suggest that three time‐dependent rhaxellid assemblages can be recognized which, despite being restricted to certain depositional environments, may have biostratigraphic applications. A Portlandian assemblage described here is species‐rich in comparison with known Oxfordian‐Kimmeridgian assemblages. Bajocian‐Callovian assemblages contain only R. sorbyana. The increased faunal diversity with time is speculatively described by an evolving Rhaxella lineage.
Graptolite dating of Ordovician vulcanicity in the Arenig area, North Wales
Authors: Zalasiewicz Jan 
Published: February 2007

AbstractGraptolite assemblages of multidens Biozone age have been recovered from mudstones immediately above and below the Llyn Conwy Formation, the local representative of the regionally extensive acid tuffs that mark the end of vulcanicity in the south and east of the Harlech Dome. They include several taxa new to Wales and are markedly different to contemporaneous faunas from the Welsh Borders. One new species, Pseudoclimacograptus isknos, is described.
The West Spitsbergen Fold Belt: The result of Late Cretaceous‐Palaeocene Greenland‐Svalbard convergence?
Authors: Lyberis Nikos , Manby Geoff 
Published: February 2007

AbstractThe West Spitsbergen Fold Belt, together with the Eurekan structures of northern Greenland and Ellesmere Island, are suggested to be the result of Late Cretaceous‐Palaeocene intracontinental compressional tectonics. The Late Palaeozoic –Mesozoic rocks of western Spitsbergen are characterized by near‐foreland deformation with ramp‐flat, top‐to‐the east thrust trajectories, whereas structurally higher nappes involving Caledonian complexes are typified by more listric thrusts and mylonite zones. A minimum of 40 km of shortening is estimated for the northern part of the West Spitsbergen Fold Belt. The axial trends in the West Spitsbergen and the North Greenland Eurekan fold belts parallel the principal fault zones which accommodated the separation of Greenland and Svalbard after Chron 25/24. In northern Greenland, north directed Eurekan thrusts associated with mylonites and cleavage formation represent at least 10 km of shortening. Between 50 and 100 km of shortening is estimated for the markedly arcuate Eurekan Fold Belt of Ellesmere Island, but the principal tectonic transport is eastwards. Kinematic reconstructions suggest that Svalbard was linked to North America before the opening of the Eurasian Basin and Norwegian — Greenland Sea. In the Late Cretaceous — Palaeocene interval, the relative motion between Greenland and North America was convergent across the Greenland — Svalbard margin, giving rise to the West Spitsbergen Fold Belt and the Eurekan structures of North Greenland.
Late Cambrian acritarchs and their age constraints on an Ediacaran‐type fauna from the Booley Bay Formation, Co. Wexford, Eire
Authors: Moczydłowska M. , Crimes T. P. 
Published: February 2007

AbstractAcritarch assemblages have been recovered from the Booley Bay Formation in Duncannon area, Co. Wexford, southeastern Eire. Twelve morpho‐species are described, including the new species Polygonium martinae n. sp., and two informal species Comasphaeridiu n. sp. A and Heliosphaeridium n. sp. B. A new combination, Retisphaeridium brayense (Gardiner and Vanguestaine 1971) comb. nov., is proposed. The relative ages provided by discrete microfossil assemblages and their sequence within the lithological succession suggest that the entire investigated portion of the Booley Bay Formation may be referred to the Upper Cambrian. This biostratigraphic evaluation constrains the age of the recently discovered Ediacaran‐type biota described in Crimes et al. (1995).
New litho‐ and biostratigraphic evidence for a Mid‐Ordovician hiatus in southern central Snowdonia, North Wales
Authors: Smith M. , Rushton A. W. A. , Howells M. F. 
Published: February 2007

AbstractDetailed mapping and biostratigraphic data provide new evidence of a major break below the base of the Caradoc succession along the northern margin of the Harlech Dome in south central Snowdonia. Within this outcrop the sequence is locally complicated by subsequent tectonic and volcanic events, but undisturbed sections indicate a break of at least 10 Ma between upper Arenig and middle, or upper, Llandeilo strata. The break is greatest between two N‐S trending fracture systems, the Cwm Pennant Fault Zone in the west and Trawsfynydd Fault Zone in the east, which both have a persistent history of reactivation. Between these two fractures neither Llanvirn nor lower Llandeilo strata occur. This contrasts with the thick, and perhaps complete, sequence preserved in the Cadair Idris district on the southern margin of the dome and suggests that, during Llanvirn times, the Harlech Dome formed a major uplifted and tilted block, with a tectonically active northern margin. Subsequently, uplift and tectonism either ceased before, or was overwhelmed by, the ensuing sea‐level rise associated with the gracilis (early Caradoc) transgression. The preservation of ooidal ironstones around the dome suggests that it may have became a large shoal or platformal area at this time. Renewed uplift and erosion along the northern margin of the Harlech Dome during the early Caradoc (gracilis to multidens) led to large‐scale disruption of the stratigraphic succession by mass gravity flow and slumping, overprinting and locally accentuating the effects of the earlier hiatus.
Geomorphological evidence from the Lleyn Peninsula constraining models of the magnitude and rate of isostatic rebound during deglaciation of the Irish Sea Basin
Authors: McCarroll Danny 
Published: February 2007

AbstractA stepped series of sand and gravel terraces on the Lleyn peninsula of North Wales is used to test the magnitude and rate of isostatic depression required by the recently proposed glacimarine model of deglaciation of the Irish Sea Basin. A relative sea‐level fall of 70 m is required while the ice remained pinned at the north Lleyn coast. Even taking the maximum known rate of isostatic uplift, the margin would have to remain stationary for 1400 years. It seems more reasonable to interpret the Lleyn terraces, and similar features around the Irish Sea Basin, as glacifluvial and glacilacustrine.
Rate and time controls on metamorphic processes
Authors: Vance Derek 
Published: February 2007

AbstractAmong the most important controls on metamorphism is the rate at which tectonic processes operate. The purpose of this paper is to review briefly a couple of recent advances in the field of geochronology and metamorphic petrology which have helped to elucidate these processes. Re‐equilibration at high temperatures often eradicates information that might have been recorded by rocks during their prograde and high‐temperature evolution. One of the major advances of recent years has been the recognition of the utility of garnet in preserving information on prograde thermal histories. A case study involving garnet‐bearing rocks from New England is described: In this area, garnet grew during the latter stages of prograde metamorphism and records heating through 100°C during decompression of around 2.5 kbar. Combined with chronological data on garnet cores and rims, which yield a time interval for garnet growth of 10 Ma, these data yield a heating rate of ∼ 10°C Ma‐1 and an exhumation rate of about 1 mm a‐1. Comparison with simple thermal models suggests that the heating rate is too high to be accounted for by simple conductive relaxation. At temperatures appropriate to crustal melting, even garnet re‐equilibrates such that any chronological information is lost. At these grades one approach is to use the extent of diffusional modification of growth zonation profiles to provide time constraints on the process operating. Mn distributions in garnets from the Zanskar Himalaya are used to limit the time available for high‐grade metamorphism. The times obtained of 1–2 Ma are extremely short and require cooling by emplacement of cold upper crustal rocks adiacent to migmatitic rocks.