bluuebunny/crossref_metadata_2025_split huggingface dataset:
The distribution of metamorphic temperatures around the Strontian Granodiorite
Authors: Ashworth J. R. , Tyler I. M. 
Published: May 2009

SummaryThe Strontian Granodiorite, a ‘Newer Granite’ emplaced late in the Caledonian orogenic cycle, has an aureole which is strongly asymmetrical: the metamorphic zones are broader to the east of the intrusion than to the west. The asymmetry is attributed to a gradient in the background, regional temperatures. The muscovite-out isograd, marking completion of dehydration of muscovite + quartz to sillimanite + K feldspar (estimated temperature 645 °C), lies within 2 km of the contact on the west, whereas the cordierite isograd, due to the onset of dehydration of biotite+sillimanite+quartz (estimated temperature 690 °C) is at least 2.5 km from the contact on the east. This temperature interval of 45 °C, which is rather insensitive to small errors in the estimated pressure (preferred value 4.1 kbar), is used in a simple geometrical treatment to estimate the regional gradient in the plane of present exposure: approximately 5 °C/km in a direction 30° S of E. Because the intrusion does not appear to have been tilted, this result is regarded as an estimate of the horizontal component of the temperature gradient on the west flank of a regional thermal dome, inherited from the regional metamorphic climax and decaying on a timescale which is suggested, by radiometric data in the literature, to be ˜ 10 Ma. A tectonic origin for the perturbed regional temperature distribution (uplift of hot rocks in the east relative to colder rocks further west) is suggested by the metamorphic petrology of the region, and supported by literature data on structural movements, notably of the Sgurr Beag Slide.
The age and palaeoecology of the St Erth Beds, southern England, based on planktonic foraminifera
Authors: Graham Jenkins D. 
Published: May 2009

SummaryPlanktonic foraminifera are recorded for the first time from the St Erth Beds but they are small and very rare. A late Pliocene G. inflaia Zone age is postulated on the presence of Globorotalia inflata and dextrally coiled Neogloboquadrina pachyderma. It is suggested that the depth of water at the time of deposition was much less than 100 m, possibly in the photic zone, and the palaeotemperature was in the range of 10–18 °C.
A new K—Ar age from uppermost Tremadoc rocks of north Wales
Authors: Kokelaar B. P. , Fitch F. J. , Hooker P. J. 
Published: May 2009

SummaryNew conventional K–Ar dating of virtually unaltered pargasite phenocrysts extracted from a metabasalt of the uppermost Tremadocian Rhobell Volcanic Group, cropping out near Dolgellau, Gwynedd, north Wales, yields an age of 508 ± 11 Ma. This result provides a valuable new time-scale calibration point although incompatible with some other versions of the radiometric time-scale for the Lower Palaeozoic which have indicated ages of less than 508 ± 11 Ma for the Tremadoc/Arenig boundary.
Chlorite-mica stacks in low-strain rocks from central Wales
Authors: Craig J. , Fitches W. R. , Maltman A. J. 
Published: May 2009

SummaryWeakly deformed, low grade, Lower Palaeozoic metasediments from central Wales contain abundant stack-like intergrowths of chlorite and white mica that closely resemble stacks described from the Devonian Hunsruckschiefer of West Germany; the Ordovician Martinsburg Slate, New Jersey, U.S.A.; and elsewhere. Several theories have been proposed to explain the origin of such stacks, including a detrital origin; strain-controlled growth of chlorite on a detrital mica nucleus; and strain-controlled intergrowth during metamorphism. None of these satisfactorily explains the central Wales stacks. A detrital origin is precluded by the presence of many stacks with shapes too delicate to have survived transportation, and a lack of hydrodynamic equivalence between the stacks and the clastic host grains. Features inconsistent with strain-controlled growth are constant alignment parallel to bedding but non-systematic orientation with respect to tectonic cleavage, their common occurrence in undeformed rocks, and petrographic evidence that they precede the tectonic cleavage. It is proposed that the stacks formed during diagenesis and low-grade metamorphism, and before the onset of deformation, through mimetic growth on a primary bedding fabric composed of clay minerals.
FabianaSilvestri (Foraminiferida) from India, with notes on its global distribution
Authors: Samanta Bimal K. 
Published: May 2009

SummaryFabianiaSilvestri, a morphologically distinctive larger foraminifer, is circum-global in distribution and is reported to be almost equally abundant in the three marine Tertiary provinces, Tethyan, Indo-Pacific and Caribbean-American. The genus is reported to range from Upper Palaeocene to the top of the Eocene. During the mid-late EoceneFabianiaseems to have been represented by three species,F. cassis(Oppenheim),F. cubensis(Cole & Bermudez) andF. saipanensisCole. In the Indian subcontinent it is known only from eastern India, where it is represented byF. cassisandF. saipanensis. F. indicaNagappa is here regarded as a junior synonym ofF. saipanensisCole.F. cassisis reported for the first time from India. In eastern India,Fabianiais found to be restricted to the middle to upper part of the Middle Eocene.
Microfossil-based biostratigraphy of the Precambrian Hecla Hoek sequence, Nordaustlandet, Svalbard
Authors: Knoll A. H. 
Published: May 2009

SummaryThe Precambrian Murchisonfjorden Supergroup of Nordaustlandet, Svalbard, contains approximately 6000 m of folded, but essentially unmetamorphosed, shallow marine sedimentary rocks. The abundant microfossils found through much of the section allow confident biostratigraphic subdivision of the succession and correlation with contemporaneous sequences in East Greenland and Scandinavia.Diamictite-bearing rocks of the Gotia Group (uppermost in the sequence) contain a depauperate assemblage of acritarchs dominated byBavlinella Javeolata. A Vendian age of deposition is indicated. Carbonates of the immediately underlying Ryssö Formation contain a wide variety of microfossils including stromatolitic associations of several types, planktonic acritarchs, and, near the top of the formation, vase-shaped heterotrophic protists. The acritarchs, includingChuaria circularis, Kildinella hyperboreica, K. sinica, Trachysphaeridiumspp., and others, and the protistan remains indicate a latest Riphean age. The underlying Hunnberg Formation is similarly fossiliferous. A typically Late Riphean acritarch suite is present, and in addition double-walled forms and large (500 μm), thick-walled spheroids bearing club-shaped 10 μm diameter spines are found. Thus, it appears that the entire carbonate sequence of the Roaldtoppen Group was deposited late in Late Riphean time.The thick detrital succession comprising the lowermost part of the unmetamorphosed Nordaustlandet sequence, the Celsiusberget and Franklinsundet groups, contains fossils at various levels. Although microfossils are often somewhat coalified, identifiable Late Riphean taxa such asChuaria circularisandKildinellaspp. are present in rocks as low as the middle Westmanbukta Formation. The presence of the distinctive carbonaceous macrofossilTawuia dalensisin the Kapp Lord Formation permits an age estimate of 850–900 Ma for this formation.All told, the entire Murchisonfjorden Supergroup of Nordaustlandet appears to have been deposited during the Late Riphean and Vendian intervals. The long-recognized lithostratigraphic parallels between this sequence and the Eleonore Bay and Tillite Groups of East Greenland are complemented by strong biostratigraphic similarities.
Diapiric deformations in the Quaternary deposits of the central Ebro Basin, Spain
Authors: Simón J. L. , Soriano A. 
Published: May 2009

AbstractFrom a study of 24 outcrops in Neogene and Quaternary deposits of the central Ebro Basin, a number of diapiric deformations have been recognized, two principal types being differentiated: domal or pillow structures, and piercement or intrusive structures. The former are incipient diapirs of gypsum. Piercing structures have reverse faulted contacts not caused by halokinesis; here Neogene marls are the active plastic material, contrasting with the competent behaviour of gypsum. These intrusive structures are viscous diapirs which easily pierce the non-consolidated, low strength Quaternary gravel overburden and submit it to a horizontal compressive stress. As a consequence, reverse faults and flexures develop in it. Generally normal faults and tension cracks do not appear. Underlying gypsum beds are frequently pulled up into diapirs and they constitute the structural core.Density contrast and conditions for plastic flow exist at the marl–gravel boundary. It seems to have been specially common at the time of Quaternary fluvial sedimentation, so that much deformation is synsedimentary. Diapiric phenomena have been very active during early to middle Pleistocene time, becoming weaker afterwards.
Formation of olivine pseudo-crescumulates by syntectonic axial planar growth during mantle deformation
Authors: Christiansen F. G. , Roberts S. 
Published: May 2009

AbstractLarge elongated euhedral olivines, resembling olivines appearing in crescumulates, from dunite bodies of ophiolite mantle sequences have been subjected to a detailed structural and fabric study. Localities from the Semail Ophiolite, Oman and the Vourinos Complex, Greece are described. The studies indicate that the regional mantle flow structures control the shape and crystallographic orientation of the large euhedral olivines, which are elongated parallel to [001] and flattened parallel to (100) due to syntectonic high temperature metamorphic growth. The growth is controlled by the deformation such that grains oriented unsuitable for slip are growing whereas grains with other orientations are selectively deformed. This being so there may be more than one interpretation of crescumulate textures developed in environments that have suffered a penetrative deformation.
Heavy minerals of Hampshire Basin Palaeogene strata
Authors: Morton A. C. 
Published: May 2009

SummaryThree heavy mineral associations have been recognized in Palaeogene sands from the Hampshire Basin: one typical of the Scottish Highlands to the north, one of the Armorican massif to the south, and one characteristic of the Cornubian massif to the west. These associations interplay throughout the sequence to produce 10 heavy mineral units correlatable over the basin. The bases of several of the units correspond to commonly accepted time-surfaces and encourage correlation between areas showing strong facies variation. Transgressive units are dominated by Scottish-type material, regressive units by Armorican or Cornubian detritus. There is a relationship between local source area uplift and regression, the main reason for which is that the widespread transgressions submerged or otherwise cut off more local sediment sources, allowing input from the Scottish Highlands, a positive feature throughout much of Tertiary time, to dominate.
Modern carbonate marine-sands in estuaries of southwest England
Authors: Merefield J. R. 
Published: May 2009

SummaryLarge deposits of marine-sand occur in the Taw, Camel and Hayle estuaries of north Devon and Cornwall. Total carbonate concentrations reach 67% in the Hayle, 62% in the Camel, and 40% in the Taw. Well mixed, the sands contain modern skeletal debris of consistent composition, which persists up to 18 km and 12 km landward from the mouths of the Taw and Camel estuaries. Although primarily a molluscan sand, remains of barnacles, bryozoans, echinoids, foraminifera, sponge spicules, decapods and coralline algae are common. Carbonate mineralogy provided by these components (on a 100% carbonate basis) consists of 45% aragonite, 38% low Mg-calcite and 17% high Mg-calcite. Two estuaries of the southeast coast of Devon (the Exe and Teign) contain smaller carbonate concentrations of up to 9 and 14%. Values are low there owing to dilution by readily eroded cliff-talus from local exposures of New Red Sandstone. These Permo-Triassic sediments provide carbonate lithoclasts, however, which supplement the modern biogenic supply. Strontium values have been used to estimate the extent of carbonate lithoclasts supplied to the Exe and Teign. The present source of marine-sand of estuaries in southwest England is considered to be mostly near-shore detritus supplemented by eroded cliff-talus, derived largely from local outcrops. Once this material enters the estuarine regime it is available as a supply of sediment for further up-estuary transport.
Indirect dating of tectonic events by Rb—Sr analysis of syntectonic garnets: an example from schists of the Seve Nappe, central Scandinavian Caledomdes
Authors: Reymer A. P. S. 
Published: May 2009

SummaryRb-Sr analyses of syntectonic single-crystal garnets from the Svartsobacken and Dikanas schist units of the Seve Nappe, Scandinavian Caledonides, show systematic differences. One group yields a Precambrian age spectrum consistent with that given by whole-rock analyses; the other group gives Caledonian ages similar to those given by mica analyses. It follows that the tectonic events reflected in the garnet inclusion patterns are also of different ages and, subject to certain limitations, the method can be used to provide a clearer interpretation of the deformational and metamorphic history of the rock.
Definition of the Tremadoc Series and the series of the Ordovician System in Britain
Authors: Whittington H. B. , Dean W. T. , Fortey R. A. , Rickards R. B. , Rushton A. W. A. , Wright A. D. 
Published: May 2009

AbstractThe Tremadoc Series and series of the Ordovician System are widely used in international correlations, and this review explains and summarizes how the base of each of these series is recognized in Britain. No type section in which the base of any one of them is displayed has ever been selected and formally designated, hence the basal horizon of each series is a matter of general understanding rather than precise definition. This general understanding is of particular biozones, or of assemblages of fossils and their relative ages. The geographical separation between type sections of series, and differences in facies, complicate the understanding of relative ages of biozones. Brachiopod and trilobite faunas of the Llandeilo, Caradoc and Ashgill Series have been studied in detail in recent years, and biozones proposed. These biozones have proved difficult or impossible to recognize outside their type areas in Britain, and brachiopod–trilobite faunas of the Tremadoc, Arenig and Llanvirn Series are likewise highly provincial. Thus for correlation within and outside Britain attention has been focused on the ‘standard’ graptolite biozones, particularly since such conodont faunas as have been found have not proved useful. Yet there are problems associated with these ‘standard’ biozones; for example, theTetragraptus approximatusBiozone is unknown in Wales or England, the relationship between the base of theGlyptograptus teretiusculusBiozone and the earliest Llandeilo shelly faunas requires clarification, and at what level the base of the Caradoc Series may lie in theNemagraptus gracilisBiozone is unknown.Thus to bring precision to definitions of Ordovician Series in Britain the identification of continuous, fossiliferous sequences that will serve as stratotypes, is required. Such a section for the basal portion of the Tremadoc Series has recently been proposed. Systematic studies related to particular biozones are needed, for example early Caradoc and early Ashgill brachiopods, and graptolites of theDidymograptus bifidusandGlyptograptus teretiusculusBiozones. The stratigraphical ranges and abundances of species in particular sections require documentation, so that the type of biozone (assemblage, acme, concurrent-range, etc.) may be recognized. Such work could lead towards chronostratigraphy, the provision of a standard stratigraphical scale in Britain for the Tremadoc Series and Ordovician series.
The British Caledonides: interpretations from Cenozoic analogues
Authors: Mitchell A. H. G. 
Published: May 2009

AbstractRecent interpretations of Cenozoic arc systems and collision belts facilitate reinterpretation of some aspects of British Caledonide evolution. End-Cambrian ‘Grampian’ collision of the passive ‘Dalradian’ foreland following southeastwards subduction beneath an island arc was accompanied by initiation of the Highland Boundary Fault as a high-angle south-directed oblique-slip thrust. Mid-Ordovician to early Devonian northwestward oblique subduction of the Iapetus Ocean beneath the Grampian orogen resulted in a continental margin magmatic arc, back-arc thrusting and development of an accretionary prism, while southeastward subduction led to arc magmatism and back-arc extension followed by initiation of the Rheic Ocean as a back-arc marginal basin; this syn-subduction N–S asymmetry of the Iapetus Ocean margins was analogous to the E–W asymmetry of the modern Pacific. Closure of Iapetus was diachronous, earlier in the northeast: during end-Silurian collision the southern Caledonides behaved as a passive foreland; post-collision foreland thrusting resulted in deposition and deformation of Lower Old Red Sandstone foreland basin deposits in Wales, and probably in northwest-directed back-thrusting in the region of the Longford-Down accretionary prism. Subsequent dextral movement in the suture zone juxtaposed the southern Caledonides with Scotland and northern Ireland, beneath which northwestward subduction had continued into the early Devonian.
Lower pleistocene dinoflagellate cyst, foraminiferal and pollen assemblages in four boreholes in the Southern North Sea
Authors: Cameron T.D.J. , Bonny A.P. , Gregory D.M. , Harland R. 
Published: May 2009

AbstractNeogene and Lower Pleistocene stratigraphy in the Southern North Sea has been investigated in four I.G.S. boreholes between East Anglia and the Netherlands. The foraminifera of the Red Crag Formation in Borehole 81/51 are closely similar to Upper Pliocene assemblages in Holland. The overlying succession is clearly punctuated by unconformities in seismic profiles, separating four early Pleistocene formations in the boreholes, and indicating intervals of significant stratigraphic hiatus offshore. The Westkapelle Ground and Smith's Knoll Formations correlate with Thurnian and Antian Stage deposits in East Anglia. Pollen spectra in the Winterton Shoal and Yarmouth Roads Formations are similar to Baventian and Bramertonian assemblages in Britain. The autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early Pleistocene palaeoclimate. The dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment. The pollen record, containing evidence of fluctuation between boreal and mixed coniferous–deciduous regional forest cover, suggests alternation between cool and warm temperate palaeoclimate.
The recognition of the base of the Westphalian D Stage in Britain
Authors: Cleal C. J. 
Published: May 2009

AbstractThe I.U.G.S. Subcommission on Carboniferous Stratigraphy recommends that the base of the Westphalian D is best recognized using plant macrofossils. In Britain, however, South Wales is the only coalfield where the distribution of the plants is sufficiently well known for them to be used to locate this boundary. Elsewhere in Britain other criteria have been used, particularly non-marine bivalves and plant microfossils, but these must be regarded with considerable caution.
The Sinian–Cambrian boundary of China and its related problems
Authors: Yusheng Xing , Qixiu Ding , Huilin Luo , Tinggui He , Yangeng Wang 
Published: May 2009

AbstractThe Sinian and Cambrian systems within the Yangtze stratigraphic province represent continuous deposits, and the strata above and below the Sinian–Cambrian boundary are rich in fossils. From all the relevant boundary sections, the Meishucun section in Jinning County, Yunnan Province serves as the stratotype section for the Sinian–Cambrian boundary and is the Chinese candidate for the global stratotype section and point for the Precambrian–Cambrian boundary. The present paper, with the various charts and tables, elaborates on several typical Sinian–Cambrian boundary sections and the distribution of fossils in them.In accordance with the characteristics of biological evolution, three biotas can be recognized for the period from the Late Sinian to the Early Cambrian. The first biota appeared in the Late Sinian, characterized by the presence of the soft-bodied metazoans; the second biota occurred during the Meishucun Stage of the early Cambrian, and is characterized by the appearance and prevalence of small shelly fossils from many different phyla; and the third biota came into existence during the Qiongzhusi Stage of the Early Cambrian; it is characterized by the first appearance and prevalence of trilobites.The Meishucun Stage of the Lower Cambrian can be divided into three fossil zones. The Sinian–Cambrian boundary is placed at the base of the first Anabarites–Circotheca–Protohertzina zone. According to isotopic dating by the Rb–Sr whole-rock isochron technique, the age of the Sinian–Cambrian boundary is inferred to be 610±10 Ma.
Magnetostratigraphy of lower Cambrian strata from the Siberian Platform: a palaeomagnetic pole and a preliminary polarity time-scale
Authors: Kirschvink Joseph L. , Rozanov A. Yu. 
Published: May 2009

AbstractFour sedimentary sections seen in continuous exposures along the Lena River on the Siberian Platform in Yakutia contain a record of the geomagnetic field during the Tommotian and Atdabanian stages of Early Cambrian time. The direction of the stable remanent magnetization indicates that the Siberian platform was located on the equator, and the corresponding palaeomagnetic pole provides a well-dated extension of the Siberian apparent polar wander path. A belt of archaeocyathid bioherms which separates two major facies zones in the lower Cambrian was positioned on and aligned more or less parallel with the palaeoequator. The geographical position of this belt appears to have tracked the southward motion of the Siberian platform during post-Tommotian time. These palaeomagnetic results combined with the extensive biostratigraphy of the Siberian Platform provide a provisional geomagnetic polarity time scale for this part of Early Cambrian time. Comparison of these results with data of similar age from Central Australia suggests that strata of Tommotian and lower Atdabanian age are not present in the Amadeus Basin of Australia.