bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Cenozoic basin development in west Turkey: Gördes basin tectonics and sedimentation
Authors: Seyítoğlu Gürol , Scott Barry C.
Published: May 2009

The early Miocene sedimentary succession in the northeast-southwest trending Gördes basin is 1000 m thick and divided into the Daĝdere, Tepeköy and Kuşlukköy formations. The age of this fill can be constrained as between 24.2 Ma and 16.3 Ma, at its widest interval. Paleocurrent directions from south to north demonstrate that the basin had a north dipping basin floor. These observations are inconsistent with a previous model of the Gordes basin as a cross graben with a south dipping basin floor, towards the Alaşehir graben, and an anomalously thick (up to 3000 m) basin filling.
Stratigraphy, structure and geochronology of the Las Cañadas caldera (Tenerife, Canary Islands)
Authors: Martí J. , Mitjavila J. , Araña V.
Published: May 2009

After a long period of subaerial fissure-fed extrusions of basaltic magmas (∼ 12 to > 3 Ma) volcanic activity was then concentrated in the central part of Tenerife. Phonolitic magma chambers formed and a central volcanic complex was constructed (the Las Canadas edifice). The formation of a large depression (the Las Canadas caldera) truncated the top of the edifice. The active twin strato-cones Teide—Pico Viejo are sited in this depression. The history of the Las Canadas caldera and edifice are established from stratigraphy, geochronology (K—Ar dates) and volcanological studies. Two different groups are recognized, separated by a major unconformity. The Lower Group is dated at 2 to 3 Ma and includes the products of several volcanic centres, which together represent several cycles. The Upper Group ranges from 1.56 to 0.17 Ma and includes three different formations representing three long-term (∼ 100 to 300 Ka) volcanic cycles. The periods of dormancy between each formation were of ∼ 120 to 250 Ka duration. The Las Canadas caldera is a multicyclic caldera which formed over the period 1.18–0.17 Ma. Each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the Las Canadas edifice. Geological observation and geochronology support an origin by collapse into a magma chamber. The minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume (45 km3), but approaches the inferred volume of the original caldera depression (> 140 km3). After the formation of the caldera, sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall.
The carbonate-flysch transition (late Maastrichtian-late Palaeocene) in the Arachova sequence of the Parnassus-Ghiona Zone, central Greece
Authors: Gregou Sophia , Solakius Nikolaos , Pomoni-Papaioannou Fotini
Published: May 2009

The transition from the carbonate to the flysch facies in the Arachova sequence of the Parnassus-Ghiona Zone is represented by argillaceous limestone beds with flaser structures deposited during latest Maastrichtian-Palaeocene time in a pelagic carbonate environment with a periodic clastic influx. Deposition was continuous except for a short interruption during the K/T boundary interval and the earliest Palaeocene when the area was subaerially exposed. This interruption gave rise to the development of a brecciated carbonate horizon through soil-forming processes. The mineralogical composition of the clastic influx (i.e. quartz, feldspars, clay minerals, amorphous iron oxides, amorphous phosphatic compounds), in particular the clay mineral assemblages (i.e. illite, chlorite, irregularly interstratified illite-vermiculite), shows that the clastic supply represents erosional material that originated from a tectonically active continental setting of both carbonate and clastic rocks, presumably the Pelagonian Zone, as for the flysch of the Beotian and Sub-Pelagonian Zones. The arrival of the first clastic material in the Arachova area as early as latest Maastrichtian time, its Pelagonian origin and the persistence of pelagic conditions of sedimentation throughout the Palaeocene, indicate that the Arachova area was situated along the northeastern margin of the Parnassus platform and that it subsided into the Beotian basin. While the central areas of the platform remained tectonically stable during middle Palaeocene times and there was an extensive development of stromatolites, the northeastern marginal areas transitional to the Beotian basin continued to subside allowing pelagic carbonate sedimentation with periods of clastic influx. The total collapse of the platform in the late Palaeocene gave rise to the deposition of the flysch over the entire zone.
Testing the climatic significance of dropstones: an example from southeast Spain
Authors: Bennett Matthew R. , Doyle Peter , Mather Anne E. , Woodfin Joanne L.
Published: May 2009

Dropstones are clasts which pose a hydrodynamic paradox or which have an exotic lithology with uncertain provenance. Dropstones are usually associated with glacial processes and have recently been used to substantiate the presence of cool climatic phases in the geological record. The aim of this paper is to demonstrate, using an example from southeast Spain, that dropstones can be unreliable palaeoclimatic indicators, and that greater care is required in their interpretation.
Introduction to papers on the Cambrian–Ordovician Boundary
Authors: Norford B. S.
Published: May 2009

The Working Group has the responsibility of recommending a specific level within a suitable stratigraphic section to serve as the global stratotype for the Cambrian–Ordovician Boundary. Commencing in 1974, comprehensive studies culminated in a plenary session in Calgary in 1985 resulting in decisions on the ‘golden-spike’ principle of selecting the boundary at a horizon just below the first influx of nematophorous graptolites. Conodonts are to be used as the primary guide for the selection of the specific horizon and the global stratotype section must have potential for studies using paleomagnetism, geochemistry and other non-biological correlation tools. The specific horizon will correspond approximately to the base of the Tremadoc Series of Wales and slightly higher than the base of Canadian Series as used in western North America.

The Calgary meeting considered the Broom Point and Green Point sections in Newfoundland, Canada, and the Xiaoyangqiao section at Dayangcha, China, as prime candidates to serve as the global stratotype. A delegation from the Working Group inspected the Dayangcha sections in 1986. For this visit, comprehensive documentation and description of the sequence were prepared and published and are briefly summarized in the present issue.

Specific uncertainties remain to be resolved for the Dayangcha and Newfoundland stratigraphic sections before the Working Group will be ready to recommend selection of a global stratotype.
Review of trilobite biofacies distributions at the Cambrian–Ordovician Boundary
Authors: Shergold J. H.
Published: May 2009

Detailed analysis of trilobite assemblages at the Cambrian–Tremadoc transition reveals the presence of four, possibly five, biogeographic provinces: Baltic, North China, Southeast China, North American, and possibly Siberian. One or more discrete biofacies characterize the transition in each province. When plotted palaeogeographically these appear to be largely temperature controlled. Interdigitation of provincialized trilobite biofacies is recognized by the representation of dominant types of trilobite, olenaceans, ceratopygaceans, remopleuridaceans, dikelocephalaceans and leio-stegiaceans in particular, on key boundary sections. These sections, at Nochixtlán, Mexico; Batyrbay, southern Kazakhstan; Broken Skull River, District of Mackenzie, Canada; and Jiangshan–Chang-shan, western Zhejiang, China, permit the correlation of biogeographic provinces globally. As a result of the application of trilobite biostratigraphy relatively few problems prevent the maintenance of a Cambrian–Ordovician Boundary stratotype section in its traditional Baltic biogeographic setting.
The Nærsnes section, Oslo Region, Norway: trilobite, graptolite and conodont fossils reviewed
Authors: Bruton D. L. , Koch L. , Repetski J. E.
Published: May 2009

New collections of trilobites, graptolites and conodonts, the latter figured for the first time, have been made from an unbroken, uniform sedimentary succession across the Cambrian–Ordovician Boundary. The zonal conodont Cordylodus proavus first appears in undoubted pre-Tremadoc strata. Additional conodonts show that the base of the Tremadoc lies within beds correlative with the Symphysurina Zone of North America and at a level above the base of the Hirsutodontus simplex subzone of the C. proavus Zone. Cordylodus lindstromi and Iapetognathus preaengensis first appear at the base of the Tremadoc. The olenid trilobite Jujuyaspis occurs in the same lower Tremadoc interval and has great potential for interregional correlation.
The Chitradurga greenstone succession in south India and evolution of the late Archaean basin
Authors: Bhattacharyya P. K. , Bhattacharya H. N. , Mukherjee A. D.
Published: May 2009

The Chitradurga greenstone succession of south India comprises a thick pile (~ 10 km) of late Archaean volcanic flows and terrigenous clastic sediments, metamorphosed from greenschist to low-grade amphilobite facies. An older near-shore sedimentary sequence of cratonic affiliation and an off-shore bimodal volcanic sequence were deposited contemporaneously on a gneissic basement. The volcanics are metasomatically altered, and major, minor and trace element data fail to discriminate the metavolcanics in terms of modern plate settings. A younger turbidite sequence of coarser elastics covered the older deposits without any apparent tectonic or erosional break. All the rocks of the succession display evidence of similar deformation, prior to invasion by younger granites (~ 2.5 Ga)in a late syn-kinematic phase.

This suggests that initially a simple flat-lying downwarp in a continental crust served as the passive receptacle of the platform-type sediments, and also witnessed volcanism along extensional faulting. This phase of the basin was not associated with any compressive deformation. Subsidence of the Chitradurga basin by the denser volcanics and uplift in the gneissic borderlands provided the infrastructure for subsequent development of the younger turbidite sequence covering the still virtually undeformed older deposits. A compressive orogeny, accompanied by granitic intrusion (~ 2.5Ga) in a late kinematic phase, ultimately deformed and uplifted the basin-fill during the declining phase of basinal activity.

There is no evidence in the belt to suggest that the plate-tectonic (Wilson cycle) processes, pending a terminal orogeny, were operative during evaluation of the Chitradurga basin.
Transgressions and regressions: a model for the influence of tectonic subsidence, deposition and eustasy, with application to Quaternary and Carboniferous examples
Authors: Collier R. E. Ll. , Leeder M. R. , Maynard J. R.
Published: May 2009

The position of a coastline in time and space is determined by (1) the vertical displacement and/or tilting of the depositional surface, (2) the rate of sediment accumulation or erosion across that surface, and (3) variation of sea-level. All three rates of change may vary through time. We present computer simulations of coastline movements that illustrate the interaction of the above variables, with (1) and (2) held at various defined levels whilst (3) is varied according to the late Quaternary glacio-eustatic sea-level curve. The Corinth Canal section in central Greece exposes uplifted late Quaternary coastal transgressive cycles, each of which may be related to a radiometrically dated, c. 100 ka duration, cycle of sea-level change. Observed stratigraphic sequence geometries are predicted by forward modelling based on the known glacio-eustatic history over the last 430 ka. Milankovitch orbital parameters are calculated for the Carboniferous period. The obliquity and precession parameters are found to have been significantly shorter than at present. A simulation is presented of the effects of sea-level changes across low gradient, fluvio-deltaic environments such as existed in northern England and other parts of the Laurentian continental margin during Upper Carboniferous time.
A model for marine shelf storm deposition in the Lower Cambrian Fucoid Beds of northwest Scotland
Authors: McKie Thomas
Published: May 2009

The Lower Cambrian Fucoid Beds of northwest Scotland are a 20 m thick mixed clastic-carbonate sequence of thinly bedded storm beds deposited on the western margin of the Iapetus Ocean. Proximal facies display plane beds, current ripple laminations and wave ripple laminations and were deposited under the influence of combined steady andoscillatory currents. The steady component of flow appears to have expanded in an offshore direction and weakened during the final stages of storm deposition with respect to the oscillatory component, producing less asymmetrical ripples with less evidence of a preferred migration direction. Distal facies are represented by thin ‘graded rhythmites’. The palaeocurrent data suggest a wide spread of sediment transport directions, but with a north to northeasterly mode which may reflect a geostrophic component of flow. Following storms these beds were burrowed and echinoderms colonized the sea floor, although the limited extent of these processes and the presence of abundant collophane suggests that the fairweather Fucoid Beds shelf was generally quiescent and possibly dysaerobic.
Thrust systems of the Southwest Pyrenees and their control over basin subsidence
Authors: Turner J. P. , Hancock P. L.
Published: May 2009

There are two thrust systems in the Southwest Pyrenees: a NW-SE trending, thin-skin system exposed in the post-Triassic cover and a larger, thick-skin system of NE-SW thrusts in the Palaeozoic basement. The ‘cover’ thrust system propagated and migrated both southward and westward in response to the non-orthogonal collision of Iberia with Europe during Palaeogene mountain building. The ‘basement’ thrust system is interpreted to be a longer-lived structure, initiated during the extensional tectonic regime in mid Cretaceous time, and inverted during the main episode of Pyrenean collision. A model in which interaction of the two thrust systems controlled the timing and magnitude of thrust-induced, flexural subsidence is presented. The development of the basement thrust system caused regional subsidence along the South Pyrenean foreland margin that was subsequently halted by local uplift associated with the west-migratingcover thrust system.
Anatomy of a channel-bank collapse structure in Tertiary fluvio-lacustrine sediments of the Lower Rhine Basin, Germany
Authors: Williams H. , Flint S.
Published: May 2009

An exceptionally well-preserved synsedimentary deformation feature is described from uppermost Miocene fluvio-lacustrine coastal plain sediments, exposed in lignite mines of the Lower Rhine Basin, Germany. The feature is interpreted as a complex, multi-stage channel-bank collapse structure. Rotational slumping of bank material into the channel along two failure surfaces extending below the channel toe generated a series ofminor compressional ‘thrust/backthrust’ structures within the muddy channel-fill sediments. A reconstruction of the failure event is proposed which is linked toa lowering of river stage and subsequent channel abandonment. The accurate description of this unusually well-preserved channel-bank collapse structure may have general application in the interpretation of similar, but less-well-exposed-preserved phenomena elsewhere.
The fauna and flora of the March Gravels at Northam Pit, Eye, Cambridgeshire, England
Authors: Keen D. H. , Robinson J. E. , West R. G. , Lowry F. , Bridgland D. R. , Davey N. D. W.
Published: May 2009

Investigations of the March Gravels of Northam Pit, Eye, Cambridgeshire, have provided previously undescribed molluscan, ostracod and foraminiferal faunas together with pollen spectra, which enable a detailed palaeoenvironmental synthesis to be developed. The sediments were laid down in brackish-water conditions and a temperate environment, during a Late Pleistocene temperate stage.
Magnetic survey of a monchiquite intrusion in central Gwent
Authors: Haslett Simon K.
Published: May 2009

A magnetic survey was carried out along a NW–SE trending monchiquiteintrusion near Llanllowell, Gwent. The intrusion was previously thought to be a dyke, 23m long and 5 m wide, and that it may have been an extension of a second monchiquite intrusion at Great House to the southeast. However, the survey revealed the intrusion to beat least 34 m long, up to 20 m wide, and independent of the Great House intrusion. Evidence suggests that both of these monchiquite intrusions in central Gwent may have been feeder pipes to post-Lower Carboniferous volcanoes.
The sedimentology, palaeoecology and preservation of the Lower Carboniferous plant deposits at Pettycur, Fife, Scotland
Authors: Rex Gillian M. , Scott Andrew C.
Published: May 2009

The Lower Carboniferous (Asbian) sediments and volcanics of the Pettycur region in Fife, Scotland, yield several important anatomically preserved floras including that from the famous ‘Pettycur Limestone’. The plant fossils are preserved as calcareous permineralizations and fusain within limestone blocks which occur at the base of basaltic lava flows or within pyroclastic sequences. The geology and sedimentology of these plant deposits have been investigated, and it is demonstrated that a number of plant-bearing facies can be recognized which reflect different modes of transport, deposition and fossilization. Of these facies the ‘Pettycur Limestone’ is the most well known. The lithology is composed of a distinct assemblage dominated by lycopods and the pteridosperm, Heterangium. Other assemblages include a limestone dominated by zygopterid ferns which are frequently fusainized and the Kingswood Limestone which contains a completely different flora to that at Pettycur, being dominated by pteridosperms, other gymnosperms and the lycopod Oxroadia. Each sediment type is characterized by a distinct mineralization history of the plants reflecting different sites of fossilization.

A hypothesis concerning the original ecology of the plant assemblages within the basaltic volcanic terrain is proposed. It is suggested that the Pettycur Limestone represents an established original peat within which the plants were permineralized. The zygopterid ferns occupied sites which were susceptible to wildfire and did not establish long-lived peat-forming communities. The Kingswood flora was established in a region where plants were prone to fire and then subsequently transported into an area of limestone deposition along with unburnt plant fragments. This flora was separated by space and/or time from the Pettycur floras. Lakes developed on lava surfaces and provided sites of fossilization for plant fragments as compressions.
Skeletal microfauna of Meishucunian and Qiongzhusian (Precambrian–Cambrian boundary) age from the Ganga Valley, Lesser Himalaya, India
Authors: Kumar Gopendra , Bhatt D. K. , Raina B. K.
Published: May 2009

The earliest skeletal microfauna of Precambrian-Cambrian age recovered from the ‘Lower Tal’ sequence (Chert-Phosphorite to Calcareous members) of the Tal Formation, exposed in the Ganga Valley, Lesser Himalaya, Uttar Pradesh, India, has been grouped into three assemblages. In ascending order these are: assemblage I, containingAnabarites trisulcatusMissarzhevsky,Tiksitheca korobovi(Miss.).Circothecasp.,Turcuthecasp.,Spirellus columnorusJiang andOlivooides alveusQian; assemblage II, yieldingAllonia erromenosaJiang,A.sp. cf.A. erromenosaJiang,Dimidia simplecaJiang,D.sp. cf.D. simplecaJiang andHyolithellussp.; and assemblage III, comprisingPelagiella lorenziKobayashi,Auriculatespira madianensisZhou & Xiao andA. anduncaHe & Pei. The assemblages I and II are correlatable to the Meishucunian Zone I and Zone III respectively, and the assemblage III to the Qiongzhusian Stage of China. Thus the ‘Lower Tal’ sequence is assigned to Precambrian–Cambrian age.
Intrusive and extrusive (micro)melange couplets as distal effects of tidal pumping by a marine ice sheet
Authors: Talbot C. J. , Brunn V. Von
Published: May 2009

Microscopic soft-sediment deformation structures in a 30 × 25 × 12 mm hand specimen of glaciogenic silty mudstone from the Permo-Carboniferous Dwyka Formation of northern Natal in South Africa are illustrated by serial sections. The processes these structures imply are interpreted using palinspastically restored sections and isopachytes reconstructed from them. The sedimentation of silts, muds, and microrhythmites is found to have been punctuated by episodes of hydraulic activity which resulted in thirteen bodies with the mixed fabrics of micromelanges. These are divisible into five melange types: (1) subconcordant intrusive; (2) disconcordant intrusive; (3) subconcordant extrusive; (4) near-surface with asymmetric internal structures, and (5) conformable near-surface with internal structures symmetric about the palaeovertical.

Remarkable similarities between isopachs for pairs of micromelanges at different levels in the specimen suggest that intrusive melanges at depth fed contemporaneous extrusive melanges on the sea floor. Each couplet of melanges with matched isopachs is linked by faults which are interpreted as having acted as hydraulic vents despite only parts of them being infilled by intrusive melange. A significant proportion of the succession could consist of sediment recycled from depth by hydraulic extrusion. Repeated hydraulic intrusions along, and extrusions from, the same disturbed interface suggest that this interface acted as the distal leaking end of one of the hydraulic sills recently described by von Brunn & Talbot (1986). Pulses of pressurized water were transmitted through a prograding marine slope of quickclay by the tidal pumping of a marine ice sheet periodically grounding upslope.

The results of this analysis are extrapolated to processes operative in subduction complexes. All four fabrics described from large-scale hydraulic melanges in modern and ancient accretionary prisms are matched on a much smaller scale in our sample from a proglacial submarine slope. Dismemberment by faults is the only fabric element described from accretionary complexes which is missing from the micro-analogues described here.
Further Australian Cambrian sphinctozoans
Authors: Kruse Peter D.
Published: May 2009

Two new genera and species of Middle Cambrian sphinctozoans, Jawonya gurumal and Wagima galbanyin, are described from the Tindall Limestone of the Daly Basin, Northern Territory, within continental platform successions of the northern Australian craton. They are ambisiphonate sebargasiids, coeval with the island-arc shelf fauna from the Ordian Stage of western New South Wales. Additionally, a new Early Cambrian (Atdabanian equivalent) species, ?Jawonya tiro, displaying some sphinctozoan and some archaeocyathan features, is documented from the Ajax Limestone of the Arrowie Basin, South Australia. It is tentatively regarded as the oldest known sphinctozoan, but raises the possibility of the derivation of sphinctozoans from archaeocyaths. A brief review charts the Early–Middle Palaeozoic history of the sphinctozoans. The use of filling tissue type as a family-level criterion in sphinctozoan classification needs some reappraisal, as some types are of secondary origin.
Probabilism in Geological Data Analysis
Authors: Philip G. M. , Watson D. F.
Published: May 2009

The way in which probability can enter the interpretation of geological data is outlined. Probabilistic models are introduced in data synopses to allow statistical inferences about samples and population parameters. Inferences of this type are a special application of mathematical theory and have little to do with testing scientific generalizations. The logic of statistical inference, as used in operations research, is contrasted with that of geological inference. Geology is a cumulative science; its methodology is not that of experimentation with formal replication; inferences are developed from observations and tested and refined against new data, often by different investigators at different times and in different places. Because of the way in which inferences are drawn, sampling in geology is purposive. Random sampling, necessary for inferences based on sampling theory, is unattainable in most geological contexts. Different classes of geological measurements require careful consideration as to their appropriate form of synopsis, and, particularly, as to whether a parametric probability model is applicable.
New fold terminology – equal and unequal folds
Authors: Tremlett W. E.
Published: May 2009

The new terms ‘equal fold’ and ‘unequal fold’ are defined by whether the ratio of dips of limbs, measured in degrees, is less or greater than 1½.
Gravitational collapse and extension along a mid-crustal detachment: the Lough Derg Slide, northwest Ireland
Authors: Alsop G. I.
Published: May 2009

Pre-Caledonian basement is juxtaposed with an inverted Upper Dalradian cover sequence along the Lough Derg Slide, in south Donegal, northwest Ireland. Shear-sense criteria indicate that the Dalradian Succession is translated via oblique dextral thrusting over high pressure granulite facies basement in the footwall. Crustal thickening induced by large scale folding associated with this ductile thrusting resulted in mid-amphibolite facies metamorphism adjacent to the sole of the Dalradian nappe. Subsequent to peak metamorphism, the overthickened Dalradian cover sequence suffered heterogenous deformation associated with ductile extension concentrated in the strain-softened mylonites of the hangingwall. The oblique ductile thrusts initiated during crystal thickening were reactivated in a normal sense. Pre-existing fold axes rotated towards the extensional transport direction, which is marked by a secondary stretching lineation with associated S–C fabrics. Ductile extension and hangingwall collapse are considered to be related to gravitational instability induced by the earlier crustal thickening episode.
The dimensions of the graptolite zooid
Authors: Sudbury Margaret
Published: May 2009

Measurements of fuselli and cortical bandages on thecae which show both of these enable a hypothesis about the dimensions of graptolite zooids to be put forward. This leads to a method for estimating zooid size when fusellus height alone can be measured. Results are shown for some species and the implications for theca formation and reproduction are discussed.
Igneous stratigraphy and internal structure of the Little Minch Sill Complex, Trotternish Peninsula, northern Skye, Scotland
Authors: Gibson Sally A. , Jones Adrian P.
Published: May 2009

Detailed sampling of the Little Minch Sill Complex reveals that it is composed of both single and multiple sills. These are formed of three main, genetically related units: picrite, picrodolerite and crinanite, which are the result of differentiation of an alkali-olivine basalt magma (approximately 10% MgO) in an upper-crustal magma chamber. Variations in igneous stratigraphy and the presence of internal chills in the Trotternish sills suggest that they were emplaced by multiple intrusion and subsequently differentiated in situ. Changes in petrography adjacent to pegmatite veins and textures within picrite units indicate compaction and filter-pressing were important processes after emplacement. Rhythmic layering (1 cm to 1 m thick) is conspicuous in the sills near contacts but does not involve cryptic mineral variation. Such modal layering may be more common than realised in relatively small-scale intrusions and maybe modelled in terms of in situ differentiation under conditions of significant undercooling in a changing thermal gradient at the synthetic for-sterite-diopside-anorthite eutectic.
Geophysical correlation of the Aptian and Albian formations in the Wessex Basin of southern England
Authors: Ruffell A. H.
Published: May 2009

Using geophysical borehole log signatures and basic lithological information from sidewall cores and well-cuttings, division and correlation of the mid-Cretaceous sediments of the Wessex Basin can be achieved. A sub-Gault (early Albian) unconformity surface is mapped with some accuracy across the Hampshire–Dorset area, and the deposits of a previous, Aptian transgression are observed. The distinctive log signatures aid in facies reconstructions and sequence stratigraphical analysis: especially the onlap of basal Gault horizons onto and across basement ‘highs’. The highly variable thickness and lithological distributions characteristic of the Wealden pass upward into laterally extensive facies distributions in the Lower Greensand and Gault. Sequence boundaries are identified at the base of the Wealden; Lower Greensand; Gault; within the Gault (cristatumsubzone); and base Chalk.
The age and tectonic significance of the Bute amphibolite, Highland Border Complex, Scotland
Authors: Dempster T. J. , Bluck B. J.
Published: May 2009

Sm–Nd and K–Ar isotopic determinations on an amphibolite from the Highland Border Complex yield Cambrian ages. Collisional events which might have generated the amphibolite appear incompatible with the passive margin character of Laurentia at that time. A possible explanation is that the part of the Highland Border Complex containing the amphibolite and associated rock units was generated outside Laurentia.
Textural responses to evolving mass-flows: an example from the Devonian Asen Formation, central Norway
Authors: Bøe Reidulv , Sturt Brian A.
Published: May 2009

The Asenvågoya Conglomerate is a thin (c. 6 m) conglomeratic body composed of mass-flow deposits and enveloped by braided-stream sandstones and conglomerates. The section studied represents the proximal part of a small-radius alluvial fan built out from the basin margin towards a flood basin. The fan was possibly generated by escarpment creation, or rejuvenation, in response to syndepositional faulting along the basin margin, and comprises sand-matrix-supported and clast-supported, sheet-like conglomerates. There is an upward change through the sequence from stream flow and surging mass-flow, through fully turbulent mass-flow and sheet flow to cohesive mass-flow deposits and then a return of braided-stream alluvium at the top of the sequence. The fan wedge demonstrates the wide range of textures possible within a ‘mass-flow” system.
The stratigraphy of a proximal late Hercynian pyroclastic sequence: the Vilancós region of the Pyrenees
Authors: Gilbert J. S.
Published: May 2009

Volcanic activity, the result of crustal differentiation during the Hercynian orogeny, generated eight explosive eruptions in the Vilancós region of the Spanish Pyrenees. The volcanic products comprise the Erill Castell Volcanic Formation of Stephanian age, which crops out as a 20 km long, WNW-trending strip < 2 km wide dipping steeply to the south.The Vilancós region represents a small fragment of an originally extensive regional terrain of silicic centres.

The explosive eruptions mainly generated strongly peraluminous and phenocrystal garnet-bearing subaerial ignimbrite facies. Proximal intra-formational breccias represent a substantial volume of the preserved erupted product and one phreatoplinian deposit is exposed. Mass-flow deposits are common, and small-volume basalt, andesite and rhyolite lava flows, minor tuffs and palaesols also occur.

Electron microprobe data show that each garnet-bearing member of the Vilancós region has a distinct garnet composition. This is used as geochemical fingerprinting tool to aid mapping and correlation between proximal intra-formational breccias and ignimbrite of the same eruption. Within one debris-flow deposit (the Vilancós Breccia Member) at least three garnet populations occur. Two of these are derived from pyroclastic members within the mapped region, the other comes from an unexposed rhyolite lava source.
Crust–mantle interaction in western Turkey: implications from Sr and Nd isotope geochemistry of Tertiary and Quaternary volcanics
Authors: Güleç N.
Published: May 2009

The isotopic composition of Sr and Nd together with the abundance data for major and trace elements are reported for Tertiary to Quaternary volcanics from a variety of localities in western Turkey. These data are used to evaluate the role of crust–mantle interaction in the petrogenesis of the western Turkish volcanics. The major and trace element chemistry reveals a general change in the nature of volcanism from dominantly calc-alkaline in Tertiary to alkaline in Quaternary times. The calc-alkaline rocks are quartz-normative and comprise andesitic to rhyolitic compositions of Miocene–Pliocene age; the trace element patterns are typical of continental margin volcanics with high Ba/Nb ratios and negative Ti anomalies. The alkaline rocks are nepheline-normative and dominantly Quaternary in age; they are basic in composition, with a change from potassic nature in Miocene–Pliocene to sodic in Quaternary times. Most of the Tertiary alkaline volcanics display trace element patterns similar to those of the calc-alkaline ones, whereas the Quaternary alkaline volcanics have low Ba/Nb ratios without negative Ti anomalies; they resemble intraplate volcanics.

The calc-alkaline rocks have high 87Sr/86Sr (from 0.705011 to 0.709529) and low 143Nd/144Nd ratios (from 0.512294 to 0.512691). With the exception of two Tertiary samples, all the alkaline volcanics plot within the so-called mantle array of the isotope correlation diagram, 87Sr/86Sr ratios ranging from 0.703128 to 0.703628 and 143Nd/144Nd ratios ranging from 0.512749 to 0.512998. The two Tertiary alkaline samples, with trace element patterns similar to those of the calc-alkaline ones, have considerably higher Sr (0.707741–0.707918) and lower Nd (0.512494–0.512514) isotope compositions. The combined isotope and chemical data suggest the derivation of the western Turkish volcanics from variable mixtures of melts generated in two different mantle regions. The calc-alkaline volcanics were essentially derived from the continental lithospheric or shallow asthenospheric mantle which was contaminated with upper crustal material during earlier subduction events. The generation of the alkaline volcanics was controlled by melts derived from relatively deep, isotopically depleted mantle regions. Most of the volcanics were subjected to contamination at crustal levels, through the operation of an assimilation–fractional crystallization (AFC) process. The nature of contaminant changed from upper crustal in the calc-alkaline to lower crustal in the alkaline volcanics, accompanying the overall decrease in the amount of contamination from about 50% down to about 10%, and broadly paralleling the transition from compressional to extensional tectonics in the region.
The role of erosion and extension in unroofing the Indian Plate thrust stack, Pakistan Himalaya
Authors: Treloar Peter J. , Rex David C. , Williams Matthew P.
Published: May 2009

In north Pakistan cooling history data show that metamorphism within the Indian Plate predated 40 Ma, and that the post-metamorphic thrust stack developed within the crystalline internal zones had cooled to less than 100 °C by c. 18 Ma. Much of this cooling occurred during late Oligocene to early Miocene time and can be equated to substantial unroofing of the metamorphic pile. This unroofing was by a combination of erosion, recorded in Lower Miocene molasse deposits within the foreland basins, and by large scale hinterland (northward) directed extensional normal faults developed within the upper parts of the Indian Plate and within the Kohistan–India suture zone and operative as late as 20 Ma. As up to 20 km of material was removed during exhumation, substantial uplift must have been synchronous with exhumation. Part of this may be accounted for by isostatic rebound of the thickened Indian Plate, and part by uplift in the hanging wall of major south-verging thrusts developed at the base of the crystalline pile.
Biostratigraphical correlation of the Campanian–Maastrichtian boundary: Lägerdorf–Hemmoor (northwestern Germany), DSDP Sites 548A, 549 and 551 (eastern North Atlantic) with palaeobiogeographical and palaeoceanographical implications
Authors: Schönfeld Joachim , Burnett Jackie
Published: May 2009

A correlation of the Campanian–Maastrichtian boundary is attempted using foraminiferal and nannoplankton data from two areas: the eastern North Atlantic and northwestern Germany. The Boreal benthic and Tethyan planktonic foraminiferal zonation schemes are applied to Site 548A, where both foraminiferal groups occur frequently. A direct comparison of both biozonations reveals that the base of the Maastrichtian, according to planktonic foraminifers, has to be placed in the Upper Campanian of the Boreal benthic foraminiferal biozonation, which concurs with the nannoplankton results. The Tethyan Middle and Upper Maastrichtian are probably equivalent to the Upper Maastrichtian in the Boreal sense. The bases of the Maastrichtian substages are thus diachronous between the Boreal and Tethyan realms. Palaeotemperatures (which were estimated using the oxygen isotopic composition of the Goban Spur chalks) indicate, in combination with palaeowind directions, that the faunal and floral distribution pattern recorded is the result of a stable, warm water outflow from the northwest European epicontinental seas through the Channel area to the Celtic Shelf sea and Goban Spur. This mechanism appears to have been a dominant separating factor of the Boreal and Tethyan bioprovinces on the western European Shelf.
The volcanogenetic significance of garnet-bearing minor intrusions within the Borrowdale Volcanic Group Eskdale area, Cumbria
Authors: Beddoe-Stephens B. , Mason I.
Published: May 2009

A number of garnetiferous minor intrusions have been mapped within the Borrowdale Volcanic Group. They underlie garnetiferous extrusive volcanic rocks which occur toward the top of a sequence of ignimbrite and lava – the Airy's Bridge Formation – which is the product of a major caldera-forming eruptive episode. Garnet and whole-rock geochemistry indicate that most of the intrusions are indistinguishable from garnetiferous dacite forming the final eruptive unit of the Airy's Bridge Formation: a co-magmatic link is therefore postulated. One of the intrusions, which intrudes the Airy's Bridge Formation, is distinct and may be related to the later Eskdale pluton.

It is suggested that following the emplacement of ignimbrites forming the basal half of the Airy's Bridge Formation, caldera collapse partially sealed a fissure-conduit system and degassed, garnet-bearing magma was intruded as dykes and sills and locally extruded as a post-explosive lava dome. It is also postulated that garnet crystallized in a high-level magma chamber (P < 3 kb) and that reverse chemical zoning was due to growth while sinking through compositionally stratified magma.
Derivation of 500 Ma eclogites from the passive margin of Baltica and a note on the tectonometamorphic heterogeneity of eclogite-bearing crust
Authors: Andréasson Per-Gunnar , Albrecht Lena
Published: May 2009

Several recent plate reconstructions of the Iapetus Ocean describe the margins of Baltica as passive until Silurian collision with Laurentia. Yet there is a variety of evidence to suggest that the accretion of the Scandinavian Caledonides began by latest Cambrian—early Ordovician subduction and imbrication of the passive continental margin. One such evidence is provided by eclogites occurring in the Seve Nappe Complex. Previous work by others dated the high-pressure metamorphism at 503±14 Ma (Sm—Nd garnet-omphacite age), and the uplift through the c. 500°C isotherm at 491±8 Ma (40Ar/39 Ar hornblende plateau ages). The protolith dolerites of the eclogites have been correlated with Iapetan rift-facies dolerites of the Baltoscandian margin. If valid, such a correlation implies early Caledonian destruction of the margin, and thus modification of those plate reconstructions which require passive margins around Baltica in latest Cambrian-early Ordovician time. This paper provides a substantially improved basis for the concept that the protoliths of eclogites and their host rocks derived from Baltoscandian rift basins. The chemical similarity between coronitic dolerites and dolerites of the rift basins pertains not only to element concentrations and variations but also to the specific T-MORB signature shared by the two groups. The variation of psammitic and pelitic schists, graphitic schists, calc-silicate gneisses and marbles of the eclogite host rocks equates with sequences of sandstones, siltstones, shales, black shale, quartzite, dolomite and limestones of Baltoscandian palaeobasins.

At the same time, the paper calls attention to the remarkable preservation of structural and metamorphic contrasts within the eclogite-bearing thrust sheets of the Seve Nappe Complex. Such disequilibrium is generally ascribed to the kinetics of localized deformation and fluid infiltration into dry crust. This paper presents evidence that disequilibrium is found also within inferred subducted sedimentary complexes, which are generally assumed to be pervasively flushed by fluids. Preservation of sedimentary, volcanic and magmatic structures and fabrics, and of both undeformed dolerite dykes and eclogitized dykes demonstrates that neither deformation nor high-pressure metamorphism were pervasive.
Geochemical evidence for the volcanic arc tectonic setting of the Dhanjori volcanics, Singhbhum craton, eastern India
Authors: Alvi Shabber H. , Raza M.
Published: May 2009

Geochemical data on the Dhanjori volcanics of the Singhbhum craton indicate that they range from basalt to andesite and show an iron-enrichment trend. Various chemical characteristics suggest that they are differentiated along the trend similar to that of orogenic suites and have a strong affinity with island arc tholeiites. The field relationships as well as other geological information also support this conclusion and indicate their eruption on a thin continental margin. It is inferred that the Dhanjori volcanics were probably erupted as a result of plate convergence in northern Singhbhum with subduction of oceanic crust below the Singhbhum craton.
Non-marine oolitic ironstones in the Lower Cretaceous Wealden sediments of southeast England
Authors: Taylor Kevin G.
Published: May 2009

Oolitic ironstones are described from the early Cretaceous non-marine Wealden sediments of southeast England. The recognition of non-marine oolitic ironstones in the geological record is rare and, therefore, warrants further study. The oolitic ironstones described take two forms, named here type-I and type-2 ironstones.

Type-1 ironstones contain pisoids and ooids of berthierine together with sandstone fragments and detrital quartz grains. The pisoids (up to 0.5 cm in size) vary from subspherical to highly irregular. The smaller ooids (up to 1 mm in size) are generally ellipsoidal but strongly asymmetrical forms are also present. The form of these pisoids and ooids suggest that mechanical accretion was not the dominant mechanism controlling their formation. It is proposed that this ironstone type formed from the reworking and redeposition of local soil material.

Type-2 ironstones, of which only one unequivocal example has been studied, is composed of iron oxide ooids set in a detrital matrix. The ooids are most commonly regularly ellipsoidal and exhibit a decrease in iron at their centres. It is proposed here that the ooids suffered post-depositional iron depletion at their centres, in a similar fashion to that proposed for the recent Lake Chad oolites. There is no unequivocal evidence as to the origin of the ooids.

This study is important in that it shows that different ironstones can be formed by different processes essentially within the same environment. Comparison of non-marine oolitic ironstones with the better-developed marine examples should prove a valuable exercise.
Significance of radiolarian age data to the Mesozoic tectoni and sedimentary evolution of the northern Pindos Mountains, Greece
Authors: Jones Gregory , de Wever Patrick , Robertson Alastair H. F.
Published: May 2009

Radiolarians were extracted from siliceous sediments of the northern Pindos Mountains, in an attempt to establish the chronology of tectonic and stratigraphic events related to the evolution of the Pindos ocean basin. Three separate phases of siliceous sedimentation were identified: (i) (mid-) late Triassic; (ii) mid-late Jurassic and (iii) mid-late Cretaceous. The first two phases are also known from the Pindos and Sub-Pelagonian zones of southern and central Greece, and elsewhere in the Dinarides andHellenides. However, the occurrence of Cretaceous radiolarites in the west central Tethyan region is somewhat unusual. Field observations suggest thatfrom the mid-late Triassic through to the mid Jurassic, radiolarites were deposited on volcanic basement, or were interbedded with sediments associated with the late rifting/spreading stages in the development of the Pindos ocean. Radiolarites of mid-late Jurassic age are commonly interbedded with clastic sediments of ophiolitic derivation. This coincides with a phase of significant compression within the Hellenides, which caused intra-oceanic deformation of the Pindos ophiolite. The ophiolite was subsequently emplaced onto the margin of the Pelagonian microcontinent in latest Jurassic time (Kim-meridgian-early Tithonian), as evidenced by transgressive marine carbonates. However, the Pindos basin survived in reduced form until the early Tertiary, allowing radiolarites to accumulate again within Cretaceous post-tectonic clastic sequences.
Lower Cambrian acritarchs from northern Spain: the Precambrian-Cambrian boundary and biostratigraphic implications
Authors: Palacios Teodoro , Vidal Gonzalo
Published: May 2009

Acritarchs are reported from basal Cambrian rock units inthe Cantabrian region of northern Spain that are known to contain archaeocyathan and trilobite faunas. Biostratigraphic correlation of the Iberian sequences with other regions has been hampered by the strong provincialism of these faunas. However, this report of evidently cosmopolitan acritarch taxaestablishes the time equivalence of early Cambrian trilobite faunas from Iberia, Baltoscandia and the East European Platform (EEP). Our data suggest that the detrital deposition of the Lower Cambrian Herreria Formation embraces at least three (and possibly four) Lower Cambrian acritarch zones previously identified in the EEP, eastern Siberia, Baltoscandia, Scotland, Greenland, Svalbard and western North America. The early Cambrian transgression in northern Spain was probably initiated in Talsy times (Schmidtiellus mickwitzitrilobite Zone in Baltoscandia and the EEP), in part corresponding to theDokidocyathus regularisarchaeocyathian Zone of the Middle Tommotian in Siberia.
Cambrian stratigraphy and stage subdivision in the Holy Cross Mountains, Poland
Authors: Orlowski Stanislaw
Published: May 2009

The lithostratigraphic and biostratigraphic subdivisions of the Cambrian sequence in the Holy Cross Mountains of Poland are briefly presented and discussed. In accordance with recent progress in Cambrian stratigraphy and correlation in Great Britain and Scandinavia, a new proposal for chronostratigraphic stages is made. It is suggested that these stages are suitable for the Cambrian areas of central and northwest Europe, comprising Great Britain, Scandinavia and Poland. The formal establishment of the stages, a task for the Commission on Cambrian Stratigraphy, could be made using British or Scandinavian stratotypes.