bluuebunny/crossref_metadata_2025 huggingface dataset:
The depositional environments and tectonic development of a Mesozoic intra-arc basin, Atacama Region, Chile
Authors: Bell C. M. , Suarez M.
Published: May 2009

A thick succession of continental redbeds was deposited in a 50 km wide intra-arc basin on the Andean active continental margin in the Atacama region of northern Chile during early Cretaceous times. Upper Jurassic to early Cretaceous marine limestones were buried by the seaward progradation of a succession of coastal dunes, saline lakes and sandflats. Aeolian dune fields migrating towards the east across these coastal plains became stabilized by the growth of vegetation. Interdune alluvial areas between the sand dunes and dune fields developed into extensive alluvial braid plains which were in turn superimposed by alluvial fans. These fans were inundated by a regionally extensive saline lake produced by tectonic or volcanic damming of the sedimentary basin. This lake dried up leaving a large area of playa-lake mudflats. The climate was warm and semi-arid with a low and seasonal rainfall. Parts of the area supported a substantial vegetation of woody plants, together with a vertebrate fauna of dinosaurs, pterosaurs and crocodiles. The continental redbeds were derived from a volcanic source and were deposited on continental crust in a deep but narrow, north-south elongated, fault-bounded graben. This extensional basin formed in an intra-arc setting within an active andesitic volcanic chain. Upwards-coarsening sedimentary successions were the product of uplift of the fault-bounded margins of the basin.
The Eocene-Oligocene planktic foraminiferal transition: extinctions, impacts and hiatuses
Authors: Molina Eustoquio , Gonzalvo Concepción , Keller Gerta
Published: May 2009

Biostratigraphic study and re-examination of 22 late Eocene to early Oligocene sections provides data in support of three and possibly a fourth late Eocene impact events in the G. index Zone during a period of about 1 Ma of the middle Priabonian between 34.7 and 35.7 Ma. No major species extinctions or significant species abundance changes directly coincide with these impact events. Species extinctions are gradual and selective, affecting primarily cool-temperature-intolerant surface dwellers. These extinctions began with the onset of global cooling during the early middle Eocene and culminated near the Eocene/Oligocene boundary. The global cooling was associated with the isolation of Antarctica as Australia moved northward, the development of a circum-Antarctic circulation, growth of Antarctic ice sheet beginning by late middle Eocene time and a change from a thermospheric to thermohaline circulation. We find no evidence that the multiple late Eocene impact events directly contributed to the climatic deterioration already in progress.
Biostratigraphy of the Upper Jurassic-Lower Cretaceous bivalves Buchia and Aucellina of eastern Heilongjiang, northeast China
Authors: Sha Jingeng , Fürsich Franz Theodor
Published: May 2009

The biostratigraphic significance of the bivalves Buchia and Aucellina in northeast China is assessed. Buchia is abundant in four assemblages of the Dong'anzhen Formation, spanning the Jurassic-Cretaceous boundary: B. russiensis-B. fischeriana (Middle Volgian), B. fischeriana-B. unschensis (Upper Volgian), B. volgensis-B. cf. subokensis-B. cf. okensis-B. unschensis (Berriasian), and B. pacifica (Lower Valanginian). Aucellina is common in two Middle Barremian-Aptian assemblages: A. caucasica-A. aptiensis-A. jeletzkii in the lower part of the Upper Yunshan Formation, Longzhaogou Group, and in the lower part of the Chengzihe Formation, Jixi Group; A. cf. caucasica-A. cf. aptiensis in the upper part of the Upper Yunshan Formation. These assemblages can be correlated on a global scale and are particularly significant in dating the Early Cretaceous coalbearing measures of eastern Heilongjiang.
The Caledonides of the Anglo-Brabant Massif reviewed
Authors: Pharaoh T. C. , Molyneux S. G. , Merriman R. J. , Lee M. K. , Verniers J.
Published: May 2009

The Anglo–Brabant Massif has formed a positive structural element since the Acadian orogenic phase in mid–Devonian times. As a consequence, the Caledonian basement lies at relatively shallow depth across the massif, encompassing a large area of southern Britain, the southern North Sea, southern Netherlands, Belgium and northern France (Fig.1).
Integrated geophysical/geological modelling of the Caledonian and Precambrian basement of southern Britian
Authors: Busby J. P. , Kimbell G. S. , Pharaoh T. C.
Published: May 2009

Quantitative modelling of potential field data has been used to test and extend geological sections constructed for the new British Geological Survey Tectonic Map of Britain and Ireland. Three of the profiles cross part of the Anglo-Brabant Massif and provide new information on the nature of the pre-Mesozoic basement. A profile across southern England (passing just to the west of London) suggests that a significant contribution to observed gravity variations in the region results from changes in the thickness of relatively low density Lower Palaeozoic rocks. It also identifies a major deep-seated body with relatively high magnetic susceptibility and low density which is interpreted as a Precambrian cratonic core underlying the southeastern part of the Midlands Microcraton. Profiles across central and eastern England reveal major boundaries within the Precambrian basement, some of which coincide with structures mapped at surface. A number of intrusions of probable Caledonian age have been recognized, including bodies beneath the Widmerpool Gulf and The Wash. Those beneath The Wash appear to lie in a discrete basement region which separates belts of more magnetic basement lying to the northwest and southeast.
Structural evolution of the Skiddaw Group (English Lake District) on the northern margin of eastern Avalonia
Authors: Hughes R. A. , Cooper A. H. , Stone P.
Published: May 2009

The Skiddaw Group comprises a marine sedimentary sequence deposited on the northern margin of eastern Avalonia in Tremadoc to Llanvirn times. It is unconformably overlain by subduction-related volcanic rocks (the Eycott and Borrowdale Volcanic groups) of mid-Ordovician age, and foreland basin marine strata of late Ordovician and Silurian age. The Skiddaw Group has a complex deformation history. Syn-depositional deformation produced soft sediment folds and an olistostrome. Volcanism was preceded (in late Llanvirn to Llandeilo times) by regional uplift and tilting of the Skiddaw Group, probably caused by the generation of melts through subduction-related processes. The Acadian (late Caledonian) deformation event produced a northeast- to east-trending regional cleavage, axial planar to large scale folds, and a later set of southward-directed thrusts with associated minor folds and crenulation cleavages. This event affected the northern Lake District probably in the late Silurian and early Devonian. The Skiddaw Group structures contrast strongly with those formed during the same event in the younger rocks of the Lake District inlier. The contrasts are attributed to differing rheological responses to varying and possibly diachronous stresses, and to possible impedence of thrusting by the combined mass of the Borrowdale Volcanic Group and the Lake District batholith.
A preliminary study of Ashgill carbonate beds from the lower part of the Fosses Formation (Condroz, Belgium)
Authors: Tourneur Francis , Vanguestaine Michel , Buttler Caroline , Mamet Bernard , Mouravieff Nicolas , Poty Edouard , Préat Alain
Published: May 2009

The sedimentology and palaeontology of carbonate beds in the lower part of the Fosses Formation (Ashgill of the Condroz area, central Belgium) have been investigated. Two depositional interpretations are suggested: deposition either near a platform-ramp margin as bioclastic turbidites and interbedded shales or on a shelf as a transgressive sequence following a regressive event. Faunal affinities with the Baltic area and Wales are confirmed, and the location of Belgium in the tropics during the Ashgill is supported by the calcareous algae and the coral fauna.
Crustal magnetization variations across the Iapetus Suture Zone
Authors: Kimbell G. S. , Stone P.
Published: May 2009

The Iapetus Suture (Solway) line coincides with a magnetic low, which lies between magnetic highs over southwestern Scotland and the Lake District-Isle of Man region. Although topography on deep magnetic basement can account for these long wavelength geophysical variations, an explanation which involves lateral basement magnetization contrasts is preferred on the basis of (a) correlations between inferred magnetization boundaries and major structures delineated from other evidence, and (b) the apparent westward continuation of the Solway low through Ireland and Newfoundland across areas with very different subsidence histories but similar position with respect to the collision of Laurentia and Avalonia. In the preferred model, relatively magnetic continental crust beneath the Southern Uplands and Lake District terranes is separated by a zone of less magnetic crust interpreted as sedimentary rock of Avalonian affinity carried to deeper structural levels within the Iapetus Suture Zone. The magnetic unit beneath the Southern Uplands is bounded to the south by the northward-dipping Iapetus Suture and to the north by a structure which may have been reactivated in late Caledonian times to produce the Moniaive Shear Zone in the overlying rocks; this unit may represent the ‘missing’ arc terrane inferred from provenance studies. Alternatively, the two magnetic basement domains may have originally been part of the same terrane, with that portion beneath the Southern Uplands rifting from the Avalonian continent during its northwards drift and being subsequently trapped in the hanging wall of the Iapetus Suture. The southern margin of the Lake District domain appears as a discontinuity in the magnetic anomaly pattern, with long wavelength anomalies to the south having a southeast ‘Tornquist’ trend.
Post-depositional processes on a buried Cambrian sequence in southern Israel, north Arabian Massif: evidence from new K–Ar dating of Mn-nodules
Authors: Segev A. , Halicz L. , Steinitz G. , Lang B.
Published: May 2009

The Cambrian sedimentary sequence in Israel and adjacent countries marks the beginning of the Phanerozoic sedimentation on the Arabian–Nubian craton. The maximal burial of this sequence, in the southernmost part of Israel, was approximaly 2.5 km. Manganese nodules hosted by shales of the marine Cambrian Timna Formation, Timna Valley, were subjected to K–Ar analysis in order to date their Mn-mineral formation. In addition, the <2 μm clay fraction in the host rock was dated by K–Ar and Rb–Sr methods. The K–Ar ages (average 365 ± 4 Ma) and Rb–Sr isochron (381 ± 10 Ma) of the illitic clay fraction yielded a Middle/Late Devonian age. The results imply that K–Ar and Rb–Sr systems of <2μm illites in the Cambrian host rocks, as well as those enclosed in the Mn nodule insoluble residues, were completely resetin a Middle/Late Devonian thermo-tectonic event, coeval with the beginning of a stratigraphically recorded epeirogenic uplift. The Mn-nodules which were studied fall into two types: (1) nodules constituted by massive, well-crystallized hollandite and pyrolusite; and (2) younger nodules of poorly crystallized massive hollandite and coronadite solid-solutions. Type-1 nodules yielded a calculated Early Cretaceous age of 112 ± 11 Ma, whereas type-2 nodules yielded calculated apparent dates of 20 and 49 Ma. The first age suggests a first stage of manganese nodule formation within the Timna Formation, in Early Cretaceous time, possibly genetically connected with the shallow basic intrusions and volcanic explosive activity in the area. The much younger K–Ar dates of type-2 Mn nodules may be due to late manganese remobilization and mineralization processes. This activity is interpreted as being related to the nearby Tertiary Dead Sea rifting, which was accompanied by low temperature hydrothermal processes.
Radioelement distribution in the Tertiary Lundy granite (Bristol Channel, UK)
Authors: Thorpe Richard S. , Tindle Andrew G. , Williams-Thorpe Olwen
Published: May 2009

The radioelement distribution and content of the Lundy granite, a coarse-grained megacrystic granite of Tertiary age, has been measured using a portable gamma-ray spectrometer in order to assess fractionation and alteration processes in the granite. Results indicate a systematic variation of K, Th and U (with a few notable exceptions) that follows a partially concentric distribution to lower concentrations inland. The plateau region of the island (particularly the southern half) is relatively depleted in all radioelements. Over the island, measurements of K vary from 1.3–4.9 wt %, Th varies from 5.0–20.3 ppm and U varies from 2.0–12.5 ppm. A petrographic, electron microprobe and autoradiography examination of the granite indicates that the radioelements mainly reside in discrete major and accessory minerals, of which K-feldspar (K), biotite (K), monazite (Th), xenotime (U), tungsteniferous columbite (U) and uraninite (U) are the most important. Uraninite is rare, being preserved only in fresh samples which come mainly from abandoned quarries. Mass balance modelling indicates that up to 76.6% of uranium could reside in uraninite and where this has been leached by secondary processes such as hydrothermal alteration or weathering then the present radioelement content no longer reflects the original rock composition. Fission track evidence is presented to show the pathways along which uranium has been mobilized from or within the granite. Secondary sites of radioelements include fractures cross-cutting all major minerals (but especially quartz), grain boundaries, altered cores of plagioclase feldspar and occasionally yellowy brown mixed chlorite/smectite replacement product after biotite. Biotite itself may exhibit secondary tracks along cleavage traces. Combined effects of crystal fractionation (primary variation) and secondary alteration best explain the distribution of radioelements, with K controlled by fractionation of the major phases K-feldspar and biotite, Th by fractionation of the accessory mineral monazite (±xenotime and uraninite) and U contents by uraninite and tungsteniferous columbite. Secondary processes have removed much of the uraninite leaving behind indeterminate Fe—U material along fractures and residual U (and Th) enrichment within altered major minerals. There is some evidence to suggest that late radioelement-bearing fluids precipitated monazite and uraniferous zircon along fractures during the waning stages of magmatic activity.
Introduction to the Welsh Basin thematic issue
Authors: Woodcock N. H. , Fletcher C. J. N.
Published: May 2009

The Welsh Basin was an area of enhanced Early Palaeozoic subsidence on the northwestern margin of the Eastern Avalonian microcontinent. It is bordered to the southeast by the Midland Platform and to the northwest by the smaller Irish Sea Platform (Fig. 1). The sedimentary rocks of the basin and its flanking platforms range from Lower Cambrian through Lower Devonian. The sequence is dominantly marine, with abundant volcanics in the Ordovician. A basinwide change to non-marine facies is preserved in the Lower Devonian, heralding basin inversion and the culminating Acadian (late Caledonian) Orogeny.
Palaeozoic palaeomagnetic studies, in the Welsh Basin-recent advances
Authors: Channell J. E. T. , McCabe C. , Torsvik T. H. , Trench A. , Woodcock N. H.
Published: May 2009

In the last two years, new palaeomagnetic data from Wales have resulted in radical revision of the Ordovician palaeogeography of Eastern Avalonia, part of the southern margin of the Iapetus Ocean. Combined with Palaeozoic palaeomagnetic data from Laurentia and Gondwana, these data suggest that Eastern Avalonia was a peri-Gondwanide high latitude continental fragment during at least part of Ordovician time, with a palaeolatitude of about 62° S and 51° S in Arenig and Llanvirn time, respectively. This implies a latitudinal width of the early Ordovician Iapetus Ocean between Eastern Avalonia and Laurentia of at least 30°. Geological evidence for the proximity of Eastern Avalonia and Laurentia suggests that the intervening Iapetus Ocean closed during Silurian time, from late Llandovery to early Ludlow. Recent palaeolatitude data from the Iapetus bordering continents are consistent with closure by middle to late Silurian time. New pre-Acadian early Devonian palaeomagnetic data from the Old Red Sandstone places the Welsh Basin at about 17° S, consistent with a palaeogeography in which Laurentia, Baltica, Avalonia, Armorica, and possibly Gondwana, were part of a single supercontinent. Pervasive late Carboniferous/early Permian remagnetization affects the Welsh Basin. The remagnetization is probably associated with fluids emanating from the Variscan thrust front. We do not observe remagnetization associated with Acadian orogeny and the remagnetizations, which have been studied in more detail in North America, appear to be a unique feature of the Variscan-Hercynian-Alleghenian orogeny.
Geochemical and isotope composition of pebbles from the Caban Conglomerate Formation and their bearing on the source of Welsh Palaeozoic sedimentary rocks
Authors: Evans J. A.
Published: May 2009

Major, trace and REE geochemistry, together with Nd isotope determinations, provide new insights into the provenance of seven pebbles of igneous origin from an early Silurian facies of the Caban Conglomerate Formation from central Wales. The geochemical composition of the pebbles supports formation in a subduction related environment on an active continental margin. Biotite whole-rock Rb-Sr systematics constrain the age of a granite pebble to 650±38 Ma. The pebbles provide discrete examples of Avalonian basement which contributed to the isotope composition of sedimentary rocks in the Welsh Basin and one granite pebble provides a rare example from the Welsh Basin of an igneous rock with a Palaeoproterozoic depleted mantle model age.
Melt-enhanced deformation during emplacement of gabbro and granodiorite in the Sunnhordland Batholith, west Norway
Authors: Andersen Torgeir B. , Nielsen Peter , Rykkelid Erling , Sølna Hanne
Published: May 2009

The Caledonian Sunnhordland Batholith comprises calc-alkaline plutons that have been assigned to three units according to their relative age and composition: a gabbro-diorite unit, a granodiorite unit and a later granodiorite-granite unit. The batholith was emplaced into an envelope including ophiolite and island-arc complexes, sediments and volcanites of early Ordovician age that were developed in a zone of plate convergence. Continued convergence resulted in the formation of a mature magmatic arc and a thickened crust; the late granitoids (unit 3), which commenced their crystallization at pressures around 6 to 7 kb, rose as permitted diapiric intrusions. The ingress and ascent of the magmas in this setting is considered to have been facilitated by the presence of major shear zones developed in relation to plate convergence. In this model, plastic instabilities were formed in an otherwise elastic middle and upper crust. Non-coaxial deformation was accelerated by the emplacement of magmas and the formation of abundant partial melts in water-rich sediments of the envelope. The deformation, which was accelerated by magma and melt lubrication in aureoles, controlled both the shape and internal structure in the gabbro and granodiorite plutons.
Palynology of the Stonehaven Group, Scotland: evidence for a Mid Silurian age and its geological implications
Authors: Marshall J. E. A.
Published: May 2009

Palynomorphs from the Stonehaven Group indicate a late Wenlock to early Ludlow age. This is older than the currently accepted Pridoli age based on fish and arthropods. Reasons for this discrepancy are discussed. A previous correlative of the Stonehaven Group has been the Old Red Sandstone of Kerrera, Argyll. However, palynological assemblages from both Kerrera and the adjacent succession at Oban are in fact younger than that from Stonehaven in being of latest Silurian to earliest Devonian age. The palynomorphs from Kerra and Oban lie beneath the important geochronological tie-point of the Lorne Lavas and suggest that the Silurian-Devonian boundary is older than currently accepted.
B1 subdivisions in thin komatiites at Kambalda, Western Australia
Authors: Thomson B.
Published: May 2009

B1 subdivisions are narrow foliated zones of stubby, skeletal olivine blades, situated at the top of the granular olivine cumulates (B2) in ponded komatiite lavas. They developed at a late stage in pond crystallization as a result of compaction-related circulation of intercumulus liquids through and along the top of the cumulates. The total thickness of a B1 and its degree of blade parallelism are related to lateral position within ponded lavas. The deeper, hotter and longer-lived core regions generated a thick B1 with a high degree of blade parallelism (ordered B1), whereas the shallower, peripheral regions produced a narrow B1 with a poor degree of blade parallelism (disordered B1), or failed to develop one at all.
The origin of the Neihart Quartzite, a basal deposit of the Mid-Proterozoic Belt Supergroup, Montana, U.S.A.
Authors: Schieber J.
Published: May 2009

The Neihart Quartzite is the basal quartz arenite unit (≍270m thick) of the Mid-Proterozoic Belt Supergroup of western North America. Petrographic studies indicate a source area with plutonic granitic, metamorphic and felsic volcanic rocks. Extreme textural maturity and bimodality indicate an episode of aeolian transport for the detrital quartz grains. The lower 80% of the Neihart Quartzite were probably deposited by braided streams, whereas the upper 20% were deposited in shoreline environments. Residual material that was ‘stored up’ on the pre-Beltian cratonic surface and underwent aeolian reworking was the likely source material for most of the Neihart Quartzite. Less mature sediments in the top portion of the Neihart Quartzite indicate uplift and erosion of new source material during Neihart deposition. Other known cratonic quartz arenites, such as the St. Peter Sandstone (Ordovician), Lamotte Sandstone (Cambrian) and Flathead Quartzite (Cambrian), are thin (tens of metres thickness) and exhibit sheet-like geometry. In contrast, the Neihart Quartzite and its probable lateral equivalents are considerably thicker and increase in thickness towards the central portions of the basin. It thus appears that Belt sedimentation began with accumulation of a basal quartz arenite unit, and that sand for that unit was transported by braided streams from the surrounding craton to a gradually subsiding Belt basin.
The sedimentary expression of regional tectonic events during the Miocene-Pliocene transition in the southern Cyprus basins
Authors: Orszag-Sperber F. , Rouchy J. M. , Elion P.
Published: May 2009

A well-known tectonic event affecting the East Mediterranean region, generally referred to as ‘the’ Miocene–Pliocene phase, occurs at, or near the Miocene–Pliocene boundary. Recent sedimentological studies in Cyprus indicate that this ‘event’, in fact, is complex. The Tortonian–Lower Pliocene period is marked by a stress involving an N20 extension in the Polemi and Pissouri basins and by an N100 extension in the Psematismenos basin. Sedimentological studies have demonstrated three tectonic pulsations during Messinian time, prior to the Pliocene transgression. These are expressed by two episodes of seismic brecciation, and a palaeo-emersion is indicated by palaeosols and detrital discharges. These phenomena suggest brief tectonic instability during Messinian time. Microtectonic studies in the South Troodos basins of Cyprus reveal that the main change in tectonic stress does not coincide with the Miocene–Pliocene contact but occurs at the end of Lower Pliocene time. The authors conclude that the so-called Miocene–Pliocene ‘event’, in reality, is a series of subtle tectonic pulsations recorded clearly by sedimentary parameters.
Hylaeosaurus, Polacanthus, and the systematics and stratigraphy of Wealden armoured dinosaurs
Authors: Pereda-Suberbiola Javier
Published: May 2009

Two genera of armoured dinosaurs (Ankylosauria) are present in the Lower Cretaceous Wealden Beds of England.PolacanthusOwencan be distinguished fromHylaeosaurusMantell on the basis of significant differences in the pectoral girdle, hindlimb and dermal armour. A comprehensive review of the dinosaurs from the Wealden Series of England and contemporary basins of western Europe adds further evidence of a biologicalseparation between Lower Wealden (Hastings Beds, containingHylaeosaurusarmatus)and Upper Wealden faunas (Wealden Group of the Isle of Wight-containingPolacanthus foxii-and nearly equivalent units in Belgium, France, Germany and Spain).
Steep-sided carbonate mud mounds in the Middle Devonian of the eastern Anti-Atlas, Morocco
Authors: Wendt J.
Published: May 2009

During the Eifelian and early Givetian, isolated mud mounds were established in a shallow basin, predominantly characterized by calcareous mudstone deposition, in the eastern Anti-Atlas of Morocco. The shapes, lithologies and faunas of these mounds stand in marked contrast with those of nearby contemporaneous, more widespread stromatoporoid/coral biostromes and small carbonate platforms adjacent to shallow shelves. With one exception, the mounds are totally exhumed, perfectly exposing their original morphologies. The smaller mounds are asymmetrical, with steeper northeastern and eastern (35–75°) than southwestern and western flanks (30–50°). The largest mound is almost circular and symmetrical, with scattered stromatoporoids, tabulate and rugose corals that do not form a rigid framework. Frame-builders are much rarer or absent in the smaller mounds. The nature and geographical distribution of the mounds reflects a bathymetric gradient, indicating that they formed on low-angle ramps which sloped gently into a shallow basin. A large reef mound was constructed at moderate depth, while small mud mounds accumulated in deeper water. Decrease of frame-builders and increase in pelagic organisms in the latter document the transition to a pelagic platform with reduced sedimentation at a short distance from the deepest mound.
Structure of veins in a gold–pyrite deposit in banded iron formation, Amalia greenstone belt, South Africa
Authors: Vearncombe J. R.
Published: May 2009

Fibrous quartz veins in deformed banded iron formation of the Amalia greenstone belt, southwestern Transvaal, are spatially related to gold–pyrite mineralization in both wallrock and vein inclusions. Poles to quartz vein orientations show a general parallelism with mineral elongation and fold plunges of the principal deformation in the wallrock. Quartz vein fibres show a consistent anticlockwise rotation, late components being subparallel to the elongation lineation, suggesting veining was probably synchronous with the principal deformation. Antitaxial fibrous veins, which dominate the mineralized banded iron formation, formed by the process of crack–seal which channelled mineralizing fluids along the vein walls, increasing the potential for fluid–wallrock interaction. Gold mineralization in quartz veins occurs in wall-parallel slivers of banded iron formation which have been plucked off the vein wall during antitaxial fibre growth. Mineralization can be explained by a process of fluid–wallrock interaction with sulphidation and gold precipitation.
Metamorphic fluids and transtension in the Cantabrian Mountains of northern Spain: an application of the conodont colour alteration index
Authors: Raven J. G. M. , Van Der Pluijm Ben A.
Published: May 2009

Conodont colour alteration index (CAI) values from Upper Paleozoic rocks in the Cantabrian zone of northern Spain show that temperatures during Hercynian metamorphism locally exceeded 300 °C. Various temperature domains have been defined, which are generally separated by fundamental structures. These domains do not correspond with the tripartite subdivision based on stratigraphic analysis.

The observed CAI values of conodonts are in general agreement with the mineral paragenesis. Areas with high CAI values display extensive alteration and mineralization, and where CAI values exceed 4–4.5 (>200 °C) slaty cleavage has developed.

The Cantabrian zone is an area of very low grade metamorphism, where peak conditions were reached in Upper Carboniferous to Lower Permian times. The characteristics of the metamorphism and its spatial relationship with major faults suggest that fluids were the main source for regional heating and that fluid transport was focussed along crustal-scale structural features.

The overall deformation regime in this part of the Variscan orogen of western Europe is interpreted to be large-scale transtension. This is in agreement with earlier proposed models for the formation of Upper Palaeozoic basins in this area.
The ultrabasic lava flows of Mashhad, North East Iran
Authors: Majidi B.
Published: May 2009

Ultrabasic and basic lavas are interbedded with metamorphosed Lower-Carboniferous sediments in the northern slope of the Alborz mountains, NE Iran. In the outcrop area at least 15 individual units of ultrabasic lava have been observed. Flow units range in thickness from a few metres up to about 70 m. The inner parts of the flow units are holo-crystalline, showing a poikilitic texture with rounded small crystals of serpentinized olivine surrounded by large crystals of clinopyroxene (‘wehrlitic facies’). The upper portions of the thicker units are olivine-free, and pyroxene, sometimes accompanied by brown hornblende, is set in a groundmass of fine-grained epidotized plagioclase (‘doleritic facies’). In the upper and lower margins of flows the groundmass is devitrified to chlorite and tremolite. Small-scale differentiation and igneous lamination is observable in transition zones between the wehrlitic and doleritic ‘facies’. The upper doleritic facies and other individual basic units have a tholeitic chemistry. In contrast, the chemical composition of wehrlitic rocks (which predominate amongst the exposed rocks in the area) is comparable with Archaean ultrabasic lava flows in Canada and southern Africa.
Overbank deposits of the Narrator Brook, Dartmoor, England
Authors: Gomez B. , Sims P. C.
Published: May 2009

Overbank deposits of the Narrator Brook, exposed by the excavation of a drainage ditch, are described. The deposits, which consist of coarse (sand and gravel), fine (silt and clay) and peat units, were laid down in a floodbasin environment. The coarse units are interpreted as crevasse-splay deposits, rather than being classified as floodbasin sediments along with the fine units. Three stages of development in the evolution of the floodbasin are identified. The first stage is represented by the development of peat at a time when the area was not subjected to flooding, the second by deposition of the fine and coarse sediment units and the third by an upper peat horizon. No precise date for the formation of the deposits is at present available, but it is thought that they may be the result of man's activity in the catchment.
Implications for the age of South African Devonian rocks in which Tropidoleptus (Brachiopoda) has been found
Authors: Boucot A. J. , Brunton C. H. C. , Theron J. N.
Published: May 2009

The Devonian brachiopod Tropidoleptus is recognized for the first time in South Africa. It is present in the lower part of the Witteberg Group at four widely separated localities. Data regarding the stratigraphical range of the genus elsewhere, combined with information on recently described fossil plants and vertebrates from underlying strata of the upper Bokkeveld Group, suggest that a Frasnian or even Givetian age is reasonable for the lower part of the Witteberg Group. The recognition of Tropidoleptus in a shallow water, near-shore, molluscan association, at the top of the South African marine Devonian sequence, is similar to its occurrence in Bolivia, and suggests a common Malvinokaffric Realm history of shallowing, prior to later Devonian or early Carboniferous non-marine sedimentation. It is noteworthy that Tropidoleptus is now known to occur in ecologically suitable environments around the Atlantic, but is absent from these same environments in Asia and Australia. Tropidoleptus is an excellent example of dispersal in geological time — first appearing in northern Europe and Nova Scotia, then elsewhere in eastern North America and North Africa, followed by South America and South Africa, while continuing in North America.
Geochemistry and petrogenesis of a nepheline syenite-carbonatite complex from the Sudan
Authors: Harris N. B. W. , Mohammed A. E. R. O. , Shaddad M. Z.
Published: May 2009

Jabal Dumbeir is a nepheline syenite-carbonatite complex of Cambrian age (550 ± 87 Ma). The earliest igneous event of the complex was the intrusion of a phlogopite-sodalite nepheline syenite (ditroite) which was derived from the partial melting of the upper mantle. K, CO2 and F-rich volatiles metasomatise both the ditroite and the gneissic country rock which results in an orthoclase-rich undersaturated syenite (orthoclasite). Carbonatitic breccias and sovite dykes were subsequently emplaced carrying high levels of F, REE, Y and Th with extremely high LREE/HREE ratios (CeN/YbN = 64 ± 8). Such carbonatiticmagmas may be derived by partial melting of an LREE-enriched upper mantle. Hydrothermal emplacement of fluorite-quartz veins represent the final phase of igneous activity and these carry high levels of REE, Y, Th and U. Their emplacement was strongly controlled by a system of NNE strike-slip faults which have been reactivated in recent times.
The Late Precambrian succession in north-west Oscar II Land, Spitsbergen
Authors: Waddams P.
Published: May 2009

This paper describes the late Precambrian rocks in north-west Oscar II Land, western Spitsbergen, with particular emphasis on an upper (Haaken Formation) and lower (Trondheimfjella Formation) diamictite sequence. It is argued that both diamictites are glacigenic, formed by ice-rafting over distal turbidite basins, and correspond to the two Varangian tillite horizons of northern Norway and elsewhere. This leads to a radical reinterpretation of the age of the Oscar II Land succession, much of which now appears to be Vendian. With the exception of the Trondheimfjella Formation, which records an early phase of deepening of the depositional basin, the lower half of the succession (St Jonsfjorden Group) comprises mainly shallow water shelf sediments. The upper half of the succession (Comfortlessbreen Group) was deposited within a basinward prograding turbidite fan system, with the Haaken Formation representing the distal component of the complex. A return to a mixed clastic-carbonate shelf environment is recorded by the overlying Palaeozoic rocks.
A cored Jurassic sequence from north Lincolnshire, England: stratigraphy, facies analysis and regional context
Authors: Bradshaw M. J. , Penney S. R.
Published: May 2009

A virtually complete Jurassic sequence recently drilled in north Lincolnshire is considered in a regional context. Liassic thicknesses and facies are largely unexceptional. The Frodingham and Pecten Ironstones are relatively thin and sandy, but the Marlstone Rock Bed is thicker and more ferruginous than elsewhere in the region. The Inferior Oolite is exceptionally thick and exhibits strong deltaic influence; equivalents of the Gristhorpe Member and Scarborough Formation of Yorkshire may be present. The Great Oolite was deposited in coastal-lacustrine-deltaic environments, more proximal than to the south or east. Thin Kellaways Clay separates the argillaceous Cornbrash from the Kellaways Sand. The organic-rich Lower Oxford Clay is thin owing to a basal non-sequence whilst the Upper Oxford Clay is condensed and less organic than in the East Midlands. The regressive West Walton Beds are followed by very thick Ampthill and Kimmeridge Clay sections beneath the Spilsby Sandstone. Regional thickness and facies analysis records the behaviour of the Market Weighton Block and reveals the influence of the Pennine High as both a positive tectonic feature and an occasionally active sediment source.
Morphology and surface sedimentary features of point bars in Welsh gravel-bed rivers
Authors: Blacknell C.
Published: May 2009

Two examples of point bars in single-channel gravel-bed rivers in Wales illustrate some of the morphological and surface sedimentary features observed during a wider examination of 40 sites of recent (less than 100 years) channel sedimentation. The point bars consist of predominantly sandy gravel bar platforms overlain by discontinuous sand bodies. Cut bank exposures show generally massive sandy gravels abruptly underlying a silt/sand unit. Morphologically the bars are platformlike, with primary inner-attached, or secondary medial, chutes. This relief, together with the effects of seasonal vegetation, determines the locations of finer-grained (non-gravel) material. The frequency with which deposits produced by this type of channel sedimentation may be encountered in Quaternary and pre-Quaternary successions is briefly discussed.
Characteristics and significance of some humate-cemented sands (humicretes) at Cape Flattery, Queensland, Australia
Authors: Pye K.
Published: May 2009

Humate-cemented sands (humicretes) are exposed at several locations along the foreshore and in gullies near Cape Flattery, North Queensland, Australia. Three broad types of humate accumulation are recognized: (a) pedogenetic; (b) groundwater; and (c) aquatic. Pedogenetic and groundwater humicretes usually have a grain-supported fabric in which quartz represents > 99% of the framework grains. Hand specimens of humicrete are brittle but disintegrate rapidly in 0.1 N-NaOH. Concentration of humate is considered to have occurred by vertically and laterally migrating groundwater, while induration has probably been caused by irreversible drying of the humic substances during periods of seasonal water-table lowering. Radiocarbon dating of an in situ root embedded in indurated humate near Cape Flattery has indicated a ‘background’ age of > 48000 C–14 years.
Morphology and dimensions of the young comendite lavas of La Primavera volcano, Mexico
Authors: Clough B. J. , Wright J. V. , Walker G. P. L.
Published: May 2009

Quantitative data on the rhyolitic lavas of the Quaternary La Primavera volcano, Mexico, are presented. Lavas vary in form from domes and mesa lavas to short coulées. Average thickness is 100 m, average surface area is 2.7 km2 and aspect ratios vary from 1:7 to 1:25. Two petrological lava types are distinguished – porphyritic and aphyric. Porphyritic lavas occur on or within an inner ring fracture and are associated with an area of caldera lake deposits. Many features suggest that these porphyritic lavas were emplaced into the wet sediments or water of the caldera lake. Aphyric lavas are largely found to the south of this region and form large polygenetic structures extruded on dry land. The porphyritic lavas generally are smaller and have higher aspect ratios than the aphyric, which are attributed to their special environment of emplacement. Some porphyritic lavas extruded on dry land, outside the region occupied by the caldera lake, are, however, the thinnest on the volcano.
Ultramafic volcaniclastics of the Precambrian Dalma Volcanic Belt, Singhbhum, Eastern India
Authors: Gupta A. , Basu A. , Ghosh P. K.
Published: May 2009

The Dalma volcanic belt in the Precambrian Eastern Indian shield is composed of a thick sequence of volcani-sedimentary assemblage with a group of predominantly ultramafic volcaniclastics having komatiitic chemistry. A volcanic origin is suggested by textural relationships and mineralogical composition, together with the presence of devitrified glass shards; these rocks are now mostly chlorite-tremolite schist.
Late Precambrian diamictites of northeastern Svalbard
Authors: Hambrey M. J.
Published: May 2009

In northeastern Spitsbergen and western Nordaustlandet well preserved Late Precambrian diamictites have variously been interpreted as tillites or the product of tectonic activity. By focusing on the sedimentology of the diamictites in two key areas, this paper presents unequivocal evidence that the diamictites are indeed glacigenic, confirming the conclusions of previous field investigations. In particular dropstones in large numbers and striated stones are diagnostic of glacial transport, while other characteristics are strongly suggestive of glacial conditions.

Stratigraphic studies indicate two discrete glacial episodes, both belonging to the Varangian epoch. The earlier resulted in a thin tillite sequence deposited in a shallow shelf-tidal-lacustrine environment. It is closely associated with stromatolitic dolostones. The later episode resulted in a tillite sequence a few hundred metres thick with two units in northeastern Spitsbergen separated and bounded by dolostone units. Deposition occurred in a shallow marine environment but occasional uplift led to terrestrial conditions and the deposition of fluvioglacial sediments and the development of periglacial phenomena.
Abundance and distribution of uranium and thorium in the northern units of the Leinster granite, Ireland
Authors: O'Connor P. J. , Hennessy J. , Bruck P. M. , Williams C. T.
Published: May 2009

Abundance data, determined by epithermal neutron activation analysis, are reported for radioelements in the northern units of the Leinster granite. Compared to similar data for silicic igneous rocks and British Caledonian granites, the Leinster granite shows normal U and K contents but is low in Th. Inter-element correlations and fission-track results suggest that most Th and up to 40% of the U is bound in resistate accessory phases (zircon, sphene, apatite), but that the bulk of U is associated with late-stage alteration products and is located at interstitial labile sites within the host-rock matrix. Mobilization of U located at such sites in the Leinster granite by hydrothermal leaching could lead to redeposition and enrichment in marginal sediments of Old Red Sandstone or younger age.
Lower Cambrian echinoderm plates from Cowley, Shropshire, England
Authors: Donovan S. K. , Paul C. R. C.
Published: May 2009

Echinoderm plates from the Protolenus Limestone are recognised as belonging to three groups; plates with folded surfaces, plates with bevelled edges and a third group. They are not comparable with other Lower Cambrian echinoderms and may be derived from a genus or genera of eocrinoid which is not known from complete specimens.
Early diagenetic bedded cherts of the Tuscan sequence (Miocene) near Città di Castello, Italy
Authors: Molenaar N. , Feyter A. J. De
Published: May 2009

Summary. A distinctive level of bedded, internally laminated, deep-sea cherts in the area west of Città di Castello, central Apennins, has been studied. These cherts form part of the Lower Miocene Monte Santa Maria Tiberina Formation, and belong to the Tuscan sequence, consisting of pelagic and turbidic sediments. The sediment is enriched in diatoms and Radiolaria. The diatoms provided silica as well as barium, now present as submicroscopical baryte concretions. Synsedimentary volcanism could have provided silica as well, through calcitization of volcanic fragments within the sediment. Since the laminations display early diagenetic microdeformations,. it can be concluded that the cherts themselves are an early diagenetic feature.
Microsolenid corals as rock-formers in the Corallian (Upper Jurassic) rocks of England
Authors: Ali O. E.
Published: May 2009

Summary.Microsolena thurmanniKoby andM. foliosaRoniewicz (Scleractinia) are important rock-formers in the Upper Oxfordian Stage of Upware and, to a lesser extent, Yorkshire.
Isomerization and aromatization of hydrocarbons in sedimentary basins formed by extension
Authors: Mackenzie A. S. , McKenzie D.
Published: May 2009

Summary. The reactions involved in oil generation are of great economic importance, but remain to be studied in detail. We have investigated the rates of three reactions which occur before and during the early stages of oil formation, and have used the predicted thermal and subsidence history of stretched basins to estimate the six reaction constants. Two of the reactions are isomerization reactions, at C-20 in a sterane and at C-22 in a hopane hydrocarbon. The third reaction converts C-ring monoaromatic to triaromatic steroid hydrocarbons. No single measure of maturity can describe the progress of these reactions. In old basins, such as the North Sea, both isomerization reactions are almost complete before appreciable aromatization has occurred, whereas in young basins, such as the Pannonian Basin in Hungary, aromatization is almost complete before appreciable isomerization of the steranes has occurred. We show that the calculated progress of these reactions agrees well with that observed in both basins if the frequency factors and activation energies are 6 x 10-3 s-1 and 91 kJ mol-1, 0.016 s-1 and 91 kJ mol-1, 1.8 x 1024 s-1 and 200 kJ mol-1 for the isomerization of steranes, of hopanes, and the aromatization of steroid hydrocarbons respectively. The rate of conversion of the R to the S form was taken to be 1.174 and 1.564 times that of the reverse reactions for sterane and hopane isomerizations respectively, and the aromatization reaction was assumed to be irreversible. All three reactions were assumed to be first order and unimolecular. The aromatization rate is consistent with laboratory observations. The rate of hopane isomerization is not, and different reaction mechanisms probably dominate at different temperatures. The same constants can be used to predict the progress of the reactions in basins which have been uplifted by inversion, such as the Lower Saxony Basin in West Germany. The geochemical observations provide estimates of the amount and time of uplift which agree with those from geological studies. Geochemical observations from the eastern part of the Paris Basin suggest that this region has also been uplifted by between 1 and 2 km.
New evidence on the age of the glacial rocks of northern Ethiopia
Authors: Saxena G. N. , Assefa G.
Published: May 2009

Summary. A fossil siphonophorid is described from the Palaeozoic rocks of the Enticho area in Tigrai, northern Ethiopia. This is the first fauna to be described from these rocks and the evidence supports an Ordovician age for the associated glacial rocks. Detailed lithostratigraphy of the area is also discussed.
Stratigraphy and palaeontology of Pleistocene cold-stage deposits at Alton Road Quarry, Farnham, Surrey, England
Authors: Bryant I. D. , Gibbard P. L. , Holyoak D. T. , Switsur V. R. , Wintle A. G.
Published: May 2009

Summary. Pleistocene deposits exposed at Alton Road Quarry, Farnham in 1980 have been sub-divided into two formal stratigraphical units of ‘member’ status. The ‘Wrecclesham Gravel’ is the lowest unit and consists primarily of fluvial sands and gravels. Silts which occurred as a channel fill within this member contained a macro- and micro-fossil flora indicative of open country conditions and included a species of moss previously unreported from the European Pleistocene. Tentative thermoluminescence dating indicates an Early Devensian age for this unit, although radiocarbon dating of the plant macrofossils yielded an age of a B.P. The overlying ‘Farnham Silty Loam’ is separated from the Wrecclesham Gravel by a discontinuous and variable thickness of matrix-supported gravels interpreted as a slope deposit. The Farnham Silty Loam appears to be, at least in part, of aeolian origin. Mineralogical investigations suggest that it is predominantly of local derivation, whilst thermoluminescence dating suggests that it is of Late Devensian age.