bluuebunny/crossref_metadata_2025 huggingface dataset:
Palaeomagnetism, magnetic fabrics and the structural style of the Hornelen Old Red Sandstone, Western Norway
Authors: TORSVIK T. H. , STURT B. A. , RAMSAY D. M. , BERING D. , FLUGE P. R.
Published: December 2007

The Old Red Sandstone of the Hornelen district, western Norway, forms part of a major fold-terrane, and the principal magnetization is associated with the Late Devonian to Early Carboniferous Svalbardian/Solundian Orogeny. The present fault margins of the Hornelen Massif, claimed by various authors to represent subordinate Devonian splay faults associated with megashearing in the North Atlantic or lateral ramps in a regional extensional tectonic setting, are shown to be post-Devonian structures, and the present outline of the Hornelen Massif is a Mesozoic (Jurassic) ‘graben’.
Overburden deformation related to the pre-piercement development of salt structures in the North Sea
Authors: JENYON M. K.
Published: December 2007

The nature of the stress regime imposed on a clastic overburden by a developing salt structure changes with time. These changes are directly related to the evolving morphology of the salt structure in a sequence of events which is now quite well understood. The stress pattern produced by initial, almost purely vertical, uplift changes rapidly into a more complex pattern as the flanks of the rising salt mass collapse progressively with flow of salt towards the crestal zone. The two main stress elements involved derive from extension within the superincumbent overburden produced by the salt uplift, and the effects of gravity that exercise an increasingly important influence as the structure develops vertically. Other factors also affecting the form taken by the overburden deformation are outlined. The discussion is illustrated with examples of migrated seismic data.
New chronology for the Early Miocene mammalian faunas of Kisingiri, Western Kenya
Authors: DRAKE R. E. , VAN COUVERING J. A. , PICKFORD M. H. , CURTIS G. H. , HARRIS J. A.
Published: December 2007

New total-fusion K-Ar ages indicate that all of the fossiliferous formations that make up the lower part of the Early Miocene Kisingiri sequence in western Kenya at Rusinga Island, Mfwangano Island, and Karungu were deposited during an interval of less than 0.5 million years at
c
. 17.8 Ma ago. This contrasts markedly with K-Ar ages previously published from these detrital-tuffaceous formations, which suggested that they were deposited over an interval of as much as 7 million years between 23 and 16 Ma, overlapping the age-ranges of all other East African Early Miocene sites including Koru, Songhor, Napak, Bukwa, Loperot, Muruarot and Buluk. In addition, the analytical problems revealed by the new Kisingiri results cast doubt on biotite ages which provide dating for the most important sites. Thus, the strong differences between the Kisingiri fauna and those of Koru, Sonhor and Napak, long held to be due to ecology because of the apparent overlap in ages, may actually be due to a difference in time. If this view of the geochronology is correct, it may now be possible to identify adaptive trends and evolutionary succession in the East African Early Miocene faunas.
The origin of late spar cements in the Lincolnshire Limestone, Jurassic of central England
Authors: EMERY D. , HUDSON J. D. , MARSHALL J. D. , DICKSON J. A. D.
Published: December 2007

The carbon and oxygen isotopic compositions of the Lincolnshire Limestone (Bajocian) of the East Midlands are shown to be determined largely by two end-member components: marine precipitates and later sparry burial cements. The origin of major quantities of such burial cement is controversial, the extreme possibilities ranging from calcite precipitation from meteoric groundwaters to precipitation from highly saline brines, with contrasting flow regimes.

This study demonstrates how formation-wide sampling and mapping of stable isotopic compositions of burial cements from the Lincolnshire Limestone, combined with a detailed knowledge of its burial history and associated thermal evolution, can be employed to distinguish the influence of different water types. Two 'Provinces' are differentiated with respect to the stable isotopic compositions of the latest, volumetrically most significant, ferroan burial cements.

(1) A 'Southern Province' associated with thinning of the Limestone, shallower depths of maximum burial (approx. 300 m) and light δ
18
O and δ
I3
C cement compositions;

(2) A 'Central Province' associated with deeper burial (approx. 550 m) but less
18
O- and
13
C-depleted cement compositions.

The relative isotopic depletion of the Southern Province ferroan burial cements is considered to be a function of their precipitation from meteoric waters, with a depleted
I8
O signature relative to seawater, at temperatures of approximately 24 °C.
13
C depletion is tentatively ascribed to the persistence of
13
C depleted soil-gas CO
2
in the precipitating waters.

In the Central Province, basinal waters of both meteoric and marine derivation are considered to have precipitated the late spar, with associated up-dip fluid movement at temperatures between 29 and 39 °C.
13
C depletion is believed to be controlled by the input of CO
2
derived from thermal oxidation of organic matter.
A K-feldspar breccia from the Mo–Cu stock work deposit in the Galway Granite, west of Ireland
Authors: DERHAM J. M. , FEELY M.
Published: December 2007

A K-feldspar breccia, spatially associated with the Mo-Cu mineralization of a stockwork in the Late Caledonian Galway Granite at Mace Head, is described for the first time. Detailed mapping reveals a network of breccia pods and veins over an area of approximately 6000 m
2
. The breccia is clast-supported and is composed of sub-angular fragments of perthitic K-feldspar megacrysts (<10 cm), granite and microgranodiorite clasts (<25 m) set in a matrix of quartz (<lcm), biotite (<5 cm) and apatite (<3 mm). Field and textural studies indicated that the feldspar megacrysts and granite clasts were brecciated and silicified as they were carried (to the present structural level) by hydrous K- and SiO
2
-rich fluids. The residue of these fluids crystallized to form the breccia matrix. The formation of the breccia predates the mineralized quartz veins of the Mo-Cu stockwork. It is concluded that the breccia formation is genetically related to ore-forming processes in the Galway Granite.
The Padstow Confrontation, north Cornwall: a reappraisal
Authors: SELWOOD E. B. , THOMAS J. M.
Published: December 2007

The Gravel Caverns section, New Polzeath, north Cornwall, shows clear evidence of multiphase deformation. Tight F1 folds with axial planar S1 slaty cleavage are reported for the first time. These are deformed by north-verging F2 folds with a south-dipping spaced cleavage. The fold and fabric relationships are inconsistent with the widely accepted model of structural confrontation previously described for the region. This model is reassessed.
Biostratigraphical correlation and the stages of the Llandovery
Authors: TEMPLE J. T.
Published: December 2007

The problems of defining biozones are discussed, and the definitions of

Holland
et al.
1978

are considered unsatisfactory. An ideal methodology of biostratigraphical correlation is outlined and is contrasted with existing practice as exemplified by recent decisions of the Subcommission on Silurian Stratigraphy relating to stages of the Llandovery series. The numbers of species in the different Llandovery graptolite biozones and the proportions of zonally diagnostic species at the inter-biozone boundaries are tabulated. The Llandovery area is considered unsuitable for the establishment of stages, and the stratotypes for the Aeronian and Telychian are considered unsatisfactorily defined in relation to graptolite zonation.
Strike-slip faulting along the Church Stretton Lineament, Old Radnor Inlier, Wales
Authors: WOODCOCK N. H.
Published: December 2007

The Old Radnor Inlier comprises Precambrian sediments unconformably overlain by Wenlock age limestones and shales. Its structure is dominated by steep strike-slip faults. Major NE-SW faults probably bound the inlier and are linked by more northerly faults to form a strike-slip duplex. Strike-slip faults within the inlier match a Riedel shear system, with observed dextral offsets on a NW striking set and implied sinistral offsets on the major inlier-parallel faults. Subordinate dip-slip faults are anomalously oriented, but may be Riedel shears reactivated during progressive sinistral transtension across the inlier.

Pre-Wenlock deformation is recorded by the tilting of the Precambrian sediments and by some faults that do not cut the unconformity. On regional grounds, this deformation might be Ashgill (late Ordovician) or late Precambrian-early Cambrian in age. The strike-slip component now predominating was imposed in post-Wenlock time, probably during the regional sinistral transpression of the Acadian (Late Caledonian) event in Early Devonian time. Later Variscan and Mesozoic components cannot be ruled out.
Emplacement of sills into wet sediments at Grunehogna, western Dronning Maud Land, Antarctica
Authors: KRYNAUW J. R. , HUNTER D. R. , WILSON A. H.
Published: December 2007

The mid-Proterozoic Ritscherflya Supergroup, Antarctica, is intruded by numerous mafic to intermediate sills and small layered bodies. Contact relations are well exposed where the Grunehogna and Kullen sills intruded argillaceous and arenaceous sedimentary rocks of the Schumacherfjellet and Hogfonna Formations of the Ahlmannryggen Group. A 3 m thick peripheral zone above the upper contact of the Grunehogna sill consists of reconstituted sedimentary rocks which have been fluidized and recrystallized due to the intrusion. Local melting and crystallization of the sediments, under hydrous conditions and pressures below 312 bars, have produced zones of granite and granophyre, which grade into arenites where primary sedimentary structures are preserved. The sedimentary rocks have been deformed into large disharmonic folds where the sill transgresses the Schumacherfjellet Formation. The contact relations suggest that emplacement of the mafic sills and sheets at Grunehogna occurred when the sediments were still water-saturated and only partially lithified.
The detection and illustration of regular sedimentary cycles using Walsh power spectra and filtering, with examples from the Lias of Switzerland
Authors: WEEDON GRAHAM P.
Published: December 2007

Power-spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter (or time series). Digitization of measured stratigraphic sections is a convenient method for generating long time series, during the examination of pelagic sequences for cyclicity related to orbital variations or Milankovitch cycles. The application of Walsh power-spectral analysis to stratigraphic sections is outlined and band-pass filtering using the Walsh transform introduced. It is shown that variations in sedimentation rate, hiatuses, bioturbation and variations in compaction have the effect of damping or destroying spectral peaks. The wavelength ratios of spectral peaks are often used, during studies of Milankovitch cycles, to decide which orbital cycles are involved. However, in some circumstances hiatuses are able to alter wavelength ratios.

Averaged Walsh power spectra were generated for three Liassic limestone/shale sequences from Breggia Gorge, Switzerland. The 21 000 year (21 ka) precession cycle was detected in all three cases, the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one. Filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles. The packets reflect the 100 ka modulation of the 21 ka precession cycle. Local disruption of the packaging can be used to locate hiatuses in pelagic strata.
Biota and palaeoatmospheres
Authors: CHALONER W. G. , COCKS L. R. M.
Published: December 2007

A meeting on Biota and palaeoatrnospheres was held at the Geological Society’s apartmenfs at Burlington House on
19
December
1987.
It was a joint Ordinary Meeting with the Linnean Society and the Palaeontological Association.

This symposium formed part of the celebrations of the Linnean Societ of London, and was held on the eve of its bicentenary year of 1988. The Linnean Society had elected to hold a series of joint meetings with other Societies with allied or overlapping interests, and the Geological Society was an obvious choice. The two societies have been linked physically, by occupying adjoining premises in Burlington House, but more importantly by shared Fellowship, from the earliest days of their co-existence in the present rooms. The principal common ground of the two Societies lies largely in palaeontology and so it was appropriate that plans for a joint meeting should also have involved the Palaeontological Association, which in turn shares membership with both the Geological Society and the Linnean Society. It was, in this way, that the three bodies came to convene a symposium which was to reflect some aspect of their common interests. The organizers decided to try to avoid any of the aspects of conventional palaeontology, but rather sought out a topic which would bring together biologists and geologists on less well-worn ground.

The theme of the interaction of the atmosphere and biota through time was chosen as one which fulfilled this aim, but one which was also topical. The recently initiated International Geosphere–Biosphere Programme has
Short Paper: Palaeocurrent evidence of a northern structural high to the Welsh Basin during the Late Llandovery
Authors: McCANN T. , PICKERING K. T.
Published: December 2007

Palaeocurrents from the northernmost Aberystwyth Grits Formation are consistently from the north, which is at variance with the generally accepted southerly source area for the rest of the formation. The anomalous directions appear to indicate a structural high and possible sediment source to the north.
Reflection seismic evidence for a Moho offset beneath the Walls Boundary strike-slip fault
Authors: McGEARY SUSAN
Published: December 2007

BIRPS has acquired two deep seismic reflection profiles across the Walls Boundary Fault, a major late Caledonian strike-slip fault that is probably the northern continuation of the Great Glen Fault of Scotland. Where crossed by the SHET deep seismic survey north of the Shetlands, the Walls Boundary Fault appears to be a narrow vertical structure which penetrates the entire crustal thickness and juxtaposes crusts of different thicknesses. The seismic data show a Moho offset in travel-time of 1.0–1.5 seconds and two high-amplitude diffractions originating at Moho travel-times. These diffractions are, as yet, unique among seismic data across strike-slip faults and can be used to argue that the Moho is offset in depth by 2–3 km over a lateral distance of less than 6 km. Seismic modelling is used to constrain this interpretation. The preservation of this Moho topography suggests that the structure and rheology of the lower crust of the Shetland Platform was not significantly modified during post-Devonian extension of the North Sea and Atlantic margin.
Metamorphic studies: research in progress
Authors: DROOP G. T. R.
Published: December 2007

A Metamorphic Studies Group meeting on ‘Metamorphic Studies: Research in Progress’ and the seventh Annual General Meeting of the Group were held on 9 March 1988. It was well attended, and 15 papers were presented on a range of metamorphic topics, including an invited contribution from J. W. Valley (University of Wisconsin, USA).Four poster contributions were also presented. The meeting was organized by G. T. R. Droop.

The morning session concentrated on techniques and low-grade regional metamorphic topics. The first talk was given by
G. E. Lloyd
who, in a joint presentation with
B. W. D. Yardley,
promoted the application of cathodoluminescence microscopy to the study of metamorphic rocks. The technique is particularly suited to carbonate minerals, and its usefulness was demonstrated with reference to marble samples from Connemara in which subtle zoning and replacement textures, invisible by conventional light microscopy, could be observed. The authors stressed the paucity of information on the applicability of the technique to metamorphic silicates and urged petrologists to try it their own samples.

In the first of two papers on very low-grade metamorphism,
D. Robinson
(jointly with
R. E. Bevins)
presented a new model in which sub-greenschist metamorphism develops in extensional settings. Building published thermal models of extensional sedimentary basins, the authors argued that this type of metamorphism should be characterized by pre-tectonic peak assemblages of high T/P facies and ‘anticlockwise’ P–T paths. Quoted examples of low–grade terranes which may have formed in this way included the Welsh Basin and some
Short Paper: Movement on proposed terrane boundaries in northern Britain: constraints from Ordovician–Devonian igneous rocks
Authors: THIRLWALL M. F.
Published: December 2007

Regional chemical and isotopic differences seen in Ordovician–Devonian igneous rocks of northern Britain are thought to be due to subduction-related and collision magmatism tapping a variety of mantle and crustal sources. Matching of spatial chemical variation across major fault zones restricts post-magmatic transcurrent movement north of the Southern Upland Fault (SUF) to a few tens of kilometres on each fault. A unique mantle isotopic signature present in the same area may restrict post-1.5 Ga movement to less than a few hundred kilometres. No such restrictions exist on displacement across the SUF, to the south of which all magmas show a Pb isotopic component derived from southern sources.
Short Paper: The age and origin of boulders in the Highland Border Complex: constraints on terrane movements
Authors: DEMPSTER T. J. , BLUCK B. J.
Published: December 2007

Mid-Proterozoic Rb-Sr muscovite ages on metasedimentary boulders within the Highland Border Complex, together with Archean
T
DM
ages on the same clasts, provide constraints on terrane movements in the Scottish Caledonides. An origin for these clasts from cratonic North America is ruled out. Combined radiometric age, T
DM
, and fauna1 province studies on basement materials provide a potentially productive method of determining the provenance of terranes.
Geochemistry of volcanic rocks from the Naga Hills Ophiolites, northeast India and their inferred tectonic setting
Authors: SENGUPTA S. , ACHARYYA S. K. , VAN DEN HUL H. J. , CHATTOPADHYAY B.
Published: December 2007

Highly disrupted and deformed slices of ophiolitic rocks occurring along a linear belt in Nagaland and Manipur states, NE India, are known as the Naga Hills Ophiolites (NHO). The principal rock types include dunite, harzburgite, lherzolite, wehrlite, pyroxenite and mafic volcanics.

The volcanic rocks of NHO have been classified into low-Ti and high-Ti groups with 2 wt.% TiO
2
as the boundary, which is corroborated by the differences in their immobile trace element and Rare Earth element characteristics. The two groups are probably not cogenetic; their chemical differences reflect variable source composition. Within group variation of incompatible elements such as La/Ta in the high-Ti group may be related to varying degrees of partial melting.

The Ti/V ratios and REE distribution pattern of low-Ti group show overlapping Mid-Ocean Ridge Basalt and island arc-like characteristics, and possibly suggest back-arc basin setting. The high-Ti group, on the other hand, has similarities with within-plate basalts erupted at off-axis sea-mounts and ocean islands. The sea-mounts and ocean islands brought to the subduction zone acted as barriers. Within the imbricate fault slices are components from the oceanic crust which were accreted to the continental margin and which represent clipped off portions from these barriers.
Alluvial fans and their tectonic controls
Authors: NORTH C. P. , TODD S. P. , TURNER J. P.
Published: December 2007

The study of alluvial fan sequences, the most proximal components of the alluvial spectrum, can be one of the most profitable avenues of research in basin analysis because fans are particularly sensitive to external influences and have a relatively high preservation potential. Tectonism has long been invoked to explain many variations in fan sediments, and increasingly the presence and nature of fan sequences in the rock record is being used to denote proximity to active faults and to document movement on these faults.

There are, however, many difficulties involved with the interpretation of alluvial fan sequences, not the least of which is deciding whether the sediments are truly components of an alluvial fan or the products of a different depositional system such as an alluvial braidplain. Many of the problems arise from a lack of knowledge about the relative roles in fan construction of allocyclic processes such as climatic change and tectonic activity, and of autocyclic processes such as channel avulsion and fanhead entrenchment.

Whilst researching alluvial fan sediments in a variety of tectonic settings and ages, it has become increasingly clear to the authors that there are many inadequacies in our understanding of alluvial fans, and hence weaknesses in the conclusions drawn from these sediments. This prompted the one-day meeting organized to promote discussion of the problems of distinguishing tectonic from other influences on the evolution of modern and ancient fans. 110 industrial and academic geologists gathered at the University of Bristol on 17th October 1987 to hear 16
Short Paper: Palynomorphs from deformed low-grade metamorphic rocks: an SEM-based technique
Authors: DEAN ANDREW
Published: December 2007

Scanning electron microscope (SEM) techniques show that the low-grade metamorphic rocks of Southwest England can yield abundant palynomorphs. The technique is outlined and the character of the material illustrated by new assemblages including
Emphanisporites, Dibolisporites
and
Leiotriletes
from the Lower Devonian Meadfoot Group, south Devon.

Progress in the resolution of many problems in the Variscides has been inhibited by lack of site-specific biostratigraphic control. Conventional biostratigraphic techniques have largely failed, particularly for clastic Upper Palaeozoic sequences at low metamorphic grades. However, the application of routine SEM methods has shown that many such rocks may yield palynomorphs. The technique has been applied with considerable success to material from Devonian clastic sequences in Southwest England in a joint programme of research between the University of Exeter and the British Geological Survey, associated with the Cornwall and South Devon Project.

From more than 100 samples routinely collected during the BGS mapping of poorly dated sequences in south Devon (Fig. 1) almost all have yielded some information and many contain well preserved palynomorphs. A local SEM-based biostratigraphy is being formulated for these previously intractable successions. This paper outlines the technique and demonstrates the character of the palynomorph assemblages recovered from a sequence of cleaved interbedded sandstones and mudstones of the Lower Devonian Meadfoot Group, which has generally been considered to be of marine origin.

Method and material.
Field samples are prepared following routine palynological procedures (see Playford & Dring 1981) but omitting the oxidation techniques usually employed. The resultant fraction, after centrifuging, is strew
Preliminary sulphur isotope data of diagenetic and vein sulphides in the Lower Palaeozoic strata of Ireland and southern Scotland: implications for Zn + Pb + Ba mineralization
Authors: ANDERSON I. K. , ANDREW C. J. , ASHTON J. H. , BOYCE A. J. , CAULFIELD J. B. D. , FALLICK A. E. , RUSSELL M. J.
Published: December 2007

Genetic models for many Irish Lower Carboniferous Zn + Pb ore deposits invoke a dual supply of sulphide. The dominant source is from the bacteriogenic reduction of Lower Carboniferous seawater sulphate, but a significant, minor supply is derived from deep-seated sources. The
δ
34
S range of the latter component varies among the deposits: from the lightest range of —15% to 0% at Keel, to the heaviest of –4% to +14.4% in the Navan/Tatestown area. We hypothesize that such sulphur is leached mainly from diagenetic sulphide minerals in the underlying Lower Palaeozoic sediments.
6”s
of pyrite in the Silurian/Ordovician Moffat Shales (—17.1% to —0.6%), and of sphalerite and galena in Lower Palaeozoic-hosted veins at Salterstown (—8.7% to -4.5%) and Wanlockhead (—10.3% to —5.1%) are consistent with the hypothesis. Below the Navan ore deposit, Lower Palaeozoic shales containing minor diagenetic pyrite with a very wide range in
δ
34
S have been found;
δ
34
S is typically heavy (+16%) but extreme values up to +62% are encountered. The general enrichment in
δ
34
S is in accord with the noticeably heavy isotopic composition of deep-seated sulphur in the Navan orebody and its Tatestown satellite. Our preliminary results therefore suggest that geographical variations in the
δ
34
S range of Lower Palaeozoic diagenetic -write_. may have contributed to the isotopic variation in the deep-seated sulphur among the Irish deposits.
Mineral Deposits Studies Group annual meeting, 1987
Authors: MANNING D. A. C.
Published: December 2007

Report of a meeting of the Mineral Deposits Studies Group held on 14—15 December 1987, at the University of Newcastle upon Tyne. The meeting included a thematic session on the use of stable isotopes in ore genetic studies.

In order to take advantage of the location, the annual meeting started with an excursion to visit sites of dolerite-associated mineralization within the North Pennine orefield, led by
B. Young
of the British Geological Survey. Thirty participants braved the seasonal weather for a most instructive day, and were joined later by a further seventy participants for the subsequent indoor activities of the conference.

Details of the thematic session on Stable Isotopes in Ore Genetic Studies have already been given as part of the thematic set of papers published elsewhere in this issue. Other contributions covered a variety of topics.
P. R. Ineson
(University of Sheffield) reminded the audience of the importance of industrial minerals in his paper on sands which stressed the construction industry's need for good quality, salt-free, sand. Returning to base metals,
D. A. C. Manning & E. 1. C. Rae
(University of Newcastle upon Tyne) reported the results of experiments to determine the behaviour of Pb-rich feldspars during dissolution, which demonstrate that clastic feldspars within sediments are a significant potential source for Pb. The role of diagenetic processes in ore formation was examined further by
M. C. Akhurst
(University of Newcastle upon Tyne), who was able to place episodes of mineralization into the diagenetic sequence at Tynagh, and
The Maradi fault zone: evidence of Late Neogene tectonics in the Oman mountains
Authors: HANNA S. S. , NOLAN S. C.
Published: December 2007

This paper documents for the first time the occurrence of Late Neogene (Plio-Pleistocene) structures in the Oman mountains. The Maradi fault zone is a major NW–SE fault near Natih, SE of the Oman mountains, traceable for at least 60 km. It separates rocks of Campanian/Maastrichtian age (Fiqa shales and mark) to the NE from Campanian/Maasttichtian and Tertiary (Palaeocene and Eocene) rocks on the SW side. The southern region of the fault is dominated by Campanian/Maasttichtian rocks which lie on both sides of the fault. Neogene intramontane wadi gravels unconformably overlie Palaeogene limestones in the area. Both are folded by movements on the fault. Investigation of the en echelon folds associated with the fault reveal a possible transtensional nature. This structure has been previously linked to the Saiwan-Nafun Fault in the HuqfHaushi area of Oman to the SE. This correlation cannot be proven on structural evidence.
Short Paper: Nares Strait was not a Cenozoic plate boundary
Authors: HIGGINS A. K. , SOPER N. J.
Published: December 2007

Nares Strait, the linear seaway between Greenland and Arctic Canada has long been regarded as a Palaeogene plate boundary, along which major transform movement accommodated opening of the Labrador Sea. Fieldwork however revealed several stratigraphic markers which cross the strait and precle substantial displacement. Current plate reconstructions based on geophysical data continue to invoke major convergence and strike-slip along the strait. The manner in which Palaeozoic structural trends curve into parallelism with the strait as they cross it has been used to support this idea: ‘restoration’ of the trends gives an apparent 200 km offset along the strait. The curvature is an original tectonic feature and cannot be restored. Stratigraphic data preclude substantial Cenozoic displacement along or across Nares Strait; reconstructions based on indirect geophysical evidence which violate the geology must be wrong.
Tectono-stratigraphic model for the Massif D'Igountze–Mendibelza, western Pyrenees
Authors: JOHNSON JEFFREY A. , HALL CLARENCE A.
Published: December 2007

The Massif d'Igountze–Mendibelza, western Pyrenees, is a fault-bounded block of Palaeozoic basement overlain by an exceptionally thick Cretaceous siliciclastic sequence. North of the Massif, the Cretaceous sequence conformably overlies Lower Cretaceous carbonates, yet, immediately south of the Massif, it is entirely absent. The sequence fines northward and has NNE palaeotransport. The basement is commonly brecciated near the contact with the sedimentary cover, and the uppermost beds dip less steeply than the lowermost. These tectono-stratigraphic relationships are best explained by Cretaceous deposition above a relatively low-angle normal fault.

The Cretaceous deposits of the Massif d'Igountze–Mendibelza are part of the western extension of the North Pyrenean basin, a basin or series of sub-basins that began to form in the latest Aptian to Albian north of and along most of the length of the North Pyrenean fault. The precise relationship between deposition on the Massif and in the rest of the North Pyrenean basin is not known. There may have been many local variations in stress regime and structural style along the basin or sub-basins, but the regional episode of basin formation was a result of the same plate-reorganizational event. Later basin inversion was due to the latest Cretaceous to Eocene Pyrenean orogeny.
Pedostratigraphic models for alluvial fan deposits: a tool for interpreting ancient sequences
Authors: WRIGHT V. P. , ALONSO ZARZA A. M.
Published: December 2007

This paper reviews the scattered literature on Quaternary arid-type alluvial fan soil sequences, and presents a series of model stratigraphies. These are primarily influenced by the degree of entrenchment and by climatic controls. These models are used to interpret well exposed Miocene fan deposits from the Madrid Basin, central Spain.
Provenance of Lower Old Red Sandstone conglomerates, SE Kincardineshire: evidence for the timing of Caledonian terrane accretion in central Scotland
Authors: HAUGHTON P. D. W. , ROGERS G. , HALLIDAY A. N.
Published: December 2007

Northerly-derived conglomerates dominate much of the thick Lower Old Red Sandstone (ORS) succession of the NE Midland Valley of Scotland. These contain a diverse suite of granitoid boulders, the provenance of which can be used to constrain the timing of the post-Caradoc displacements which juxtaposed the Highland Border Complex against the Grampian terrane.

Rb-Sr muscovite-whole rock ages for two-mica granite boulders from the Crawton Group are 473–457 Ma, confirming the persistence of an Ordovician two-mica granite source first recognized in the Dunnottar Group. The Rb-Sr muscovite ages are supported by a U-Pb age of 475 ± 5 Ma for monazite separated from one of the clasts. A Rb-Sr biotite age of 412 ± 4 Ma for a clast of porphyritic biotite granite and geochemical evidence linking this clast to many of the other biotite granite clasts, suggests that late Silurian granitoids and related hypabyssal intrusions have also made an important, hitherto unrecognized, contribution to the conglomerates. Mica-whole rock ages for accompanying psammitic clasts suggest the source included metamorphic rocks (of up to at least staurolite grade) whose uplift overlapped with the intrusion of crustally-derived melts.

The chemistry, chronology and Sr and Nd isotopic compositions of the various igneous clasts are shown to resemble closely the Ordovician through to Silurian magmatic history of a small area of the Grampian terrane in NE Scotland. This is taken as strong evidence for a pre-Lower ORS juxtaposition of the Highland Border Complex and the Grampian terrane, to within several tens of kilometres of their present position. Ashgill–Silurian terrane displacements are invoked to achieve this. Discrepancies in the proportions and types of clast occurring in the conglomerates are explained by: uplift and unroofing of the Grampian terrane prior to docking; the involvement of polycyclic sediment, perhaps as a local veneer of pre-existing sediment on the Grampian terrane; and the likelihood that the source involved parts of the local Grampian terrane which are no longer exposed.
A buried granite batholith beneath the East Midland Shelf of the Southern North Sea Basin
Authors: DONATO JOHN A. , MEGSON JOAN B.
Published: December 2007

Published BGS gravity data of the UK Southern North Sea Basin show the presence of a gravity low trending to the ESE across the northern half of Quadrant 47. Two simplified geological cross-sections have been constructed across this feature with sedimentary structure based upon well information and reflection seismic data. Gravity modelling of these sections demonstrates that the gravity anomaly is unlikely to be produced by the presence of thick, low density sediments. Consequently, the presence of a large, buried granite batholith is postulated. The buoyant influence of such a granite may have exerted considerable tectonic control during the development of the Southern North Sea Basin. In particular, its presence may help to explain the development of the East Midland Shelf, the associated complex fault movements along the Flamborough Head and Dowsing Fault Zones, and the areal distribution and thickness of the Rotliegendes sand.
SLM confocal microscopy: an improved way of viewing fission tracks
Authors: PETFORD N. , MILLER J. A.
Published: December 2007

Fission track analysis as a geochronological, and more recently a palaeothermal technique is a lengthy process, often complicated by problems of track recognition. While recent developments in computerized track counting systems should lead to improved efficiency, they still rely on transmitted light as the principal means of track detection, and do not deal with the problem of track recognition. We present here some preliminary results using confocal scanning laser microscopy (SLM) of a study of fission tracks in apatite from the Fish Canyon tuff, and show how the technique can lead to improvements in track identification.

Defects formed in solids as a result of the spontaneous fission of the heavy nuclide
238
U are called fission tracks (Silk & Barnes 1959) and are found in a number of geologically important uranium-bearing phases including micas, titanite, zircon and apatite. The analysis of fission tracks has, until quite recently, been primarily concerned with age determination where it has proved useful in both the earth sciences and archaeology (

Fleischer
et al.
1975

). More recently, the recognition that at elevated temperatures the tracks become unstable and ultimately anneal (
Naeser 1981
;

Green
et al.
1986

), has led to the study of track lengths, especially in apatite, where track annealing occurs over the hydrocarbon maturation window temperature. (

Gleadow
et al.
1983

).

Although the study of fission track length data promises to be a useful tool in evaluating palaeotemperatures in some sedimentary basins (

Gleadow
et al.
1983

, 1986
;
Green 1989
), the measurements involved in both track counting and
Results of global atmospheric circulation experiments on an Earth with a meridional pole-to- pole continent
Authors: HAY WILLIAM W. , BARRON ERIC J. , THOMPSON STARLEY L.
Published: December 2007

Four general circulation models, forced by mean annual insolation and having an energy balance ocean, have been run for pole-to-pole continents: (1) low relief, 750 m average elevation; (2) high plateau, 1500 m average elevation; (3) mostly low, 750 m, but with 3 km mountains on the west, and (4) mostly low, 750 m, but with 3 km mountains on the east. The high plateau continent emphasizes the contrast between high and low pressure systems. Marginal mountains on either coast enhance moisture transport from the west to the continental interior, but mountains on the east eliminate the tropical wet belt and produce the most arid scenario. In none of the experiments do zonal climate boundaries trend steeply equatorward from east to west. All of the models produce more arid continental conditions than exist today.
Geochemistry of late Palaeocene and early Eocene tephras from the North Sea Basin
Authors: MORTON A. C. , KNOX R. W. O’B.
Published: December 2007

The late Palaeocene to early Eocene Balder and Sele Formations of the North Sea Basin contain over 200 air-fall, water-lain tephras. These occur over the entire North Sea area, extending onshore into Denmark, NW Germany, The Netherlands and SE England; they have also been recorded in the Bay of Biscay and Goban Spur areas of the NE Atlantic and offshore mid-Norway. Results from cores drilled in two widely separated areas of the North Sea have been integrated with earlier work on the northern North Sea and Danish sequences, to demonstrate that the stratigraphic and geochemical development of the tephra sequence is regionally consistent. This indicates that a single source or group of sources was responsible, rather than a number of geographically-separated intrabasinal volcanoes for which little geophysical evidence can be found. The sequence comprises a lower group of sporadic thin tephras of variable composition, including tholeiitic, alkalic, trachytic, trachyandesitic and peralkaline varieties, and an upper group of thicker, more abundant tephras, almost exclusively of Fe-Ti tholeiitic composition. General thickness trends and geochemical evidence indicates that the source volcanoes lay on the proto-Greenland-Scotland Ridge, with the tephras showing several features that ally them to the early Palaeogene Faeroe-Greenland igneous province. The reasons behind the highly explosive nature of the basaltic magmatism remain enigmatic.
Metamorphic studies: research in progress
Authors: DROOP G. T. R.
Published: December 2007

A Metamorphic Studies Group meeting on ‘Metamorphic Studies: Research in Progress’ and the eighth Annual General Meeting of the Group were held on 8 March 1989. It was attended by 81 delegates and 13 papers were presented on a range of topics, including an invited contribution from C. Chopin (Ecole Normale Supérieure, Park). Two poster contributions were also presented. The meeting was organized by G. T. R. Droop.

The morning session was concerned mainly with high-grade metamorphism and fluid-rock interactions. The first talk was given by
R. L. Oliver
who gave an account of some hitherto undescribed high-
T
, high-
P
Al-rich ferruginous granulites from the western margin of the Gawler Craton, South Australia. Extreme metamorphic conditions of
c.
10 kbar and 900–1000°C were inferred from the presence of the assemblage hypersthene + sillimanite + quartz. The coexistence of magnetite and Ti-hematite was taken as evidence for a relatively high oxygen fugacity. The rocks are apparently of much higher grade than those in the interior of the Gawler craton, but show similarities with granulites at the edge of the Yilgarn Block further west.
D. J. Waters
(with
J. M. Moore)
described an unusual granulite-facies assemblage of boron-rich aluminosilicate minerals (kornerupine + werdingite + grandidierite + sillimanite) from the highest grade part of the Namaqualand metamorphic complex (the spine1 + quartz zone). They noted that the mobility or otherwise of boron in high-grade metasediments could have important implications for partial melting in view of the effect of this element on the temperature
Granite magmas: their sources, initiation and consequences of emplacement
Authors: LEAKE BERNARD ELGEY
Published: December 2007

Geochemical and other evidence shows that granite magmas are generally derived from a mixture of melted crust and mantle material and the existence of a spectrum of types varying from largely mantle-derived to mainly crustal-derived is emphasized. Each pluton possesses a unique mix or range of mixtures which preserves an adumbrate history of the deeper levels of the crust and mantle at the particular location. Four illustrative granite-forming provinces are considered: (1) Archaean cratons with their voluminous tonalites, (2) magmatic arcs as exemplified by the western Americas, (3) the British Tertiary Province as an example of the results of extensional faulting and (4) the British and Irish Caledonide granites, the main phase (440–390 Ma) of which was produced during major Acadian strike-slip faulting. All these granites provide evidence of mixing of source materials. Geochemistry, especially of the Rare Earth Elements, U-Pb ages and isotopic studies of Sr, Nd, Pb, O, H and in some volcanic rocks Be, is beginning to enable quantification of the source components. The importance of major fracturing of the crust and mantle in providing magma triggers, magma focusses and magma consolidation sites is stressed; major batholiths probably occupy holes created by pulling apart the crust.

Geophysical evidence does not suggest that granite plutons are distributed throughout the thickness of the crust, but rather that they are concentrated relatively near the surface. The extant elevation of the whole of the north British crust, its altitude over the last 400 Ma and even in places the present shape of the coastline, are significantly influenced by Caledonian granites, the tops of which are generally within about 3 km of the present landsurface. Thus relatively little erosion of most of these bodies has taken place and the dominant sources of post-Silurian clastic sediments in the area were stripped off volcanic cover rocks and recycled sediments and metasediments. By inference, other continental areas with numerous exposed granite pluton roofs had a similar history.

The process of granite formation is an important means of density-stabilization of the crust with high-level emplacement of light sialic granite refined out of the mantle and lower, middle and even upper crust. The refractory mafic residues generally become denser and sink or stay down in the density-stratified crust but the division into residue and magma is not sharp with some granite magmas including significant quantites of restite.
Antarctic Peninsula continental magnesian andesites: indicators of ridge-trench interaction during Gondwana break-up
Authors: ALABASTER TONY , STOREY BRYAN C.
Published: December 2007

Subduction of young, hot oceanic lithosphere and a major episode of lithospheric extension have been considered as key tectonomagmatic factors in the genesis of ‘Setouchi-type’ continental magnesian andesites. We present data on a new discovery of such andesites from the northern part of the Antarctic Peninsula and propose that subduction of newly created oceanic lithosphere occurred along the proto-Pacific margin of Antarctica during the Middle Jurassic. Continental magnesian andesite magmatism was contemporaneous with the early stages of Gondwana break-up and we suggest that subduction of young, hot oceanic lithosphere and ridge-trench interaction may have contributed to the disintegration of Gondwana by thermally weakening the lithosphere and developing a broad, linear extensional zone along the proto-Pacific margin.
Structural age of the Connemara gabbros, western Ireland
Authors: TANNER P. W. G.
Published: December 2007

A ‘D2’ age of intrusion for the Connemara gabbros is rejected. The gabbros were intruded 490 Ma ago, probably just prior to the D3 deformation and, together with younger members of the Metagabbro and Gneiss complex, were responsible for a widespread sillimanite-grade contact metamorphism which overprinted the regional ‘D2’ gamet-staurolite ± kyanite metamorphism and the major D3 folds. Comparison with the NE Scotland gabbros is thereby strengthened, supporting the idea that they were both part of a coeval magmatic arc developed at the margin of the Caledonian fold belt.
Palynofacies in a Late Silurian regressive sequence in the Welsh Borderland and Wales
Authors: RICHARDSON J. B. , RASUL S. M.
Published: December 2007

The Upper Whitcliffe and lower part of the Downton Castle Sandstone Formations (Ludlow and Pridoli Series) have been sampled from sequences distributed over an area roughly 4800 square km in west-central England and Wales. Ludfordian age rocks have been interpreted as the deposits of shelf and basin environments, and those of the lower Downton Group as near-shore to beach. Sections sampled from the ‘shelf’ area are in the Ludlow type area, and in the Usk, May Hill and Woolhope inliers. ‘Basin’ sediments were sampled at Knighton, the Long Mountain, Capel Horeb and Kington. The samples were analysed for their palynological content, and all the organic-walled microfossils were studied together with the fragmentary remains of larger plants and animals. Using a series of ratios between different groups of microfossils, it is apparent that there are consistent changes through time in both the palynomorph assemblages and in the structured and unstructured organic material. Dominance of some microplanktic groups/taxa is used to define a new microphytoplanktic phase concept and to compare the sequence of palynoevents. Depositional environments inferred from palynofacies interpretation of the Ludlow type area are closely comparable with those proposed previously from sedimentological data. Palynofacies sequences differ for the shelf and basin areas but show similar trends. We have also recognized a dramatic shift in palynofacies at a level within the Downton Castle Sandstone Formation and its correlatives in both shelf and basin areas; this change is tentatively interpreted as a ‘storm’ event.
Further evidence for diversity in late Silurian land vegetation
Authors: FANNING U. , EDWARDS D. , RICHARDSON J. B.
Published: December 2007

Small coalified plant fragments from basal Pridoli (Silurian) strata at Perton near Hereford, England comprise isotomously branching smooth axes terminating in vertically elongate sporangia. The latter, which occasionally bifurcate, are characterized by prominent, distally concentrated, spinous emergences and contain trilete, retusoid, smooth-walled isospores. The plants are placed in a new genus and species,
Caia langii.
Comparisons are made with a number of Silurian and Lower Devonian plants with elongate sporangia and particularly with
Horneophyton.
A hypothesis is developed that spines on sporangia had a nutritive function. The spores are discussed in terms of other records of late Silurian-Early Devonian in situ spores.
Global atmospheric circulation experiments on an Earth with polar and tropical continents
Authors: HAY WILLIAM W. , BARRON ERIC J. , THOMPSON STARLEY L.
Published: December 2007

Two general circulation models forced by mean annual insolation and having an energy balance ocean have been run on an Earth with polar continents and a tropical continent. Polar continents produce strong meridional temperature gradients and a maximum hydrological cycle. A tropical continent produces the warmest planet and a minimal hydrological cycle. Both models produce more arid continents than exist today.