bluuebunny/crossref_metadata_2025 huggingface dataset:
Lower Palaeozoic convergent plate margin volcanism on Bømlo, SW Norway, and its bearing on the tectonic environments of the Norwegian Caledonides
Authors: Brekke Harald , Furnes Harald , Nordås Jan , Hertogen Jan
Published: December 2007

The island of Bømlo presents a geological section through a Caledonian convergent plate margin. The Lykling Ophiolite and the overlying ensimatic are sequence of the Geitung Unit were emplaced onto the Baltic Shield, probably in Arenig times. After a period of deep erosion, the Basin and Range type volcanics of the Siggjo Complex were deposited followed by a hiatus in the magmatism and a weak but widespread phase of vertical tectonism, possibly due to the successful subduction of a spreading ridge. At the top of the mainly sedimentary Ashgill/Llandovery Vikafjord Group, the Basin and Range type volcanism resumed. This was probably preceded immediately by the calc-alkaline, subaerial volcanism at the base of the Langevåg Group, which passes stratigraphically upwards into basin-fill lithologies such as submarine volcaniclastics, cherts, turbidites and submarine greenstones of chemistry compatible with the early stages of ensialic back-arc basin development. The stratigraphy and volcanism are discussed in context with recent views on the rest of the Norwegian Caledonides.
A review of Mesozoic climates
Authors: Hallam A.
Published: December 2007

There is overwhelming evidence, based on the distribution of distinctive sediments and fossils and oxygen isotope data, that the climate of the Mesozoic world was appreciably more equable than that of today, with no polar ice caps, but precise quantitative data are not available. Except for an episode of late Cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era. The distribution of coals and evaporites, together with other criteria, indicates a pattern of humid arid and zones appreciably different in important respects from that of today. During the Triassic and Jurassic, western Pangaea in low to middle latitudes was largely arid, but in the early Cretaceous the lands on the margin of the newly opening Central Atlantic and western Tethys experienced a humid climate. By late Cretaceous times arid zones had become very restricted in extent. Because of insufficient suitable data, attempts at climatic modelling have had only modest success, and only to a limited extent can the major long-term changes in climate between the Permian and the present be explained in terms of changing geography. The most probable explanation of Mesozoic equability is an increased atmospheric CO
2
content. A number of enigmas remain, such as the existence of flourishing forests in polar palaeolatitudes. Whereas for the late Cenozoic short-term climatic changes can be related successfully to variations in the geometry and mechanics of the earth-sun system, there is a long way to go before comparable success can be claimed for the Mesozoic.
Application of a seasonal climate model to Cenozoic glaciation
Authors: North Gerald R. , Crowley Thomas J.
Published: December 2007

Mathematical modelling of climate has matured as a discipline to the point that it can be useful in palaeoclimatology. As an example a new two-dimensional energy balance model is described and applied to several problems of current interest. The model includes the seasonal cycle and the detailed land-sea geographical distribution. By examining the changes in the seasonal cycle when external perturbations are forced upon the climate system, it is possible to construct hypotheses about the origin of mid-latitude ice sheets and polar ice caps. In particular, the model predicts a rather sudden potential for glaciation over large areas when the earth’s orbital elements are only slightly altered. Similarly, the drift of continents or the change of atmospheric carbon dioxide over geological time can induce radical changes in continental ice cover. With the advance of computer technology and our improved understanding of the individual components of the climate system, it should be possible to test these ideas in far more realistic models in the near future:
Late Neogene and Quaternary vertical movements in eastern Crete and their regional significance
Authors: Peters J. M. , Troelstra S. R. , van Harten D.
Published: December 2007

Geological and geomorphological investigations along the E Cretan coast allow us to set up a model for the genesis of a staircase-morphology formed by a series of wave-cut platforms. Field observations indicate that the early Pliocene period was characterized by stepwise subsidence. The area stabilized in the middle Pliocene and subsequently underwent Quaternary uplift. The character of late Cenozoic sedimentation is closely related to this Plio-Quaternary inversion of vertical movements.

The discovery in early Pliocene mark of the psychrospheric ostracod Agrenocythere pliocenica, which was known before almost exclusively from the western Mediterranean, shows that deep marine circulation extended as far as the Levantine basin during this period. In addition, it substantiates the postulated relatively deep marine depositional environment in eastern Crete during the early Pliocene, as opposed to continental-shallow marine late Messinian conditions.

Reversal of vertical movements around the Pliocene-Quaternary boundary is not only found on eastern Crete. Data from other Cretan districts and adjacent islands support the proposed model, which therefore appears to be significant for the S Hellenic arc. Its timing is concurrent with an important geodynamical revolution in the Aegean region.
Palaeogeomorphology and the occurrence of diamondiferous placer deposits in Koidu, Sierra Leone
Authors: Thomas M. F. , Thorp M. B. , Teeuw R. M.
Published: December 2007

The geomorphology and diamond distribution within the Koidu alluvial diamond field in Sierra Leone are examined to provide a methodology for palaeoplacer appraisal within a humid tropical environment of diverse relief and headwater drainage containing local diamond sources. A morphogenetic terrain model is proposed for use in devising prospecting programmes, based on geomorphological mapping and sediment analysis of terrain units mapped at 1:1250. Valley floors including headwater swamps and stream floodplains provide a radiocarbon-dated late Quaternary stratigraphic framework for deductions concerning interfluvial domains containing remnant river terraces, and colluvial stoneline deposits interspersed with non-alluvial erosional slopes. Planar interfluves as well as piedmont ‘glacis’ contain alluvial indicators within gravels composed of bedrock quartz and iron concretions derived from former landsurfaces. A process history for the interfluvial domain indicates downwasting and diagenesis of ancient degraded alluvials, lateral shifts of drainage lines and continued supply of diamonds from erosion of local sources, the ‘stonelines’ functioning as feeders of coarse clasts from the interfluves towards the valley floors. The use of geomorphology to provide descriptive and genetic terrain models to guide prospecting for alluvial placers is advocated as a standard procedure for use by mining geologists.
Fossils and tectonics
Authors: FORTEY R. A. , COCKS L. R. M.
Published: December 2007

‘Fossils can date rocks’ is a statement recognizable by all earth scientists, but all too many geologists stop there in their appreciation of how palaeontology can help them to solve their other problems, or of how to use it as an independent check of hypotheses reached by other methods. This thematic of papers, deriving from the Geological Society meeting organised on the same topic in February 1985, aims to help bridge the divide that exists between palaeontologists on the one hand and earth scientists of many other disciplines on the other.

The histories of geology and palaeontology were intimately intertwined until the last two or three decades. More recently, the sheer proliferation of literature and the growth of geological subdisciplines have perhaps displaced palaeontological data from the main stream of geological reasoning. Newer fields have apparently offered an objectivity that the deliberations of the palaeontologist may have seemed to lack. During this time British palaeontologists have established their own very successful Association, but the growth of palaeobiology and other aspects of the science may still obscure the geological roots of the subject, or its applicability to current problems of, for instance, structural geology. In short, the role of fossils has often tended to become a routine service in the dating of rocks—or just one of a series of potential‘event stratigraphic criteria’.

We regard this as unfortunate. The fossil record has several advantages which make it particularly important in the interpretation of structural and geotectonic problems: 1. The information from
Conodont palaeobiogeography and thermal maturation in the Caledonides
Authors: ALDRIDGE R. J.
Published: December 2007

Conodont elements are important in biostratigraphy, in palaeoenvironmental and palaeobiogeographical analyses, and in assessing the thermal history of Lower Palaeozoic strata throughout the Caledonian belt. The differentiation of Ordovician conodont faunas into the North Atlantic and North American Midcontinent provinces is not closely comparable with the provincial patterns shown by other faunal groups and does not relate clearly to criteria for recognizing continental separation across the Iapetus Ocean. Some species associations adapted to cool, normal marine waters were able to cross the ocean at the time of its presumed maximum extent.

The colours of conodont elements reflect the thermal history of strata and can be used in studies of low-grade metamorphism. In S. Wales, for example, metamorphic temperatures indicated by conodont colour are too high to he accounted for by simple burial beneath the known stratigraphical overburden under normal heat flow conditions. Elsewhere, conodont colour trends also serve to constrain and test models of metamorphism that involve sedimentary burial in subsiding basins, tectonic burial under nappes, or the thermal effects of intrusions.
Lineaments and basement domains: an alternative view of Dalradian evolution
Authors: FETTES D. J. , GRAHAM C. M. , HARTE B. , PLANT J. A.
Published: December 2007

This paper examines the evidence for basement structures of predominantly non-Caledonoid trend which appear to have influenced the development of the Dalradian belt in Scotland. A number of domains or blocks separated by dominantly trans-Caledonoid lineaments are recognized on the basis of geophysical, stratigraphical and geochemical patterns. These are thought to reflect fault-bounded depositional basins controlled by basement lineaments during the extensional phases of the Caledonian 'orogeny'. In addition the recognition of a number of these domains and lineaments in the structural, metamorphic and igneous data-sets for the Dalradian belt, shows the continuing influence of these basement controlled features throughout the compressional and uplift phases of the orogenesis.

A possible tectonic model is proposed which envisages the depositional basins forming in a setting dominated by Caledonoid trending transcurrent faults and a major pull-apart basin forming on a trans-Caledonoid axis.
Geothermal resources of the United Kingdom
Authors: DOWNING R. A. , GRAY D. A.
Published: December 2007

Geothermal prospects in the UK are represented by low enthalpy resources in deep sedimentary basins and 'Hot Dry Rock' (HDR) resources in radiothermal granites, and possibly in deep basement rocks where they are overlain by thick low conductivity sediments. The low enthalpy resources are in Permo-Triassic sandstones at temperatures of more than 40°C. Four deep exploration wells have been drilled to investigate the potential of these sedimentary aquifers. The main HDR resource potential is associated with major granite batholiths in southwest and northern England where temperatures are predicted to be 200°C at about 5.4 and 6 km respectively. The HDR potential is being investigated by the Camborne School of Mines at their test site in Cornwall where three boreholes have been drilled to depths of between 2 and 2.5 km.

The Hot Dry Rock Accessible Resource Base at temperatures of more than 100°C and depths of less than 7 km is 36 X 10
21
joules (equivalent to 130 × 10
4
million tons of coal). The low enthalpy Geothermal Resource of the Permo-Triassic sandstones at temperatures of more than 40°C is 200 × 10
l8
joules (equivalent to about 8000 million tons of coal). If only a small fraction of these resources could be developed, it would be significant in terms of the UK’s energy balance.
The granites of the Southeast Asian Tin Belt
Authors: COBBING E. J. , MALLICK D. I. J. , PITFIELD P. E. J. , TEOH L. H.
Published: December 2007

Four granite provinces have been delineated each with its own distinctive pattern of mineralization.

1. The Main Range Province. Endogenous greisen-bordered vein swarms of cassiterite and wolframite.

2. The Eastern Province. Magnetite–cassiterite skarns ± base metal sulphides with antimony in Thailand.

3. The Western (Peninsular Thailand–Burma) Province. Endogenous greisen-bordered vein swarms and pegmatites of cassiterite and wolframite.

4. The North Thailand Migmatitic Province. Endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony.

In all provinces, but particularly in the Main Range, granitoids designated as two-phase variants have been recognized where xenocrysts and xenoliths of coarse, primary texture granite are enclosed in, and corroded by an invasive, equigranular quartzo–feldspathic matrix. These rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids.

Whole rock geochemistry from Peninsular Malaysia shows that the granites from the Main Range and Eastern Provinces comprise two contrasted suites which correspond approximately to the I and S-type categories advocated by Chappell & White (1974). In addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters. Variation diagrams of plutons having the intrusive sequence primary texture granite—two-phase granite—microgranite show linear trends with increasing SiO
2
, Na
2
O, Rb, W, Sn and U, and decreasing Sr, Ba, Th and all other major elements.
Volcanic chronology of the Men–Kilimanjaro region, Northern Tanzania
Authors: WILKINSON P. , MITCHELL J. G. , CATTERMOLE P. J. , DOWNIE C.
Published: December 2007

New conventional K-Ar dates for volcanic rocks from a recently mapped area in northern Tanzania, which includes the large volcano Meru, confirm rift-faulting episodes around 2.1 Ma and 1.2 Ma. Alkaline volcanic activity in the Meru area occurred in two main episodes, the earliest around 2.0–1.5 Ma. The later, main phase began about 0.3 Ma and peaked between 0.15 Ma and 0.06 Ma, although minor activity continued into the present century. Available data suggests that Meru and the neighbouring Kilimanjaro volcanic massif were never substantially active during the same periods.
Near-surface geochemical processes in Quaternary sediments
Authors: DAHMKE A. , MATTHESS G. , PEKDEGER A. , SCHENK D. , SCHULZ H. D.
Published: December 2007

Pore water analyses and mineralogical investigations from the unsaturated zone of Quaternary glacial outwash sediments were carried out to investigate the major geochemical reactions that control the chemistry of seepage and groundwater. The kinetics of rock/water interaction especially that of dissolution/precipitation are strongly influenced by secondary minerals and amorphous phases on grain surfaces. The role of buffer systems such as calcite dissolution, ion exchange and silicate weathering is discussed with help of a lumped model. The kinetics of these systems and the methods for their investigation are presented.
Geochemical aspects of granite and related rocks
Authors: COE K.
Published: December 2007

Report of a meeting held in Burlington House on 28 November 1985. The meeting was convened by K. Coe, and chaired by W. S. Pitcher and M. Brown, morning and afternoon sessions respectively.

A special scientific meeting of the Society was held on Thursday 28 November 1985, with the title
Geochemical aspects aspects of granite and related rocks.
From the papers offered, ten were selected which dealt with data and concepts derived from British and Irish granitic bodies.

One exception to this was the first contribution, presented by
R. Macdonald.
In this it was proposed that because of late crystallization and subsolidus processes, plutonic granites may not record magmatic chemistry. Macdonald and his co-workers suggested that silicic obsidians, rhyolites and acid ash-flow sheets may be better indicators of original composition, implying that these extruded rocks are the chemical equivalents of unmodified granitic liquids. This precept was used in interpreting data derived mainly from the Western Cordillera to show that compositions of source rocks were in some cases more important than the tectonic setting of the magma.

The second paper, by
D. A. C. Manning
, emphasized the importance of the volatiles B, F, Li and P in granites, manifest in familiar ‘accessory’ minerals and exerting controls on various aspects of the melt, including its emplacement mechanism. Other trace and some major element abundances correlated with these indicating a genetic relationship. A lower crust source for the volatiles was suggested.

Two papers followed on the younger and older granites of the
The evolution and mechanics of modern intertidal and subtidal bedforms: their relevance to geological structures
Authors: LANGHORNE D. N. , READ A. A.
Published: December 2007

Standard levelling techniques, carried out daily for 13 days during a semi-lunar tidal cycle, were used to obtain cross sectional profiles perpendicular to sandwave crestlines on a drying bank. The results were used to study bedform movement and to infer internal structure (
Langhorne 1982
). Sedimentary evidence of such structures, or master bedding, was verified by box coring. The conclusions, compared with those obtained on previous occasions at a subtidal site, indicate the difficulties of distinguishing the apparently contrasting hydrodynamic regimes using structural criteria. This has important implications for the interpretation of palaeo-environments from ancient sediment-tary structures.
The geochemistry and petrology of an alkaline lamprophyre sheet intrusion complex on Maio, Cape Verde Republic
Authors: FURNES H. , STILLMAN C. J.
Published: December 2007

The Atlantic island of Maio in the Cape Verde archipelago has a Basement Complex of Mesozoic and Tertiary age which is invaded by an intense swarm of sheet intrusions ranging in age from c. 16 to 8 Ma. These cut an alkaline ultramafic, mafic and felsic plutonic complex (Central Igneous Complex) and its host, a segment of Jurassic ocean floor with pillow lavas and abyssal sediments. The Basement Complex is dissected and unconformably overlain by a sequence of lavas of basanitic and nephelinitic composition.

The sheet intrusions comprise sills and dykes of alkaline lamprophyre, many of which are aphyric or sparsely porphyritic. Phenocrysts are predominantly clinopyroxene, with smaller amounts of olivine and Ti-magnetite. Microphenocrysts are kaersutite, apatite and biotite. The groundmass is dominated by potassium feldspar and analcime. Calcic plagioclase is extremely rare. Chemically the intrusions are basanitic, with major and minor element compositions directly comparable with the Neogene and Pleistocene basanitic lavas which cap the island. Calculations based on observed phenocryst phases suggest that the liquids involved in the crystallization of the sheet intrusions may have been derived by crystal fractionation from a range of basanitic parents. These were similar to those from which the later lavas were generated, but modified to some extent by variable water-rock interactions enhanced by trapped volatiles.
Coal and coal-bearing strata: problems and perspectives
Authors: SCOTT A. C.
Published: December 2007

For the past 15 years oil, of all the fossil fuels, has been the most prominent in both geological and non-geological literature. Significant progress has been made on many aspects, especially in exploration by employing interdisciplinary approaches to make scientific and economic gains. Technical advances have allowed exploration to move into more hostile geographical areas. The effect on research of this increased exploration effort has been to stimulate new interpretations in several areas of geology, especially in sedimentology, tectonics, geophysics and geochemistry.

Coal has, to some extent, remained a poor relation. Effort has been directed to more technical aspects of production and utilization rather than in the investigation of more fundamental aspects concerning its origin. In spite of this there has been significant progress in several aspects of coal geology over the past 15 years. In addition, new geographical areas are opening up for exploration, most notably China, Australia, western North America and Indonesia. The time is right, therefore, to highlight recent advances in coal research.

In 1968, following an inter-university student conference,
D.
G. Murchison and T.
S.
Westoll edited an important volume on
Coal and Coal-bearing Strata
which synthesized several important aspects of coal research. Soon after this, the second edition of Stach’s classic
Textbook
of
Coal Petrology
was published (

Stach
et al.
1975

, now in its third edition). Much is owed to work of M. & R. Teichmiiller on coalification and its uses. The recent upsurge of interest in coal geology is indicated by the publications of
CHARM II—A deep reflection profile within the central England microcraton
Authors: MAGUIRE P. K. H.
Published: December 2007

The results of a deep reflection profile crossing the Precambrian rocks of Charnwood Forest and the postulated buried Caledonian Mountsorrel granodiorite in central England are reported. A prominent subhorizontal reflector to the NE of Charnwood Forest is suggested as marking the base of the pre-Carboniferous Widmerpool Gulf, and possibly arises from the top surface of the granodiorite intrusion. A lack of returned energy from the upper crust beneath Charnwood Forest contrasts with a mass of reflectors beneath the intrusion, which itself appears relatively transparent to seismic energy. Two subparallel bands of reflectors within the lower crust, continuous across the whole profile and previously observed on another section about 20 km to the east, suggest that the emplacement of the granite has caused little disturbance within the lower crust in the plane of the section. The origin of the twin reflections is unexplained. Similar twin reflections occur in the lower crust in northern Germany immediately to the SE of the London–Brabant massif over whose NW region the CHARM profile was sited.
Tectonic development of the Southern Belt of the Southern Uplands accretionary complex
Authors: KEMP A. E. S.
Published: December 2007

Detailed structural studies in the Wenlock age Southern Belt of the Southern Uplands have identified major controls on tectonic development. Original thickness and composition of sediment control the style of faulting: thin, poorly consolidated, interbedded sandstone/mudstone sequences form broad sheared zones, while thicker, well consolidated sandstone-dominated sequences fail along thin, bedding-parallel brittle fractures with vein infill. The structural evolution of the sheared zones provides an insight into melange development. Depth of burial within the accretionary pile governs the development of cleavage and intensity of post Fl deformational phases. The intensity of imbrication within accreted material probably relates to subduction rate with early Wenlock sequences being highly imbricated and mid Wenlock sediments preserved in internally coherent fault-bounded packets. Sinistral strike-slip movement controls the development of steeply plunging folds, sub-horizontal stretching directions and sideways facing bedding cleavage relationships, and strongly influences fabric development in sheared zones. Determination of the relative importance of these factors permits a fuller understanding of the deformational history.
The role of hybridization and crystal fractionation in the evolution of the Cairnsmore of Carsphairn Intrusion, Southern Uplands of Scotland
Authors: TINDLE G. , McGARVIE D. W. , WEBB P. C.
Published: December 2007

The petrology of the Cairnsmore of Carsphairn granitic intrusion in the Southern Uplands of Scotland was the subject of several classical studies by Deer about 50 years ago. The presence of concentric zonation from dioritic margins to granitic core with petrologically transitional contacts was explained in terms of successive episodes of intrusion and hybridization. Magmas of gabbroic, granodioritic and finally granitic composition were involved, producing extensive intermediate zones of hybrid diorite and hybrid granite.

These proposals are examined in the light of recent field observations and new major and trace element data. Using suitable end-member compositions, it is shown that hybridization (or mixing) alone could not have produced the intermediate rock types, although a form of hybridization may locally account for transitional boundaries between the main rock types. It is shown that geochemical variations through all units are consistent with crystal fractionation as the dominant mechanism of magma evolution, but field observations of locally sharp contacts between different rock types and varying compositional gradients preclude a simple model of
in situ
fractional crystallization.

The preferred model for the pluton is that a large volume of dioritic magma was emplaced, assimilated country rocks near the margins and crystallized inwards to form the diorite/quartz diorite unit. The enclosed melt fractionated towards a granodioritic composition and broke through the partially crystallized carapace to form the zone of granodiorite. The melt continued to fractionate at depth and, after a further interval, a granitic melt was intruded through the largely crystallized granodiorite to form the inner zone of granite. The first intrusion of granite formed the finer-grained microgranite (where more rapid cooling and/or volatile loss occurred). This was intruded by a second pulse of compositionally similar melt to form the coarse-grained granite.
A fluid inclusion model for the genesis of the ores of the Dolgellau Gold Belt, North Wales
Authors: BOTTRELL S. H. , SHEPHERD T. J. , YARDLEY B. W. D. , DUBESSY J.
Published: December 2007

The results of a detailed fluid inclusion study of a zone of auriferous quartz vein in the Clogau-St Davids goldmine, North Wales are presented. These show that both aqueous and an immiscible pair of H
2
O-CH
4
fluids were present during the mineralizing event. Compositions of the immiscible fluid pair are estimated from Laser Raman and bulk inclusion volatile analysis data. Thermometry and barometry using these fluid compositions shows that the ores were formed at
c.
300–320°C and
c.
1.8 kbar.

A model is developed which is consistent with both the fluid inclusion data and other considerations. This involves the introduction of aqueous fluid into the graphitic shales hosting the mineralized veins which proceeds to react with graphite in the wall-rocks to produce H
2
O–CH
4
fluids. As H
2
O is consumed to produce CH
4
, an increase in salinity is observed in the residual aqueous inclusion fluids. Deposition of gold is ascribed to destabilization of either AuCl
−
2
or Au(HS)
−
2
complexes in the incoming fluid as a result of interaction with graphite. Auriferous zones within the veins are defined by high CH
4
values and low CO
2
/CH
4
ratios in bulk inclusion analyses. These effects are thought to be the result of increased fluid-rock interaction in these zones, related to structural features in the wall-rocks.
Taolin Zn–Pb–fluorite deposit, People’s Republic of China: an example of some problems in fluid inclusion research on mineral deposits
Authors: ROEDDER E. , HOWARD K. W.
Published: December 2007

The large Taolin zinc–lead–fluorite deposit in the People’s Republic of China was discovered 28 years ago, but whether its genetic affiliation is Mississippi Valley-type, epithermal, or mesothermal has remained uncertain. Both the ore and gangue (cherty to coarse quartz, plus barite, chlorite and calcite) occur as open space filling in a major fault zone between granite and metasedimentary rocks. Following barren, pre-ore quartz, three stages of ore are recognized by
Wang (1978)
and

Wang
et al.
1981

. Our studies on 400 fluid inclusions, from all 4 stages, show homogenization temperatures of 120–200°C (av. =160) and salinities of 0 to 14wt% equiv. NaCl (av. 7.7). These results differ greatly from some previously published sulphur isotopic temperatures (221–344°C), and data for five inclusions that are more saline (9.0–17.7 wt% equiv. NaCl) and much hotter (up to 345°C).

This study provides good examples of a variety of problems that are encountered in the application of fluid inclusion data to mineral deposit research in general. These problems include mine sampling, inclusion sampling, inclusion measurement, changes in inclusions after trapping, disagreement with other data, genetic affiliation of the deposit, and possible application of the results to exploration.
The structural evolution of the northern Viking Graben and its bearing upon extensional modes of basin formation
Authors: BADLEY M. E. , PRICE J. D. , RAMBECH DAHL C. , AGDESTEIN T.
Published: December 2007

Recent advances in the understanding of rift basin formation, coupled with the increasing public availability of seismic and well data across the northern Viking Graben (60–61°N), have enabled a detailed analysis of its development. Two rifting episodes can be recognized: ?Late Permian–early Triassic and Bathonian–Ryazanian. Major regional unconformities, thought to be primarily tectonic rather than eustatic in origin, separate and subdivide the rifting episodes. The earlier episode involved extension about a N–S axis; ensuing (Triassic–Mid-Jurassic) thermal subsidence was accommodated on steep faults. During the later episode a new NE–SW fault trend was superimposed on pre-existing patterns. Major block rotation, marking active rifting, ceased at the end of the Ryazanian. During the second post-rift episode there was a progressive migration of active faulting towards the basin margins and, as a result, a widening-with-time of the area undergoing subsidence. Asymmetric subsidence of the central part of the basin was hinged at the western margin of the Horda Platform, and accommodated to the NW on major faults within the Tampen Spur,
β
factors, for the second rifting episode were calculated both by relating subsidence to extension, and by measuring observed extension. Values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases, but are greater for the latter phase. Subsidence patterns are similar for both rifting and thermal subsidence episodes, so that there is vertical stacking of relatively thick sequences in the axis of the northern Viking Graben. These factors preclude the application of models involving uniform and non-uniform stretching and also preclude oblique extension; depth-dependent stretching is preferred.
Emplacement mechanism and lateral correlation of pyroclastic flow and surge deposits in northen St Kitts, Lesser Antilles
Authors: TATE M. P. , WILSON M.
Published: December 2007

Thick accumulations of pyroclastic deposits have emanated from the Mt Misery volcano on St Kitts, Lesser Antilles, during two major eruptive episodes (2-3000 and 41000 a BP). Systematic logging of coastal sections in the northern part of the island has revealed a variety of deposits, including pyroclastic flows, surges and intermittent air fall. Palaeosols and one laterally persistant surge deposit provide important marker horizons, permitting correlation of the intervening and less persistent flow deposits.

Block and ash flows (traditionally termed
nuée ardentes)
can be subdivided into andesitic Pelean-type and basaltic andesite St Vincent-type deposits, closely corresponding to the products of historic pyroclastic eruptions in the Lesser Antilles. Finer grained ash flows are equally voluminous and comprise scoria, semi-vesicular andesite and mixed magma and ash deposits. A significant pyroclastic surge component has been recognized with characteristic bedforms. Field evidence suggests that there is a continuous gradation between flow and surge deposits. Collectively the pyroclastic flow deposits are all of the small volume type and are commonly stratified, with poor to moderate sorting and coarse tail grading. Where thickly developed they show an internal depositional sequence compatible with the standard ignimbrite flow unit. Well developed bedforms include steeply incised U-shaped gullies eroded by the infilling flows.

The depositional characteristics of these pyroclastic flows appears to be a function of the physical properties of the magma on eruption, initial flow magnitude, potential energy and degree of topographic channel formation. In general grain-size and the erosive potential of the flow increases with increasing channel formation, whilst sorting and the degree of stratification decrease. The development of graded bedding is, however, apparently unaffected.
Relationships between the Cumberland Bay and Sandebugten Formations, South Georgia, and some tectonic implications
Authors: TURNBULL I. M. , CRAW D.
Published: December 2007

The late Jurassic to early Cretaceous Cumberland Bay and Sandebugten formations of South Georgia have different detrital petrography, although some of their detrital components are common to both units. Cumberland Bay strata become progressively more deformed with depth, and the more deformed portions strongly resemble Sandebugten rocks. Estimates of pressure and temperature of metamorphism suggest that Sandebugten rocks underwent pumpellyite-actinolite or greenschist facies metamorphism, at least 1 kbar and about 50°C higher than prehnite-pumpellyite facies metamorphism of the Cumberland Bay sediments. Both units are now separated by a low angle fault. Palaeocurrent data from Cumberland Bay strata show definite patterns, but data from Sandebugten Formation are equivocal. Variations in petrography are no more than occur in similar island arc-derived sediments from other areas around the Pacific margin. It is postulated that both units, and possibly other formations on South Georgia, may have been derived from one evolved volcanic arc with a sialic basement, rather than from two sides of a marginal basin, as has been previously suggested.
Early Carboniferous floodplain deposits from South Wales: a case study of the controls on palaeosol development
Authors: WRIGHT V. P. , ROBINSON D.
Published: December 2007

Two palaeosol sequences are described from early Carboniferous floodplain deposits from South Wales, which exhibit a complex series of pedogenic profiles. Soil types recognized include vertic Aridisols and Entisols, as well as dolomite-bearing Sulphaquents. The sequential and lateral changes in these soil types are interpreted as due to both intrinsic factors, such as channel avulsion and changing proximity to channel belts (causing changes in sedimentation rates), and extrinsic factors, such as possible climatic changes and a marine transgression.
Plesiosaur locomotion
Authors: HALSTEAD L. B.
Published: December 2007

Plesiosaurs are unique in being the only underwater fliers with four ‘wings’, and how the two pairs worked in relation to one another is a matter of some controversy. Newman's hypothesis of porpoising seems to provide a possible solution.

Any discussion of plesiosaur locomotion must take into account the different modes of plesiosaur life: the long-necked forms were fish-eating surface paddlers and the short-necked were diving cephalopod feeders.
Magnetic susceptibility contrasts in Ordovician greywackes of the Southern Uplands of Scotland
Authors: FLOYD J. D. , TRENCH A.
Published: December 2007

Ordovician greywacke formations of the Southern Uplands are demonstrated to have consistent differences in magnetic susceptibility, which parallel differences in petrography. The observed susceptibilities range from a minimum of 0.16 X 10
−3
SI for the quartz-rich, feldspar-poor Glenwhargen Formation to a maximum of 13.81 X 10
−3
SI for the quartz-poor, feldspar-rich March-bum Formation, and are considered to be directly related to variation in the amount of detrital magnetite in the greywackes. Rapid measurement of magnetic susceptibility is demonstrated to be a valuable field technique for distinguishing otherwise uniform sedimentary sequences on the basis of differing magnetite content. Detailed field observations illustrate considerable variation in suscep-tibility within metre-scale sections perpendicular to bedding through graded sedimentary units, which may be caused by density and/or grain-size effects. Laboratory measurements of the intensity of natural remanent magnetisation in the petrographically contrasting Kirkcolm and Galdenoch forma-tions show a similar variation to that observed in susceptibility. Thermally distributed, scattered magnetization directions indicate that no primary remanence has survived the low-grade burial metamorphic event in the Southern Uplands.
Fossil charcoal as an indicator of palaeoatmospheric oxygen level
Authors: CHALONER W. G.
Published: December 2007

Charcoal results from incomplete combustion of plant material. It is produced naturally by wildfire, and being relatively tough and unbiodegradable it may be transported and incorporated into a variety of sedimentary environments. Wildfire requires adequate atmospheric oxygen for the combustion of plant fuel (wood, leaf litter). Fossil charcoal from the Devonian onwards suggests that the oxygen level in the atmosphere has not fallen below 13% in this interval. Further, the extreme flammability of even wet plant fuel at oxygen levels above 35% makes this the highest figure compatible with the occurrence of terrestrial vegetation.
Petrology of two Tertiary oil shale deposits from Queensland, Australia
Authors: Gibson P. J.
Published: December 2007

Sediments from two Queensland Tertiary lacustrine oil shale deposits, the Lowmead and Duaringa Basins, have been petrologically characterized from standard X-ray powder diffraction analyses, backscattered electron microscopy and electron microprobe data. The results presented illustrate the potential of backscattered electron imagery for the study of diagenesis in fine-grained, organic-rich sediments.

The Lowmead Formation consists of lamosites, claystones and brown coals deposited in freshwater lacustrine and fringing peat-swamp environements. Their dominant constituents are kaolinite and quartz, with opaline silica and siderite important as eogenetic phases. Despite its similar geological setting, the Duaringa Formation contains a more varied lithological assemblage with less organic matter being preserved. Freshwater lacustrine claystones and lamosites are interbedded with carbonate sediments deposited during periods of saline/alkaline conditions in the lake. Within these carbonate sediments, major growth of eogenetic mineral phases occurred, principally dolomite and analcite. As in the Lowmead Basin, siderite is an important eogenetic phase in the Duaringa Formation. Two types of sideritic ironstone band occur throughout both basins; sphaerosiderites within claystone/coal sediments and fine-grained bands of siderite within lamosites. The bulk mineralogy of the siliciclastic detritus shows no significant trends with depth within either basin.
Short Paper: Time of docking of the Connemara terrane with the Delaney Dome Formation, western Ireland
Authors: TANNER P. W. G. , DEMPSTER T. J. , DICKIN A. P.
Published: December 2007

The Connemara Dalradian terrane was emplaced over the Delaney Dome Formation from the NNW by near orthogonal movement on the Mannin Thrust, a linkage that has survived later movement. Rb-Sr isotopic analyses of micas and whole rocks from the Delaney Dome mylonites constrain the age of movement on the thrust to 447 ±4Ma. This time of thrusting correlates with much other tectonic activity in the Caledonides and may represent a time of ‘docking’ of the Midland Valley block with the more northerly terranes.
Short Paper: The Start-Perranporth line: a Devonian terrane boundary in the Variscan orogen of SW England?
Authors: HOLDSWORTH ROBERT E.
Published: December 2007

In the Variscides of SW Britain, the Start-Perranporth line (SPL) trends E-W and shows a history of dextral transpression. It is proposed that during the Devonian the SPL marked a major basement fault which formed the northern margin of a continually infilled group of dextral pull-apart basins, locally floored by oceanic crust. In SW Britain transtension may have arisen due to dextral motions along a terrane boundary which separated the ORS Continent from an Armorican microplate to the south. The faulted continental margin may then have acted as an oblique buttress to the advancing Variscan nappes, inducing dextral transpression, large scale backfolding, and forming the SPL.
Early Ordovician alluvial fan deposits of the Marmul oil field, South Oman
Authors: HEWARD A. P.
Published: December 2007

Fine grained shaly sands of the Mahwis Formation (Haima Group) form one of the reservoir intervals of the Marmul field. Six lithofacies can be distinguished from cores: shale clast conglomerates, trough cross-stratified sands, horizontally stratified sands, massive sands, rippled sands and interbedded shales and sands. Horizontally stratified sands make up 45% of the cored reservoir. Two scales of fining upward sequence occur. Small sequences are 0.3-1.5 m thick and are interpreted as sheetflood deposits on the distal portions of semi-arid alluvial fans. The larger sequences are 25-50 m thick, can be correlated on well logs fieldwide, and probably represent periodic tectonic rejuvenation and erosional lowering of the sediment source area.

It is interpreted (from regional correlation, sediment provenance, and a knowledge of possible source areas) that the alluvial fans were predominantly sandy, had radii of several tens of kilometres and formed an extensive apron bordering a highland area which lay to the southeast. The thinly bedded and shaly character of these sheetflood sands causes problems of petrophysical log evaluation and hence oil-in-place estimation. Reservoir quality is related to lithofacies occurrence and variation in grain size. The large-scale fan sequences correspond to an upward decrease in porosity and permeability and form useful subdivisions for field-scale correlation and reservoir prediction.
Facies distributions and structure of a Dharwar volcanosedimentary basin: evidence for late Archaean transpression in southern India?
Authors: CHADWICK B. , RAMAKRISHNAN M. , VASUDEV V. N. , VISWANATHA M. N.
Published: December 2007

The Bababudan–Nallur basin (
c
. 60 km × 125 km) is part of a series of late Archaean basins accommodating volcanic and sedimentary rocks of the Dharwar Supergroup within the low-grade terrain of the province of Karnataka. Initial development of the Bababudan-Nallur basin was characterized by rapid subsidence with eruption of mainly basaltic lavas. Breaks in eruption were marked in some instances by thin but persistent deposits of shallow marine quartz sands and muds. Subsidence in the south continued with accumulation of banded ferruginous cherts and muds, whilst uplift of the volcanic pile took place in the north. This uplift promoted erosion of the volcanic cover and its basement gneisses and granodiorites with deposition of alluvial and shallow marine fans and debris flows adjacent to the uplifted blocks. The fans passed laterally into intertidal and offshore quartz sands, greywackes and muds with interbedded dolomitic limestones. Accumulation of rhyolites, banded ferruginous cherts and greywackes took place further north. The structure of the basin is dominated by mainly upright folds and faults, with the trend of the folds broadly parallel to the boundaries of exposed blocks of basement. The basement deformed cataclastically on myriad fractures in contrast with the ductile behaviour of the cover. Many cover-basement contacts are faults with mylonites, although unconformities are preserved, especially in the south. The facies distributions and structure of Bababudan–Nallur and other Dharwar belts have characteristics in common with mixed-mode basins developed as a consequence of strike- or oblique-slip on long-lived fault zones. These relations suggest that transcurrent plate interactions comparable with those of the Phanerozoic were significant in the late Archaean evolution of southern India.
The geometry of normal faults
Authors: ROBERTS ALAN , YIELDING GRAHAM , FREEMAN BRETT
Published: December 2007

This meeting took place at Burlington House on
14
and
15
June
1989.
Until recently a specialist structural geology meeting on a theme such as this would have been solely the preserve of the Tectonic Studies Group. There is, however, currently much encouraging collaboration between industry and academia on research into all aspects of extensional faulting and thus this meeting was held under the joint aegis of the Petroleum Group and Tectonic Studies Group. The hope that such a meeting would draw participation from industry and academia was fulfilled, with the number of talks presented and the overall attendance dividing roughly equally between these two groups of Earth scientists. The programme included
31
papers and a number of poster displays; nearly
200
people attended
.

Ultimately the proceedings of the meeting will, it k hoped, appear as a Special Publication of the Geological Society. The intention of this report is therefore not to review each contribution in turn, but rather to synthesize the main themes and conclusions of the meeting, in order that they should be disseminated into the Earth sciences community as rapidly as possible and prior to any future volume.

The recent involvement of industry in published basin analysis studies has resulted in an increase in the availability of seismic reflection data to all Earth scientists. A major emphasis at the meeting was therefore placed on what can be learnt about normal fault geometry from seismic reflection data. This main theme was amply supported by papers based on field
A computer simulation of evolution by natural selection
Authors: SWAN A. R. H.
Published: December 2007

A computer simulation of evolution by natural selection must incorporate three processes: construction of morphology according to specified parameters, generation of descendants by random mutation of parameter values, and assessment of differential efficiency to allow the automated choice of a survivor. These processes are described with respect to a simple 2-dimensional dichotomous branching morphology. This structure may be relevant to some fossil graptolites and bryozoans. Simulated evolution using this model shows gradualism, punctuation, reversals,
k
and
R
type selection and other features claimed to occur in fossil lineages. These properties are explained in relation to the heterogeneities of morphospace. This simulation may be a valid model for real evolution: evolutionary mode, tempo and direction may often be the result of constraints inherent in the geometry of the organism.
Advances and problems in Ordovician palynology of England and Wales
Authors: MOLYNEUX S. G.
Published: December 2007

Acritarchs and chitinozoa are used to date Ordovician rocks in England and Wales, but the data-base for both groups is poor. Study of chitinozoa has been neglected in the UK, in contrast
to
North America and southwest Europe where biozonations have been established. Formal definition of acritarcb biozones may soon be possible in the Tremadoc–Arenig, but acritarch biostratigraphy in the Llanvirn–Ashgill is insufficiently documented.