bluuebunny/crossref_metadata_2025 huggingface dataset:
A latest Cretaceous hotspot and the southeasterly tilt of Britain
Authors: COPE J. C. W.
Published: December 2007

The southeasterly regional dip of England and Wales is usually ascribed
to
Miocene movements. Loss of up to 2 km of cover from northern England, shown by apatite fission track analysis, has been related to uplift and erosion induced by a mantle hotspot, but its effects were far more widespread than considered hitherto. Outcrop patterns throughout much of England, Wales and eastern Ireland can be related to a hotspot beneath the Irish Sea. Uplift occurred within the late Maastrichtian and erosion continued into the late Palaeogene. After post-Oligocene down-faulting of the Irish sea, the modern drainage was initiated on the eroded surface.

Unconformities provide the best means of dating orogenic movements; in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision. Thus in southeastern Britain the major E-W structures of the Hampshire Basin, the Weald and the London Basin can be dated as Miocene, as rocks of Oligocene age are involved in the folding in the Hampshire Basin and Pliocene sands rest in erosional pockets of the Chalk of SE England. Because fold movements tend to affect large areas of the crust at discrete intervals of time, the southeasterly tilt of Britain, evident from the fact that a NW-SE transect from Anglesey to London crosses outcrops of rocks getting progressively younger from the Precambrian of Anglesey to the Tertiary of the London Basin, has
Deep structure of the Vale of Glamorgan, South Wales, UK
Authors: BROOKS M. , MILIORIZOS M. , HILLIER B. V.
Published: December 2007

The deep structure of the Vale of Glamorgan is investigated using recently acquired seismic data. Reflection sections from a commercial seismic survey in the Vale enable the Carboniferous Limestone, Old Red Sandstone and Silurian sequences to be mapped in the subsurface. The Old Red Sandstone sequence thins westwards under the southern part of the Vale, and in the southwest corner of the Vale the base of the Old Red Sandstone is interpreted to overstep across the underlying Silurian sequence in an analogous manner to its regional overstep in west Wales. The Precambrian basement surface is not clearly represented on the sections but may coincide with the base of a reflective sequence observed in places along one of the reflection lines. Basement depth estimates from the reflection sections are compared with estimates derived from a new time term analysis of data from long seismic refraction lines. Basement depths remain uncertain to 1–2 km but appear to be greater under the central part of the Vale than under the western part and along the south coastal zone. A linked system of Variscan forethrusts is traced to outcrop in the core of the Cowbridge anticline but none involves major displacement. The Ty'n-y-Nant-Moel Gilau fault system of the South Wales coalfield is shown to be a component of the linked fault system and its current net extension is attributed to Mesozoic reactivation of a Variscan thrust involving only limited displacement. The individual thrusts appear to connect to a basal thrust that may extend northwards into or under the South Wales coalfield. The amount of displacement along the basal thrust cannot be determined reliably but it may exceed 10 km and involve large scale repetition of Palaeozoic sequences under the Vale.
Caledonian plutonism and major lineaments in the SW Scottish Highlands
Authors: JACQUES J. M. , REAVY R. J.
Published: December 2007

Within the SW Grampian Highlands several NE–SW-trending shear zones and faults related to the Caledonian transpressional collision are recognized as being distinct from an intersect­ing set of NW–SE-trending pre-Caledonian crustal lineaments which were reactivated during Caledonian orogenesis. The geochemical and isotopic characteristics of the 425–400 Ma granitoids of this region show that they were derived by anatexis of the lower crust associated with a mantle component which provided an influx of mantle heat and/or metasomatic fluids; their spatial distribution suggests a close genetic relationship with Caledonian shear zones. Having made the fundamental distinction between ascent (transport) and emplacement (arrival) configurations possible for granitoid magmas, new data are presented for these plutons which show that: (i) a common modal sequence of intrusive phases can be recognized; (ii) these phases are all sited at shear zone or lineament intersections where transtensional zones allowed and facilitated ascent; (iii) emplacement was often by a process of localized
in situ
ballooning. The existence of such lineaments in these orientations in the SW Highlands may indicate that the structure of the lower crust can be regarded as a series of blocks bounded by intersecting ductile zones of high strain. The establishment of such a pattern of structural interactions within the lower crust could provide a mechanistic framework within which the location of anatectic zones, siting and ascent pathways and any subsequent emplacement phenomena can be explained in orogenic belts.
Thermobarometric constraints on the conditions of metamorphism in the Canigou massif, Pyrenees: implications for Hercynian geothermal gradients
Authors: GIBSON R. L. , BICKLE M. J.
Published: December 2007

Quantitative thermobarometry of garnet + biotite + sillimanite f cordierite pelitic assemblages from the Canigou massif, and constraints based on consideration of high-grade metapelitic reaction equilibria, indicate that peak temperatures during Hercynian metamorphism reached 725 ± 25°C at depths of 16 = 2 km (4.5 ± 0.5 kbar). This corresponds to an average peak geothermal gradient of 45–50°C km
−1
, which is in broad agreement with results from studies of granulite-facies assemblages in the Pyrenees, but is significantly lower than gradients proposed for some other amphibolite-facies areas in the terrane. It is suggested that the claims by numerous authors for peak Hereynian geothermal gradients in the Pyrenees in excess of 70–100°C km
−1
fail to consider the effects of post-metamorphic attenuation of metamorphic sequences and the unreliable nature of
P
estimates made in the absence of suitable assemblages for quantitative thermobarometry.
Sm–Nd isotopic characteristics of sedimentary provenance: the Windermere Supergroup of NW England
Authors: McCAFFREY W. D.
Published: December 2007

Nd model ages of Windermere Supergroup sediments increase from the upper Ashgill to the upper Ludlow. Below the lower Llandovery, increasing
t
DM
reflects mixing between the underlying Borrowdale Volcanic Group and hemipelagic detritus, possibly sourced from the Lauren-tian margin. The ongoing rise of
t
DM
into the upper Ludlow probably reflects the growing influence of sediment sourced from the Scandian Orogen. A Pøiadoli drop in
t
DM
is interpreted as recording the re-establishment of supply from the local Laurentian margin: north to south sediment dispersal indicating the effective demise of the Iapetus Ocean as a barrier to sediment dispersal.
Classification of Carboniferous non-marine bivalves: systematics versus stratigraphy
Authors: VASEY G. M.
Published: December 2007

Carboniferous non-marine bivalves are usually classified at the ‘species’ level using external morphological criteria through comparison with figured and described type specimens. This system of nomenclature has allowed the recognition of stratigraphically useful morphospecies.

Biometric analysis of a large number of shells of the genusAnthraconautaPruvost, collected from the Sydney coalfield, Nova Scotia, suggests. that this system of nomenclature cannot be justified biologically. The genus appears to be morphologically homogeneous in the Upper Carboniferous of Western Europe and North America. Shell shape variation is influenced by mode of life and palaeoenvironment, as suggested by the study of modern analogues and fossil shells. If a biological classification were adopted for this group of fossils, then all their stratigraphical value would be lost.

To reconcile systematics with the needs of stratigraphers, the adoption of a trinomial nomenclature is recommended. The use of cluster analysis has shown that varieties can be identified that correspond morphologically to previously named and described ‘species’. Nomenclature of the form genus, species and variety would be both biologically correct and stratigraphically useful.
Concentration of carbon dioxide in the Late Cretaceous atmosphere
Authors: ANDREWS J. E. , TANDON S. K. , DENNIS P. F.
Published: December 2007

Stable carbon isotope data from Late Cretaceous (Maastrichtian) palaeosols in India are used to estimate the concentration of carbon dioxide in the Late Cretaceous atmosphere. We show that the Maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of CO
2
.This value agrees with an independently modeled value of CO
2
in the Late Cretaceous atmosphere. A low concentration of the greenhouse gas carbon dioxide in the Maastrichtian atmosphere (relative to concentrations in the earlier Cretaceous) is consistent with palaeotemperature information from terrestrial plant and marine fossils, which suggest that the global climate cooled toward the end of the Cretaceous Period.
Biogenic acid rain during the Late Cretaceous as a possible cause of extinctions
Authors: ROBINSON N. D.
Published: December 2007

Modern-day coccolithophorids are known to be the most significant producers of dimethylsulphide (DMS) in the marine phytoplankton. Part of this DMS passes from the seawater into the atmosphere, where it oxidizes to form H
2
SO
4
and falls as acid rain. During the Late Cretaceous coccolithophorids were superabundant, their remains now forming the Cretaceous Chalk.

The Late Cretaceous transgression gave rise to extensive shelf seas and progressively increased the areal extent of the coccolithophorid’s habitat. Assuming that coccolithophorids produced DMS during the Late Cretaceous, it is likely that acid rainfall was common and that the level of acidification of the atmosphere increased progressively, in parallel with the progress of the transgression. The increasing rate of extinctions documented by the Late Cretaceous fossil record may therefore be a reflection of an increasing level of acidification of the atmosphere during this period.
Complex cementation textures and authigenic mineral assemblages in Recent concretions from the Lincolnshire Wash (east coast, UK) driven by Fe(0) to Fe(II) oxidation
Authors: Al-AGHA M. R. , BURLEY S. D. , CURTIS C. D. , ESSON J.
Published: December 2007

Concretions are common in some of the modern intertidal sediments on the Lincolnshire coast of the Wash. The mineralogy and geochemistry of numerous examples of these concretions have been studied in detail. The majority have metallic nuclei and those that do not, exhibit textures which suggest that they originally did so. Petrographic observations indicate that the cements within these concretions precipitated in a distinct sequence that is spatially developed around the metallic nucleus and that are arranged from core to periphery: (a) a ferrous hydroxy chloride mineral (similar in bulk composition to akaganeite) together with iron monosulphide (amorphous FeS and mackinawite), pyrite and possibly elemental sulphur; (b) ferroan carbonate cements (including siderite, ankerite and calcite); (c) mixed ferrous and ferric minerals (“green rust” together with magnetite and possibly greigite); (d) fully oxidized minerals (including akaganeite, goethite, hematite, gypsum and a complex basic sulphate of Fe, Ca, Mg, Si and Al). This latter material has not been possible to characterize fully but is probably an amorphous mixture.

The initiating reaction for the precipitation of these cements is anaerobic corrosion of iron at zero valence state with sulphate as an oxidant. Metal, hydroxide and monosulphide are found in close spatial association, indicating the reaction:

4

Fe

0

+
S

O
4

2
−

+
4

H
2

O
→
3
Fe

(
OH
)

2

+
2

OH

−

+
FeS

Further away from the metallic nucleus, carbonates cement the host clastic sediment. These are the products of reaction between the first-formed hydroxides and pore water solutes (principally HCO
−3
, Mg
2+
and Ca
2+
). When oxygen gains access to the growing concretion, Fe(II) minerals are replaced very rapidly by akaganeite and either goethite or hematite. Gypsum and other sulphate minerals also precipitate as new cements around the periphery of the concretions.

The cementation process in these concretions is driven by the extreme instability of metallic iron (here, relic military armaments and shrapnel fragments) in contact with saline, anaerobic water and is indicative more of cathodic corrosion than the growth of ancient carbonate–sulphide concretions.
Early silica diagenetic fabrics in Late Quaternary sediments, south India
Authors: GARDNER R. A. M. , HENDRY D. A.
Published: December 2007

Late Pleistocene aeolian and marine sediments on the coastal plain of south India show extensive evidence of very early diagenetic change that has involved the leaching of original carbonates and subsequent lithification of the sediments by opal-A. The diagenesis is closely associated with both intense pedological weathering of the sands in the vadose environment and the former presence of roots. Silica rhizoliths (petrifactions and micro-petrifactions) are major components of the diagenetic fabric together with pore-filling opaline silica precipitates. Three distinct fabric types can be identified within the diagenetic profile: an upper deeply weathered fabric with a matrix of clays and iron oxides and limited preservation of silica petrifactions and clay root cutans (tubules); a mid-profile, mottled fabric having a distinctive high porosity and in which well-preserved silica petrifactions and micro-petrifactions are best developed, together with opaline silica cements and clay root cutans; and a lower profile fabric in which less common silica petrifactions occur within carbonate-cemented sediments. The early diagenetic fabrics, the first described of their kind, provide evidence of widespread and rapid silicification of organic matter in a vadose, seasonally moist, tropical weathering environment. As such, they have potentially important implications for the interpretation of silica diagenesis in the terrestrial geological record.
Tertiary and pre-Tertiary palaeosurfaces: recognition, reconstruction and environmental interpretation
Authors: WIDDOWSON M.
Published: December 2007

A meeting embracing current research on palaeosurfaces in the geological record was convened by M. Widdowson at the Department of Earth Sciences, Sheffield University on the 15–16 April 1994. The meeting attracted over 40 participants from Europe, and comprised 16 talks in five sessions. A discussion forum followed the final presentation.

The meeting aimed to provide a UK venue for presentation of current palaeosurface research, and a forum for multi-disciplinary discussion. It forms part of the UK contribution to the current
IGCP 317

Paleoweathering Records and Paleosurfaces.

Contributions from the fields of geomorphology, geology, geochemistry, palynology, and palaeoenvironmental studies were represented and included studies of lateritization and bauxitization, palaeokarstification, geochemistry of rock alteration, and the preservation of ancient palaeosurface elements in both glaciated and tropical terrains. The areas of study were widespread and included research from Australia, Africa, Europe, Scandinavia, Sri Lanka, and India. Presentations incorporated discussion of aspects of evolution, reconstruction, and palaeo-environmental interpretation of ancient palaeosurfaces

Following a brief welcome by
D. A. Spears
on behalf .of the Sheffield University Earth Sciences Department, the morning sessions were chaired by
M. Widdowson,
the first of which began with a presentation by
D. Subasinghe
(PRIS, Reading University), who outlined the effects of silicification and associated phophatization in a Sri Lankan saprolite derived from Precambrian apatite-bearing marbles. Diagenetic processes involving the chemical replacement of primary apatite crystals during the silicification have lead to mobilization of phosphorus resulting in complex patterns of phosphate depletion and enrichment: these currently form the economically
Hydration during uplift is recorded by reset Rb–Sr whole-rock ages
Authors: EVANS J. A. , MILLAR I. L. , NOBLE S. R.
Published: December 2007

The Garn Fadryn sub-volcanic intrusion of N Wales gives a U–Pb zircon age of 4533 ± 2.2 Ma. This is the first reliable emplacement age from the Welsh Caradoc volcanic province proving that the Rb–Sr whole rock age of 392 ± 32 Ma does not date intrusion but reflects resetting during early Devonian low-grade metamorphism. Resetting in this setting is chemically controlled and is a function of disturbance during water rock interaction; it is not analogous to the predominantly thermally controlled resetting of K–Ar systems. Post-volcanism Rb–Sr whole rock secondary ages in this region have a mean age of 399 ± 9 Ma and record a specific ‘event’ which is the time of hydration. It is proposed that this event was triggered by uplift which opened fractures, increased permeability, facilitated formation of secondary hydrated minerals and reset the Rb-Sr system. This model for resetting should have widespread applicability to other volcanic provinces affected by low-grade metamorphism.
Partial melting of subducted continental lower crust in the Pyrenees
Authors: POUS J. , MUÑOZ J. A. , LEDO J. J. , LIESA M.
Published: December 2007

A magnetotelluric profile through the Central Pyrenees indicates the présence of very high conductive zones at lower crustal and upper mantle depths. High conductivity at upper mantle depths is interpreted as partial melts within subducted lower crust, whereas high conductivity at lower crustal depths is interpreted as rising magmas derived from the melting crustal slab. Such melts suggest that the continental lower crust, together with its lithospheric mantle may have been subducted into the mantle during the Pyrenean continental collision. Thus, magma generation can be related to thermal reequilibration of a subducted lower crust, a scenario that may serve as a model for understanding the late evolution of other collisional orogens.
An early Cambrian assignment for the Caerfai Group of South Wales
Authors: SIVETER D. J. , WILLIAMS M.
Published: December 2007

The existence of the early Cambrian in South Wales is demonstrated. The ostracode
Indiana lentiformis
occurs in the Caerfai Bay Shales, South Wales and the Olenellid Zone Red Callavia Sandstone, Comley, Shropshire. The Caerfai Group (basal Conglomerate, St Non's Sandstone, Caerfai Bay Shales, Caerbwdy Sandstone) of South Wales is therefore correlatable with the Lower Comley Group of Shropshire. The Conglomerate and St Non's Sandstone are inferred to correlate with the 'Non-trilobite' Zone and eady part of the Olenellid Zone of Shropshire. The early or mid-Cambrian age of the Caerhwdy Sandstone and the definition of the Protolenid-Strenuellid Zone in South Wales remain undetermined.
Silurian turbidites used to reconstruct a volcanic terrain and its Mesoproterozoic basement in the Irish Caledonides
Authors: MENUGE J. F. , WILLIAMS D. M. , O'CONNOR P. D.
Published: December 2007

The Lettergesh Formation, Co. Galway, Ireland, comprises a 1.5 km thick sequence of turbidites deposited
c.
430 Ma ago during closure of the Iapetus Ocean. Petrographic and geochemical data show that the turbidites consist overwhelmingly of detritus derived from a young volcanic terrain. Palaeocurrent data indicate that the detritus was derived from the north. Modelling of the chemical compositions of the turbidites indicates provenance from a high-K calc-alkaline, subduction-related volcanic province built on continental crust. A subordinate ultrabasic component may represent detritus from either an ophiolite or tectonically emplaced serpentinite. The turbidites are characterized by low variability of initial ɛ
Nd
(−6.5 to −3.2) and highly variable initial
87
Sr/
86
Sr ratios. Modelling of the isotopic data suggests a mean crustal residence age of 1440–1600 Ma for the continental foundation of the volcanic terrain. Such a model age is consistent with a mixture of crust having
T
DM
ages of
c.
1.9 Ga and c. 1.3 Ga, both of which are known from the Annagh Gneiss Complex of NW Ireland.
40
Ar/
39
Ar chronology, petrology and geodynamic setting of Mesozoic to early Cenozoic magmatism from the Benue Trough, Nigeria
Authors: MALUSKI H. , COULON C. , POPOFF M. , BAUDIN P.
Published: December 2007

The Benue Trough is a continental-scale intraplate tectonic megastructure which is part of Mid-African Rift System. This rift, initiated in the latest Jurassic, was related to the opening of the Central and South Atlantic oceans. Mesozoic to early Cenozoic magmatism accompanied this evolution. Two principal magmatic domains are evident, the Northern and Southern Benue. In the northern domain, magmatism is characterized by transitional alkaline basalts and transitional tholeiitic basalts. Acidic magmatism of peralkaline nature is also present. In the Southern Benue, several magmatic districts exhibit alkaline or tholeiitic affinities. A detailed chronology of emplacement of this volcanism has been established using the
40
Ar/
39
Ar radiometric method which lead to recognition of three periods of magmatic activity: (1) 147–106 Ma, well expressed in the Northern Benue represefited by transitional basaltic types; (2) 97–81 Ma, occurring only in the Southern Benue, represented exclusively by alkaline intrusive rocks; (3) 68–49 Ma, restricted also to the Southern Benue, with alkaline intrusions followed by tholeiitic subvolcanic rocks. In the light of the general geodynamic evolution, a scenario is proposed, supported by the three chronological periods. The late Jurassic to Albian magmatism occurred when the Equatorial Atlantic was still closed, contemporaneous with the NE Brazilian magmatism. Both magmatism could represent the forerunners of opening of the Equatorial Atlantic. This activity occurred under a general extensional regime during which crustal strike-slip faults gave rise to the emplacement of transitional alkaline basalts. Transitional tholeiitic basalts erupted along normal faults. The second period of activity, Cenomanian to Santonian, restricted to the Southern Benue, occurred after the opening of Atlantic Ocean during a period of decreasing extension. This period ended with a Santonian compressional episode. The last period of activity, from late Maastrichtian to Eocene, is characterized by subsidence, generated as an isostatic response to the Early Cretaceous crustal thinning and post-rift thermal relaxation of the lithosphere, expressed by Tertiary E–W extension.
Metamorphism and cooling of the NE Dalradian
Authors: DEMPSTER T. J. , HUDSON N. F. C. , ROGERS G.
Published: December 2007

The Buchan area of Dalradian rocks represents a distinct tectonothermal domain within the Scottish Highlands, and the Portsoy-Duchray Hill lineament on the western margin of this block is one of the best examples of a long-lived domain boundary. Rb-Sr mica cooling ages, from metamorphic rocks from across the trace of this lineament, document a prolonged Ordovician cooling history. Delayed, but then relatively rapid, cooling to the west of the Portsoy-Duchray Hill lineament is recognized whereas to the east the age data point to a high heat flow regime lasting more than 50 Ma. The isotopic ages suggest that
c.
460 Ma was a time of active tectonism, resulting in final cooling of the low-grade rocks and differential uplift and rapid cooling of deeper structural levels to the west. The radiometric ages do not support previous tectonic models for the region that have invoked thrust thickening along the line of the Portsoy-Duchray Hill lineament and a new model for the metamorphism is proposed. The overprinting of andalusite-bearing assemblages by kyanite to the west of the Portsoy-Duchray Hill lineament is linked to pressure increases associated with the intrusion of the Newer Gabbros and represents a magmatic loading related to the same tectonothermal event that generated the low-pressure metamorphism, rather than a separate tectonic episode.
A Neoproterozoic multi-phase rift sequence: the Grampian and Appin groups of the southwestern Monadhliath Mountains of Scotland
Authors: GLOVER B. W. , KEY R. M. , MAY F. , CLARK G. C. , PHILLIPS E. R. , CHACKSFIELD B. C.
Published: December 2007

The Grampian and Appin groups of the southwestern Monadhliath Mountains form the earliest known syn-rift sequences of the Scottish central Highlands. They were likely to have formed in an intracontinental setting and represent deposition of mixed clastic and carbonate shallow and deep marine strata.

The Grampian Group of the southern Monadhliath Mountains was deposited during a period of initial basin rifting (NW–SE extension) followed by a phase of thermal subsidence. Syn-rift sediments comprise a 2.5–6 km thick turbidite system. Thermal subsidence brought about the basinward progradation of shallow marine shelf sediments resulting in the infilling of pre-existing basin topography.

The overlying Appin Group commenced with deposition of a shallow marine sequence alternating between nearshore tidal sand and offshore mud deposition. This formed in response to renewed rifting and concomitant subsidence. Accelerated rifting resulted in localized footwall uplift and erosion while sedimentation continued in the hanging-wall areas. Resultant subsidence, perhaps partly thermally driven, caused gradual basin widening and produced an onlapping marine sequence. There followed a period of progressive clastic deprivation when carbonates were precipitated, and at the onset of anoxic conditions, deposition of organic muds.

The fundamental structural elements responsible for the formation of the Grampian and Appin group basins were also influential in the orogenic evolution of the basin-fill. Half-graben fills were deformed to produce regionally extensive folds such as the Stob Ban–Craig a’ Chail Synform.
Late Devensian and Holocene shorelines of the British Isles and North Sea from models of glacio-hydro-isostatic rebound
Authors: LAMBECK K.
Published: December 2007

Sea-level change around the British Isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern Britain and the concomitant melt-water loading of the adjacent seas and Atlantic Ocean. Minor, but not insignificant, contributions also result from the rebound caused by the unloading of the distant ice sheets, including Fennoscandia and North America. Observations of sea-level change for this period constrain the glacio-hydro-isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity, as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum. The models permit palaeobathymetry and palaeoshorelines to be predicted for the British Isles region, including the North Sea. The resulting evolution of the coastlines exhibits a complex behaviour through time, one that is quite different from the usual models in which sea-level change is assumed to be a function of time only. In part this is because of the delayed response of the mantle to the spatially variable and time-dependent ice and water loads, and in part because the unloading history of the British ice sheet is different from those of the major global ice sheets. Thus, maximum emergence of the North Sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 (radiocarbon) years BP. During this relative sea-level still-stand shoreline features could have formed, for example, along the western edge of the Norwegian Trough when access to the firths of eastern Scotland would have been via a long and shallow marine inlet. Shoreline retreat across the North Sea became relatively rapid after about 10000 years. The model predictions for the Irish and Celtic Seas also suggest a complex behaviour, with the formation of a wide land bridge between about 20000 and 13 000 years ago. The model also suggests that as long as the Scottish ice extended across the northern Irish Sea, until about 14 000 years ago, there would have been a large freshwater periglacial lake located further south. Both the predicted sea-level height-age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur, particularly in northern Scotland and Ireland where the ice heights may have been somewhat greater than assumed in the model.
Wenlock (Silurian) oceanic episodes and events
Authors: JEPPSSON L. , ALDRIDGE R. J. , DORNING K. J.
Published: December 2007

Biotic and sedimentological cycles in the Wenlock are related to episodic changes in oceanic state. These may be explained by alternations between primo and secundo conditions, the former being characterized by cold oceanic bottom waters and high nutrient supply, and the latter by salinity-dense bottom waters and diminished nutrient supply. The lithological pattern, together with the turnover of conodont faunas and of other fossil groups, permits the identification of a sequence of episodes and events in the Wenlock, following the extinctions associated with the earliest Wenlock Ireviken Event: the Vattenfallet Secundo Episode, the Sanda Primo Episode, the Boge Event, the Lansa Secundo Episode, the Allekvia Primo Episode, the Valleviken Event, the Hellvi Secundo Episode, the Mulde Event and the Klinte Secundo Episode. The Mulde Event differs from others in separating two secundo episodes, and may represent an interval when deep waters remained saline and vertical circulation virtually ceased. The effects of the events and episodes were stronger in the early and late Wenlock than in the middle part of the epoch.
Constraints on the early Cambrian radiation and correlation of the Tommotian and Nemakit-Daldynian regional stages of eastern Siberia
Authors: VIDAL G. , MOCZYDLOWSKA M. , RUDAVSKAYA V. R.
Published: December 2007

Acritarchs of early Cambrian age occur in strata attributed to the Middle Tommotian in northeastern Siberia. A diagnostic assemblage from a part of the Tyusersk Formation referred to the
Dokidocyathus regularis
Zone (Middle Tommotian) at Chekurovka, and a much poorer assemblage from Ulakhan-Aldyarkhay, indicate time-equivalence with the
Heliosphaeridium dissimilare–Skiagia ciliosa
acritarch Zone and the correlative
Holmia kjerulfi
trilobite Zone in Baltica. The bulk of the species turnover which is part of the Cambrian explosion, including archaeocyathans, small shelly fossils, trilobites and acritarchs, is inferred to occur in the
Skiagia ornate–Fimbriaglomerella membra-nacea
(=
Schmidtiellus/Rusophycus
faunal zone) and
H. dissimilare–S. ciliosa
(=
Holmia kjerulfi
trilobite Zone) acritarch zones.
Transfer zones in the southern Rio Grande rift
Authors: MACK G. H. , SEAGER W. R.
Published: December 2007

Despite recent interest in transfer zones in regions of continental extension, their detailed geometry and kinematics remain unclear. Four late Palaeogene and Neogene transfer zones within the southern Rio Grande rift, USA, are described, based on geological mapping at the scale of 1:24 000 and analysis of synrift stratigraphy. The Cutter Sag transfer zone is located between the overlapping tips of north-trending, west-dipping faults, and is characterized by a north-dipping structural ramp segmented by closely spaced, NE-trending normal faults. Similarly, the West Potrillo transfer zone occupies a position in the zone of overlap of north-trending, west-dipping faults, but the structural details of the transfer zone are largely hidden beneath Quaternary lava flows. However, isolated bedrock exposures outside the lava field, gravity data, and the alignment of cinder cones suggest that the West Potrillo transfer zone is a NW-dipping synclinal ramp cut by NE-trending fractures and/or faults. Positioned between north-trending, overlapping border faults that dip toward each other, the Cedar Hills transfer zone is a broad, north-trending arch whose summit collapsed into a graben along a series of north-trending normal faults. The Rincon transfer zone separates border faults that do not overlap and has a long history of faulting and sedimentation beginning in latest Oligocene and extending into the Quaternary.

With the possible exception of reactivated early Tertiary compressional structures in the Rincon transfer zone, the transfer zones described here do not appear to be influenced by pre-rift zones of weakness. However, the Cutter Sag and West Potrillo transfer zones are preferred sites of basaltic volcanism, and the Cutter Sag.- Rincon, and Cedar Hill transfer zones influenced the location of the Plio-Pleistocene ancestral Rio Grande.
Facies analysis in the Lower Greensand using ground-penetrating radar
Authors: BRISTOW CHARLIE
Published: December 2007

This paper presents the results of a ground-penetrating radar survey in the Woburn Sands Formation, Lower Greensand Group near Leighton Buzzard. A total of almost 4 km of survey has been acquired to investigate the internal structure of the sands. The radar survey achieved a resolution on the order of tens of centimetres with penetration up to 10 m and revealed a variety of horizontal, dipping and curved reflectors. The reflections are interpreted using seismic interpretation methodology. Two scales of unconformity-defined radar sequences are described. First-order radar sequence boundaries can be identified at the termination of primary reflectors. Second-order radar sequence boundaries can be identified at the terminations of both primary reflectors and first-order surfaces. First-order radar sequence boundaries are interpreted as reactivation surfaces within bedforms which are produced by changes in bedform geometry in response to a change in hydraulic regime or superimposed bedforms. Second-order surfaces are interpreted as the product of bedform migration. Reflection character and geometry are described and form the basis of a ground-penetrating radar facies analysis. Nine different radar facies have been identified. These are interpreted as large sets of planar cross-stratification, sets of trough cross-stratification, cosets of cross-stratification, tidal bundles, clay drapes, diagenetic concretions and possibly bioturbated sands. A reconstruction of the bedforms suggests that they were formed by very large curved crested dunes. These interpretations are checked against outcrop as the sands are excavated in working sand pits.
Neogene supra-subduction zone extension in the Polis graben system, west Cyprus
Authors: PAYNE ANNE S. , ROBERTSON ALASTAIR H. F.
Published: December 2007

The Neotectonic Polis graben and adjacent Pegia half-graben in west Cyprus are extensional basins developed within the convergent tectonic regime of the Eastern Mediterranean. Both basins contain an early fill of Miocene carbonates including reef limestones. Messinian extension, oriented ENE–WSW, produced the asymmetrically faulted Polis graben structure. Evaporites were deposited in the south of the area while unconformity surfaces developed in the north. Pliocene mark and chalks were then deposited in a relatively quiescent phase in the north of the graben, while faulting continued into the Early Pliocene in the south. Plio-Pleistocene to Recent sediments record regional uplift of Cyprus. Contemporaneous NNE–SSW-oriented extension formed the Pegia half-graben and renewed minor faulting in the Polis graben.

The extensional structures of the Polis graben system are thought to result from extension above a subduction zone located south of Cyprus, driven by subduction 'roll-back' and trench migration. Accelerated convergence and rapid roll-back during Late Miocene times caused the first stage of extension, whilst the Plio-Pleistocene faulting was driven by differential extension in the overriding plate as the Eratosthenes Seamount collided with the trench and locally impeded subduction. The Polis graben system may provide a model for the early stages of development of major suprasubduction zone extensional areas such as the Aegean region.
Syn-rift sedimentation and structural development of the Gediz and Büyük Menderes graben, western Turkey
Authors: COHEN H. A. , DART C. J. , AKYÜZ H. S. , BARKA A.
Published: December 2007

The Büyük Menderes and Gediz graben of western Turkey developed during Miocene to Recent extension in the Aegean region. New mapping of structures and sedimentary lithofacies in exhumed basin-fill strata is used to reconstruct the evolution of the graben. Field evidence shows that extension was primarily accommodated by tilted fault-blocks 0.2–0.8 km wide, bounded by planar faults, with some modification by antithetic faulting. The basins are faulted on both margins, although they are highly asymmetric, with dominant 'footwall' margins characterized by steeper topography and greater thicknesses of exhumed strata. Within exhumed graben-fill sequences, lacustrine, axial fluvial, and laterally-derived sedimentary facies can be identified. Palaeocurrent orientations, divergent wedge geometries and intra-basin unconformities all indicate that exposed sediments are syn-tectonic. The present day map patterns demonstrate that the position of graben-bounding faults has migrated basinward with time. As a result, large-scale erosion and recycling of the uplifted basin fill have created extensive footwall-derived alluvial fans. These displace the axial drainage towards the hanging-wall margins, away from the locus of greatest subsidence.
Early Cambrian carbonatite in Antarctica
Authors: HALL C. E. , COOPER A. F. , PARKINSON D. L.
Published: December 2007

Nepheline syenite bodies intrude the basement, Koettlitz Group, gneisses of the Transant-arctic Mountains of South Victoria Land, Antarctica. A calcite–fluorite–biotite–alkali feldspar dyke has mineralogical, trace element, stable isotope, and radiogenic isotope characteristics similar to the host syenite and distinct from the country rock, Koettlitz Group, marble. The dyke is interpreted as the first carbonatite to be described from Antarctica. Zircon in the carbonatite has been dated by U–Pb techniques as 531±5.5 Ma, early Cambrian. This age occurs within the range of metamorphism, deformation and subduction-related granitoid intrusive events associated with the Ross Orogeny. Whether the nepheline syenite and carbonatite igneous activity occurred strictly contemporaneously with plate convergence and granitoid genesis or marks an extensional interlude, awaits the detailed unravelling of tectonic events along this segment of the Neoproterozoic to early Cambrian margin of Antarctica.
Evidence for Caledonian sinistral strike-slip motion and associated fault zone weakening, Outer Hebrides Fault Zone, NW Scotland
Authors: BUTLER C. A. , HOLDSWORTH R. E. , STRACHAN R. A.
Published: December 2007

The Outer Hebrides Fault Zone is a major ESE-dipping reactivated fault within the Lewisian gneisses of the Laurentian craton in NW Scotland. Early thrust structures are overprinted by a network of retrograde ductile shear zones in which fluid channelling has hydrated the pre-existing basement rocks at low temperatures, forming chlorite-white mica phyllonites in regions of highest strain. Strike-parallel mineral lineations and shear-sense indicators suggest sinistral displacements that are thought to be late Caledonian based on isotopic data and regional considerations. The phyllonites have focused extensional movements that overprint strike-slip fabrics and may control the location of the Mesozoic Sea of Hebrides and Minch basins.
New evidence for Neoarchaean, hydrothermally altered granites in south-central Botswana
Authors: KAMO S. L. , KEY R. M. , DANIELS L. R. M.
Published: December 2007

Recent drilling in south-central Botswana intersected hydrothermally altered dolerite and granitic rocks beneath Karoo strata on the western side of a domical structure. This structure occurs within the western part of the Kaapvaal Craton and is bounded to the west by the N-trending Palaeoproterozoic Kheis Belt. U–Pb dating of zircon and titanite from the cored granitic rock gives an age of 2928 ± 4 Ma, which provides a temporal correlation with hydrothermally altered rocks along the northern margin of the, Witwatersrand basin, South Africa. These hydrothermally altered rocks may form part of the source area for the Neoarchaeau Witwatersrand gold deposits. The age also indicates that the Kaapvaal Craton extends as far west as Mabuasehube.
The relationship between bitumens and mineralization in the South Pennine Orefield, central England
Authors: EWBANK G. , MANNING D. A. C. , ABBOTT G. D.
Published: December 2007

Like many examples of Mississippi Valley-type mineralization, the South Pennine Orefield is well-known for the occurrence of hydrocarbons within hydrothermal mineral veins. Bitumens from this area along with oils from the East Midlands have been characterized using standard organic geochemical techniques and compared with potential source rocks. Lower Namurian mudstones from the Widmerpool Gulf and the Gainsborough and Goyt Troughs were rejected as possible sources for the bitumens and oils on the grounds of lack of sufficient thermal maturity and/or essential biomarker correlation. Lower Namurian mudstones with type II kerogen from the Edale Gulf are proposed to offer a likely hydrocarbon source for the area, with a minor, more localized contribution from organic-rich type II mudstone partings within the Dinantian limestones. Simple geochemical models, consistent with recent sequence stratigraphic interpretation, suggest a late Carboniferous age for hydrocarbon generation, where geothermal gradients were slightly higher (
c
.50°C km
−1
) than the present day.

Microthermometric analysis of fluid inclusions from fluorite and calcite allowed three fluid types to be distinguished. One Na–Ca–Cl bearing fluid was discerned to be dominant throughout the orefield, being of low temperature (uncorrected
T
h
= 70-110 °C) and high salinity (c. 20equiv. wt% NaCl). A second high salinity Na–Ca–Cl fluid (uncorrected
T
h
= 70-120 °C,
c
. 24equiv. wt% NaCl), distinguished from the first by varying Na-Ca contents, was observed in the westernmost extremities of the orefield. A third NaCl bearing fluid of higher temperature
(T
h
= 100-145 °C) and lower salinity (4 wt% NaCl) was detected in the northernmost part of the orefield. Hydrocarbon-bearing inclusions were not observed in any of the three fluids in this study. Sulphur isotopic analyses performed on a selection of sulphides, sulphates and bitumens to gauge the role of organic matter in sulphate reduction reactions proved inconclusive. The mineralization is thought to have occurred as several events. That in the north is thought to be derived from the dewatering of the Edale Gulf towards the end of the Carboniferous, whilst other mineralization events occurred from the early Permian onwards, with the ore fluids having more distal sources, predominantly from the east with a minor input from the west.

The main phases of hydrocarbon generation and mineralization appear to be unrelated.
Geochronology and stratigraphy of the Roque Nublo Cycle, Gran Canaria, Canary Islands
Authors: PÉREZ-TORRADO F. J. , CARRACEDO J. C. , MANGAS J.
Published: December 2007

The Roque Nublo Cycle, of Pliocene age, is the second main cycle of subaerial volcanic activity in Gran Canaria. During this cycle a stratovolcano at least 2500 m high developed in the central part of the island; its volcanic products covered an area of about 540 km
2
. The detailed stratigraphy of the Roque Nublo Cycle, together with a magnetostratigraphic study and six new K–Ar dates, which complement 22 previously published ones, have led to the reconstruction of the volcanic history of this cycle in which six main stages have been distinguished.

The revised chronology of the Roque Nublo Cycle implies an overlap in age with the earliest rocks of the third cycle of subaerial activity in Gran Canaria. No volcanic hiatus occurred between the second and third cycles, as was previously thought to be the case.
Syntectonic burial and post-tectonic exhumation of the southern Pyrenees foreland fold–thrust belt
Authors: CONEY P. J. , MUÑOZ J. A. , McCLAY K. R. , EVENCHICK C. A.
Published: December 2007

In the Oligocene to earliest Miocene the entire southern Pyrenean foreland fold and thrust belt was backfilled and buried in up to 3 km of syntectonic continental conglomerates from the range's own erosional debris. Then, starting in the mid to late Miocene, the Pyrenees were exhumed by erosional excavation to their present relief. A model is proposed for this unusual development whereby late Eocene–Oligocene tectonic uplift of the margins of the Ebro basin raised local base level and blocked normal dispersal of erosional debris to adjacent oceans, thus causing the basin to fill then backfill northwards across the entire southern flank of the Pyrenees. Subsequent Miocene rifting of the Catalan Mediterranean margin, and the Messinian salinity crisis, lowered base level allowing the Ebro River to cut headward, capture the Ebro basin, and re-excavate the Pyrenees.
The tectonic setting and earthquake ground hazards of the 1993 Pyrgos earthquake, Peloponnese, Greece
Authors: KOUKOUVELAS I. , MPRESIAKAS A. , SOKOS E. , DOUTSOS T.
Published: December 2007

The Pyrgos earthquake in western Greece (26 March 1993) (
M
L
= 5.2) was caused by oblique-normal slip on a north-dipping and WNW-trending fault, and produced significant damage in the town of Pyrgos. Several lines of evidence from the epicentral area suggest that faults within two active graben in the Pyrgos basin, the Grape and Alfios grabens, were reactivated during this earthquake and subsequent aftershocks. Evaluation of morphotectonic data, the fault slip-rate between 0.05 and 0.35 mm a
−1
and seismic activity associated with the 1993 earthquake, suggest that the Alfios graben is the most active structure in the basin. This graben, which is 25 km long and crosses the Pyrgos basin, is segmented along its strike by transfer zones. Analysis of the seismic activity in this graben shows that transfer zones are the focus for the concentration of seismic activity and thus the concept of transfer zones is important for understanding the Pyrgos earthquake.

The 1993 earthquake caused landslides at 47 locations and liquefaction phenomena at 7 localities within an area of 145 km
2
. The lower threshold level to induce landslides was
M
L
= 4.0 and to induce liquefaction was 5.0. The majority of landslides occurred along fault scarps and either caused the slope to retreat and/or acted to protect the slope gradient.