bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards a statistical system for palaeontologists
Authors: HARPER D. A. T. , RYAN P. D.
Published: December 2007

Since the pioneer studies of Trueman and others in the 1920s, some palaeontologists have used a considerable variety of statistical techniques to describe and analyse individuals and associations of fossil taxa. The increasing sophistication of the algorithms used partly reflects advancing technology from long-hand calculations to computer-based analyses. A progression from univariate graphical and statistical techniques through bivariate analysis to the more sophisticated multivariate analyses can be illustrated by reference to a series of classic case histories on a wide variety of fossil organisms. Nevertheless, despite the necessity for the accurate description of fossils and fossil assemblages and a framework within which to test hypotheses, statistical analysis in palaeontology is far from routine. Access to powerful microcomputers is now widespread amongst palaeontologists but there is a shortage of specialist software packages designed to meet their needs. The PALSTAT package is one of a number of attempts, using the many advantages of the microcomputer, to provide a centralized system of routine graphical and statistical techniques within an investigative framework. The strategy is illustrated with two case histories.
Deep crustal structure and Carboniferous basin development within the Iapetus convergence zone, northern England
Authors: CHADWICK R. A. , HOLLIDAY D. W.
Published: December 2007

Seismic reflection data from northern England are interpreted to show a northward dipping Caledonian thrust zone lying beneath the faulted southern margin of the Northumberland Trough. The thrust zone lies upon the updip projection of a northward dipping high conductivity layer in the middle and lower crust, identified by magnetotelluric sounding. Together, these features indicate the presence of a crustal-scale Caledonian shear zone, dipping north at an average angle of 20–25°. Extensional reactivation of the middle and upper crustal parts of the shear zone, in Carboniferous times, led to development of the Northumberland Trough. Reappraisal of the BIRPS NEC seismic profile suggests the presence of the same (or similar) crustal shear zone, reactivated to form the offshore extension of the Northumberland Trough. The shear zone probably formed as a major compressive or transpressive feature during late Caledonian (Acadian) continental collision. In the lower crust, the shear zone lies close to, or may actually represent, the Iapetus suture. At middle to upper crustal levels the shear zone lies wholly within Avalonian (English) crust, well to the south of the (faunally determined) Iapetus suture. Westward extrapolation of the shear zone indicates that it may crop out within the northern Lake District, perhaps as the Causey Pike and associated thrusts. The faunal suture is likely to subcrop north of the Lake District and Alston Block, beneath the central part of the Northumberland Trough.
The late Alpine evolution of an extensional shear zone, Naxos, Greece
Authors: BUICK I. S.
Published: December 2007

The mid-Miocene structural evolution of the metamorphic complex on Naxos involved deformation in a kilometre-scale low angle ductile shear zone. The structures described are consistent with exhumation of the metamorphic complex during crustal extension after, and possibly during, localized high temperature Barrovian-style metamorphism. Non-coaxial fabrics developed throughout the structural history indicate that upper levels were transported to the north during ductile extension. This shear Sense is opposite that inferred previously for the development ‘Cordilleran-style metamophic core complexes’ in the Cvclades. Ductile deformation was accompanied during its later stages by E-W directed compression.
Tectono-stratigraphy and evolution of the Mesozoic Pindos ophiolite and related units, northwestern Greece
Authors: JONES GREGORY , ROBERTSON ALASTAIR H. F.
Published: December 2007

The northwest Pindos Mountains expose Mesozoic and Tertiary thrust sheets, which include the Jurassic Pindos ophiolite, composed of ultramafic and mafic oceanic crustal rocks. The tectono-stratigraphy of these units is: (i) mainly ultramafic ophiolitic thrust sheet and basal metamorphic sole (Dramala Complex and Loumnitsa Unit); (ii) Late Cretaceous platformal limestones (Orliakas Group); (iii) dismembered intrusive and extrusive ophiolitic rocks (Aspropotamos Complex): (iv) tectonic melange and olistostromes, dominated by Triassic-Jurassic volcanic and sedimtntary rocks (Avdella Melange); (v) coherent thrust sheets of Late Jurassic–Late Cretaceous deep-water sediments (Dio Dendra Group); (vi) Early Tertiary flysch (Pindos Flysch). Immobile trace-element studies indicate that Triassic and Jurassic extrusives of the volcanic-sedimentary melange formed mainly at within plate and/or mid-ocean ridge settings. By contrast, structurally overlying ophiolitic extrusives include boninitic volcanics and island arc tholeiites, of supra-subduction zone origin. Initial ophiolite displacement (
c
. 165 Ma) is recorded in metamorphic sole formation, including basal peridotite mylonite, amphibolites and greenschists. The sole rocks have MORB and WPB chemical affinities. In our favoured model, the Pindos ophiolite formed above a Mid-Jurassic westerly-dipping intra-oceanic subduction zone, accompanied by accretion to form melange, followed by collision and emplacement with the Pelagonian margin. Final suturing of the Pindos ocean, however did not take place until Early Tertiary times.
Pliocene Burdur basin, SW Turkey: tectonics, seismicity and sedimentation
Authors: PRICE SIMON P. , SCOTT BARRY
Published: December 2007

The Pliocene Burdur Formation of SW Turkey was deposited in a NE-SW trending half-graben with a major basement fault along its SE margin. Hangingwall-sourced fans were confined proximally by basement topography. Distally, they developed 'ideal' fan geometries. These fans became submerged by the lake that occupied the centre of the basin. This transgression was caused by the migration, with time, of the hangingwall pivot away from the basin-controlling fault. Footwall-sourced fans exhibit three distinctly different geometries. At the northern end of the basin a wide braidplain developed due to the rapid erosion of both penecontemporaneous volcaniclastic deposits to the east and the footwall crest of a newly formed fault within the basin. Along the footwall scarp in the central part of the basin a narrow bajada formed. In the south, a large alluvial fan had its source in the relay structure between two left-stepping en echelon fault segments. The small size of footwall-sourced fans compared with those sourced on the hangingwall slope was due to rapid subsidence of the basin floor adjacent to the footwall scarp. Although this suggests high levels of seismicity, the general paucity of wet-sediment deformation within the Burdur Formation indicates that seismicity in the Burdur region during the Pliocene was more subdued than at present.
Devonian basin initiation in East Greenland: a result of sinistral wrench faulting and Caledonian extensional collapse
Authors: LARSEN POUL-HENRIK , BENGAARD HANS-JØRGEN
Published: December 2007

Following the Caledonian orogeny, large scale ESE–WNW extensional faulting and N–S directed sinistral wrenching affected East Greenland leading to the initiation of the Devonian basin. The NNE–SSW trending extensional faults have very large downthrows to the east exceeding 10 km and separate up to 90 km wide fault blocks, which during deformation were tilted approximately 12°. The tilting of one of the fault blocks led to uplift of deep-seated hot crystalline rocks in the eastern part causing contact metamorphism in the adjacent downfaulted block to the east. Based on K-Ar cooling ages, the faulting seems to have taken place during the Middle Devonian around 385 Ma, coinciding with the initiation of deposition within the Devonian basin. A N–S trending sinistral wrench fault zone developed in addition to the extensional faults leading to formation of synthetic and antithetic Riedel shears along the present-day western border of the Devonian basin. The timing of the wrench displacement cannot be younger than Middle Devonian. The extension faults and the wrench fault can be followed as regional structures in East Greenland and can be compared to similar Devonian extensional structures in northern Great Britain and to the major wrench faults in Scotland. No clear separation in time is possible between the extension and the wrenching, and a transtensional kinematic history is the most plausible. The basin-forming tectonic evolution in East Greenland during Middle Devonian can be related to an extensional collapse of an overthickened Caledonian crustal welt associated with wrench deformations due to late Caledonian shear displacements along plate boundaries. This evolution is analogous to the Devonian basin formation in northern Great Britain.
U-Pb zircon ages for Late Precambrian igneous rocks in southern Britain
Authors: TUCKER R. D. , PHARAOH T. C.
Published: December 2007

Seven new U-Pb zircon ages for volcanic and intrusive igneous rocks from southern Britain are as follows: 613 ± 4 Ma for the Coedana Granite, Anglesey, and 614 ± 2 Ma for the Padarn Tuff Formation of the Arfon Group, North Wales; 677 ± 2 Ma for a deformed granite of the Malvernian Complex and 566 ± 2 Ma for a rhyolitic tuff in the Warren House Formation, Malvern Hills; 603 ± 2 Ma for a granophyric diorite ('markfieldite') intrusive into the Caldecote Volcanic Formation at Nuneaton; 566 ± 2 Ma for the Uriconian volcanic group, Shropshire, and 560 ± 1 Ma for the Ercall Granophyre, which is intrusive into Uriconian volcanic rocks. Three of the four dated intrusive rocks contain a component of inherited zircon, but the dated volcanic rocks are composed of simple, single-stage zircon populations with no detectable amount of secondary Pb-loss. The ages clarify the timing of Precambrian magmatic events in southern Britain, and conform well with those in neighbouring Avalonian terranes. The new age of the Ercall Granophyre provides a reliable maximum age for the Early Cambrian (Atdabanian—late Tommotian) strata of England, and reconfirms a Precambrian age for the Padarn Tuff Formation and granophyric diorite ('markfieldite') which demonstrably underlie Early Cambrian strata.
An estuarine facies model for the Middle Jurassic Sleipner Formation: Beryl Embayment, North Sea
Authors: RICHARDS P. C.
Published: December 2007

The Middle Jurassic Sleipner Formation is sub-divided into three units in the Beryl Embayment area of the North Sea. The lowermost two units, the 'Interbedded Unit' and 'Lower Coal Marker', overlie Lower Jurassic marine silts and were probably deposited in progressively shallowing, coastal environments during a eustatic sea level fall. An estuarine deposit overlies the 'Lower Coal Marker', and was deposited following sea level rise or tectonic subsidence of the area. The 'Estuarine Succession' forms the bulk of the Formation, and is composed of seven facies, grouped into three facies associations representing sub-tidal, inter-tidal and salt marsh sub-environments.

The sub-tidal facies association is dominated by sandstones deposited in tidal channels and sand flats. The inter-tidal association is characterized by alternations of sandstone and siltstone on a scale of millimetres to several metres and consists of tidal channel sandstones, lenticular bedded siltstones and other tidally-influenced facies. The salt marsh association is dominated by coals and rooted siltstones, with minor amounts of creek-fill sandstones.

The estuary mouth probably lay towards the northern end of the Embayment, where a connection existed through the Viking Graben to the Boreal Ocean.
Refolded nappes formed during late Archaean terrane assembly, Godthåbsfjord, southern West Greenland
Authors: FRIEND C. R. L. , NUTMAN A. P.
Published: December 2007

Recent work has provided a new tectono-metamorphic framework for the Archaean evolution of the Godthåbsfjord region which can be divided into discrete tectonic units each characterized by different magmatic, structural and metamorphic histories. These tectonic units were assembled in the late Archaean, post-2750 Ma. The present structural patterns seen in the region date from the period 2750–2600 Ma and do not reflect earlier structural events, as was previously considered. Late Archaean structural evolution began with a period of interthrusting of early Archaean sialic and late Archaean oceanic crustal segments coeval with, or followed by, isoclinal nappe formation under amphibolite-facies conditions. Linear fabrics in early Archaean rocks were rotated into parallelism with those newly formed parallel to F1 hinge lines in the late Archaean rocks. A second major thrusting event emplaced granulite facies rocks structurally on top of the amphibolite facies rocks. Subsequent to this event a series of F2 upright or steeply inclined basin and dome structures formed, some of which have sheath morphology. This second folding episode acting upon the isoclinal nappes produced the regional scale interference patterns observed. The early linear fabrics were re-oriented around these second generation structures. Data are produced from selected areas to illustrate the fabric patterns and structural continuity that exists throughout the region.
Experimental compaction of quartz sand at low effective stress and temperature conditions
Authors: SCHUTJENS PETER M. T. M.
Published: December 2007

Experiments have been carried out on dry and fluid-saturated quartz sands to investigate the behaviour during compaction under diagenetic conditions and to evaluate the importance of stress-induced solution transfer ('pressure solution') as a compaction mechanism. The experiments were performed at temperatures (
T
) in the range 150–350°C, applied effective stresses (σ
e
) up to 20.7 MPa and pore fluid pressures (P
1
) of 12.5 and 15.5 MPa, using material with a grain size (
d
) in the range 20–100 μm and an initial porosity of 45–52%. Dry quartz sands underwent significant compac­tion during the loading stage, but showed very little compaction creep once full load was achieved (i.e. essentially time-independent compaction). In contrast, fluid-saturated material at constant applied effective stress showed substantial time-dependent compaction (i.e. creep). With increasing temperature, there is a decreasing number of grains in the wet-compacted sand which show intragranular cracks and an increasing number of grains which show dissolution features at contacts with adjacent grains. In addition, there is a decreasing dependence of the volumetric strain rate, β on σ
e
, with both increasing volumetric strain (e
v
) and increasing σ
e
and a decreasing dependence of β on e
v
with increasing temperature. These observations suggest that, for wet quartz sand, a gradual change might occur from compaction creep controlled by time-dependent microcracking, at
T
= 250–300 °C, to compaction creep controlled by stress-induced intergranular solution transfer at
T
= 300–350 °C.
Infrared monitoring of volcanoes by satellite
Authors: OPPENHEIMER C. M. M. , ROTHERY D. A.
Published: December 2007

Sensors on future satellite platforms will be used routinely for volcano monitoring, with infrared channels offering the potential to detect and measure temperatures of features such as lava bodies and fumarole fields. This is possible even though the surface temperature distributions associated with such phenomena are typically inhomogeneous at the pixel scale, so long as simplifying assumptions can be made. To test the applicability of the technique, we have carried out field studies of a range of volcanic thermal manifestations using portable infrared thermometers. Rock surface temperatures around fumarolic vents exhibit greater stability with time than those associated with actively degassing lava bodies, but in both cases volcanogenic fumes can significantly attenuate the emitted infrared radiation. The scale of the temporal variability, at a given wavelength, dictates the quantitative value of isolated satellite 'snapshots'. If more spectral channels in the infrared were available on remote sensing platforms then more components of the surface temperature distribution could be extracted from the data. Imaging spectrometry offers the greatest flexibility, although data processing, including correction for atmospheric effects, would present difficulties.
Volcano monitoring by microgravity and energy budget analysis
Authors: BROWN G. C. , RYMER H. , STEVENSON D.
Published: December 2007

Microgravity monitoring of active volcanoes can provide evidence of sub-surface mass and/or density changes that precede eruptions. If, in addition, precursory increases in thermal emissions are observed, an integrated mechanistic model for volcanic activity may be developed with the potential for forecasting eruptions. Crater-lake volcanoes provide an interesting target for such studies since thermal output can be monitored simply through lake water calotimetry. Here we summarize 10 years of gravity and thermal data from Poás volcano, Costa Rica. Mass/energy balance calculations demonstrate that, in the steady-state, the large thermal inertia of the crater lake acts as a buffer to short-term changes in the energy input from the cooling magma feeder pipe. Since February 1986, it is postulated that there has been gradual emplacement of a shallow magma intrusion associated with vesiculation and gas loss to the surface. This follows from unambiguous, gravity increases, constrained by elevation control, that are coincident in time with a period of long-term increased energy input to the crater lake. Progressive reduction of the lake volume by evaporation/seepage culminated in an (April 1989) ash eruption providing a good documented record of combined gravity and thermodynamic precursors to volcanic activity.
Resetting of Rb–Sr whole-rock ages during Acadian low-grade metamorphism in North Wales
Authors: EVANS J. A.
Published: December 2007

Ordovician volcanic rocks and associated sub-volcanic intrusions in North Wales give Devonian, metamorphic Rb-Sr whole-rock ages. Isotopic resetting is not confined to acid volcanic rocks. Three intrusions preserve Ordovician ages. The closed system resetting is not directly related to metamorphic grade, but appears to correlate with the extent to which the secondary metamorphic mineral assemblage is developed. Rocks giving Devonian ages have a well developed secondary mineralogy whereas those retaining Ordovician ages are less extensively altered. The metamorphic ages combine to give a Lower Devonian mean age and weighted
2a
error of 399 f 9 Ma. Metamorphism is therefore synchronous with Acadian deformation in the North Wales area.
An Ordovician basalt to peralkaline rhyolite fractionation series from Avoca, Ireland
Authors: McCONNELL B. J. , STILLMAN C. J. , HERTOGEN J.
Published: December 2007

The Upper Ordovician Avoca volcanic rocks host a Kuroko-type massive sulphide deposit in southeast Co. Wicklow, Ireland. Immobile element geochemistry of lavas shows a bimodal subdivision into acid and basic groups. Basalts have characteristics of magmas from both subduction zone and enriched mantle sources, and are interpreted as products of the rifting of a volcanic arc. Rhyolites are highly enriched in HFS-elements and were originally peralkaline. Constant incompatible element ratios throughout the compositional spectrum indicate a fractional crystallization relationship between the basic and acid end members. The basaltic magmas evolved by crystallization of an assemblage in which plagioclase feldspar was an important component, producing large negative Eu anomalies. The transition to peralkalinity is marked by LREE depletion and no further increase in the Eu anomaly, which may represent the interval of minor phase precipitation and fO
2
variation seen in other peralkaline series. A group of acid pyroclastic Avoca volcanic rocks are subalkaline and are probably unrelated to the main evolutionary series. The Avoca volcanic rocks were erupted in an extensional tectonic setting within a continental margin volcanic arc, similar to the contemporaneous Welsh marginal basin.
A guide to stratigraphical procedure
Authors: WHITTAKER A. , COPE J. C. W. , COWIE J. W. , GIBBONS W. , A E. , HAILWOOD  , HOUSE M. R. , JENKINS D. G. , RAWSON P. F. , RUSHTON A. A. W. , SMITH D. G. , THOMAS A. T. , WIMBLEDON W. A.
Published: December 2007

The continuing development of stratigraphical concepts and the application of new methods has led the Stratigraphy Committee of the Geological Society of London to present a new guide to stratigraphical procedure. Some of the principal types of stratigraphy are outlined and guidelines and recommendations are given on procedure, practice and terminological usage.
The IUGS systematics of igneous rocks
Authors: LE BAS M. J. , STRECKEISEN A. L.
Published: December 2007

In order to create a sustainable classification of igneous rocks which all geologists might use, an international body was set up by the IUGS: the IUGS Subcommission on the Systematics of Igneous Rocks. In the course of creating the classification, the Subcommission has established ten principles for its construction and for defining an appropriate nomenclature. The principles are: (1) use descriptive attributes; (2) use actual properties; (3) ensure suitability for all geologists; (4) use current terminology; (5) define boundaries of rock species; (6) keep it simple to apply; (7) follow natural relations; (8) use modal mineralogy; (9) if mode not feasible, use chemistry; (10) follow terminology of other IUGS advisory bodies. These principles and their rationale have not previously been enunciated.

The classification separates and individually classifies the pyroclastic, carbonatitic, melititic, lamprophyric and charnockitic rocks before entering the main QAPF classification for plutonic and volcanic rocks which is based on the modal mineral proportions of quartz (Q), alkali feldspar (A) and plagioclase (P) or of alkali feldspar (A), plagioclase (P) and feldspathoids (F). Rocks with mafic content >90% have their own classification. If the mineral mode cannot be determined as is often the case for volcanic rocks, then a chemical classification of total alkalis versus silica (TAS) is used. The nomenclature for these classifications necessitates only 297 rock names out of the
c
. 1500 that exist.
Chemostratigraphy, K-Ar ages and illitization of Silurian K–bentonites from the Central Belt of the Southern Uplands–Down–Longford terrane, British Isles
Authors: HUFF W. D. , ANDERSON T. B. , RUNDLE C. C. , ODIN G. S.
Published: December 2007

The Central Belt of the Southern Uplands Terrane, in both Scotland and Ireland, is a faulted and imbricated sequence of Caradoc to Llandovery shales and Llandovery turbidites with numerous interbedded K-bentonites. The bentonites are composed dominantly of R3-ordered mixedlayer illite/smectite (I/S) containing 90–95% illite, and represent the product of illitization during low-grade metamorphism. K-Ar age determination on the <0.5
μ
m size fraction gave a range from 379 ± 10 to 406 ± 10 Ma. The fixed K is thought to have originated in the precursor ash, and was remobilized during the transformation of smectite to I/S. K-Ar ages record a retrograde thermal event that post-dates Wenlock prehnite—pumpellyite facies metamorphism and is contemporaneous with cooling and uplift during the end-Silurian—early Devonian collision of Laurentia with the East Avalonian terrane. Differences in Rb and other trace elements between the K–bentonite beds are due, in part, to differences in original ash composition, and can be used to group the beds within biostratigraphically-defined boundaries. The chemical identification of groups of K-bentonite beds offers additional criteria for their stratigraphical correlation on a regional scale.
New evidence on the structure of the Labrador Sea/Greenland continental margin
Authors: CHALMERS J. A.
Published: December 2007

A 275 km section of a regional seismic reflection profile from the Greenland side of the Labrador Sea has been reprocessed and interpreted. Three zones of different structural style have been identified, the innermost of which is block-faulted. Magnetic modelling based on the seismic line shows that sea-floor spreading anomalies are confined to the outermost zone and the oldest identified anomaly is 27N. All attempts to model the area landward of anomaly 27N as a series of remanent magnetizations of alternating polarity failed. However a model in which the innermost zone is interpreted as extended and block-faulted continental crust and the intermediate zone as continental crust intruded and overlain by reversely magnetized igneous material fits the magnetic and seismic data. It is concluded that, at least in the northern Labrador Sea, sea-floor spreading started in Palaeocene times (chron 27), and large areas formerly thought to be underlain by oceanic crust should now be considered to be continental. One plate kinematic consequence may be a reduced need to postulate large strike-slip movements along Nares Strait.
Geochemistry and tectonic implications of two Ordovician bimodal igneous complexes, southern French Massif Central
Authors: BRIAND B. , PIBOULE M. , SANTALLIER D. , BOUCHARDON J. L.
Published: December 2007

Two bimodal meta-igneous complexes from the southern Massif Central provide important tectonic constraints on the initial stage of the Palaeozoic orogen. The metabasites may be subdivided into two groups according to the distribution of the Large Ion Lithophile (LIL) and High Field Strength (HFS) elements: N-type MORBs with low LIL/HFS ratios and subduction-type basalts with high LIL/HFS ratios. These associations suggest a complex tectonic setting such as an extensional zone or a back-arc basin above a subduction zone. The great volume of felsic rocks with low incompatible trace element contents indicates partial melting of an underlying continental crust. The association of terrigeneous sediments with N-type MORBs, subduction-type basalts and high-silica peraluminous rhyolites argue against an intra-oceanic setting, and suggest that the area was one of ensialic crustal tension during middle Ordovician. The two complexes are identified as remnants of ensialic back-arc basins rather than relicts of major oceanic sutures. Such marginal basins could have been located in a mainly continental domain, such as the Armorican microplate.
Vein cements and the geochemical evolution of subsurface fluids in the Visean of the Campine Basin (Poederlee borehole, Belgium)
Authors: MUCHEZ P. , VIAENE W. A. , KEPPENS E. , MARSHALL J. D. , VANDENBERGHE N.
Published: December 2007

Upper Visean reef-mound carbonates from the Campine Basin, northern Belgium, have a complex diagenetic history, which reflects the evolution of subsurface fluids in the basin. Primary pores became cemented by marine fibrous (stage A) and shallow burial (stage B, C and D) scalenohedral and blocky calcites. Tectonic deformation then created successive networks of fractures which acted as conduits for aggressive fluids and which were subsequently cemented by six stages of carbonate cement.

Fluid inclusion evidence suggests that the first cloudy columnar calcite cements in fractures (stage E) formed at or below 50°C. These calcites have a
δ
18
O of - 13.3% PDB and they are interpreted to have grown in meteoric waters (
δ
18
O = −6.7‰ to −7.4‰ SMOW). After a further period of fracturing and dissolution, white blocky calcites (stage F,
δ
18
O = −9.1‰PDB) precipitated around 60°C from fluids with a
δ
18
O = −0.9‰ SMOW. Later fractures contain brown columnar and blocky calcites (stage G) with a
δ
18
O of −12.1‰ PDB and a minimum homogenization temperature (T
H
) of
c
. 90°C, giving a pressure-corrected precipitation temperature of 95°C. An oxygen isotopic composi­tion of +0.6‰ SMOW is indicated for the fluid. Granular to bladed ferroan calcites (stage H), blocky ferroan calcites (stage I,
δ
18
O = 9.8‰ PDB and T
H
=128°C) and saddle dolomites (stage J,
δ
18
O= −10.0‰ PDB and T
H
= 147°C) are the last diagenetic carbonate phases. Methane has been detected in the vapour phase of the fluid inclusions in the blocky ferroan calcites. The ferroan calcites and the saddle dolomites are interpreted to have formed respectively at 150°C and 200°C in
18
O-rich fluids (+7.9‰ SMOW and +10.9‰ SMOW). The stable isotope values of the fluids indicate an abrupt change from a meteoric composition towards marine-derived compactional fluids and basinal brines. Enrichment in
18
O is mainly attributed to the dewatering/dehydration of clay minerals in the adjacent Upper Carboniferous strata.

The paragenetic sequence of cements described here is comparable to that encountered in other Lower Carboniferous limestones where there is not such an extensive data base of fluid inclusion and stable isotopic data. It is suggested that the large change in the pore fluid composition documented here might be a common subsurface process and that the interpretation of diagenetic temperatures from isotopic data alone can be very misleading.
A Miocene Gilbert-type fan-delta from a volcanically influenced lacustrine basin, Rusinga Island, Lake Victoria, Kenya
Authors: BESTLAND E. A.
Published: December 2007

A lacustrine, volcanically influenced fan-delta is recognized in the Kulu Formation of the Miocene Rusinga Group in western Kenya. In the Nyamsingula Gully area on Rusinga Island in Lake Victoria, mapped lithologic units include the classic topset, foreset (mega-foreset) and bottomset structure of a Gilbert-type delta. A distinctive mega-breccia unit of colluvial origin interfingers laterally with the delta deposits and consists of pyroclastic and sedimentary rock fragments derived from underlying and laterally adjacent strata. The breccia formed from the bevelling of a fault escarpment, from which the fan-delta also originated. Away from the fan-delta axis, slumping of fault-scarp colluvium into the lake produced matrix-supported debris flows that are interbedded with lacustrine shales. In the topset beds of the delta, clasts of a distinctive melilitite–nephelinite tuff of airfall origin can be identified and traced down a palaeoslope through laterally adjacent units from the original bedded tuff, into the mega-breccia unit, and finally into debris-flow deposits in the foreset and bottomset beds. During resedimentation the tuff behaved in a brittle fashion due to quick cementation as a result of its water soluble, ultra-alkaline composition.

The Kulu Formation is a distinctive facies that interfingers with the lowermost Hiwegi Formation. Both formations are part of the Rusinga Group. The bulk of the Rusinga Group, excluding the Kulu Formation, represents braidplains and alluvial aprons that flanked the Miocene volcano of Kisingiri. The braidplain and alluvial apron deposits have primary dips away from the volcano and were derived from material erupted and eroded from the volcano. The Kulu Formation, in contrast, was deposited in two small, elongate lacustrine basins separated by a small horst (approximately 5 km long and 2–3 km wide), from which the deposits were largely derived. The fan-delta systems prograded symmetrically away from the horst margins, into the adjoining lacustrine basins. The long dimensions of the horst and lake basins roughly parallel the local slope of the Kisingiri volcano, and therefore deposition in the Kulu Formation was perpendicular to deposition of the other Rusinga Group formations in the vicinity
The Ordovician biogeography of the Grangegeeth terrane and the Iapetus suture zone in eastern Ireland
Authors: OWEN A. W. , HARPER D. A. T. , ROMANO M.
Published: December 2007

The Caradoc trilobite and brachiopod faunas of the Grangegeeth terrane show marked Scoto–Appalachian/Laurentian affinities. Contrary to some plate tectonic models, this indicates that the terrane must lie to the north of the Iapetus suture. More limited graptolite evidence from the Llanvirn of Grangegeeth suggests that the terrane may have been closer to the Gondwanan margin or at least at higher latitudes earlier in the Ordovician and migrated to low latitudes prior to its eventual accretion onto the Laurentian margin.
Tectonic and sedimentary evidence for synchronous and out-of-sequence thrusting, Larache-Acilah area, Western Moroccan Rif
Authors: MORLEY C. K.
Published: December 2007

Syn-tectonic turbidites were analysed using measured sections, structural relationships and bio-and litho-correlations of sedimentary units to determine the tectonic evolution of the alpine thrust belt of the Northwestern Moroccan Rif. The external zones of the northwestern Moroccan Rif contain two Tertiary turbidite sequences which can be sub-divided into type I, II and III turbidite packages
sensu
Mutti 1984. One turbidite sequence, the Acilah sandstone (Oligocene–earliest Miocene), is found at the leading edge of the Tangier thrust sheet while a second, the Sidi-Mrait flysch, is seen in the underlying Prerif thrust sheet. The Lower Sidi-Mrait flysch was probably deposited in a foredeep basin. At the end of the Eocene-early Oligocene the advancing thrust front incorporated the foredeep basin deposits into the thrust belt. Subsequent turbidite deposition occurred in piggyback basins. Palaeocurrent directions indicate sediment transport from SSE to NNW, along troughs elongated parallel to the tectonic strike. Creation of piggyback basins, turbidite onlap relationship, unconformities and structural relationships indicate that complex synchronous and out-of-sequence thrusting accompanied the overall foreland-progressing deformation sequence.
Structural constraints on closure geometry across the Iapetus suture in eastern Ireland
Authors: VAUGHAN A. P. M. , JOHNSTON J. D.
Published: December 2007

The east coast of Ireland is one of the few places where Lower Palaeozoic rocks are exposed adjacent to the supposed surface trace of the Iapetus Suture. North of the Tinure Fault (the local surface expression of the suture), Llandovery and Wenlock strata correlated with the Central and Southern Belts of the Southern Uplands were deformed by post-Wenlock deformation (D1), characterized by southward-verging, northerly-inclined, upright F1 folding and NNE-trending faulting with a component of sinistral transpression. South of the Tinure Fault, D1 structures are northward-verging, southerly-inclined, upright folds also associated with sinistral transpression. Structures on both sides of the Tinure Fault were modified by northwest-directed thrusting and north-verging folding with a component of dextral transpression. This second event affected lamprophyres intruding D1-deformed rocks of Wenlock age, but pre-dates the emplacement of uncleaved, probably Lower Devonian lamprophyre dykes and the unconformable deposition of Lower Carboniferous clastics and limestones. Other southerly-dipping thrusts with a dextral component of motion which occur in Lower Palaeozoic rocks in Ireland and Britain may be of Caledonian rather than Variscan age as is commonly assumed. The northward thrusting accounts for the mismatch between the inferred surface trace of the Iapetus Suture, and that projected from seismic reflectors at 10 km depth.
The petrogenesis of Tertiary microgranites and granophyres from the Slieve Gullion Central Complex, NE Ireland
Authors: GAMBLE J. A. , MEIGHAN I. G. , McCORMICK A. G.
Published: December 2007

Granophyres and microgranites of the Tertiary central intrusive complex of Slieve Gullion, NE Ireland are intimately associated with appreciably larger volumes of mafic rocks whose compositions extend between basalt and basaltic andesite. These felsic intrusions show near minimum melt compositions and are characterized by trace element abundances and ratios consistent with evolution by crystal fractionation
within
a suite of granite magmas. Rb, Cs, Th and U all increase while Sr and Ba and Eu decrease with differentiation, suggesting an important feldspar control on the development of this felsic suite. All rocks are enriched in light rare earth elements relative to heavy rare earth elements and show negative Eu-anomalies (Eu/Eu* = 0.5–0.05), the extent of the anomaly increasing with differentiation. Isotopic ratios of Sr and Nd (
87
Sr/
86
Sr
57.6Ma
= 0.70983–0.71044 and
143
Nd/
144
Nd = 0.512379–0.512384) rule out an origin through straightforward crystal fractionation of basaltic magmas, and the Nd isotopes are distinct from those of the Scottish Hebridean centres such as Skye. The δ
l8
O and δD values on whole rock and mineral separates show evidence for interaction between the granitoids and a meteoric groundwater system. However, the extent of the interaction is not as extreme as that in the Skye granitoids. We interpret the
granites
as end products of advanced crystal fractionation of mantle-derived mafic liquids which interacted with lithosphere. The isotopic distinction between our data and those from the Hebridean islands are a further argument for lithospheric provinciality in the NW British Isles.
Absolute dating of fault movements
Authors: MADDOCK R. H.
Published: December 2007

The papers in this thematic set arise from a meeting jointly organized by the Tectonic Studies Group and the Stratigraphy Committee of the Geological Society and held at Burlington House on 28 November 1990. About 80 people heard oral presentations of 15 papers of which seven are published in this thematic set. Abstracts of most of the papers presented at the meeting were given in the Geological Society Newsletter for September 1990.

In a recent essay criticizing the way in which scientists apply the term absolute, Wendell Duffield (1990, p. 1774) wrote ‘Still more liberty is taken with the ‘A-word’ [absolute] by people concerned with ages of geologic materials’. In choosing the title for this meeting, the convenor quite purposefully took such liberty in an attempt to attract presentations on dating fault movements using a diversity of absolute, comparative, direct and high-resolution relative age dating techniques. More accurate and more precise dating of fault movements has relevance not only to academic studies of the dynamics and kinematics of fault movements but also engineering seismic hazard assessment, radwaste disposal, the timing of hydrocarbon migration and entrapment, and the economic mineralization of fault zones. This relevance was made apparent at the meeting by an audience which included representatives of a number of sectors of industry, regulatory bodies and academia.

Commencing the meeting with an amusingly titled presentation (‘Doctor-is my fault active?’),
R.
Muir Wood
(Principid Yard Limited) examined the taxing geological and regulatory questions of how to classify faults as seismically ‘active’
Remarks on ESR dating of fault movements
Authors: GRÜN RAINER
Published: December 2007

Laboratory experiments and detailed investigations of natural fault gouge indicate that it is, in principle, possible to date the last movement of a fault by ESR. This paper gives a brief introduction to ESR dating and outlines the specific problems that have to be addressed before ESR can be established as a reliable technique for the dating of fault movements.
Recurrent fault activity in the Grimsel Test Site (GTS, Switzerland): revealed by Rb-Sr, K-Ar and tritium isotope techniques
Authors: KRALIK M. , CLAUER N. , HOLNSTEINER R. , HUEMER H. , KAPPEL F.
Published: December 2007

Fault gouge and mylonite samples of prominent faults (AU 126 m and AU 96 m) occur at the Grimsel Test Site (underground research laboratory) in the Aar Massif. Fractions < 40, 5–20 and < 1 μm were separated, and the minerals investigated and compared with the Grimsel ‘granodiorite’. Size fractions were separated and their mineralogy was examined by SEM, XRD, DTG and IR-spectroscopy techniques.

The phengite, green biotite, plagioclase and K-feldspar of the penetratively deformed host Grimsel ‘granodiorite’ form a Rb-Sr isochron of 19 ± 3.9 Ma. The deformation has a similar K-Ar age. The Rb-Sr data from the phengite and albitic plagioclase of the gouges and the mylonite samples suggest an earlier isotopic exchange 26 Ma years ago. The fault gouge and mylonite seems to have been formed during an early hydrothermal-tectonic pulse of the Alpine metamorphism. However, there may be small amounts of inherited
87
Sr, and a mixing line cannot be excluded.

The apparent K-Ar ages of the <40 size fractions of the Grimsel ‘granodiorite’ decrease from 10.4 Ma to 6.6 Ma, suggesting recrystallization processes during continuous fault activity. Small amounts of chlorite/smectite (vermiculite?), developed from biotite or chlorite, indicate continuous activity at low temperatures. Radium 226 mobilization and tritium,
18
O,
2
H values from percolating waters in a parallel fault confirm the existence of recent fluid activities from
<
8000 years BP to the present day.
Tectonic implications of fore-arc magmatism and generation of high-magnesian andesites: Alexander Island, Antarctica
Authors: McCARRON J. J. , SMELLIE J. L.
Published: December 2007

Alexander Island, situated off the west coast of the Antarctic Peninsula, contains a suite of Late Cretaceous to Early Tertiary subduction-related magmatic rocks. The rocks occupy a fore-arc position 100–200 km trenchward of the main arc (Antarctic Peninsula) and they become younger northward along the length of the island. Major and trace element geochemistry for 222 samples shows the suite to be a medium to high-K calc-alkaline series, ranging in composition from picro-basalt to rhyolite. Andesite samples show a large range in MgO and Mg#, with nine samples representing high-magnesian andesites.Sr and Nd isotopic data indicate that the andesites range isotopically to more depleted mantle compositions than the associated basalts. The dacite/rhyolites can be related compositionally to the andesites by assimilation of typical Pacific rim accretionary material. To produce high-magnesian andesite lavas, it is necessary to introduce a suitable source of heat into the fore-arc, thus enabling partial melting of depleted sub fore-arc hydrous peridotite. A causative link with ridge subduction prior to magmatism is proposed, with successive ridge–trench collisions producing a temporal migration of the magmatism and high geothermal gradients in an anomalously hot fore-arc region.
Role of regional extension and uplift in the Plio-Pleistocene evolution of the Aksu Basin, SW Turkey
Authors: GLOVER CLARE P. , ROBERTSON ALASTAIR H. F.
Published: December 2007

The Aksu Basin, within the Isparta Angle area of SW Turkey, documents Plio-Pleistocene crustal processes at the interface between the Tauride Mountains and the Eastern Mediterranean Sea. Basin sedimentation began in the Late Miocene, following an earlier history of emplacement of Mesozoic allochthonous units (Antalya Complex), Miocene basin development and localized Late Miocene compression (Aksu Phase). Late Miocene–Early Pliocene transtension deformed the Aksu Basin, exploiting pre-existing zones of structural weakness. During Early–Mid-Pliocene, muddy sediments accumulated in a shallow shelf sea (<150 m deep), open to the Mediterranean Sea to the south. Regression in the Late Pliocene then resulted in coarse deltaic progradation. Mature erosion surfaces developed on adjacent elevated areas throughout the Pliocene and were accompanied by fanglomerate deposition along the high-relief western margin of the basin. East–west extension then formed the present Aksu Basin as a N–S half graben in the Late Pliocene–early Pleistocene associated with greatly enhanced fluvial downcutting. Accumulation of very extensive (600 km
2
) and locally thick (up to 250 m) cool-water Antalya tufa deposits then followed, prior to glacial times. Initial localized lacustrine carbonate deposition was followed by development of mainly algal carbonates that are thickest in the west. The terraced nature of the tufa (terraces at 300, 250, 100 m above present sea level) is explained in terms of fluvial processes. Regional comparisons suggest a two-stage history for the Aksu Basin: first, Late Miocene–Early Pliocene transtension and subsidence; secondly, Late Pliocene–Early Pleistocene rifting and marginal uplift. The overall tectonic setting reflects interplay between supra-subduction zone extension and tectonic ‘escape’ of Anatolia westwards towards the Aegean.
Development of glacial Llyn Teifi, west Wales: evidence for lake-level fluctuations at the margins of the Irish Sea ice sheet
Authors: FLETCHER C. J. N. , SIDDLE H. J.
Published: December 2007

A thick sequence of Quaternary laminated silt and clay, sand, gravel, and diamict has recently been proven at Llandudoch (St Dogmaels), west Wales. Most of these deposits accumulated in a tributary valley of Afon (River) Teifi, that formed prior to the last glaciation. The laminated silt and clay occur up to 103 m above present sea level, and are considered to have been deposited in Llyn (Lake) Teifi—a large ice-dammed lake that developed in the Teifi valley as the Irish Sea ice sheet impinged onto the Welsh mainland during the late Devensian. Rhythmic units are interpreted as annual varves, whose composition was determined by the distance from the sediment discharge point. Short-term climate fluctuations during the summer months are evident in some of the varve units. Stratigraphic variations within the laminated deposits are considered to reflect different levels of Llyn Teifi, which varied according to the position of the Irish Sea ice sheet in the Teifi valley and the elevations of three overspill channels. The overlying diamict, sand and gravel deposits are thought to have accumulated close to the ice front as it encroached into Llyn Teifi. During the final retreat of the Irish Sea ice sheet a series of kamiform sand and gravel deposits formed along the margins of the glacier.
Antarctic Peninsular cryosphere: Early Oligocene (
c.
30 Ma) initiation and a revised glacial chronology
Authors: DINGLE R. V. , LAVELLE M.
Published: December 2007

Strontium isotope stratigraphy provides a chronology for Cenozoic cryogenic strata in the northern Antarctic Peninsula and allows an assessment of diachronism in onset of glacial conditions between East and West Antarctica. The earliest observed event on the Antarctic Peninsula was late Early Oligocene (29.8 ± 0.6 Ma) (at least
c.
4 Ma later than in East Antarctica), with a second in the early Early Miocene (22.6 ± 0.4 Ma). Both glacials and intervening interglacial were continent-wide phenomena. Two late Neogene glaciations are distinguished: early Late Miocene (9.9 ± 0.97 Ma) (Hobbs Glacier/Jones Mountains) and latest Miocene (Alexander Island). A further late Neogene glacial deposit (Weddell Formation) can be constrained only as <
c.
10 Ma.
Chitinozoan chains and cocoons from the Upper Ordovician Soom Shale lagerstätte, South Africa: implications for affinity
Authors: GABBOTT SARAH E. , ALDRIDGE RICHARD J. , THERON JOHANNES N.
Published: December 2007

The Upper Ordovician (Ashgill) Soom Shale lagerstätte preserves chitinozoans on the bedding planes as scattered individuals and, more significantly, in linked chains, in aggregated masses and associated with organic envelopes. Chitinozoan affinites are problematical, but the Soom Shale has a restricted biota, providing constraints on hypotheses of relationship. No graptolites or gastropods, which are possible contenders for chitinozoan production, occur. The chitinozoans are, however, associated with conodonts and orthocone cephalopods and, of all the known Soom Shale biota, these organisms present the most likely candidates for chitinozoan origination.