bluuebunny/crossref_metadata_2025 huggingface dataset:
Global and regional palaeoceanographic changes as recorded in the mid-Cretaceous (Aptian–Albian) sequence of the Ionian zone (NW Greece)
Authors: Danelian T. , Tsikos H. , Gardin S. , Baudin F. , Bellier J.-P. , Emmanuel L.
Published: December 2007

Micropalaeontological and chemostratigraphic results from the mid-Cretaceous ‘upper siliceous zone’ of the Ionian zone, studied in two localities of NW Greece (Paliambela and Panaya), provide new insights into the palaeoceanographic evolution of Tethys and better correlation with well-studied Italian successions.
δ
13
C carbonate and organic-carbon isotope stratigraphy allows an improved correlation of the early Aptian Fourcade Level with Oceanic Anoxic Event 1a. Calcareous nannofossils point to intervals of reduced sedimentation within the late Aptian part of the limestones overlying the Fourcade Level. Combined calcareous nannofossil, radiolarian and planktonic foraminiferal biostratigraphy suggests that the overlying radiolarites (named herein the ‘Dercourt Member’) are essentially mid-Albian in age. Radiolarites of this age and thickness have not been identified in the well-explored Italian sections or in southern Albania. It is therefore likely that the Dercourt radiolarites reflect a high-productivity event localized in the Greek area of the Ionian zone, possibly caused by a bathymetrically induced upwelling of intermediate to deep waters that entered the Ionian trough following the opening of new oceanic gateways in the Eastern Mediterranean Tethys.
The White Stone Band of the Kimmeridge Clay Formation, an integrated high-resolution approach to understanding environmental change
Authors: Pearson S. J. , Marshall J. E. A. , Kemp A. E. S.
Published: December 2007

The Kimmeridge Clay is a Jurassic mudrock succession that shows Milankovitch Band climatic cyclicity. A key issue is to determine how the subtle changes that define this cyclicity result from climatic change. Using material from the Natural Environment Research Council Rapid Global Geological Events (RGGE) Kimmeridge Drilling Project boreholes, the White Stone Band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies. Fabric analysis shows the lamination to represent successive deposition of coccolith-rich and organic-matter-rich layers. Individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components. Such mixed organic matter input is interpreted as the result of storm transport. Linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria. As the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon. This was significantly increased by late season storm-driven mixing of euxinic water into the photic zone. Increased frequency of storm systems would therefore dilute the coccolith input to give an oil shale. Hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal.
Reactivation of a rhyolitic magma body by new rhyolitic intrusion before the 15.8 ka Rotorua eruptive episode: implications for magma storage in the Okataina Volcanic Centre, New Zealand
Authors: Smith Victoria C. , Shane Phil , Nairn Ian A.
Published: December 2007

The 15.8 ka Rotorua rhyolite eruptive episode from the Okataina Volcanic Centre comprises a plinian pumice fall deposit followed by the extrusion of two rhyolitic lava domes or flows and their associated block-and-ash flows, with a total volume >1 km
3
(dense rock equivalent). Variations in mineralogy, whole-rock, glass and mineral chemistry, and calculated magmatic properties suggest that two distinct rhyolitic magmas were sequentially tapped during the eruption. The first magma erupted (T1) is characterized by low SiO
2
(
c
. 76.5 wt% in glass), calcic feldspars (An
44
), magnesian hornblendes (MgO
c
. 14.45 wt%), clinopyroxene, and high temperatures (
c
. 835 °C) and
f
O
2
(1.8–2.1 ΔFMQ (where FMQ is the fayalite–magnetite–quartz buffer)). The second magma (T2) was more evolved and is characterized by higher SiO
2
(
c
. 77.4 wt% in glass), Na-rich feldspars (An
24
), less magnesian hornblendes (MgO
c
. 11.8 wt%), biotite, and low temperatures (
c
. 750 °C) and
f
O
2
(0.65–1.1 ΔFMQ). Both magmas are homogeneous, but evidence for some magma mingling indicates that they were in contact during eruption. However, there was only a minor degree of hybridization, perhaps reflecting the contrasting temperatures and viscosities of the two magmas. The crystal-rich, poorly vesicular nature of the T2 ejecta indicates that it originated from a cooling, high-level magma chamber that was reactivated by intrusion of hotter, volatile-rich T1 magma. The ponding of rhyolite magmas at shallow depth and their subsequent reactivation by later rhyolitic intrusion may be an important process in the compositional evolution and eruption dynamics of many Okataina Volcanic Centre rhyolite magma bodies.
Evidence for a major Neoproterozoic orogenic unconformity within the Dalradian Supergroup of NW Ireland
Authors: Hutton D.H.W. , Alsop G.I.
Published: December 2007

An intriguing and contradictory scenario has recently developed in the Caledonides of the British Isles concerning the ages of deposition and deformation of the Neoproterozoic Dalradian Supergroup. Isotopic evidence, although limited, suggests that the lower parts of the sequence may have been deposited and undergone Precambrian deformation (i.e. pre-600 Ma) prior to deposition of the upper parts of the sequence (i.e. post-600 Ma). Given these existing constraints, it is clear that a major break (or breaks) would be required in the intervening sequence to maintain a coherent tectonostratigraphy. We present evidence for such an unconformity preserved at the base of the Easdale Subgroup in NW Ireland. Reworked clasts that contain a pre-existing tectonometamophic history are identified within a conglomerate that lies along this regionally recognized boundary. The underlying sequence also exhibits pre-existing deformational fabrics that display erosional truncation at the base of the conglomerates. These relationships, together with significant erosion and excision of the footwall sequence, and extensive thickness and facies variations in the hanging-wall units, imply that a major tectonic unconformity exists within this succession. As the conglomerate lies stratigraphically below Precambrian (
c
. 600 Ma) lavas, the structural fabrics contained within the clasts and the underlying sequence must also be of Precambrian age and totally unrelated to the well-established Early Palaeozoic (Caledonian) orogenic deformation observed in the younger parts of the sequence. The Dalradian Supergroup, as defined, may actually comprise (at least) two distinct tectonostratigraphic sequences.
Nested strike-slip duplexes, and other evidence for Late Cretaceous–Palaeogene transpressional tectonics before and during India–Eurasia collision, in Thailand, Myanmar and Malaysia
Authors: Morley C.K.
Published: December 2007

The Late Cretaceous–Palaeogene structural and tectonic events in the northern region of Sundaland represent a poorly known, but potentially important orogenic development in SE Asia. Extensive Late Cretaceous S-type granites extending from Malaysia through Thailand to Myanmar have long been used to infer an episode of crustal thickening, an inference supported by the presence of late Cretaceous–Eocene ophiolites in Myanmar. However, structural evidence for a well-developed associated fold and thrust belt has been lacking. Apatite and zircon fission-track studies of Thailand indicate a broad regional uplift from about 80 Ma to 40 Ma, suggesting an episode of crustal thickening, but the uplift amount is modest, and not that expected for a major fold and thrust belt. Left lateral motion on major NW–SE-trending strike-slip fault zones (Mae Ping and Three Pagodas faults) in Myanmar and Thailand has been attributed to Himalayan–Tibetan escape tectonics. This paper demonstrates that the fault zones are considerably more complicated than just NW–SE trends. They are a network of branching faults with important north–south trends as well as NW–SE trends, they form large-scale, nested strike-slip duplex structures and affect a region over 1000 km long and up to 250 km wide. This diffuse, branching network of strike-slip fault trends may represent a substantial Late Cretaceous–Palaeogene transpressional belt. Himalayan escape tectonics represent later increments of deformation with both Oligocene sinistral and late Oligocene–Recent dextral reactivation.
The 3D facies architecture of flood basalt provinces and their internal heterogeneity: examples from the Palaeogene Skye Lava Field
Authors: Single Richard T. , Jerram Dougal A.
Published: December 2007

Quantifying the facies architecture of flood basalt provinces is important as it can be used to understand the physical volcanology and rock property variations throughout the lava sequence. The 3D facies architecture and internal heterogeneity of the Skye Lava Field, for example, provides important insights into the evolution of the British Tertiary Igneous Province, and valuable information to aid in the exploration of potential offshore reservoirs underlying significant flood lavas along the North Atlantic margin. The volcanic stratigraphy of the Talisker Bay area of Skye comprises: (1) lower compound-braided lavas (flow lobes <3 m thick); (2) transitional lavas (flows <8 m thick); (3) upper tabular-type lavas (flows <20 m thick), representing a relative increase in eruptive volume. A 3D model of the lava sequence was reconstructed using detailed digital geological mapping, revealing estimated volumes of: the lower sequence (12.7 km
3
), the transitional sequence (7.4 km
3
) and the upper sequence (17.0 km
3
). The lower sequence lavas formed on the flanks of a shield volcano and were sourced from the NE. Volcanological features such as lava feeder tubes, pahoehoe textures and lobes indicate a scale of volcanism similar to that of present-day Hawaii. The within-flow heterogeneity of the basalts is characterized using an ‘intrafacies scheme’, allowing comparison of variations in lithofacies with characteristic (geophysical) rock properties of compressional-wave velocity and density.
Transitional geometries between gently plunging and steeply plunging folds: an example from the Lower Palaeozoic Brabant Massif, Anglo-Brabant deformation belt, Belgium
Authors: Debacker T.N. , Sintubin M. , Verniers J.
Published: December 2007

Although many studies have dealt with markedly different fold orientations and associated cleavage–fold relationships within individual, single-phase deformed fold belts, there are very few descriptions of possible gradual, transitional fold geometries. The Lower Cambrian steep core of the single-phase deformed Brabant Massif contains steeply plunging, west-facing folds with a Z-shaped asymmetry, whereas the Ordovician–Silurian southern rim consists of gently plunging, upward facing folds. A gradual transition is observed between these end-member orientations, in a NW–SE-trending zone 1–1.5 km wide, in which the folds appear to be strongly curvilinear and locally downward facing. The structural geometries within this transition zone are described in detail and the geometric changes analysed in the light of the fold transition. The strongly variable fold orientations are tentatively attributed to a bulk oblate tectonic strain. The transition zone overlies an aeromagnetic lineament, classically interpreted as a dextral shear zone. The steeply plunging folds, the transition zone and the aeromagnetic lineaments are all attributed to a local dextral transpression, in which deformation is partitioned both vertically and laterally. The results indicate that within zones of heterogeneous transpression, the different deformation domains are not necessarily always fault bounded.
Early Mississippian lycopsid forests in a delta-plain setting at Norton, near Sussex, New Brunswick, Canada
Authors: Falcon-Lang H.J.
Published: December 2007

Mississippian lycopsid forests in growth position are extremely rare, and their community-scale ecology remains enigmatic. This is a significant gap in our knowledge, not least because they represent the precursors of Pennsylvanian ‘Coal Forests’. In this paper, nearly 700
in situ
fossil trees are described from 13 entisol or inceptisol horizons in the mid-Tournaisian Albert Formation (Horton Group) at Norton, near Sussex, New Brunswick, Canada. These trees, almost all of which are lycopsids of the
Protostigmaria
–
Lepidodendropsis
-type, are rooted mostly in the flood-disturbed interdistributary wetland deposits of prograding wave-dominated deltas. Tree mapping on extensive palaeosol surfaces indicates the existence of extremely dense forest vegetation. Scaled up to standard forestry units, densities of 10 000–30 000 trees per hectare are inferred. A significant inverse linear relationship between tree diameter and density for the five most extensive palaeosols indicates that inter-tree competition led to natural self-thinning as the forests matured. Forest maturation also led to a reduction in tree-spacing heterogeneity. Flood events regularly killed whole stands at Norton, burying trees in sandstone sheets, and preventing establishment of climax vegetation. Charcoal remains demonstrate that wildfire was another important disturbance process.
Isotopic signals from late Jurassic–early Cretaceous (Volgian–Valanginian) sub-Arctic belemnites, Yatria River, Western Siberia
Authors: Price G.D. , Mutterlose J.
Published: December 2007

This contribution presents the first detailed oxygen and carbon isotope record from the latest Jurassic–early Cretaceous interval of the Yatria River, subpolar Urals, Siberia. Isotopic compositions have been determined on well-preserved belemnite samples from the genera
Lagonibelus
,
Cylindroteuthis
and
Acroteuthis
. These new data indicate a shift to lower temperatures from the late Volgian into the late Valanginian, with some warmer phases recognized within the Ryazanian and earliest Valanginian. The lowest temperatures of the late Valanginian, consistent with subfreezing polar temperatures, are coincident with an inferred eustatic sea-level fall. A late Valanginian positive shift in carbon isotopes correlates with the carbon isotope excursion recorded from Tethyan successions. The most positive carbon isotope values correspond to the most positive oxygen isotope values (and hence lowest palaeotemperatures). In the absence of widespread Valanginian organic-rich black shale deposition, the carbon isotope excursion may point to increased storage of organic carbon in coastal areas and/or enhanced preservation within stratified waters in high-latitude basins. At these higher latitudes, where rates of weathering were presumably much lower because of the prevalent cold climate, the isotopic data may point to pulses of productivity being brought about by increased riverine nutrient transfer and also by nutrients being released by the melting of ice. The correlation between positive carbon isotopes and cool climates may indicate the effectiveness of these high-latitude carbon sinks and their ability to draw down atmospheric CO
2
, resulting in an ‘inverse greenhouse’ effect.
Fault zone weakening and character of slip along low-angle normal faults: insights from the Zuccale fault, Elba, Italy
Authors: Collettini C. , Holdsworth R.E.
Published: December 2007

A seismically active low-angle normal fault is recognized at depth in the Northern Apennines, Italy, where recent exhumation has also exposed ancient examples at the surface, notably the Zuccale fault on Elba. Field-based and microstructural studies of the Zuccale fault reveal that an initial phase of pervasive cataclasis increased fault zone permeability, promoting influx of CO
2
-rich hydrous fluids. This triggered low-grade alteration and the onset of stress-induced dissolution–precipitation processes (e.g. pressure solution) as the dominant grain-scale deformation process in the pre-existing cataclasites leading to shear localization and the formation of a narrow foliated fault core dominated by fine-grained hydrous mineral phases. These rocks exhibit ductile deformation textures very similar to those formed during pressure-solution-accommodated ‘frictional–viscous’ creep in experimental fault rock analogues. The presence of multiple hydrofracture sets also points to the local attainment of fluid overpressures following development of the foliated fault core, which significantly enhanced the sealing capacity of the fault zone. A slip model for low-angle normal faults in the Apennines is proposed in which aseismic frictional–viscous creep occurs on a weak, slow-moving (slip rate <1 mm a
−1
) fault, interspersed with small seismic ruptures caused by cyclic hydrofracturing events. Our findings are potentially applicable to other examples of low-angle normal faults in many tectonic settings.
1.2 Ga thermal metamorphism in the Albany–Fraser Orogen of Western Australia: consequence of collision or regional heating by dyke swarms?
Authors: Dawson Galvin C. , Krapež Bryan , Fletcher Ian R. , McNaughton Neal J. , Rasmussen Birger
Published: December 2007

Compressive fabrics in the Late Palaeoproterozoic Mount Barren Group of the Albany–Fraser Orogen, southwestern Australia, record Mesoproterozoic collision between proto-Australia and proto-Antarctica. Petrographical evidence establishes that peak thermal metamorphism produced largely random growth of kyanite, staurolite, biotite, monazite and xenotime that overprinted those fabrics. SHRIMP U–Pb geochronology of xenotime and monazite yields an average age of 1205 ± 10 Ma. Thermal metamorphism therefore occurred at least 45 Ma after fabric formation, and was unlikely to have been caused by collision. Rather, thermal metamorphism overlapped with the emplacement of 1215–1202 Ma dyke swarms into the Orogen and the adjacent Yilgarn Craton, and was followed by emplacement of 1200–1180 Ma granites. Regional heating associated with mafic magmatism was the probable cause of thermal metamorphism, but previous proposals that the dyke swarms were the consequence of collision or extensional orogenic collapse cannot be substantiated. A regional thermal anomaly, craton-scale extension and adiabatic decompression melting of the asthenosphere are implied, but causal mechanisms such as a mantle plume or intracontinental rifting require substantiation from other parts of East Gondwana. The significant time gap between orogenic deformation and thermal metamorphism implies that metamorphism in many other orogens may not necessarily be due to compressive tectonics.
Laurentian provenance and an intracratonic tectonic setting for the Moine Supergroup, Scotland, constrained by detrital zircons from the Loch Eil and Glen Urquhart successions
Authors: Cawood Peter A. , Nemchin Alexander A. , Strachan Rob A. , Kinny Peter D. , Staci Loewy
Published: December 2007

Detrital zircons in psammite from the type section of the Loch Eil Group of the Moine Supergroup, NW Scotland, and from an unnamed quartzose psammite, interstratified with marble, at Glen Urquhart yield similar U–Pb detrital zircon ages ranging from
c
. 2300 to 900 Ma. Both samples show age peaks at
c
. 1680–1630 Ma, 1510–1490 Ma, 1430–1330 Ma and 1110–1040 Ma. Archaean age grains are absent and Palaeoproterozoic grains older than 1800 Ma are rare. Sediment accumulation occurred in the early Neoproterozoic post
c
. 900 Ma but prior to emplacement of the 870 Ma West Highland granite gneiss. The Glen Urquhart sample has previously been considered to form part of the Albynian sequence lying between the Moine and Dalradian supergroups. The similar detrital zircon age signature of the two samples is consistent with the Glen Urquhart material representing part of the upper Moine succession. In both samples, detrital age peaks at around 1650 Ma and 1500 Ma correspond closely to the Labradorian and Pinware magmatic events in NE Laurentia and Baltica whereas the younger age peaks at
c
. 1400 and 1100 Ma correspond to phases of the Grenville orogen in Laurentia. The presence of detritus at
c
. 1650 Ma argues against input from Amazonia, which lacks any recorded magmatic activity in the range 1700–1600 Ma. The absence of Archaean and late Palaeoproterozoic detritus, which is present in Laurentia-derived units younger than the Moine, such as the Dalradian and Western Newfoundland strata, suggests that the Labradorian and Pinware magmatic arcs retained sufficient topographic relief to mask and block any input of older detritus into the Neoproterozoic Moine basin. The Laurentian provenance of the zircons argues against an exotic origin for the Moine Supergroup. Palaeogeographical reconstructions suggest that the Moine succession accumulated in an intracratonic setting within Rodinia near the nexus of Laurentia, Baltica and Amazonia. Closure during the mid-Neoproterozoic of this site of lithospheric extension along with its record of Knoydartian deformation and metamorphism may be analogous to the intracratonic tectonic history of central Australia during the Neoproterozoic and Palaeozoic that developed in response to far-field effects on the active Gondwana margin.
The timing of quartz cementation in Mesozoic sandstones from Haltenbanken, offshore mid-Norway: fluid inclusion evidence
Authors: GRANT S. M. , OXTOBY N. H.
Published: December 2007

The temperature of quartz cementation in Mesozoic sandstones from the Haltenbanken area, offshore mid-Norway has been evaluated by micro-thermometry of primary aqueous fluid inclusions in quartz overgrowths. Samples were collected from a wide range of burial depths (1.6 to 4.4 km) and large area (7500 km
2
). There is a systematic increase in homogenization temperatures (
T
h
) of approximately 75 °C between the shallowest and deepest wells. When converted to time using burial histories, the
T
h
data indicate that cementation was short-lived and started roughly synchronously throughout Haltenbanken within the last 5 Ma. It therefore seems that depth and/or temperature alone are not enough to bring about quartz cementation, some other factor(s) must also be involved.
The geochemistry of young volcanism throughout western Panama and southeastern Costa Rica: an overview
Authors: DEFANT M. J. , JACKSON T. E. , DRUMMOND M. S. , DE BOER J. Z. , BELLON H. , FEIGENSON M. D. , MAURY R. C. , STEWART R. H.
Published: December 2007

Oblique aseismic subduction below western Panama and southeastern Costa Rica has produced Recent arc-related volcanism. The aseismicity is probably related to the subduction of relatively hot oceanic lithosphere. The volcanism throughout this region over the past 2 Ma has been quite distinct, consisting of felsic magmas (andesites to rhyolites but mainly dacites) with geochemical signatures suggesting a metamorphosed basaltic source. It is believed that the subduction of young oceanic crust sets up conditions under which the slab melts rather than the overlying mantle wedge. Rocks with slab-melt geochemistries and associated with young subducted crust have been termed adakites elsewhere. The young adakite melts are sometimes associated with a few rare young high-Nb basalts, but there is no obvious genetic link between them through differentiation. High-Nb basalts may also be derived from the partial melting of the subducted oceanic crust. High-Nb basalt migmatites have been found with pegmatites of adakite compositions in the exposed subduction terrain of the Catalina Schist, California. Alternatively, the high-Nb basalts may be partial melts of phlogopite-rich mantle that has previously reacted with adakite magmas.

Eruption of adakites and high-Nb basalts was preceded by a 2-3 Ma period of relative quiescence. Prior to this, there was a 7 Ma period of calc-alkaline volcanism typical of the present-day magmatism (associated with a distinct Benioff zone) found throughout the Central American arc. The abrupt transition in volcanism with time from an early calc-alkaline sequence to a later adakite-high-Nb basalt sequence may record a change in the tectonic setting of western Panama and southeastern Costa Rica over the past 12 Ma.
Early Cambrian continental reconstructions
Authors: McKERROW W. S. , SCOTESE C. R. , BRASIER M. D.
Published: December 2007

Climatically-related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early Cambrian world. Laurentia, Baltica and Siberia appear to have formed a continental group which rifted apart from each other prior to 600 Ma. The consolidation of much of Gondwana probably occurred (in the Pan-African orogeny) well before the Cambrian, though the assembly of several east Asian terranes is still speculative. The archaeocyathan reefs of Siberia, southern Europe and Morocco, with their bigotinid trilobite fauna, suggest that these areas were adjacent to each other and at low latitudes. Avalonia had close faunal links with western Gondwana, but lacked bigotinids and archaeocyathans and may have been situated off west Africa and Florida. During the early Cambrian, there was a northward migration of Laurentia towards the Equator as its separation from Baltica and Siberia increased, and a southward movement of Gondwana.
Phosphogenesis around the Proterozoic-Phanerozoic transition
Authors: COOK PETER J.
Published: December 2007

There was a very significant and widespread phosphogenic event around the Proterozoic-Phanerozoic transition. This is reflected in the occurrence of many major and minor latest Proterozoic and Cambrian phosphate deposits (phosphorites) in Asia, Australia, Africa and South America, as well as minor occurrences in many other parts of the world. The major peak in phosphogenesis was in the Tommotian, with lesser events in the Ediacaran and the Lenian, bracketed by other minor though significant events. Recent evidence on the timing of Proterozoic phosphogenesis does not now support the suggestion of a phosphogenesis-glaciation link. These peaks in phosphogenesis are taken as evidence that there was a marked increase in the phosphate content of the shallow seas at about this time, possibly as a result of the circulation of deep, phosphorus-rich ocean waters into the photic zone. Not only was this responsible for the formation of phosphorites but it also had a profound effect on the biota, and may have been a driving mechanism for the Cambrian faunal ‘explosion’ and the initiation of biomineralization.
Geological applications of GIS
Authors: WADGE G.
Published: December 2007

Geological Information Systems (GIS) was the theme of the AGM of the Geoscience Information Group held at the NERC Unit for Thematic Infomation Systems, Reading University on 17 September 1991. The meeting was convened by G. Wadge to discuss what geological problems can be addressed by current GIS and what new technical capabilities are required to solve other problems. Eight papers were presented to an audience of 61 and five GISs were demonstrated over an extended lunch break.

GIS has the potential for making published map revision easier and cheaper in the way that word processing has done away with repeat typing of draft manuscripts.
J. L. Laxton
(BGS Edinburgh) illustrated this potential by describing how a series of ten thematic geological maps from the Wrexham area, derived from solid and drift geological maps, mine plans, borehole and quarry information, were created. ARC/INFO was used for input, editing and overlay operations to produce vector maps. These were then transferred to a LEGIS (now HORIZON) system for combination with a raster base-map prior to plotting and production of masters for printing. Despite a number of technical problems it was argued that the data checking involved in this process produced a better quality product than traditional methods.

In the first of three papers involving engineering geology applications,
P. Nathanail
(Wimpey)
& M. Rosenbaum
(Imperial College) gave an overview of the requirements of a GIS for this discipline. Data, particularly data structure , data storage and models of ground conditions were seen as
Mobility of the high field strength, rare earth elements and yttrium during late diagenesis
Authors: HOLE M. J. , TREWIN N. H. , STILL J.
Published: December 2007

Authigenic titanite occurs as a secondary, pore-filling cement in the Permian sandstones of the Cock of Arran, Scotland. The titanite is apparently not associated with in situ alteration of a specific mineral phase or phases, suggesting it crystallized from fluids migrating through these porous and permeable sandstones. The titanite contains significant concentrations of Zr, Nb, P, Ce, Nd, Gd and Y, implying that these elements were also carried in solution, probably in the form of halogen or carbonate complexes associated with hydrothermal circulation related to the intrusion of the adjacent Northern Granite.
The Iapetus suture zone in England, Scotland and eastern Ireland: a reconciliation of geological and deep seismic data
Authors: SOPER N. J. , ENGLAND R. W. , SNYDER D. B. , RYAN P. D.
Published: December 2007

Deep seismic profiles in the Irish and North seas have successfully imaged crustal structure across the Iapetus suture zone. A problem with current interpretations is that the reflectors chosen as the suture project to the top of the basement well to the south of the Solway Line, the palaeontologically defined trace of the suture. We present a revised interpretation in which a reflectivity boundary common to all the profiles is identified as the leading edge of imbricated Avalonian crust, in effect the footwall of the suture zone. This projects to the surface close to the Solway Line, obviating the need to invoke northward backthrusting of the suture.
Post-emplacement extension within a thrust sheet from the central Pyrenees
Authors: GRANT N. T.
Published: December 2007

Secondary faults and related veins in a small thrust sheet (the Pic de Port Vieux thrust sheet) in the footwall of the Gavarnie thrust in the central Pyrenees are used to infer the deformation sequence that accompanied its emplacement. Initial deformation was characterized by distributed bedding-parallel simple shear. This was superseded by localized deformation involving arrays of extensional faults. The first faults to form were X-shears and were succeeded first by conjugate faults (X-X' shears) and then arrays of R-shears that locally cut the thrust, i.e. developed subsequent to its emplacement. Extension veins are used to infer the orientation of the ambient stress system during the deformation sequence. A forward rotation of the stress sytem (towards the vertical) was associated with the X and X-X' shears and is considered to reflect loading of the 4 km thick overlying Gavarnie thrust sheet. A later, backward rotation of the stress system then occurred, returning σ
1
to 45° obliquity to the Pic de Port Vieux thrust, and was associated with the R-shear development. This later event produced extensional shearing of the thrust sheet and is equated with a proposed episode of spreading/gliding within the overlying thrust pile. A model for this spreading/gliding relates it to the active tectonics of the developing south Pyrenean thrust belt.
New constraints on the formation of the non-volcanic continental Galicia–Flemish Cap conjugate margins
Authors: SIBUET JEAN-CLAUDE
Published: December 2007

Numerous multichannel seismic data acquired on the starved continental margin off Galicia show that the prominent intra-crustal S reflector is observed only below the oceanward portion of the continental margin, close to the ocean–continent boundary. Superficial extension has been computed from the geometry of the well-imaged tilted fault blocks of the entire margin by using a series of parallel seismic lines specifically designed for this purpose. The pure shear model clearly accounts for the lithospheric extension of the continentward portion of the continental margin but not for the oceanward portion of the continental margin where the S reflector is present. The S reflector is a detachment zone which presents a decreasing offset in the direction of the continent, and this detachment zone has been active since the beginning of rifting. Recent kinematic reconstructions show that the conjugate margin to Galicia is the southeastern Flemish Cap margin. From the few seismic profiles available on this Canadian margin, a major master fault is observed beneath the continental slope and is interpreted as the outcropping portion of a main detachment zone identified on the Galicia margin as the S reflector. The proposed mechanism of extension for these two conjugate margins is pure shear which affects the whole lithosphere, but in the upper part of the crust, the rifting mechanism is either pure shear for the continentward portion of the Galicia margin or simple shear for the oceanward portion of the Galicia and the whole southeastern Flemish Cap margins where the detachment zone is active. I consider that pure shear is the basic lithospheric mechanism and that simple shear is a mechanism which affects only the upper crust.
The closure of the Iapetus Ocean and Tornquist Sea: new palaeomagnetic constraints
Authors: TRENCH A. , TORSVIK T. H.
Published: December 2007

Early Wenlock volcanic rocks from the East Mendips inlier, SW England, yield primary palaeomagnetic directions which indicate that southern Britain (Eastern Avalonia) occupied a palaeolatitude of 13 ± 5°S in Mid-Silurian (430 Ma) times.

When combined with coeval data from Laurentia, the southern Laurentian margin (Scottish terranes), and Baltica, the collective data indicate that: (1) the British and Scandinavian sectors of the Iapetus Ocean were closed, to within the limits of the palaeomagnetic resolution, by the Early Wenlock; (2) Acadian deformation across Britain, which culminated in Early Devonian time, post-dated initial docking of Eastern Avalonia and Laurentia; (3) a previous palaeomagnetic requirement for the Tornquist Sea to remain open into Mid-Silurian times is removed, thereby reconciling palaeomagnetic and biogeographical constraints upon the convergence of southern Britain and Baltica.

Recently-acquired palaeomagnetic data from southern Britain and Baltica have facilitated more reliable reconstructions of the early Palaeozoic palaeogeography of Northern Europe (Fig. 1). Palaeomagnetic data now record the progressive drift of southern Britain across the Iapetus Ocean during Ordovician times (Torsvik & Trench 1991;

Channell
et al.
1992

) and a predominant northward drift and counterclockwise rotation of Baltica from Cambrian to Devonian times (

Torsvik
et al.
1991
a

Torsvik
et al.
1992
a;

Perroud
et al.
1992

). Nevertheless, details on the closure history of the Iapetus Ocean and Tornquist Sea (Fig. 1) have remained sketchy due to a sparseness of coeval Late Ordovician–Mid-Silurian data from the bordering continents. These palaeomagnetic uncertainties permit competing geological models.

In this contribution, we address two outstanding problems relating to the closure
Geochemical evidence for the position of the Caples–Torlesse boundary in the Otago Schist, New Zealand
Authors: MORTIMER N. , ROSER B. P.
Published: December 2007

Comparison of the whole rock geochemical compositions of 142 samples of Otago Schist with greywackes and argillites from the Caples and Torlesse terranes confirms the essentially isochemical nature of Otago Schist metamorphism and permits correlation of individual schist samples to each terrane. These correlations, along with lithological, structural and petrographical information, have been used to establish a preliminary position for the long-sought-after Caples-Torlesse terrane boundary in the Otago Schist.

The boundary has been involved in Late Mesozoic and Cenozoic deformation, follows a sinuous course near the schist axis for some 350 km between Dunedin and the Barrier Range and divides the Aspiring lithologic association into Caples and Torlesse parts. A number of pods of ultramafic schist are exposed in the vicinity of the terrane boundary. The methods used in this paper may have application to the location of terrane boundaries in major schist belts elsewhere.
Temporal variation in calcification in marine cyanobacteria
Authors: RIDING R.
Published: December 2007

Periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes (CCEs). Intense such episodes occurred in the Cambrian-early Ordovician, Late Devonian and Mid-Late Triassic. Mild episodes occurred during the Early Carboniferous and Jurassic-Early Cretaceous. Possible episodes during parts of the Silurian and Permian await confirmation. Cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation. Cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation. This is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes.

Cyanobacterial calcification episodes correspond with Phanerozoic periods for which elevated global temperatures have been inferred. They do not appear to correlate closely with inferred changes in aragonite/calcite facilitation (the Sandberg curve) and
P
CO2
through time. It is concluded that variations in the precipitation rates of abiotic and quasi-abiotic marine carbonates through time have been controlled primarily by temperature. The mineralogy of these precipitates appears instead to have been mainly influenced by
P
CO2
and the Mg/Ca ratio, also linked to sea-level through plate tectonic processes. Thus, the controls on rate and mineralogy of precipitation were independent of one another.
Mesozoic radiolarian faunas from the Antarctic Peninsula: age, tectonic and palaeoceanographic significance
Authors: HOLDSWORTH B. K. , NELL P. A. R.
Published: December 2007

New assemblages of Radiolaria, including some of the few occurrences of high southern latitude Jurassic and Cretaceous radiolarian faunas, show that several localities in the LeMay Group of Alexander Island range in age from latest Jurassic–earliest Cretaceous to at least Albian. By demonstrating that sedimentation and deformation in the LeMay Group was diachronous, younging oceanwards to the northwest, these new age assessments support the model of the LeMay Group as an accretionary complex. The polarity of subduction beneath Alexander Island was not affected by arc collisions from at least the Lower Jurassic to the Oligocene, and such a long period of continuous accretion appears to be unusual. Deposition of the LeMay Group spans the Kimmeridgian to Albian sedimentation in the Fossil Bluff Group fore-arc basin, thus making the earlier concept of the LeMay Group as pre-Jurassic ‘basement’ untenable.

Allochthonous latest Jurassic–earliest Cretaceous radiolarian assemblages with some supposed Tethyan affinities are present in the LeMay Group. In contrast, an in situ latest Jurassic assemblage from the Nordenskjöld Formation of the back-arc basin and a further Jurassic assemblage from a probable trench-slope basin have characteristics believed diagnostic of high latitudes. The biogeographic affinities of radiolarians from cherts in the LeMay Group accretionary complex suggest that both these cherts, and associated basalts, are far-travelled slices of the Phoenix plate.

Rocks from the probable trench-slope basin, formerly assigned to the younger Fossil Bluff Group fore-arc basin sequence, now appear to be part of a new, previously unrecognized formation.
7th Himalaya-Karakoram-Tibet Workshop
Authors: SEARLE M. P. , TRELOAR P. J.
Published: December 2007

The first Himalayan Workshop held in Leicester University in 1985 was so successful that it was then agreed to hold the informal conference and workshop annually. Subsequently the Himalayan Workshops were held in Vandoevre-les-Nancy, France in 1986, London (1987), Lausanne, Switzerland (1988), Milan, Italy (1990) and Grenoble, France (1991). The upsurge in research throughout the Himalayan and Tibetan regions in the last ten years has warranted these annual meetings, and the dissemination of new research throughout the Himalayan community has been invaluable. This year the meeting was held in the Department of Earth Sciences, Oxford University, under the auspices of The Geological Society, London, from 6-8 April 1992. Over 120 participants from 15 countries attended.

The Himalayan chain has long been recognized as the world's most spectacular example of a continent-continent collision belt resulting from the collision of the Indian plate with the central Asian landmass some 50 Ma ago. Since then India has moved northwards with respect to Asia by over 2000 km at an average speed of 50mm a
−1
resulting in compressional tectonics not only in the Himalaya to the south of the main Indus suture zone, but also active compression in the mountain ranges north of the Indus suture: the Karakoram, Hindu Kush, Pamirs, Kun Lun and Tien Shan, as well as uplift of the 5 km high Tibetan plateau. Crustal shortening has mainly been accommodated by thrusting and folding in the Himalaya, by internal, diffuse lithospheric thickening within the Tibetan plateau, by limited, underthrusting of the
Chemostratigraphy versus biostratigraphy: data from around the Cenomanian–Turonian boundary
Authors: GALE A. S. , JENKYNS H. C. , KENNEDY W. J. , CORFIELD R. M.
Published: December 2007

A detailed isotopic profile is presented for a stratigraphically expanded Cenomanian–Turonian boundary section in Chalk facies exposed at Eastbourne, Sussex and compared with data from Pueblo, Colorado. In both sections macro- and micropalaeontological markers (first appearances and disappearances) are well-constrained, and their relative positions and relationship to the structure of the carbon-isotope curve are identical. This consistent relationship between two independent phenomena, one geochemical, the other biostratigraphical, is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon-isotope excursion in these two areas. This interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon-isotope excursion in Europe and North America.
Evidence for a major Tertiary dyke swarm in County Fermanagh, Northern Ireland, on digitally processed aeromagnetic imagery
Authors: GIBSON P. J. , LYLE P.
Published: December 2007

Digitally processed aeromagnetic imagery has revealed an extensive swarm of reversely magnetized Tertiary dykes in County Fermanagh, Northern Ireland, 50 km west of the main outcrop of the Tertiary Antrim Lava Group. The swarm covers an area >2000 km
2
, and ground magnetometer profiles across one example near Enniskillen show a negative anomaly of
c.
2000 nT. Synergistic display of the available gravity and aeromagnetic data for the area shows a close coincidence between the Dromore gravity high and this dyke swarm and suggests the presence of a basic intrusive body at depth as the source of the magma for the dykes.
Metallogenic evolution in Wales: constraints from lead isotope modelling
Authors: FLETCHER C. J. N. , SWAINBANK I. G. , COLMAN T. B.
Published: December 2007

Galena has been collected from different styles of mineralization throughout Wales. Galenas from the Ordovician volcanogenic mineralization at Parys Mountain, north Wales, give highly variable lead isotope ratios, which could have been produced either by a two-stage history or by the mineralizing fluids interacting and mixing with radiogenic lead derived from uranium-rich upper crust. The variation in the lead isotopic ratios of galena from veins cutting lower Palaeozoic sediments is considered to be due to separate periods of mineralization during the early Devonian and early Carboniferous. The most likely source for this mineralization is the thick sequence of lower Palaeozoic basinal mudstones. Both the disseminated galena in Mesozoic sedimentary rocks and galena from veins within the underlying Carboniferous Limestone give Triassic and Jurassic model lead ages, which agree with mineralization ages deduced from geological considerations. It is suggested that the source for this lead mineralization is the underlying Carboniferous shales. These and other galenas from Wales have significantly different isotope ratios to those from the Irish carbonate-hosted ore deposits, which would indicate that the mineralizing fluids had either different sources or evolutionary histories.
A possible concealed granite beneath part of Anglesey, North Wales
Authors: CORNWELL J. D. , SMITH I. F.
Published: December 2007

A closed Bouguer gravity low is revealed by land and marine gravity survey data centred on Holyhead Bay, northwest Anglesey. The anomaly extends across areas on land and offshore mainly occupied by Precambrian rocks. A concealed granite offers the best explanation for the anomaly and a late Caledonian age seems most probable for the intrusion, although Precambrian–early Cambrian ages are also possible. The existence of a granite in this area could have influenced the development of mineralization and the low density rock mass also formed a relatively buoyant core to the basement block. It could therefore have been instrumental in the preservation of this Precambrian structural high.
Cratons, mobile belts, alkaline rocks and continental lithospheric mantle: the Pan-African testimony
Authors: BLACK R. , LIEGEOIS J.-P.
Published: December 2007

Several late-collision and intraplate features are not entirely integrated in the classical plate tectonic model. The Pan-African orogeny (730–550 Ma) in Saharan Africa provides some insight into the contrasting behaviour of cratons and mobile belts. Simple geophysical considerations and geological observations indicate that rigidity and persistence of cratons are linked to the presence of a thick mechanical boundary layer, the upper brittle part of the continental lithospheric mantle, well attached to an ancient weakly radioactive crust. The surrounding Pan-African mobile belts, characterized by a much thinner mechanical boundary layer and more radioactive crust, were the locus of A-type granitoids, volcanism, tectonic reactivation and basin development during the Phanerozoic. During oceanic closures leading to the assembly of Gondwana, lithosphere behaviour was controlled by its mechanical boundary layer, the crust being much less rigid. We suggest that the 5000 km wide Pan-African domain of Saharan Africa, a collage of juvenile and old reactivated basement terranes, has suffered regional continental lithospheric mantle delamination during the early stages of this orogeny, as has been postulated for the more recent Himalayan orogeny in Tibet. Delamination of the continental lithospheric mantle and juxtaposition of crust against hot asthenosphere can explain many features of the late Pan-African (around 600 Ma): reactivation of old terrains, abundant late-tectonic high-K calc-alkaline granitoids, high temperature-low pressure metamorphism, important displacements along mega-shear zones and mantle-derived post-tectonic granitoids linked to a rapid change in mantle source. Recycling into the asthenosphere of large amounts of continental lithospheric mantle delaminated during the Pan-African, can provide one of the reservoirs needed to explain the isotopic compositions of ocean island basalts. Lastly, the lithospheric control over the location of the alkaline rocks enjoins us to consider the thermal boundary layer (the lower ductile part of the continental lithospheric mantle) as a major mixing source zone for these rocks.