bluuebunny/crossref_metadata_2025 huggingface dataset:
Geophysical evidence for basement structure in Suffolk, East Anglia
Authors: CORNWELL J. C. , KIMBELL G. S. , OGILVY R. D.
Published: December 2007

Boreholes through the Quaternary, Tertiary and Mesozoic sequences of East Anglia provide general evidence that the Palaeozoic basement in the northern part of the UK segment of the London-Brabant Massif occurs at depths of less than 150 m to more than l000 m below sea level. The widely scattered nature of the borehole evidence gives an impression that the basement surface is planar. However, in the northern part of Suffolk, Bouguer gravity anomaly data indicate an elongate basement ridge which also seems to be related to the presence of a concealed Chalk high separating basins of Crag (Plio-Pleistocene) deposits. An investigation of this gravity feature using transient electromagnetic (TEM) soundings confirmed that the gravity high is due to a ridge rising to 140 m below sea level, about l00 m above the surrounding basement. The ridge is believed to be associated with NE- to NNE-trending faults, which also exerted some form of overall structural control on the deposition of the Crag. The feature appears to be comparable with structures affecting Eocene and older rocks reported in the southern North Sea. Part of the success of the TEM method in the area is due to the presence of a very low resistivity zone in the power part of the Chalk which contrasts strongly with the underlying resistive basement. Modelling of the geophysical data indicates that the zone is almost certainly due to the presence of saline formation water in the Chalk. The TEM method therefore has potential applications to the hydrogeological investigation of the Chalk, the major groundwater aquifer in the UK.
The sedimentological significance of concentrically laminated burrows from Lower Cretaceous Ca-bentonites, Oxfordshire
Authors: GOLDRING R.
Published: December 2007

Concentrically laminated burrows are common at outcrop and in core in Mesozoic and younger shallow marine siliciclastic sedimentary rocks. They are generally referred to
Cylindrichnus concentricus
Howard. an imperfectly understood ichnotaxon here considered to be a
nomen dubium.
Concentric lamination can be formed in several ways: either actively contrived by the producer, or by passive filling (draught filling) of a burrow with constricted apertures. In the latter case the fill cannot be regarded as an ichnotaxobase. Passive infilling of concentrically laminated, bow-form, deep-tier burrows is described from Lower Cretaceous (Aptian) sedimentary rocks associated with fuller's earth (Ca-bentonite) at Baulking, Oxfordshire. The distribution and taphonomy provide information on the sedimentological setting of the tephra and associated sediments. The lower seam was already compacted and of clay grade before it was repeatedly eroded and colonized the latter has significantly reduced seam quality. Subsequent sedimentation was essentially aggradational, including the uniquely preserved upper bentonite which had a complex recovery history.

Among other ichnotaxa, concentrically laminated
Thalassinoides
(and possibly
Diplocraterion
) may be misidentified as
‘Cylindrichnus’.
Since
Thalassinoides
and
Diplocraterion
are important indicators of bounding surfaces, information of significance in sequence stratigraphy may be lost as a consequence. Citations of
Cylindrichnus
in the literature are briefly discussed: many must be assigned to other ichnotaxa.
The Ansó transect of the southern Pyrenees: basement and cover thrust geometries
Authors: TEIXELL A.
Published: December 2007

A balanced geological section through the western central Pyrenees allows the Alpine geometry of Hercynian basement to be determined. This shows marked differences with other transects of the southern part of the chain. Basement-involved thrust sheets do not form an antiformal stack, but are imbricated and define steps separated by frontal culmination limbs. Basement thrusts propagate upwards and have formed distinct thrust systems in the cover. In this transect, the North Pyrenean Zone is bounded to the south by gently dipping thrusts of large displacement, and the Axial Zone massif, at its western termination area, is a flat-topped culmination caused by a single thrust fault, the Gavarnie thrust. This thrust emerges to the south in the interior of the syntectonic Jaca Basin, the geometry of which is also controlled by underlying basement thrusts. Various generations of structures can be correlated with distinct episodes of syntectonic sedimentation. A sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation. Tectonic shortening is 48 km, almost half of that estimated further to the east for the southern Pyrenees. The structure deduced at the ECORS-Pyrenees seismic section cannot be translated to this transect.
The Caledonian strike-swing and associated lineaments in NW Ireland and adjacent areas: sedimentation, deformation and igneous intrusion patterns
Authors: HUTTON D. H. W. , ALSOP G. I.
Published: December 2007

Part of the major swing in strike associated with the Greenland-Labrador Promontory of the North Atlantic Caledonides is exposed in considerable detail in the metasedimentary and meta-igneous rocks of the Neo-Proterozoic Dalradian Supergroup in northwest Ireland. We show that the strike swing controlled Dalradian stratigraphy and sedimentation patterns and is therefore at least
c.
600 Ma in age. Our interpretation of the stratigraphy allows a reconstruction of this promontory in the Laurentian continental margin and shows that it separated a NE-trending. gently inclined and broad continental shelf in the north from an E-trending. more steeply inclined and narrower shelf to the south. Once established in the geometry of the Dalradian sequence, the strike swing and basement promontory had a major influence on Caledonian deformation patterns. It controlled: the nucleation of major folds: the geometry of the regionally developed primary cleavages; the facing direction of the early folds: and it also acted as a major buttress in perturbing and deflecting. on a regional scale, the orogenic transport vector.

Accurate restoration of the sinistral displacement on a late Caledonian fault system shows that the apices of the strike swing at different stratigraphic levels, and their associated sedimentary facies changes, define a line trending approximately N12ºE. This line is coincident with (again, after fault restoration): six out of the eight Devonian Donegal granites: the vast majority of the mantle-related, ultrabasic ‘Appinite’ suite (with most of these bodies concentrated at the intersection of this line and the NE-trending Main Donegal Granite shear zone): and the highest density of the Neo-Proterozoic basic tholeiite suite. Thes e and other data are used to suggest that the Donegal Lineament is the expression of a major steeply inclined fault in the basement beneath the Dalradian which is intimately related to the morphology of the promontory. The fault, which might be as old as 1800 Ma, probably reached down into the lithospheric mantle. controlling igneous activity, including the ascent, emplacement site and perhaps sources of the magmas. Another complementary strike swing and parallel lineament is described from the Dalradian rocks of the adjacent part of Scotland. It is suggested that these and other major lineaments (i.e old pre-Caledonian faults) which have either NNE. NE, or ESE trends reflect not so much the location of the northern British Isles at a 120º triple junction during Iapetus rifting. but rather the exploitation of these pre-existing trends in the pre-Caledonian Atlantic borderlands during Iapetus opening.
Insights on the thermal evolution of the Ligurian Apennines (Italy) through fission-track analysis
Authors: BALESTRIERI M. L. , ABBATE E. , BIGAZZI G.
Published: December 2007

Apatite fission-track analysis has been applied on 24 samples from the geometrically upper units (Internal and External Ligurids) of the Northern Apennines nappe pile. They yield ages between
c.
20 Ma and c. 6 Ma. Two samples were also dated with fission tracks in zircon (ages of
c.
155 Ma and c. 199 Ma). Together the data reveal that during post-Late Cretaceous compression the Internal Ligurids reached temperatures to completely anneal fission tracks in apatite
(T>c.
120 °C) but not in zircon
(T<c.
300°C). After Eoccne continental collision these rocks were cooled (below c. 120°C) and started again to retain fission tracks in apatite. Since the Oligocene a further burial under episutural sediments ensued that caused a partial to total apatite fission-track annealing. During a final phase of cxhumation the sedimentary cover was removed. This exhumation can be linked to Late Miocenc extensional tectonics, that started at c. 8–9 Ma in the central and southern portions of the study area.
Silurian turbidite provenance on the northern Avalonian margin
Authors: McCaffrey W. D. , Kneller B. C.
Published: December 2007

The Windermere Supergroup of NW England was deposited in a foreland basin on the northern margin of Eastern Avalonia and preserves an almost complete Ashgill to Pøídolí sequence. It was ideally positioned to record provenance changes associated with the closure of the Iapetus Ocean. Petrographic, geochemical and Nd isotopic parameters show distinct and concordant temporal trends. The late Ashgill to early Llandovery is characterized by progressive hemipelagic dilution of material derived from the underlying Borrowdale Volcanic Group. From the Llandovery onward, petrographic and geochemical data indicate supply from a recycled orogen source: input from the Scandian orogen may be inferred. No conclusive evidence is recorded of Laurentian input into the basin. By the late Wenlock a unified sedimentary system probably spanned the Iapetus ocean. An abrupt reversal in provenance trends towards the end of the Ludlow records basin inversion, the occlusion of the Iapetus seaway and concomitant cannibalization of older foreland basin sediments. Provenance data derived from upper Wenlock to Pøídolí sediments aid the characterization of marine foreland basins.
Devonian marine incursions into the Orcadian Basin, Scotland
Authors: MARSHALL J. E. A. , ROGERS D. A. , WHITELEY M. J.
Published: December 2007

BP/Chevron well 14/6–1 drilled in the East Orkney Basin has penetrated Devonian sedimentary rocks which can be dated palynologically as within the latest Givetian to early Frasnian interval. This microflora contains the first substantiated record in Western Europe of
Archaeoperisaccus,
a spore hitherto regarded as restricted to northern Laurasia. Three grey-green intervals within the well contain marine microfossils which provide the first direct evidence for the movement of marine waters into the northern part of the Old Red Sandstone continent.

Onshore an Eday Marls section in the Bay of Berstane, Orkney contains a marine microfauna which demonstrates the presence of a marine incursion of mid––late Givetian age. This is the first record of a Devonian marine incursion in Scotland.

Combination of this palaeontological data with sedimentological studies of the Eday Marls and Upper Old Red Sandstone suggests that a wide flat sabkha plain extended eastwards from the onshore Orcadian Basin during the later stages of its infill, and was subjected to episodic marine incursions. These incursions are tentatively linked with marine transgressions into the Argyll area of the Central North Sea.

Two orders of cyclicity occur within the dated Devonian interval of 14/6–1, and are interpreted as resulting from orbital cyclicity (at periodicities of 39.5 and 413.9 ky). This indicates that the control on the Devonian sea level maxima may have been orbital cyclicity. These marine incursions are speculatively correlated to high-stands on the Devonian sea-level curve. The Bay of Berstane marine incursion representing the Taghanic Onlap whilst those in 14/6–1 are the Rhinestreet, Middlesex and Genundewa transgressions. Reconsideration of the palaeogeography of the northern margin to the marine Devonian indicates that the sea entered the Orcadian Basin from the east along the Tornquist Zone at the margin of the Fenno-Scandian High.
Evolution of landscapes in northern South Australia in relation to the distribution and formation of silcretes
Authors: SIMON-COINÇON R. , MILNES A. R. , THIRY M. , WRIGHT M. J.
Published: December 2007

Geomorphological features on the southwestern margins of the Lake Eyre Basin provide a basis for interpreting the evolution of old landscapes containing pedogenic and groundwater silcretes. and thick bleached and weathered profiles. Recurrent sequences of cut-and-fill and duricrust formation have been identified and related to major sea level changes and tectonic movements in the Lake Eyre Basin.

An extensive high pediment had formed around a basement inlier by the late Eocene. An armour of pedogenic silcrete developed on this pediment under alternating dry and wet climates during the late Eocene and Oligocene. The characteristic kaolinite + opal + alunite + gypsum assemblage of the bleached profiles formed in acid saline groundwaters during the Miocene at a time of regional low water table and arid climate. Groundwater silcretes formed in the bleached profile in response to dissection of the high pediment. They are related to a period of high groundwater tables. humid climate. and gradual sinking of the Lake Eyre basin. In the meantime, widespread low pediments (glacis) formed in Lake Eyre catchment, possibly in the early Pliocene.

There is a good correspondence between a geomorphic approach, taking in to account the relationship between weathering features and palaeolandscapes, and the information provided from stratigraphic studies in the region.
Early Cretaceous denudation related to convergent tectonics in the Baikal region, SE Siberia
Authors: VAN DER BEEK P.A. , DELVAUX D. , ANDRIESSEN P.A.M. , LEVI K.G.
Published: December 2007

We present 24 new apatite fission track (AFT) ages and 18 track length measurements from the Baikal region, SE Siberia. Most samples have AFT ages between 140 and 100 Ma, with relatively high mean track lengths (
c.
13.2
μ
m). The relationship between AFT ages, elevation and mean track lengths indicate that the samples record rapid cooling during the Early Cretaceous (140–120 Ma), as also shown by thermal history inversion of track length distributions. Cooling took place during a Late Jurassic-Early Cretaceous orogenic phase, related to closure of the Mongol-Okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting, basin inversion and large vertical motions. The variation in AFT ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role. Minimum amounts of Early Cretaceous denudation are estimated at 2–3 km.
Dinoflagellate cysts and mid-Oligocene chronostratigraphy in the central Mediterranean region
Authors: WILPSHAAR M. , SANTARELLI A. , BRINKHUIS H. , VISSCHER H.
Published: December 2007

Two new dinoflagellate cyst zones are proposed, linking previously established zonal schemes for the Eocene–Oligocene and Oligocene–Miocene successions in the central Mediterranean region. The
Hystrichokolpoma pusillum
(Hpu) and
Chiropteridium lobospinosum
(Clo) interval zones are based on the Contessa Quarry and Monte Cagnero sections (central Italy), and are correlated with previously established magnetostratigraphical and biostratigraphical schemes. The base of the Chattian is considered to correlate with Chron Cl0n. In central Italy, the most distinct dinoflagellate cyst event associated with this chron is the first occurrence of
Distatodinium biffii,
marking the base of the
Distatodinium biffii
(Dbi) Zone. Indirect evidence also suggests that the first occurrence of
Distatodinium biffii
is above but close to the base of the Chattian Stage in its type area in northwest Germany, thus making it an important marker. Other possible markers for the base of the Chattian are the last occurrence of
Areosphaeridium pectiniforme
and the lowest acme of
Chiropteridium
spp. The latter may be related to the major mid-Oligocene sea-level fall (TA–TB Exxon supercycle boundary), also considered to represent the base of the Chattian and previously correlated with Chron Cl0n. However, in the Contessa Quarry section this dinoflagellate cyst event is associated with the older Chron C11.
Crystallization of the Shap Granite: evidence from zoned K-feldspar megacrysts
Authors: COX R. A. , DEMPSTER T. J. , BELL B. R. , ROGERS G.
Published: December 2007

Textural, chemical and Sr isotopic studies of feldspars from the subsolvus Shap granite, northern England, demonstrate that a number of magma mixing events have dominated the evolution of this pluton. K-feldspar megacrysts are phenocrysts formed in the magma chamber. They contain a number of Ba-rich zones that developed during periods of slight dissolution and regrowth linked to the hybridization of the granite by the intrusion of basic magmas. Diorite enclaves represent the relicts of these magmas and these also contain K-feldspar megacrysts, which show evidence of major dissolution. They are xenocrysts picked up from the host granite and incorporated in the basic magma. Increasing H
2
O contents during fractional crystallization caused a late switch from growth of megacrysts to finer-grained K-feldspars in the matrix. The chemically and isotopically zoned K-feldspar megacrysts preserve an exceptional record of the evolution of the magma, and the zones also had a significant influence on the development of exsolution microtextures during cooling.
Aluminium loss during sandstone diagenesis
Authors: WILKINSON MARK , HASZELDINE R. STUART
Published: December 2007

Petrographical observations from a sandstone buried to between 3.2 and 5.7 km in the North Sea Central Graben suggest a significant change in bulk chemistry during burial. The sand contained 35% or more feldspar upon deposition, but due to extensive dissolution, only 5% remains in the deep sandstones. This has released much more Al than is currently contained as authigenic minerals: up to 1460
μ
mol cm
−3
of Al have been exported. This deep secondary porosity is economically important, but its recognition by petrographic textures is unreliable, as are bulk-chemical provenance studies of deeply buried sedimentary and metamorphic strata.
Miocene, north-vergent extensional displacements along the Main Mantle Thrust, NW Himalaya, Pakistan
Authors: VINCE KATHRYN J. , TRELOAR PETER J.
Published: December 2007

Structural data from N Pakistan show that early Tertiary, S-vergent structures within the upper part of the Indian Plate and the Himalayan suture zone were overprinted by regionally developed N-vergent extensional structures. Such extension has been suggested, but not previously described from the NW Himalaya. Cooling histories suggest extension was Miocene in age. Extension was most likely the result of isostatic rebound resultant from crustal, or lithospheric, thickening and/or delamination.
Pan-African magmatism in the Wadi El-Imra district, Central Eastern Desert, Egypt: geochemistry and tectonic environment
Authors: FURNES H. , EL-SAYED M. M. , KHALIL S. O. , HASSANEN M. A.
Published: December 2007

The Late Proterozoic rocks of the Wadi El-Imra district of the Central Eastern Desert, Egypt, comprise a metagabbro-diorite complex (oldest) and Older and Younger Granitoid complexes. Trace element characteristics show that the basic and granitoid rocks are of calc-alkaline affinity, but some of the Younger Granitoids grade into alkaline granites. The º
Nd
values of the the basic and granitoid rocks range from +8.3 to +4.9, and Nd model ages are younger or rather similar to crystallization ages. These data suggest a predominant depleted mantle derivation, indicating formation by subduction in an oceanic setting. REE patterns of the granitoid rocks suggest different modes of petrogenesis. This, coupled with the occurrence of amphibolite xenoliths in the Older Granitoids, may indicate that some of these rocks represent partial melts from basic rocks that have been amphibolitized at deep crustal levels of the oceanic arc.
Implications of new microfloral evidence from the Clew Bay Complex for Silurian relationships in the western Irish Caledonides
Authors: WILLIAMS D. M. , HARKIN J. , HIGGS K. T.
Published: December 2007

The supposed Laurentian margin in western Ireland is separated from an Ordovician arc-related basin by the Clew Bay Complex and two Silurian successions, informally termed the Croagh Patrick Silurian and the Louisburgh Silurian, whose relationships are enigmatic. Palynomorphs, tubular structures and sheets of cuticle from turbidites within the Clew Bay Complex indicate a Silurian (Wenlock) age. In the light of these new data and reappraisal of contacts, the Croagh Patrick Silurian is now considered to be in tectonic contact with the Clew Bay Complex. The Louisburgh Silurian may also be in tectonic contact with parts of the Clew Bay Complex and unconformable on other parts, but is probably younger than previously thought. The Silurian age of elements of the Clew Bay Complex, and the relationship of the complex with other Silurian successions in western Ireland, indicate that significant deformation occurred in this part of the Caledonides during mid to end Silurian times, and imply that significant Silurian-Devonian terrane movement took place.
First evidence of ultrahigh-temperature decompression from the granulite province of southern India
Authors: BROWN M. , RAITH M.
Published: December 2007

Sapphirine-bearing, orthopyroxene-sillimanite ± garnet granulites of the Palni Hill Ranges record evidence of ultrahigh-temperature metamorphism during which primary mineral assemblages were partially overprinted by a succession of reaction coronas and symplectites that together suggest decompression. Model system petrogenetic grids allow constraints to be placed on the evolution of
P–T
conditions as recorded by reaction relationships of successively developed mineral assemblages; thermobarometry on garnet-bearing assemblages allows minimum constraints to be placed on
P–T
conditions for the primary mineral assemblages. Primary mineral assemblages suggest
P–T
conditions of
c.
12 kbar and
c.
900-1000 "C. Secondary mineral assemblages in reaction textures show a two-stage decompression to probable
P–T
conditions of
c.
5 kbar and
c.
850 °C. The inferred
P–T
path is clockwise.
A late Vendian age for the Kinlochlaggan Boulder Bed (Dalradian)?
Authors: EVANS RICHARD H. S. , TANNER P. W. Geoff
Published: December 2007

The Kinlochlaggan Boulder Bed occurs in Neoproterozoic Dalradian rocks of the Grampian Mountains of Scotland. It is currently thought to represent a glacial event (
c.
800 Ma) unique in the North Atlantic region, and be part of a sequence correlated by different workers with either the Grampian or Appin groups. We correlate the Boulder Bed with the Port Askaig Tillite of Vendian (
c.
650 Ma) age, and deduce that the sequence in which it occurs belongs to the younger Argyll Group. The latter is preserved within the D2 Kinlochlaggan Synform, and a previously unrecognized discontinuity of regional importance may separate inverted Argyll Group rocks from the underlying Grampian Group.
A pliosaur (Reptilia, Sauropterygia) exhibiting pachyostosis from the Middle Jurassic of England
Authors: CRUICKSHANK A. R. I. , MARTILL D. M. , NOÈ L. F.
Published: December 2007

A new and unusual pliosaurid from the Peterborough Member, Oxford Clay Formation (Callovian, Jurassic) of Cambridgeshire, UK, exhibits a type of pachyostosis and bone thickening of the rib cage and vertebrae.
Pachycostasaurus dawni
gen. et sp. nov. was most probably a benthic feeding carnivore with a generalist diet that included fish and invertebrates, and was a slow swimming underwater flyer with ventrally placed ballasting of the skeleton to resist roll. The apparent rarity of this pliosaur may indicate that it is allochthonous in the Oxford Clay biota.

From a palaeoecological viewpoint, the find is significant for two reasons. Firstly, as an air breathing animal that is thought to have fed on benthos or nektobenthos,
Pachycostasaurus
may have been important in transferring resources from the benthic food web to the surface food web. In a more general sense, the new find provides further insights into the possible trophic structure of aquatic animal communities during deposition of the Oxford Clay.
Interaction of Permo-Triassic and Jurassic extensional fault-blocks during the development of the northern North Sea
Authors: FÆRSETH R. B.
Published: December 2007

The main structural elements resulting from Late Permian-Early Triassic extension have been resolved across the total width of the northern North Sea. The northern segment of the basin (north of 61°N), bounded to the west by the Hutton Fault and to the east by the Norwegian mainland, was occupied by four westerly tilted half grabens, 25–35 km in width, prior to Jurassic extension. The central segment of the basin (60°20′–61°N) exhibits a full graben beneath the Jurassic Horda Platform, flanked by half grabens tilted towards the basin margins. The change in Permo-Triassic fault-block configuration, defining structural domains, is largely constrained by a basement discontinuity which runs diagonally (NE-SW) across the basin.

Maximum Jurassic extension is represented by several centres of subsidence, aligned NNE-SSW across a N-S-oriented and broader Permo-Triassic basin. Jurassic extension was concentrated within the Viking Graben proper south of 60°N, which in this area is represented by single westerly-tilted, en échelon half graben segments 20–25 km wide. The area affected by Jurassic extension becomes progressively wider to the north, again governed by the basement discontinuity, eventually encompassing the total width of the basin (
c.
200 km) north of 61°N.

The central segment of the northern North Sea displays the greatest contrast in Permo-Triassic and Jurassic structural styles and basin geometry. Jurassic stretching and faulting was negligible to the east (Horda Platform), precisely the area which had been the site of maximum Permo-Triassic stretching and fault activity. It has generally been assumed that Jurassic fault configuration along the eastern margin of the central segment of the Viking Graben, to a large extent reflects the reactivation of major Permo-Triassic faults. This study demonstrates the interference of Permo-Triassic and Jurassic basin geometries in this area, due to major faults of the two generations dipping in opposite directions. As a consequence, the E-tilted Oseberg Fault Block of Jurassic origin and
c.
20km in width, is underlain by a wider (
c.
35 km) and W-tilted Permo-Triassic fault-block.
Separation of multiple stress events by fault striation analysis: an example from Variscan and younger structures at Ogmore, South Wales
Authors: LISLE RICHARD J. , VANDYCKE SARA
Published: December 2007

The study of minor structures in Carboniferous and Triassic sedimentary rocks at Ogmore- by-Sea, Bridgend. reveals that the observed microstructures are the consequence of successive brittle deformation events. Age relationships can be deduced from sets of structures consisting of conjugate faults, oblique slip faults, tension gashes and stylolites. from which deductions can be made about the orientations of principal stresses corresponding to pre-and post-Triassic events. The demonstrable polyphase tectonic history at Ogmore and the occurrence of large numbers of striated faults at four sites allow the opportunity of testing a newly proposed strategy for palaeostress analysis from striated faults with complex stress histories. The new technique, based on the statistical procedure of cluster analysis, involves the sorting of fault-slip data into coherent dynamic setsasa preliminary stage of formal stress inversion. The fault sets separated using this technique yield stresses which are similar to those deduced from field observations. Four stress configurations are distinguished, of which two are pre-Triassic in age. Correlations with previously derived stresses are discussed.
New isotopic age determinations for the Torridonian, NW Scotland
Authors: TURNBULL MATTHEW J. M. , WHITEHOUSE MARTIN J. , MOORBATH STEPHEN
Published: December 2007

Isotopic data are used to determine a new chronology for the Torridonian of NW Scotland. The calcite fraction of the Stoer Group Limestone Member yields a Pb–Pb age of 1199 ± 70 (2
σ
) Ma (MSWD = 1.1). Rb–Sr whole-rock regressions from siltstones of the Diabaig and Applecross Formations (both Torridon Group) produce ages of 994 ± 48 (2
σ
) Ma (MSWD = 17) and 977 ± 39 (2
σ
) Ma (MSWD = 10) respectively. These dates, which agree well with palaeomagnetic estimates, are interpreted as the time of early diagenesis which is probably within error of the time of deposition. Previous isotopic age determinations are shown to be in error.

Size fractionsfrom shales of the Stoer Group and Applecross Formation have been analysed for Rb–Sr and produce ages of 689 ± 87 (2
σ
) Ma (MSWD = 14) and 667 ± 66 (2
σ
) Ma (MSWD = 55) respectively. They are used, together with Sm-Nd isotopic data, to suggest a thermal event affecting the entire Torridonian at this time.

Our new chronology for the Torridonian is consistent with the Proterozoic geology of Scotland and Laurentia. It suggests that deposition of the Stoer Group is contemporaneous with uplift of the Lewisian and the Torridon Group may be associated with the extensional collapse of the Grenville orogen. The
c.
700Ma diagenetic event is possibly related to Neoproterozoic rifting of the Laurentian margin.
Sm–Nd dating of garnet granulites from the Kohistan complex, northern Pakistan
Authors: YAMAMOTO HIROSHI , NAKAMURA EIZO
Published: December 2007

Sm–Nd mineral-isochron ages of garnet granulites in the southern part of the Kohistan complex are determined. The 91.0 ± 6.3 Ma age is obtained from a granulite body of the Jijal complex at Pattan and the 69.5 ± 9.3 Ma age is obtained from a granulite body of the Chilas complex at Zambil. These ages indicate that the granulite bodies at Pattan and at Zambil had cooled to below upper amphibolite facies by about 90 Ma and about 70 Ma respectively. The time of cooling of the granulite of the Jijal complex is comparable to the time-lapse of the Asia–Kohistan collision (102–75 Ma), although that of the Chilas complex is probably younger than the Asia–Kohistan collision and certainly older than the Asia–India collision (
c
50 Ma).
Formation of the Late Palaeozoic–Early Mesozoic Karakaya Complex and related ophiolites in NW Turkey by Palaeotethyan subduction–accretion
Authors: PICKETT ELIZABETH A. , ROBERTSON ALASTAIR H. F.
Published: December 2007

Several pre-Jurassic tectonic units in NW Turkey are crucial to the current debate regarding the timing and direction of subduction of Palaeotethys, a major ocean that separated Eurasia and Gondwana in Late Palaeozoic–Early Mesozoic times. The most critical unit is the Karakaya Complex, a deformed, low-grade assemblage of oceanic origin which comprises a NW-verging, SE-dipping stack of tectonostratigraphic units, here interpreted as a Palaeotethyan accretionary complex. The units display lithologies consistent with origins in seamount, trench, abyssal and rifted carbonate platform settings. Clastic basin sequences developed on top of the complex. Other relevant tectonostratigraphic units in the area include ultrabasic rocks of supra-subduction zone affinity, which tectonically overlie Permian carbonate platform units with intervening metamorphic soles and mélanges. Restored structural trends suggest the presence of a southward-dipping Palaeotethyan subduction zone bordering Gondwana-related units during the Late Permian–Triassic. This was probably additional to more important regional northward subduction along the southern margin of Eurasia from the Eastern Mediterranean to the Himalayas.
From small-scale faults to plate kinematics: palaeostress determinations in a fragmented arc complex (SE Livingston Island, S Shetlands, Antarctica)
Authors: SANTANACH P. , PALLÀS R. , SÀBAT F. , MUÑOZ J. A.
Published: December 2007

Analysis of the polyphase fault population of southeastern Livingston Island led us to establish three brittle deformation phases characterized by homoaxial stress tensors. One of the horizontal axes trends NW-SE, parallel to the transform faults governing the relative movement between the Phoenix and Antarctic plates. On the basis of the principles of symmetry these tensors are interpreted as corresponding to the regional stress field, and the transition between the phases is seen as reflecting changes in the relative values of the principal axes of their corresponding stress tensors. Phases 1 and 2 correspond to strike slip regimes, the first having NW-SE-oriented (σ
l
(maximum principal compressive stress), whereas σ
1
of phase 2 has a NE-SW trend. Phases 2 and 3 show a NW-SE-oriented σ
3
(minimum principal compressive stress). The decreasing magnitude of the NW-SE stress axis during the recorded history is interpreted as being related to the decreasing velocities of the interacting plates caused by the cessation of the accretion at the Antarctic-Phoenix Ridge. The kinematic evolution of the analysed fault population can be understood assuming that faults form according to the Anderson model, that extensional dykes and veins form perpendicular to u3, and that fault slip on pre-existing fractures occurs parallel to the maximum shear stress direction on those planes.
Generation of the Tay Nappe, Scotland, by large-scale SE-directed shearing
Authors: KRABBENDAM M. , LESLIE A. G. , CRANE A. , GOODMAN S.
Published: December 2007

Recent mapping in the Glen Shee Area, Central Scotland, has revealed an array of several large-scale F1 folds within the 'Flat Belt' of the Tay Nappe. Strata within the 'Flat Belt', forming part of the lower limb of the Tay Nappe, are thus not entirely inverted, and the traditional view that the Nappe in this area comprises a single SE-facing, recumbent anticline is rejected. It is demonstrated that the sense of shear of D2 was top-to-the-SE, resulting in NW-verging F2 folds by strong D2 strain partitioning. Strain estimates indicate adisplacement of 10–50 km during D2 shearing. In the proposed model, originally upright F1 folds were modified by a major D2 shearing event that produced a shallow NW dipping S2 foliation in the 'Flat Belt'. The upper limit of D2 deformation forms the boundary between the strongly deformed and inverted 'lower limb' and the right-way-up 'upper limb' which is undeformed by D2, and is now mostly removed by erosion. The D2 shear event was responsible for the gross stratigraphic inversion in the Flat Belt. The Tay Nappe is considered here as formed by a crustal-scale shear zone; in this model there is no necessity to invoke a root zone.
Late Archaean to early Proterozoic granitoid magmatism and high-grade metamorphism in the central Limpopo belt, South Africa
Authors: JAECKEL P. , KRÖNER A. , KAMO S. L. , BRANDL G. , WENDT J. I.
Published: December 2007

The Central Zone of the Limpopo belt in southern Africa has previously been interpreted as a segment of Archaean crust which experienced its main deformation and metamorphism around 2.7 Ga ago. We report new single zircon U/Pb and Pb/Pb ages for granitoid gneisses, supracrustal rocks and anatectically derived granitic melt patches in the area around Messina, South Africa. The Sand River Gneiss is a composite suite of tonalitic to trondhjemitic rocks with protolith ages between 2.6 and 3.2 Ga.

The Singelele gneiss, a heterogeneous granodioritic to quartz monzonitic rock, has protolith ages between 2.55 and 2.58 Ga. Since both the Sand River and Singelele gneisses experienced polyphase high-strain ductile deformation this must have occurred later than 2.55 Ga ago.

Granulite-facies pelitic gneisses of the Beit Bridge Complex contain abundant spherical, multifacetted zircons which reflect new zircon growth near or at the peak of metamorphism. These zircons provide ages with a mean at 2026.5 ± 6.3 Ma which is interpreted as reflecting a high
P
–
T
event (>10 kbar, 825 ± 25°C).

Granitic melt patches in the metapelites as well as in the Sand River Gneiss and anatectic granites are probably related to rapid near-isothermal decompression to below 3–5 kbar and 600–750°C. These rocks contain new magmatic zircons which yielded a mean age of 2005.6 ± 4.4 Ma and probably reflect a crustal melting event resulting from rehydration of the granulitic assemblage.

Our zircon data support previous suggestions for only one single granulite-facies event in the Central Zone, and we suggest that this event occurred
c.
2027Ma ago. Since most of the deformation seen in the gneisses of the Messina area must have occurred later than 2.55 Ga ago, it is likely that the ‘Limpopo Orogeny’, at least in the Central Zone, is not an Archaean event but took place in the early Proterozoic.
Occurrence and field relationships of ultrahigh-pressure metagranitoid and coesite eclogite in the Su-Lu terrane, eastern China
Authors: WALLIS S. R. , ISHIWATARI A. , HIRAJIMA T. , YE K. , GUO J. , NAKAMURA D. , KATO T. , ZHAI M. , ENAMI M. , CONG B. , BANNO S.
Published: December 2007

Coesite eclogite is associated with metagranitoid in a 50×100 m
2
outcrop within the regionally developed amphibolite-facies Su-Lu orthogneiss. Primary intrusive relationships between the metagranitoid and basic rocks and bulk-chemistry analyses show that together they represent a composite igneous body that has subsequently been strongly deformed and metamorphosed. The presence of rutile, sodie pyroxene, corona garnet, and possible pseudomorphs after coesite all suggest very high pressures of metamorphism in the metagranitoid. This is the first documented occurrence of ultrahigh-pressure (UHP) metagranitoid outside of the European Alps. The existence of UHP metagranitoid shows that low density of rocks does not necessarily prevent subduction to mantle depths. Even at peak metamorphic conditions the UHP composite igneous body reported here would have a bulk density less than the mantle. Buoyancy forces may, therefore, have been important in the early exhumation of this unit. Other outcrops of coesite eclogite in the Su-Lu region may also have been originally metamorphosed along with low-density granitoid rocks.
Palaeoecological and evolutionary significance of anatomically preserved terrestrial plants in Upper Carboniferous marine goniatite bullions
Authors: SCOTT A. C. , GALTIER J. , MAPES R. H. , MAPES G.
Published: December 2007

Anatomically preserved plants are described from marine goniatite bullions of Marsdenian age (Namurian B, Upper Carboniferous) from Star Wood, Oakamoor, Staffordshire, England. They comprise stems and petioles, up to 15 cm long, predominantly of cordaites
(Mesoxylon)
and pteridosperms
(Sutcliffia),
with rare calamites, ferns and lycopsids, and are preserved as calcareous permineralizations. Rare fusainized plant fragments are also found. The flora is similar, although comprising fewer species, to the roof nodule floras of Langsettian (Westphalian A) age from Lancashire which occur above coal seams yielding calcareous coal balls. The plants preserved in these roof nodules probably grew in well-drained, slightly elevated lowlands, not inundated during marine transgression, and contrast in botanical composition to the floras of lowland peat-forming mires represented in typical coal ball floras. The Oakamoor assemblage likewise probably represents an assemblage living in well-drained elevated areas which drifted into the sea and was preserved in sediment-starved carbonates during the height of the marine transgression. These species of plants appear not to have become part of lowland mire ecosystems until later in the Carboniferous. The occurrence of this flora pre-dates that previously described from the Westphalian Coal Measures, and extends the range of several important Upper Carboniferous plant taxa.
Reactivation of Archaean strike-slip fault systems, Amazon region, Brazil
Authors: PINHEIRO ROBERTO V. L. , HOLDSWORTH ROBERT E.
Published: December 2007

The Itacaiúnas Belt on the southeastern margin of the Amazonian Craton comprises two E-W-trending Archaean fault zones (Carajás and Cinzento strike-slip systems) developed sub-parallel to a broad zone of earlier ductile shearing. Older basement rocks display a pervasive E-W-trending mylonitic fabric, formed at high temperatures during sinistral transpression
c.
2.8 Ga. A sequence of younger Archaean cover rocks was deformed under low greenschist facies conditions during a second phase of sinistral transpression associated with retrogression and reworking of basement fabrics. All these rocks are overlain unconformably by very low grade to unmetamorphosed volcanic and sedimentary rocks of Late Archaean-Early Proterozoic age. The Carajás and Cinzento strike-slip fault systems formed during subsequent regional dextral transtension (c. 2.6-2.7 Ga) which down-faulted cover sequence rocks into dilational fault jogs. Later sinistral transpression (>
c
. 1.9 Ga) partially inverted these dilation zones, producing oblique compressional faults and folds evident mainly in cover rocks. Renewed fracturing, regional emplacement of granitic plutons and swarms of dykes
c.
1.8 Ga were followed by fault-controlled deposition of immature sandstones and conglomerates. Phanerozoic activity is limited, although some faults display evidence of minor neotectonic activity. The waning influence of the basement architecture and decreasing intensity of later reactivations is consistent with lithosphere-scale weakening with a finite life span.
A mechanical model for the reactivation of compartmental faults in basement thrust sheets, Muzelle region, Western Alps
Authors: WIBBERLEY C. A. J.
Published: December 2007

Most inherited Mesozoic extensional faults in the French external Alps strike approximately NNE–SSW, perpendicular to Alpine thrusting directions. In the Muzelle region of the NW Pelvoux Massif, the Vallon compartmental fault is a Mesozoic WNW–ESE-trending basement fault which was reactivated as a dextral strike-slip fault during the Alpine orogeny. Because this fault is parallel to the emplacement direction of the thrust sheet, it divides the thrust sheet into regions of diVerent emplacement rates at diVerent times. A model is proposed for compartmental-fault reactivation in which a varying proportion of compressible cover to rigid basement either side of the fault results in a strain incompatibility during Alpine shortening, which is resolved by reactivation.
The East Irish Sea and adjacent basins: new faults or old?
Authors: NEEDHAM T.I.M. , MORGAN RICHARD
Published: December 2007

The East Irish basin is characterized by three sets of faults, striking N-S, NE-SW and E-W. The Menai Strait fault system bounds the basin to the south and shows pre-Caledonian to Cenozoic movement. This span of activity contrasts with similarly oriented faults, to the north of the basin, which did not exist before the early Carboniferous. N-S faults have a similarly diverse history. Some may have influenced Silurian sedimentation and controlled the disposition of Ordovician volcanic centres in Snowdonia, a contrast with N-S-striking faults in the north of the area which originated as steep strike-slip faults during the late-Silurian. E-W faults control Dinantian and Permo-Triassic thickness variations although, unlike the other fault trends, pre-Carboniferous precursors are not apparent. Some of the basin-bounding faults developed as wholly new faults during Permo-Triassic extension.
Fault reactivation in the Junggar region, northwest China: the role of basement structures during Mesozoic-Cenozoic compression
Authors: ALLEN MARK B. , VINCENT STEPHEN J.
Published: December 2007

Basement structures exposed at the margins of the Junggar Basin were created during the Altaid orogeny in the Late Palaeozoic. The most prominent structures are backstops to subduction-accretion complexes (North Tien Shan Fault), or major thrusts within these complexes (Dalabute and Kelameili faults). Both types of basement structure are far more common in accretionary, Turkic-type, orogens such as the Altaids than true sutures. Probably the only suture
sensu stricto
in the Junggar area is cryptic, and lies under the Junggar Basin’s thick Mesozoic-Cenozoic cover. The exposed Palaeozoic fault zones have been reactivated by Mesozoic-Cenozoic compressional events, which are the long-distance expression of orogenies at the southern margin of Asia. Latest Palaeozoic and Mesozoic events reactivated a larger number of fault zones than have been affected by the Cenozoic India-Asia collision, possibly because of an increase in the strength of the Junggar basement over time, following Late Permian rifting. Cenozoic strain is partitioned between strike-slip motion on basement structures within the Palaeozoic orogenic belts around the Junggar Basin, and numerous thrusts and transpressive faults in regions marginal to and within the basin itself. Most major strike-slip faults are reactivated structures, and occupy narrower zones than their Palaeozoic precursors. Thrust zones follow the Palaeozoic basement grain, but active faults have propagated into the Mesozoic-Cenozoic cover.
Backthrusting on the BIRPS deep seismic reflection profiles, Banda Arc, Indonesia, a response to changing slab inclination?
Authors: CHARLTON T. R.
Published: December 2007

The recently published BIRPS BANDA deep seismic profiles across the Banda arc-continent collision complex indicate major backthrusting both internal to the volcanic arc and between the volcanic arc and forearc ridge. This is significantly different from the West Timor-Savu Sea and Tanimbar sectors of the arc where backarc thrusting is absent and the interarc region is extensional. The primary control on these very different structural styles is interpreted to be whether the underlying subducted slab is steepening or straightening through tune. Whilst straightening of the slab through buoyant post-collisional rebound induces extension normal to the arc, steepening of the subducted slab is associated with arc-normal compression.
An Eifelian U-Pb zircon date for the Enagh Tuff Bed from the Old Red Sandstone of the Munster Basin in NW Iveragh, SW Ireland
Authors: WILLIAMS E. A. , SERGEEV S. A. , STÖSSEL I. , FORD M.
Published: December 2007

The first geochronological data from the Minister Basin (SW Ireland) contradict the accepted biostratigraphical maximum age (late Givetian-early Frasnian) of the oldest alluvium in the basin depocentre. Magmatic zircons from the Enagh Tuff Bed, a sub-plinian air-fall tuff within fluviatile Old Red Sandstone of NW Iveragh, give a Pb/Pb isotope age of 384.9 ± 0.7 Ma. This confirms Middle Devonian (probably Eifelian) sedimentation and allows possible Early Devonian basin initiation. Associated second-cycle gravels suggest a pre-385 Ma minimum age for the Caherbla Group of the Dingle Basin. Correlation with alluvium containing tetrapod trackways indicates a pre-385 Ma age for the trace maker.