bluuebunny/crossref_metadata_2025 huggingface dataset:
Early Cretaceous strata of the Nepal Himalayas: conjugate margins and rift volcanism during Gondwanan breakup
Authors: GIBLING M. R. , GRADSTEIN F. M. , KRISTIANSEN I. L. , NAGY J. , SARTI M. , WIEDMANN J.
Published: December 2007

Early Cretaceous sandstones, shales and marlstones (Chukh, Tangbe and Muding Formations, at least 625 m thick) crop out north of the Main Central Thrust in central Nepal. They were strongly deformed during Himalayan collision, with telescoping of facies transitions as a result of crustal shortening. The sediments show northerly palaeoflow and were deposited on the steadily subsiding northern (Tethyan) margin of Gondwana. Berriasian deltaic deposits pass upward into Valanginian-Albian, storm-dominated shelf deposits and into latest Albian pelagic slope carbonates. An unconformity, probably of Valanginian age, separates the Chukh and Tangbe formations locally, and is overlain by volcanic conglomerates.

The Gondwanan margin succession matches well with that observed on the formerly conjugate margin of NW Australia, which separated from Greater India during the Valanginian to Hauterivian. Volcanic detritus, where suitable for analysis, shows within-plate geochemical affinity and reflects Gondwanan fragmentation. Abundant volcanic detritus in Aptian strata may have been derived from extensions of the Rajmahal Traps of northeast India. However, volcanism was active near central Nepal in the Valanginian and volcanic detritus, possibly far travelled, reached the area during the Berriasian. Early Cretaceous strata1 successions and relative sea-level changes show a first-order relationship to tectonism associated with Gondwanan break-up.
Late Palaeozoic marginal basin and subduction-accretion: the Palaeotethyan Küre Complex, Central Pontides, northern Turkey
Authors: USTAÖMER T. , ROBERTSON A. H. F.
Published: December 2007

The Küre Complex, located in the Central Pontides of northern Turkey, is a
c
. 20 km thick pile of thrust-imbricated deep-sea sediments, intercalated with a dismembered ophiolite. The ophiolitic rocks include serpentinized harzburgite, massive gabbro (cumulate and isotropic), sheeted dykes and basic volcanic rocks. The extrusive rocks are mainly pillow lavas, sheet flows and lava breccias. Geochemical evidence of immobile major- and trace-elements and pyroxene chemistry indicate mid-ocean ridge (MOR) and volcanic arc basalt (VAB) compositions, and suggest that the Küre Ophiolite was generated above a subduction zone. Chrome spine1 analysis also supports this interpretation. In some thrust sheets the extrusives are depositionally overlain by hemi-pelagic shales, passing up into terrigenous turbidites and shales, which are up to several hundred metres thick in intact successions. Cyprus-type massive sulphides, interpreted as precipitates from black smokers, are located along the lava-sediment contact. Individual, intact sediment units, up to several kilometres thick within the Küre Complex are separated by narrow (up to 10 m wide) zones of intense shearing, layer-parallel extension and melange formation. Asymmetrical folds, reverse faults, thrusts and duplex structures throughout the Küre Complex indicate mainly northwards emplacement.

The Küre Complex is thought to have opened in the late Palaeozoic, as a marginal basin above a northward-dipping Palaeotethyan subduction zone, located along the southern margin of Eurasia. The Küre marginal basin later closed, in response to inferred southward subduction, leading to development of an accretionary prism, prior to late Jurassic time. The Küre Complex is unlikely to represent the main Palaeotethyan suture, as has been suggested in some earlier tectonic reconstructions. Regional comparisons with Dobrogea, Crimea and Caucasus suggest the Küre basin opened, then closed, along a south Eurasia active margin.
A high-resolution North Sea Eocene dinocyst zonation
Authors: BUJAK J. , MUDGE D.
Published: December 2007

Abundant dinoflagellate cysts (dinocysts) from Eocene strata of the North Sea exhibit a consistent succession of events, based on the analysis of 120 wells from Quadrant 3 in the north to Quadrants 21 and 22 in the south. These events have a constant relationship with stratigraphic sequences and subsequences throughout the area. Eight Eocene dinocyst zones and 23 subzones, and the uppermost Palaeocene
Apectodinium augustum
Biozone are defined by last occurrence or abundance events. The North Sea dinocyst succession is similar to that in Denmark, northwest Germany, Belgium, The Netherlands and southern England, permitting correlation with calcareous nannoplankton zones for sections in these areas, and hence allowing correlation of North Sea stratigraphy with northwest European and worldwide events.
Uplift, deformation and fluid involvement within an active normal fault zone in the Gulf of Corinth, Greece
Authors: ROBERTS GERALD , STEWART IAIN
Published: December 2007

The active Pisia Fault Zone is exposed close to the crest of a rotated carbonate fault-block that forms part of the southern margin to the Gulf of Corinth half-graben in central Greece. The crest of the fault-block lies above sea-level whilst in the hanging-wall a marine basin exists. As a result, the diagenetic and structural characteristics of the fault zone record complex fluid involvement. Both early phreatic carbonate syn-kinematic cements (characterized by drusy fabrics, baroque dolomites and crack-seal textures) and late vadose carbonate syn-kinematic cements (characterized by flowstones containing cave-collapse debris) exist in the uplifted footwall to the fault. Downward percolation of vadose meteoric waters and the upwelling of pore waters with elevated temperatures produced the diagenetic features observed within the fault zone. The co-existence of early phreatic and late vadose cements within the fault zone is related to footwall uplift across the water-table and subsequent erosional unroofing. The present-day elevation of phreatic cements to
c
. 650m above current sea-level, provides a minimum estimate of footwall uplift along the fault. The wider implication is that temporal changes in deformation and fluid flow may typify fault-block evolution.
Deformation mechanism paths for oceanic rocks during subduction and accretion: the Mesozoic forearc of Alexander Island, Antarctica
Authors: DOUBLEDAY P. A. , TRANTER T. H.
Published: December 2007

The LeMay Group of Alexander Island, Antarctica, is a Mesozoic accretionary prism that contains slivers of ocean floor and ocean island material, accreted under a range of conditions and depths. It provides a rare opportunity to compare the deformation mechanism paths between oceanic and trench-fill lithologies during subduction and accretion by offscraping or underplating.

Ocean floor slivers consist of a bedded basalt–volcaniclastite–chert rock association, overlain by trench-fill sedimentary rocks. The oceanic lithologies initially deformed by cataclasis, combined with particulate flow in the volcaniclastic rocks. At shallow levels the clastic trench-fill sedimentary rocks deformed by independent particulate flow, which changed to cataclastic flow at depth. At those depths crystal plasticity affected the cherts and jaspers. At the deepest levels achieved in the subduction zone, crystal plasticity was the dominant deformation mechanism in the clastic sedimentary rocks, whilst cataclasis continued in the lavas. Deformation was synchronous with metamorphism up to transitional greenschist–blueschist facies. All lithologies were affected by pressure solution after accretion, with the formation of a bedding-parallel or sub-parallel cleavage. The deformation mechanism paths indicate that (1) there is a crystal plastic deformation field at deep levels in the subduction zone, and (2) that the base of the pressure solution field is concordant with the decollement.

A frontally accreted ocean island is exposed in the Lully Foothills, and consists of a basalt–volcaniclastite–tuff rock association. Deformation is represented only by a patchily distributed bedding-sub-parallel pressure solution cleavage in the tuffs and volcaniclastites, and is probably related to loading. Metamorphism does not exceed prehnite–pumpellyite facies. The accreted ocean island indicates that such features can be incorporated into accretionary prisms at shallow levels without significant segmentation.
A structural and palaeomagnetic study of a section through the eastern Subbetic, Southern Spain
Authors: ALLERTON S. , REICHERTER K. , PLATT J. P.
Published: December 2007

A well-exposed 2 km section through the Eastern Subbetic, immediately to the south of the Crevillente wrench fault zone can be divided into an upper thrust sheet of Triassic rocks, a middle thrust sheet of Cenomanian-Turonian basinal sediments, and a lower thrust sheet of Jurassic limestones unconformably overlain by Upper Cretaceous-Palaeocene sediments. Structural relationships suggest that the middle sheet overthrust the lower sheet; and both units were subsequently folded and imbricated. This sequence was then overthrust by the upper sheet, incorporating a footwall duplex of Cenomanian-Turonian sediments. These structures can be related to the complex deformation associated with a single overthrusting event. The dominant thrust transport direction is to the east, strongly oblique to the overall trend of the orogen. However, a palaeomagnetic study isolates stable components which indicate no cumulative vertical axis rotation of the thrust sheets. The section is cut by strike-slip faults whose displacements appear to be relatively minor. The Triassic rocks of the upper thrust sheet form a highly disrupted thrust sheet extending over much of the Subbetic, rather than being local to the Crevillente fault zone. This section through the Subbetic can be interpreted as the result of a major east-directed thrust of basinal sediments of the Median Subbetic over marginal shelf facies of the Internal Subbetic, strongly oblique to the general ESE trend of the orogen. The shortened sequence is cut by a later set of strike slip faults which are probably related to movement on the Crevillente fault.
Sedimentary hiatuses as indicators of fluctuating oceanic water masses: a new model
Authors: RAMSAY A. T. S. , SYKES T. J. S. , KIDD R. B.
Published: December 2007

The upper, and sometimes lower, boundaries of deep-sea disconformities, recognized as sedimentary hiatuses at ocean drilling sites, are shown to be diachronous. The age-depth relationships of these hiatuses are used, in conjunction with the geographical location of sites relative to individual water masses, in order to explain the formation of hiatuses as the product of interaction between fluctuating oceanic water masses and the sea floor. The fluctuations in the water masses are related to the glacial history of Antarctica. The method used is a departure from a traditional approach in which deep-sea hiatuses were considered to have no diachronous component and were viewed as the products of instantaneous regional or global events.

Sedimentary hiatuses have commonly been identified in deep sea cores recovered by the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP). The disconformity associated with a hiatus has three components:
firstly,
an upper boundary which represents a point in time when sedimentation recommenced;
secondly,
a lower boundary that is the product of either erosion (i.e. of no temporal significance), or non-deposition (i.e. of potential temporal significance); and
thirdly,
the time interval between these two boundaries (termed intra-hiatus in this paper). Earlier studies of hiatuses and hiatus-forming events have been used to infer the influence of climatic (e.g. Keller & Barron 1987) and/or tectonic (e.g. Watkins & Kennett 1972) changes on the development of erosive oceanic watermasses. Hiatus distributions have been interpreted as having ocean-wide (e.g.

Davies
et al.
1977

; Keller & Barron 1987) or, even,
Late Llandovery bentonites from Gotland, Sweden, as chemostratigraphic markers
Authors: BATCHELOR R. A. , JEPPSSON L.
Published: December 2007

Geochemical analysis of two distinctive bentonites and their constituent apatite crystals from the Late Llandovery of Gotland, has provided unique chemical signatures for each bentonite. These data have allowed the beds to be correlated across the island. The chemical composition of constituent apatite crystals indicates that apatite crystallized in a transitional alkaline environment. Chemical and mineralogical evidence suggests that the earlier Lusklint Bentonite originated from a potassic magma generated in a waning subduction zone, while the later Ireviken Bentonite was not consanguinous with its predecessor, but was derived from a medium-K calc-alkaline magma produced in a continental margin environment. The volcanoes which gave rise to these bentonites probably lay in the Tornquist Sea, during its late stages of closure, somewhere between southern Poland and Denmark. These chemically distinct bentonites could act as sensitive chemostratigraphic tools for correlation of Late Llandovery horizons elsewhere in Northern Europe.
The Variscan structural and metamorphic evolution of the eastern Southalpine basement
Authors: RING U. , RICHTER C.
Published: December 2007

The basement of the Southern Alps (northern Italy) belongs to the southernmost part of the European Variscan mountain belt. In contrast to other areas of the Alps, the post-Variscan metamorphic and tectonic overprint is weak and therefore permits the unravelling of the Variscan tectonometamorphic evolution of this region. Overprinting criteria and the mapping of the penetrative structural elements (S2 and L2) allow three deformational events to be distinguished. Major Variscan deformation (D2) in the Southern Alps commenced in the Carboniferous and lasted until the end of the Late Carboniferous. Tectonic movement during D2 was north-directed and was accompanied and followed by greenschist facies metamorphism. Peak metamorphic conditions reached 450–550°C and 5–6.5 kbar in the Brixen area and decreased in a southeasterly direction. Tectonic movement during D2 followed subduction of the Plankogel terrane and collision of the Noric terrane (northernmost part of Gondwana) with Laurasia and is interpreted to result from late orogenic extensional collapse of the Variscan mountain chain. Extensional deformation caused exhumation of the basement rocks as evidenced by greenschist facies basement pebbles, which show no substantial retrograde overprint, in Late Carboniferous/Early Permian conglomerates.
The Oko Shear Zone, Sudan: post-accretionary deformation in the Arabian-Nubian Shield
Authors: ABDELSALAM M. G.
Published: December 2007

The Oko Shear Zone is a late Precambrian, N- to NW-trending, post-accretionary deformational belt in the Red Sea Hills of the Sudan. It left-laterally offsets the
c
. 800–750 Ma old, NE-trending Nakasib suture by about 10 km. The Shear Zone evolved through three phases of deformations: (1) an early E-W-directed flattening deformation which produced N-trending upright folds; followed by (2) major NW-trending, left-lateral and, minor NE-trending, right-lateral strike-slip faulting; and (3) late E- and W-verging thrusts and buckles associated with a flower structure.

The structural similarities between the Oko Shear Zone and other post-accretionary deformational belts in the Arabian-Nubian Shield suggest an evolutionary sequence for these belts: (1) suturing events were completed by
c
. 700 Ma ago 'and resulted in the formation of E- to NE-trending ophiolite-decorated sutures; (2) an E-W-directed flattening deformation was superimposed due to collision of the Arabian-Nubian Shield with the Nile craton in the west and the Ar Rayn micro-plate to the east at c. 670–610 Ma ago; this produced discrete zones of N-trending upright folds; (3) the flattening deformation culminated in the initiation of major NW-trending, left-lateral, and minor NE-trending, right-lateral strike-slip faults as conjugate sets at
c.
640–560 Ma ago.
Nd and Sr isotope constraints on the origin of the Cornubian batholith, SW England
Authors: DARBYSHIRE D. P. F. , SHEPHERD T. J.
Published: December 2007

Combined Nd and Sr isotope data for the Hercynian granites of SW England provide important new evidence for the origin of the Cornubian batholith. The Nd isotope systematics are shown to be robust even in areas of extensive hydrothermal alteration. E
Nd
values for the main plutons range from −4.7 to −7.1 whereas values for the Palaeozoic country rocks are significantly lower, typically –8 to –11. Depleted mantle Nd model ages (1.3–1.8 Ga) indicate a heterogeneous source region for the granite magmas and imply that the age of the basement beneath southern England is significantly older than previously estimated. Calculated
E
Nd
values for the Palaeozoic country rocks at the time of granite intrusion suggest that they were unlikely to have been the main source material for the magmas.
E

ND

-E

Sr

data for the granites do not define a simple binary mixing array between a mafic, depleted mantle melt and Proterozoic crust. The best fit model is consistent with partial melting of a composite lower crustal source comprising immature metasedimentary and mafic meta-volcanic rocks, and mixing with a relatively minor contribution of basaltic magma extracted from a slightly enriched mantle source. Such hybrid magmas are thought to have been generated during an Ivrea-type underplating of the lower crust during continental collision; their isotope signatures being determined by the relative proportions of crust and mantle material.
Modern perspectives on magmatic processes
Authors: ROGERS N. W.
Published: December 2007

The papers presented in this thematic set evolved from the 1993 annual two day meeting of the Volcanic Studies Group, held at the Open University. The papers are dedicated, as was the meeting, to the memory of Richard Thorpe who tragically died whilst on fieldwork on Lundy during August 1991. The meeting shared the title of this thematic set and included a session on magmatic processes at destructive plate margins and one on within-plate magmatism. These two broad subjects were chosen to reflect Richard's wide-ranging interests in petrological and geochemical problems and this is also reflected in the subjects of the following six papers.

An obituary to Richard Thorpe appeared in the 1991 Annual Report of the Geological Society and it is not my purpose to repeat what was said about Richard there. However, he will probably be best remembered for his edited book entitled Andesites and related rocks and an unusual but topical aspect of the petrology of andesites is the subject of the first paper in this thematic set.
Matthews

et al

. investigate the influence of sulphur redox reactions on the oxygen fugacity of calc-alkaline magmas from Lascar in Chile and Pinatubo in the Phillipines. Both of these volcanoes are known for the presence of primary igneous anhydrite, implying unusually oxidizing conditions during crystallization and high concentrations of sulphur in the parental basaltic magma. They conclude that large quantities of SO
2
gas are liberated during mixing between basaltic and more silica-rich magmas. Observed T-f
o2
relationships in both volcanoes
Sr isotope data for the Tertiary lavas of Northern Ireland: evidence for open system petrogenesis
Authors: WALLACE J. M. , ELLAM R. M. , MEIGHAN I. G. , LYLE P. , ROGERS N. W.
Published: December 2007

The lavas of NE Ireland represent the largest remnant of the British and Irish Tertiary Igneous Province. In this paper we present new Sr isotope data which, by virtue of extreme variation, provide evidence of extensive open system behaviour in the petrogenesis of these flood basalts. To some extent the initial
87
Sr/
86
Sr ratios (
87
Sr/
86
Sr
(60Ma)
= 0.703–0.715) record the effects of late-stage hydrothermal processes. However, leaching experiments allow primary magmatic signatures to be inferred with confidence. Coherent increases in initial
87
Sr/
86
Sr ratio with differentiation indices and incompatible trace element ratios imply a role for crustal contamination. Very significant differences in the style of crustal interaction are recorded by discrete units within the basalt pile. Further, there are also marked contrasts with Tertiary basalts elsewhere in the United Kingdom. In both cases such variations appear to respond to changes in the basement geology reflecting the important control of crustal wall-rocks on the geochemistry of these basalts.
Quantitative analysis of Triassic extension in the northern Viking Graben
Authors: ROBERTS A. M. , YIELDING G. , KUSZNIR N. J. , WALKER I. M. , DORN-LOPEZ D.
Published: December 2007

It has been recognized for over a decade that large-displacement, pre-Jurassic faults are present in the Northern Viking Graben, part of the North Sea rift. These faults define a series of major fault-blocks below the more obvious Jurassic rift basin. We attempt here to quantify the amount of extension associated with this older rift event, which is probably of early Triassic age.

Quantitative modelling of the Triassic rift and the succeeding period of thermal subsidence has been undertaken, using a combination of flexural backstripping and flexural-cantilever forward modelling. These techniques suggest that Triassic extension across the Horda Platform (Norwegian sector) reached
c.
40% (
ß
= 1.4). The consequences of this extension were deposition of a thick (>3 km) Triassic-Upper Jurassic syn-rift and post-rift sequence, prior to renewed, but minor, extension in the Late Jurassic-earliest Cretaceous. The thickness of the Viking Group reservoirs in the Troll area appears to have been almost entirely controlled by sediment loading during post-Triassic thermal subsidence. Jurassic extension on the Horda Platform was <5%, an order of magnitude less than the Triassic event. The Horda Platform is therefore principally an area of Triassic extension marginal to the main Jurassic rift further west.

In the UK sector of the Viking Graben, Triassic structures are less obvious than those below the Horda Platform, because of Jurassic overprinting. They are, however, still present. Average Triassic extension across the East Shetland Basin was
c.
15%, comparable with the magnitude of Jurassic extension in the same area. We believe that the Tern/Eider and Cormorant fault-blocks, with proven shallow basement, comprised a large eroded horst during the early Triassic, uplifted in the footwalls of major faults flanking the Magnus and Statfjord half-graben. During the Triassic, the Magnus half-graben was contiguous with the Unst Basin, now situated in the western footwall of the younger Jurassic basin. The presence of the Unst Basin suggests that Triassic extension occurred across the area that is now the northern Shetland Platform, continuing into the West Shetland area.

Although the more obvious structures in the Viking Graben are Jurassic in age, the earlier Triassic event was equally as important in controlling the structural and stratigraphic history of the basin.
Seismic sequence stratigraphy of the Palaeogene offshore of Belgium, southern North Sea
Authors: DE BATIST M. , HENRIET J.-P.
Published: December 2007

A fine-scale seismic stratigraphic model has been developed for the Palaeogene of the southern North Sea on the basis of interpretation of a dense high-resolution reflection seismic grid, covering the Belgian sector of the continental shelf and the adjacent parts of the Dutch, French and UK sectors. Classical seismic stratigraphic criteria have allowed up to 13 major units to be defined; the geometry and seismic facies characteristics of each have been analysed in detail. The seismic stratigraphy has been compared with the results of four offshore boreholes. ‘Events and trends’ identified on seismic sections and in outcrops in northern Belgium have been correlated, and offshore seismic facies have been tentatively matched with onshore lithofacies. The geological history of the study area is discussed in terms of eustatic sea level changes and regional tectonic events, and the main characteristics of the offshore Palaeogene deposits are evaluated in a sequence stratigraphic context.
Parasequence-scale organic facies variations through an Early Carboniferous Yoredale cyclothem, Middle Limestone Group, Scremerston, Northumberland
Authors: FRANK M.C. , TYSON R.V.
Published: December 2007

The Early Carboniferous (Brigantian) Middle Limestone Group of Northumberland represents a prolonged period of rhythmic Yoredale-type deltaic sedimentation. Optical and geochemical analyses were undertaken on the minor Berwick Limestone Cyclothem, a prograding coarsening- and shallowing-upward cycle (parasequence) within the major Oxford Limestone Cyclothem. These indicate an overwhelming dominance of Type III–IV land-plant derived kerogen (woody phytoclasts). The hydrogen index shows a strong negative correlation with the palynologically determined b1ack: brown phytoclast ratio. The total organic carbon content of the fine-grained lithologies increases upwards through the cycle and is positively correlated with silt content, presumably due to the hydrodynamic equivalence and common fluvial source of phytoclasts and silt particles. The 1ath:equant ratio of the black phytoclasts increases upwards through the cycle (i.e. in a proximal direction); this pattern is ‘atypical’ and results from the lath-shaped phytoclasts being larger than the equant ones. The section is marginally mature (about 0.64% vitrinite reflectance); reflectance is correlated with hydrogen index. The distribution of pyrite and siderite is apparently related to sediment accumulation rate, with siderite most common in the interval of probable highest sedimentation in the lower half of the cyclothem above the limestone. The marine flooding surface at the base of the cycle is overlain by black shale, not limestone; the traditional (limestone) base of the cyclothem does not correspond to the true base.
Peraluminous granites in NE Palmer Land, Antarctic Peninsula: early Mesozoic crustal melting in a magmatic arc
Authors: WEVER H. E. , STOREY B. C. , LEAT P.
Published: December 2007

A suite of Early Jurassic metaluminous to strongly peraluminous granitoids occupy a rear-arc position in Palmer Land, Antarctic Peninsula with respect to a Mesozoic–Cenozoic magmatic arc. Fractional crystallization of a range of mafic to silicic magmas yielded feldspar megacrystic granites, orthogneisses and foliated granodiorites. Leucogranites are strongly peraluminous and have the highest
87
Sr/
86
Sr initial ratios of 0.7205–0.7208, somewhat lower than those of older paragneiss. Isotopic and elemental data are used to model generation of leucogranite magma by partial melting of paragneiss, followed by mixing of basalt magma with the crustal melt to form parent magmas of the rest of the granitoids. The crustal partial melting was a result of heat convected by the mafic magma, intruded into an extensional back-arc basin setting contemporaneous with the initial stages of Gondwana break-up. The mafic magma had relatively low
143
Nd/
144
Nd ratios, distinct isotopically from the MORB-like basalt thought to represent the mantle input to granitoid genesis in the north western part of the Antarctic Peninsula. The nature of the mantle source(s) of the enriched basalt is uncertain, but it is isotopically similar to approximately contemporaneous basalts associated with the Karoo mantle plume.
Quantitative micro-porosity and orientation analysis in soils and sediments
Authors: TOVEY N. K. , HOUNSLOW M. W.
Published: December 2007

A technique to quantify the fabric of soils and sediments involving image processing and analysis is described in this paper. Such techniques are becoming popular in the Earth sciences, but, unlike most other studies which investigate the porosity of coarse-grained sediments, this method examines the fine porosity between clay size particles to be investigated. The usual problems associated with thresholding a grey-level image to provide the necessary binary image for analysis are partly overcome by the use of Wiener filtering methods to remove much of the degradation inherent in all imaging systems. A new algorithm based on the relative contrast histogram method is then used to determine the optimum value at which to set the threshold. The micro-porosity determined is in good agreement with gravimetric porosity measurements. Unlike normal methods, once the procedure has been initiated, no further action is required from the operator and the method can thus be used for batch processing of large numbers of images thereby enhancing the statistical reliability of the results.

Extensions of the technique allow for the variation in micro-porosity from one region of a specimen to another to be studied. Further, by segmenting the original image into domains of sub-parallel particles, it is possible to examine the intra-domain porosity. Contrary to expectations, the porosity in horizontal domains is greater than that in the vertical domains.
Stratigraphic control on laterally persistent cementation, Book Cliffs, Utah
Authors: TAYLOR K. G. , GAWTHORPE R. L. , VAN WAGONER J. C.
Published: December 2007

Field data from the Upper Cretaceous Blackhawk Formation in the Book Clitfs (Utah–Colorado) demonstrate the presence of laterally extensive carbonate cements beneath major marine flooding surfaces. The occurrence of firmgrounds, compaction around concretions, and high minus-cement porosities indicate that cementation occurred during early diagenesis. It is proposed that the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non-depositional hiatuses linked to abrupt deepening during marine flooding. These reduced sediment accumulation rates extended sediment residence time within early diagenetic zones, leading to enhanced early cementation in shallow marine sandstones and mudstones.
Brackish-water and evaporitic Ca–Mg carbonates in the Holocene lacustrine/deltaic deposits of southern Mesopotamia
Authors: AQRAWI A. A. M.
Published: December 2007

Authigenic dolomite, Mg-calcite and calcite occur in the Holocene near-surface marshland (Ahwar) sediments and some subsurface strata of southern Mesopotamia. Dolomite has been detected in evaporitic and brackish/marine sedimentary units of both the siliciclastic and carbonate sequences, whereas high-Mg calcite and low-Mg calcite are mainly restricted to brackish/marine and lacustrine carbonate units respectively.

The dolomite, which is polygenetic, is highly calcian and has the composition Ca
1.12–1.22
Mg
0.88–0.78
(CO
3
)
2
. The calcite is of two distinct phases, low-Mg and high-Mg, consisting of 5 mole% or less and 10 mole% or more MgCO
3
respectively. The dolomite samples show a spread of δ
18
O values from –8‰ PDB for detrital dolomite, –3 to –6.5‰ for inferred dilute brackish samples, –1 to +l‰ for mixing zone samples and +3 to +5‰ for evaporitic types.

The influence of sea-level fluctuations during the Holocene evolution of the Tigris–Euphrates Delta has resulted in the formation of different sedimentary environments of mixing marine and fresh waters favourable for Ca–Mg carbonates formation. Evaporitic environments were the main source for dolomite formed in the early Holocene.
Implications of the infra- and inter-trappean biota from the Deccan, India, for the role of volcanism in Cretaceous-Tertiary boundary extinctions
Authors: PRASAD G. V. R. , KHAJURIA C. K.
Published: December 2007

The fossil record shows a remarkable similarity between the biota that existed before and after the initiation of Deccan volcanic activity. Virtually all the available palaeontological evidence, such as the fauna and flora of the freshwater infra- and inter-trappean beds and the planktonic foraminifera from the subsurface infra- and inter-trappean beds of the southeastern coast, do not favour the initiation of Deccan volcanism as the cause of mass extinctions at the Cretaceous-Tertiary (K-T) boundary. Instead, a combination of events, such as an extended period of volcanism, changes in sea-level and related climatic changes, and certain local factors, may have played a significant role in selectively eliminating various groups of organisms. This view is further reinforced by the biotic changes across the K-T iridium layer in the Um Sohryngkew River section of Meghalaya, northeastern India.
Numerical ages of volcanic rocks and the earliest fauna1 zone within the Late Precambrian of east Poland
Authors: COMPSTON W. , SAMBRIDGE M. S. , REINFRANK R. F. , MOCZYDEOWSKA M. , VIDAL G. , CLAESSON S.
Published: December 2007

U–Pb age determinations by ion microprobe on zircons from two tuff samples within the Neoproterozoic–early Cambrian successions in Poland are presented. One sample, from the Kaplonosy borehole is within, or conformably below, rocks that contain the
Sabellidites–Vendotaenia
fossil assemblage of the Upper Vendian. The second sample is from the Ksi¹¿ Wielki IG-l borehole, from rocks that were referred alternatively to the early Cambrian or to the Vendian on lithostratigraphic evidence.

The Kaplonosy zircons are euhedral and free of visible zircon cores, both optically and as back-scattered electron images, but they exhibit a range in
206
Pb/
238
U ages that exceeds analytical error. The combined data-set can be resolved into three age-components in different proportions, which overlap in apparent age due to measurement errors. There is a well-defined principal age component at 551 ± 4 Ma (95% limits) and two minor detrital or inherited components at 588 ±8 Ma and 635 ± 10 Ma. The age of the Kaplonosy tuff is interpreted as equal to that of the youngest and principal component, 551 Ma. This age allows a maximum time difference of 17 ± 4 Ma between the top of the Stawatycze Formation and Lower Cambrian strata of the
Heliosphaeridium dissimilare-Skiagia ciliosa
acritarch Zone, the latter being time-equivalent to Middle Tommotian strata in northeastern Siberia, recently dated as 534.6 ± 0.5 Ma.

The tuff from the Ksi¹¿ Wielki IG-l borehole has a similar spectrum of zircon ages, but also contains several detrital grains that have concordant and separate early Proterozoic and Archaean ages. The age of the major component is 549 ± 3 Ma (72% of the totak), and there are two older components at 578 ± 9 Ma (13%) and 619 ±s8 Ma (15%). The deposition of the tuff from the Ksig Wielki Formation therefore occurred at 549 Ma, indicating that the Ksi¹¿ Wielki Formation is not early Cambrian but Upper Vendian, unless all zircons in the tuff are detrital.
Late Quaternary rhyolitic eruptions from the Acigöl Complex, central Turkey
Authors: DRUITT T. H. , BRENCHLEY P. J. , GÖKTEN Y. E. , FRANCAVIGLIA V.
Published: December 2007

Two major rhyolitic tephra units (Lower and Upper Acigöl Tuffs) have been erupted from the Acigöl Complex. The Lower Acigöl Tuff (>13km
3
uncompacted volume) was erupted more than
c.
180 ka ago, forming an extensive Plinian pumice-fall deposit with associated ashfall and ignimbrite. Well-developed ignimbrite veneer facies are preserved where the pyroclastic flows passed over hilly topography. Following the eruption, a thick rhyolite coulée (Bogazköy obsidian) was extruded. The Upper Acigöl Tuff eruption (age 70 < t< 150 ka) generated a second major Plinian deposit, an ignimbrite preserved up to 24 km from the vent, and an 80 m thick proximal succession of surge and fallout deposits; it resulted in collapse of the 6×5 km Acigöl caldera. The two major tuffs are chemically similar but can be distinguished on the basis of lithic populations. Subsequent rhyolitic activity formed the
c.
0.25 km
3
dome of Kocadag Tepe (c.70ka) and five dome/maar clusters (c. 20 ka). Late Quaternary and/or Holocene basalts and andesites surround the Acigöl caldera, which developed in a zone of sinistral shear associated with approximate N-S compression. Vent distribution patterns, the eruption of young basalts, and the crystal-poor nature of the
c.
20 ka rhyolites are consistent with basaltic stoking of a sizeable silicic magma chamber beneath the Acigöl Complex.
The Cretaceous Separation Point batholith, New Zealand: granitoid magmas formed by melting of mafic lithosphere
Authors: MUIR R.J. , WEAVER S.D. , BRADSHAW J.D. , EBY G.N. , EVANS J.A.
Published: December 2007

The Early Cretaceous Separation Point batholith of the South Island, New Zealand, represents the final magmatic stage of an extensive arc system located on the SW Pacific margin of Gondwana during the Mesozoic. The batholith consists of Na-rich, alkali-calcic diorite to biotite-hornblende monzogranite. The rocks are distinct from calc-alkaline subduction-related granitoids, but comparable with those of adakite and Archaean trondhjemite-tonalite-dacite suites.

Primitive Sr and Nd isotopic ratios and the absence of inherited zircon, indicate that the granitoids experienced little, if any, interaction with felsic crust. Their geochemistry is consistent with melting of a basaltic protolith of amphibolite mineralogy, either young, hot, subducted oceanic crust or newly underplated material beneath a thickened continental arc. The latter model is preferred because Separation Point rocks do not posess MORB isotopic characteristics, and cannot be explained as mixtures of MORB-melt and continental crust. Most likely it involves melting of basal arc material in response to the collision and thrusting of the arc beneath the continental margin following subduction of a back-arc basin. On the basis of strong geochemical similarities, the Early Cretaceous Western Fiordland Orthogneiss of SW New Zealand is considered to be the lower crustal equivalent of the Separation Point batholith.
Petrogenesis of Silali volcano, Gregory Rift, Kenya
Authors: MACDONALD R. , DAVIES G. R. , UPTON B. G. J. , DUNKLEY P. N. , SMITH M. , LEAT P. T.
Published: December 2007

Basalts of the Silali volcano are of high-Fe transitional affinity and range from plagioclase-phyric varieties, probably formed by selective accumulation, to aphyric. They have compositional similarity to oceanic island basalts, but are isotopically variable and have strong, negative Zr anomalies on chondrite-normalized plots. Major and trace element and isotopic evidence indicates that the basalts represent several liquid lines of descent, each equilibrated at crustal pressures. All Silali basalts are relatively evolved; primitive basalts were probably held close to the Moho, where they evolved by gabbro fractionation to produce basalts with less than 8% MgO. These magmas were subsequently held at several levels in the crust, including the rift-axial lava-sediment sequence. Fractionation was along a high-Fe trend through mugearite to metaluminous, two-feldspar trachyte and thence to peralkaline, one-feldspar, silica-oversaturated and -undersaturated trachytes. Magmas intermediate in composition between basalt and trachyte were very rarely erupted at Silali, but their evolution can be deduced from an extensive suite of dolerite blocks, which contain residual glasses varying from mugearitic to peralkaline phonolitic compositions. Magma mixing between basalt and trachyte has been common at Silali, implying complexity of the plumbing system. Evolution of the trachytes was by fractional crystallization combined with assimilation of crust during or after fractionation.
Incipient India-Eurasia collision and plutonism: the Lower Cenozoic Batura granites (Hunza Karakorum, North Pakistan)
Authors: DEBON F.
Published: December 2007

Plutonism of the Karakorum, north of the India-Eurasia suture zone, comprises two major intrusive stages: the oldest, mid-Cretaceous, predates the collision; the youngest, Miocene, is post-suturing. In between, Lower Cenozoic plutonism, roughly syn-suturing and represented by the Batura complex, is made up of a few small and usually undeformed plutons. The complex has a subalkaline (i.e. intermediate between alkaline and calc-alkaline) and ferriferous association, dominated by light-coloured metaluminous and slightly peraluminous granites and adamellites with biotite ± amphibole ± titanite. Whole rock Rb-Sr isochron ages of 63 Ma (this study) and 43 Ma (

Debon
et al.
1987b

) have been obtained for two plutons, with rather low initial
87
Sr/
86
Sr ratios (0.7050, 0.7056). A comparison with granitoids of similar age from Kohistan suggests that the complex relates to the subduction of the Tethys ocean, and originates from a mantle source with but small crustal contribution, through a two-stage melting process. The apparently limited extent of Lower Cenozoic plutonism in the Karakorum contrasts with its wider development in the Transhimalaya and Kohistan. This contrast could be partly accounted for by changes in tectonic and magmatic suduction-related processes after the initial contact between India and Eurasia was established, in the NW Himalaya.
The Silkstone Rock (Westphalian A) from the east Pennines, England: implications for sand body genesis
Authors: GUION PAUL D. , BANKS NIGEL L. , RIPPON JOHN H.
Published: December 2007

The Silkstone Rock (Westphalian A, Langsettian) is a major multistorey channel sandstone formed in a delta plain environment with minimal marine influence. It occupies up to three interseam intervals in the east Pennine coalfield, England, and exceeds 50 m in thickness and 15 km in width at its maximum development, which is larger than many Westphalian channel sand bodies. The high ash content of coal adjacent to the channel belt indicates that regional peat accumulation took place contemporaneously with the existence of the channel system. The major channel system fed a number of minor channels during different interseam intervals, and conducted sediment and water into nearby delta plain lakes, via lacustrine delta and crevasse splay systems. These minor channels, which show a range of fills, are sub-parallel and show lateral offset stacking, suggesting that differential compaction was an important control on their location. The major channel belt acted as a long-lived distributary system that flowed towards the east, away from the overall basin depocentre, with its position being controlled mainly by deltaic processes.
Rift flank segmentation, basin initiation and propagation: a neotectonic example from Lake Baikal
Authors: AGAR S. M. , KLITGORD K. D.
Published: December 2007

New surficial data (field, Landsat TM and topography) define morpho-tectonic domains and rift flank segmentation in the Ol'khon region of the Central Baikal rift. Deformation, drainage and depositional patterns indicate a change in the locus of active extension that may relate to a recent (<l Ma) change in the kinematics of the Siberian plate boundary. The westwards migration of the border fault location has broadened the rift with concomitant shifts in depocentres. Within the hanging wall of the new western border fault, distinct segments control the location of drainage paths and syn-rift deposits. Morphology, sediment thicknesses and fault scarp amplitude indicate that a segmented rift flank graben has propagated southwards along the rift flank and is still actively fragmenting. These surficial data are used to constrain a model for the time-dependent topographic variations during progressive subsidence along a rift flank, involving the transfer of footwall units to hanging-wall domains. Rapid changes in border fault footwall relief in this model are associated with change in the active border fault location with widespread mass-wasting. The model shows that time-dependent histories need to be integrated with flexural uplift models for active normal faults. The active, syn-rift depositional systems of the Ol'khon region provide a valuable analogue for the early evolution of continental margins and the structural controls on syn-rift hydrocarbon sources and reservoirs.
Tectonic controls on stratigraphic evolution of the Adana Basin, Turkey
Authors: WILLIAMS G. D. , ÜNLÜGENÇ U CAN , KELLING G. , DEMIRKOL C.
Published: December 2007

The Neogene Adana Basin of SE Turkey was initiated after thrust emplacement of the Tauride Belt to the north of the basin. Seismic reflection profiles across the southern part of the Adana Basin provide information on structural and stratigraphic evolution of the basin. Based on seismic character and the identification of unconformities, three megasequences and two mega sequence boundaries are identified. The first megasequence is partly coincident with an early Miocene rifting event and it comprises reefs that have grown on fault footwall crests with fore and back-reef sediments in intervening lows. Subsequent rapid flexurally induced subsidence generated an underfilled basin which was then passively filled by turbiditic sediments (megasequence 2) showing aggradational character on seismic profiles. Further extensional faulting and coupled sinistral wrench faulting took place after the deposition of megasequence 2. Erosional truncation of its upper part is followed by the deposition of continental and shallow marine sediments of megasequence 3 which shows localized progradational sequences characteristic of shallow water deposition. Further minor extensional faulting took place after the deposition of megasequence 3.
U–Pb chronology of the Ennerdale and Eskdale intrusions supports sub-volcanic relationships with the Borrowdale Volcanic Group (Ordovician, English Lake District)
Authors: HUGHES R.A. , EVANS J.A. , NOBLE S.R. , RUNDLE C.C.
Published: December 2007

U-Pb analyses of zircons from the Ennerdale granitic intrusion and Eskdale Granite (English Lake District) give ages of 452 ± 4 Ma and 450 ± 3 Ma respectively. These data confirm the sub-volcanic association of these intrusions, and show that previously published Rb–Sr whole-rock and K–Ar mineral ages do not correspond to the emplacement and cooling of these igneous bodies. The new ages show that only two phases of acid magmatism can now be linked to the exposed parts of the Lake District batholith. The Caradoc (late Ordovician) phase was caused by the subductionrelated processes which gave rise to volcanism, and was followed by a separate early Devonian phase of granite emplacement.
Molar-ratio and Harker diagrams in portraying the actual chemical variability of granitoid suites
Authors: WHITTEN E. H. T.
Published: December 2007

Recent publications show that molar-ratio diagrams preserve absolute compositional variations of certain mafic igneous rock assemblages, while traditional Harker diagrams for all igneous rocks obfuscate relationships. For some Australian granitoid suites, molar-ratio diagrams illustrate chemical variations accurately and permit quantitative objective testing of petrogenetic models (e.g., restite model) with observed chemical compositional data.