bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deep structure of southern Ireland: a new geological synthesis using BIRPS deep reflection profiling
Authors: FORD M. , KLEMPERER S. L. , RYAN P. D. 
Published: December 2007

The BIRPS deep seismic reflection data of WIRE (West of IREland) 1/1B from Galway Bay to the Celtic Sea are integrated with geological and other geophysical data to produce a synthesis of the fundamental tectonic character of the crust in and around southern Ireland. The Iapetus Suture forms a zone of north-dipping reflectors which projects up between the Shannon estuary and the Dingle peninsula and is overlain by a late Caledonian reflector with a shallow, south dip. Across the Iapetus Suture zone the crust thickens southward and the lower crust becomes less reflective. It is proposed that the Lower Palaeozoic volcano-sedimentary rocks which form the Leinster massif extend southwestward beneath the Variscan province and at least 30 km offshore to the WIRE lines. We argue that the weak south-dipping reflectors in the upper and middle crust south of the Iapetus Suture represent an early-Caledonian fault system linked to a mid-crustal detachment which formed during the south-dipping subduction event recorded onshore by the Ordovician volcano-sedimentary successions. These faults were selectively reactivated causing the predominant ENE trend of younger regional tectonic features in and around southern Ireland. The three onshore Upper Palaeozoic basins close east of the WIRE lines.
We point out that the ‘Variscan Front’ is only a map line across the British Isles with no consistent tectonic character. Thus the south-dipping reflector below the north margin of the North Celtic Sea Basin on SWAT 4, generally referred to as the ‘Variscan Front’, is correlated by us with the northern boundary of the Rosslare complex, thus making it the northern tectonic boundary of the Caledonian basement block known as the Rosslare-Monian Terrane. Furthermore the north-dipping South Irish Sea Lineament on WINCH 4 can be correlated with the Menai Straits Lineament and could thus be the southern boundary of this terrane. The south-dipping reflector on SWAT 2, also previously called the ‘Variscan Front’ is correlated with the Johnston-Benton fault system in southwest Wales.
Fracture patterns in clasts of diamictites (? tillites)
Authors: HARKER R. I. 
Published: December 2007

Fracture patterns in some of the clasts of the Gowganda Formation, Ontario, are inconsistent with aqueous deposition and suggest that locally the diamictites are tillites.
Similar fracture patterns have been found in the clasts of modern tills in the Cascade Mountains. Rare examples were also seen on the Garvellachs, Scotland.
Laboratory experiments indicate that such patterns can be developed by the impaction of one clast against another while surrounded by a compliant matrix. The stresses which induced cracking were of the same order of magnitude as those which can be expected to occur in a sub-glacial environment.
Tectonic evolution of the Nakasib suture, Red Sea Hills, Sudan: evidence for a late Precambrian Wilson Cycle
Authors: ABDELSALAM M. G. , STERN R. J. 
Published: December 2007

The Nakasib suture is a late Proterozoic (Pan-African) ophiolite-decorated structural belt in the central Red Sea Hills of the Sudan. It represents one of the sutures along which the island arc/back-arc terranes and continental microplates of the Arabian-Nubian Shield are welded together. The Nakasib suture separates the 900–850 Ma old Haya terrane in the south from the 830–720 Ma old Gebeit terrane to the north. Five thrust-bounded stratigraphical groups are identified across the suture. These are, from south to north, Arbaat volcanic group (c. 730 Ma rift-related volcanic rocks), Salatib group (early passive margin volcanic and sedimentary rocks), Meritri group (the lower part of which contains alluvial and submarine fans of an incipient ocean basin, while its upper part can be tentatively equated with a platform of clastic sedimentary and carbonate intercalations which mark the stage of mature ocean basin opening), Nakasib ophiolite, and Shalhout group (arc-related volcanic and sedimentary rocks). These are intruded by syn-tectonic and post-tectonic plutonic rocks.
The tectonic setting of the above lithological groups suggests that the early stage of the Nakasib suture development was marked by rifting of older crust, probably the Haya terrane, which culminated in development of a passive margin on the south margin of an oceanic basin prior to collapse into an ophiolite-decorated suture. This indicates that the Nakasib suture evolved through a complete Wilson cycle orogeny from rifting, through passive margin formation, to closure of the basin and suturing.
Sediment dynamics of the Severn Estuary and inner Bristol Channel
Authors: McLAREN P. , COLLINS M.B. , GAO S. , POWYS R.I.L. 
Published: December 2007

Net sediment transport pathways have been determined in many environments by studying grain size trends. This approach is extended here to an inner shelf environment, with improved statistical techniques.
Patterns of net surficial sediment transport are proposed, indicating that the area is dominated by up-estuary transport. Exceptions exist in the form of radial mud transport at the river mouths and (clockwise) sand circulation around linear sandbanks.
Six different sedimentary environments are defined on the basis of the shape of the ‘transfer function’ and its relationship to the grain size distributions. Erosion takes place along the axis of the estuary. Dynamic equilibrium is reached around the linear sandbanks, whilst accretion occurs at the head of the estuary and where there are riverine inputs.
The results are compared with numerical model outputs, representing water movement and sediment transport. Over the seaward part of the study area, there is agreement between the two approaches; contradictions increase, however, towards the upper reaches of the estuary. The discrepancies can be attributed to: (1) inherent differences between patterns of water and sediment movement; (2) difficulties in modelling intertidal boundary conditions; (3) inadequate representation of river influences in the models; and (4) time-scale differences, associated with sediment transport processes.
Incremental caldera collapse of Suswa volcano, Gregory Rift Valley, Kenya
Authors: SKILLING I. P. 
Published: December 2007

Suswa volcano, located at 1°10′S, 36°20′E, is Quaternary in age (<0.4 Ma), dominantly trachytic-phonolitic in composition, and has two calderas. Regional extension was a fundamental control on caldera collapse, providing pathways for the siting, drainage and recharge of magma chambers. Caldera I collapse was associated with magmatic overpressure from volatile exsolution, magma-water interaction, influx of denser magma and magma drainage at depth. Trachybasalt ash, trachyte globular-ash ignimbrites, trachyte pumice lapilli air-fall tuffs and carbonate-trachyte ignimbrites characterize the initial subsidence. Air-fall tuffs, erupted during caldera collapse at Longonot, are interbedded, suggesting a regional collapse event. Incremental, but dominantly Valles-type, collapse continued with the eruption of trachyte agglutinate flows from concentric ring-fractures outside the caldera ring-fault (Ring-Feeder Zone) and trachyte pumice lapilli air-fall tuffs from west caldera I.
Following caldera I collapse, phonolite lava flows were erupted from the caldera floor. Centrally-erupted phonolite lava flows led to the construction of Ol Doinyo Onyoke lava cone. A pit-crater on the cone was a precursor to the collapse of caldera II, both of which were generated entirely by magma withdrawal. Regional decompression caused ring-fault bounded, block-resurgence of the caldera floor
Reappraisal of Middle Pleistocene fluvial deposits near Brandon, Warwickshire and their significance for the Wolston glacial sequence
Authors: MADDY D. , COOPE G. R. , GIBBARD P. L. , GREEN C. P. , Group S.G. LEWIS 
Published: December 2007

Recent exposures at Pools Farm Pit, Brandon have allowed a reinvestigation of strat-igraphic relationships critical to the debate concerning the status of the Wolstonian Stage of the British Pleistocene. Central to the original case for maintaining the type site of the Wolstonian Stage at Wolston, Warwickshire is the acceptance that the fluviatile Baginton Formation (Shotton’s Baginton-Lillington Gravel and Baginton Sand) forms, together with the glacigenic Wolston Formation, a series of sediments (Shotton’s Wolston Series) deposited during a single post-Hoxnian (i.e. post-oxygen isotope stage 9) glacial stage. Evidence presented in this paper suggests this interpretation is no longer tenable.
The sediments of the Baginton Formation exposed at Pools Farm Pit record the facies changes identified by Shotton in 1968. A predominantly gravel unit, the Brandon Gravels (Baginton Gravel Member), is overlain by a sandy unit, the Brandon Sands (Baginton Sand Member), the bounding surface being erosional. Two newly exposed fine-grained organic channel fills are described. The Brandon Lower Organic Sands and Silts lie within the Brandon Gravels and contain a temperate coleopteran fauna and a boreal forest flora. Correlation of these organic deposits on fauna1 grounds with the nearby site of Waverley Wood suggests a correlation with oxygen isotope stage 15. The Upper Organic Silts and Clays lie within the Brandon Sands and contain a cold climate fauna and flora. The Brandon Sands are overlain locally by the Brandon Upper Sands and Gravels which are correlated with the Ailstone Member of the Avon Valley Formation (stage 6). The younger Avon Valley Formation is known to extend back to at least stage 9 and therefore given that the Wolston Formation is younger than the Baginton Formation as indicated by a borehole nearby, it could represent any of the cold stages 10, 12 or 14. However, stage 12, the Anglian, remains the most likely attribution.
A record of late Cenozoic stratigraphy, sedimentation and climate change from the Hebrides Slope, NE Atlantic Ocean
Authors: STOKER M. S. , LESLIE A. B. , SCOTT W. D. , BRIDEN J. C. , HINE N. M. , HARLAND R. , WILKINSON I. P. , EVANS D. , ARDUS D. A. 
Published: December 2007

A punctuated 103.3 m thick succession of upper Palaeogene to Quaternary sediments has been recovered in a borehole from the upper Hebrides Slope, west of Britain. The borehole proved 11.2m of upper Oligocene, carbonate-rich muds at the base, unconformably overlain by 2.85 m of middle to upper Miocene, glauconitic sands. This is in turn unconformably overlain by 89.25 m of predominantly Plio-Pleistocene sands and muds, with a Holocene sea-bed veneer. The post-Miocene succession is subdivided into two units: the sand-dominated, Pliocene to lower middle Pleistocene, Lower MacLeod sequence between 89.25 and 67.82 m, and the mud-dominated, middle Pleistocene to Holocene, Upper MacLeod sequence above 67.82 m. Regional mapping indicates that these sequences are commonly associated with large-scale shelf-margin progradation and slope-front fan construction.
The borehole core provides an excellent record of the transition from pre-glacial to glacial conditions in the mid-latitude NE Atlantic Ocean. Climatic conditions warmer than present prevailed in the late Oligocene, mid- to late Miocene and Pliocene, although the influx of ice-rafted detritus in the late Pliocene marks the onset of climatic deterioration. This deterioration continued, in a fluctuating manner, until the early mid-Pleistocene (0.44 Ma) when fully glacial conditions were established on the Hebridean Margin.
Element supply to surface sediments and interrelationships with nodules along the Aitutaki-Jarvis Transect, South Pacific
Authors: MILLER S. , CRONAN D. S. 
Published: December 2007

A suite of surface sediment samples has been studied from sites on the Aitutaki-Jarvis Transect, between the equator and 17°S at approximately 160°W in the Central Pacific Ocean. The sediments were analysed by bulk and partition analysis in order to characterize changes in sediment geochemistry with water depth and with latitude, with particular reference to the effects of variation in supply and dissolution of biogenic material. The surface sediments are heterogeneous, ranging from carbonate or siliceous oozes to pelagic red clays. The elements in the sediments are variably partitioned into different sediment fractions. Examination of the sediments along the Transect has also provided a profile of the carbonate compensation depth, which shows it to deepen from approximately 4800 m at 16°S to approximately 5300 m at the equator.
The relationships between the bulk sediments and the sediment reducible fraction and associated Mn-Fe nodules has been examined. Variations in the interrelationships between the nodules and the sediment reducible fraction are ascribed to variations in element supply and early diagenetic reactions. A major decoupling of the relationship between nodules and associated sediment reducible fraction is observed in the north of the Transect at water depths close to the position of the CCD. Diagenetic reactions involving the destruction of organic matter which result in the reductive remobilization of Mn and the release of trace metals from labile material are thought to be important causes of this decoupling.
Wave-dominated nearshore sedimentation and ‘forced’ regression: post-abandonment facies, Great Limestone Cyclothem, Stainmore, UK
Authors: AINSWORTH R. B. , CROWLEY S. F. 
Published: December 2007

Investigation of sedimentary successions and depositional structures from the post-abandonment phase of the Great Limestone Cyclothem (Upper Carboniferous), Stainmore, UK suggests that deposition occurred in a sand-dominated coastal setting. Recognition of sedimentary structures produced by storms and interpretation of palaeocurrent and palaeowave data indicate that a W—E oriented, southwardly prograding, high-energy shoreline system existed in the Stainmore region. Two equally plausible interpretations suggest that the trough cross-stratified facies lying towards the top of the shoreface succession may either represent: (1) upper shoreface deposits formed by high energy fairweather waves, or (2) the deposits of a tidally influenced deltaic distributary or incised valley fill estuarine system. These interpretations contrast significantly with the N-S oriented, transgressive barrier island model proposed in an earlier study.
The sharp contact between lower shoreface and underlying offshore facies suggests that progradation of the shoreline occurred during a relative sea-level fall (‘forced’ regression). Palaeocurrent evidence indicates that deposition occurred within a system in which sediment was periodically flushed from a contemporary delta lobe and subsequently transported to the Stainmore shoreline by longshore currents.
Classification of Carboniferous non-marine bivalves: systematics versus stratigraphy
Authors: VASEY G. M. 
Published: December 2007

Carboniferous non-marine bivalves are usually classified at the ‘species’ level using external morphological criteria through comparison with figured and described type specimens. This system of nomenclature has allowed the recognition of stratigraphically useful morphospecies.Biometric analysis of a large number of shells of the genusAnthraconautaPruvost, collected from the Sydney coalfield, Nova Scotia, suggests. that this system of nomenclature cannot be justified biologically. The genus appears to be morphologically homogeneous in the Upper Carboniferous of Western Europe and North America. Shell shape variation is influenced by mode of life and palaeoenvironment, as suggested by the study of modern analogues and fossil shells. If a biological classification were adopted for this group of fossils, then all their stratigraphical value would be lost.To reconcile systematics with the needs of stratigraphers, the adoption of a trinomial nomenclature is recommended. The use of cluster analysis has shown that varieties can be identified that correspond morphologically to previously named and described ‘species’. Nomenclature of the form genus, species and variety would be both biologically correct and stratigraphically useful.
A Neoproterozoic multi-phase rift sequence: the Grampian and Appin groups of the southwestern Monadhliath Mountains of Scotland
Authors: GLOVER B. W. , KEY R. M. , MAY F. , CLARK G. C. , PHILLIPS E. R. , CHACKSFIELD B. C. 
Published: December 2007

The Grampian and Appin groups of the southwestern Monadhliath Mountains form the earliest known syn-rift sequences of the Scottish central Highlands. They were likely to have formed in an intracontinental setting and represent deposition of mixed clastic and carbonate shallow and deep marine strata.
The Grampian Group of the southern Monadhliath Mountains was deposited during a period of initial basin rifting (NW–SE extension) followed by a phase of thermal subsidence. Syn-rift sediments comprise a 2.5–6 km thick turbidite system. Thermal subsidence brought about the basinward progradation of shallow marine shelf sediments resulting in the infilling of pre-existing basin topography.
The overlying Appin Group commenced with deposition of a shallow marine sequence alternating between nearshore tidal sand and offshore mud deposition. This formed in response to renewed rifting and concomitant subsidence. Accelerated rifting resulted in localized footwall uplift and erosion while sedimentation continued in the hanging-wall areas. Resultant subsidence, perhaps partly thermally driven, caused gradual basin widening and produced an onlapping marine sequence. There followed a period of progressive clastic deprivation when carbonates were precipitated, and at the onset of anoxic conditions, deposition of organic muds.
The fundamental structural elements responsible for the formation of the Grampian and Appin group basins were also influential in the orogenic evolution of the basin-fill. Half-graben fills were deformed to produce regionally extensive folds such as the Stob Ban–Craig a’ Chail Synform.
Transfer zones in the southern Rio Grande rift
Authors: MACK G. H. , SEAGER W. R. 
Published: December 2007

Despite recent interest in transfer zones in regions of continental extension, their detailed geometry and kinematics remain unclear. Four late Palaeogene and Neogene transfer zones within the southern Rio Grande rift, USA, are described, based on geological mapping at the scale of 1:24 000 and analysis of synrift stratigraphy. The Cutter Sag transfer zone is located between the overlapping tips of north-trending, west-dipping faults, and is characterized by a north-dipping structural ramp segmented by closely spaced, NE-trending normal faults. Similarly, the West Potrillo transfer zone occupies a position in the zone of overlap of north-trending, west-dipping faults, but the structural details of the transfer zone are largely hidden beneath Quaternary lava flows. However, isolated bedrock exposures outside the lava field, gravity data, and the alignment of cinder cones suggest that the West Potrillo transfer zone is a NW-dipping synclinal ramp cut by NE-trending fractures and/or faults. Positioned between north-trending, overlapping border faults that dip toward each other, the Cedar Hills transfer zone is a broad, north-trending arch whose summit collapsed into a graben along a series of north-trending normal faults. The Rincon transfer zone separates border faults that do not overlap and has a long history of faulting and sedimentation beginning in latest Oligocene and extending into the Quaternary.
With the possible exception of reactivated early Tertiary compressional structures in the Rincon transfer zone, the transfer zones described here do not appear to be influenced by pre-rift zones of weakness. However, the Cutter Sag and West Potrillo transfer zones are preferred sites of basaltic volcanism, and the Cutter Sag.- Rincon, and Cedar Hill transfer zones influenced the location of the Plio-Pleistocene ancestral Rio Grande.
Neogene supra-subduction zone extension in the Polis graben system, west Cyprus
Authors: PAYNE ANNE S. , ROBERTSON ALASTAIR H. F. 
Published: December 2007

The Neotectonic Polis graben and adjacent Pegia half-graben in west Cyprus are extensional basins developed within the convergent tectonic regime of the Eastern Mediterranean. Both basins contain an early fill of Miocene carbonates including reef limestones. Messinian extension, oriented ENE–WSW, produced the asymmetrically faulted Polis graben structure. Evaporites were deposited in the south of the area while unconformity surfaces developed in the north. Pliocene mark and chalks were then deposited in a relatively quiescent phase in the north of the graben, while faulting continued into the Early Pliocene in the south. Plio-Pleistocene to Recent sediments record regional uplift of Cyprus. Contemporaneous NNE–SSW-oriented extension formed the Pegia half-graben and renewed minor faulting in the Polis graben.
The extensional structures of the Polis graben system are thought to result from extension above a subduction zone located south of Cyprus, driven by subduction 'roll-back' and trench migration. Accelerated convergence and rapid roll-back during Late Miocene times caused the first stage of extension, whilst the Plio-Pleistocene faulting was driven by differential extension in the overriding plate as the Eratosthenes Seamount collided with the trench and locally impeded subduction. The Polis graben system may provide a model for the early stages of development of major suprasubduction zone extensional areas such as the Aegean region.
SHRIMP constraints on sediment provenance and transport history in the Mesozoic Statfjord Formation, North Sea
Authors: MORTON ANDREW C. , CLAOUÉ-LONG JONATHAN C. , BERGE CATO 
Published: December 2007

Detrital zircons in sandstones of the Statfjord Formation (late Triassic-early Jurassic) in the northern North Sea have been dated with the sensitive high resolution ion microprobe (SHRIMP). These sandstones lack detailed biostratigraphic control, but display distinct variations in heavy mineral assemblages which facilitate a three-fold subdivision of the sequence. The lower and middle zones (heavy mineral Zones A and B) have similar characteristics, both displaying a marked upward decline in garnet abundance which has proved difficult to attribute unambiguously to change in either provenance or sedimentation history. The base of the highest zone (heavy mineral Zone C) is marked by changes in several heavy mineral indicators attributable to a shift in ultimate provenance compared with the underlying zones.
The detrital zircon ages are a direct fingerprint of the sediment source terrains, and so resolve ambiguities in interpreting provenance from heavy mineral abundances alone. The age spectra indicate that both low-garnet and high-garnet parts of Zone A have the same ultimate provenance. This strongly suggests that garnet removal was not a function of changing provenance, but took place during the sedimentation process, probably by weathering during periods of prolonged alluvial storage. The source of Zone A is not represented in any presently exposed landmass: the required combination of Caledonian granitoids intruding or in immediate proximity to high-grade Archaean-sourced metasediments is likely to have been either to the west, in the northern part of the Shetland Platform, or to the north, in what is now the Norwegian Sea. Zircons in Zone C have a distinctly different age spectrum consistent with a source in the Western Gneiss Region of southern Scandinavia, where there is the required combination of Proterozoic protoliths and Caledonian reworking.