bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of Resistivity At Bit (RAB) images within an Eocene submarine channel complex, Alba Field, UKCS
Authors: McGarva R. M. , Bell C. , Bedford J. 
Published: April 2008

Abstract
To aid reservoir description a Resistivity At Bit (RAB) tool was run in a series of near-horizontal wells within the Alba Field. The tool characterized lithology types and detailed bed geometry through oriented resistivity images of the borehole. Image quality ranged from good to uninterpretable through zones of image artifact, and image resolution was less than that of conventional resistivity imaging tools. Shale intervals locally display good bedding detail, whereas sandstones display hole spiralling and yield little meaningful information. Shales are conductive, but locally, images show the presence of thin and sharp-based, relatively resistive shale beds that progressively ramp upward into the background shales. These resistivity ramp-defined bedding units may be individual mud-flows, with the resistive beds being possibly coarser grained or cemented. Following correction for structural tilt, bedding surfaces between and within shale successions range from uniform to irregular and possibly indicate some degree of shingling between individual flow units. Tool runs typically encounter long near-uniform sections of sandstones and shales with well defined lithological boundaries. RAB images show that these sandstone-shale transitions are sharp and steep (22°–88°). Such dips imply either steep channel margins, faulted contacts or more likely, the result of borehole bias in horizontal wells drilled into channellized successions. The lateral margins to an individual sandstone body, sampled as entry and exit points along the well path, commonly display discordant strikes, possibly implying lenticular geometries. Sandstone-shale contacts may allow qualitative estimation of the direction of the channel element thickening. Compactional shale drape deformation is often present away from the sandstone masses. Sedimentation is modelled as a two phase system with slope-supplied, mud-dominated gravity-flows temporally disconnected from deposition of shelf-derived turbiditic sandstones. Infrequent depositional events resulted in channels that were infilled with sand from high-density turbidity currents. Fractures and faults are imaged with the RAB tool and indicate a possible topographical control to structural development.
Insights from simultaneous acoustic and resistivity imaging
Authors: Hansen T. , Parkinson D. N. 
Published: April 2008

Abstract
We describe a method of thin-bed petrophysical analysis that exploits the availability of both acoustic and resistivity images of the same rock. In developing our method we have gained a number of insights into the contrasting response of these images to rock properties, which may be of general interest to the imaging community. The case-study we present is from a thin-bedded, deep-water siliciclastic depositional environment. The resistivity image was used to increase the resolution of a conventional resistivity device. Comparison of bedding dips between the two images suggests a resistivity depth of investigation of around three inches. However, the best fit between image and conventional resistivity was obtained using a somewhat deep-reading resistivity measurement. The acoustic image was used to increase the resolution of our porosity measurement. The best fit to acoustic image amplitude was with the neutron porosity log, rather than with density, slowness, or with any combination of two porosity logs. Given high-resolution resistivity and porosity measurements from the images, and the precise information on bed boundaries that images provide, we proceeded with petrophysical analysis at a much higher resolution than obtainable from the conventional logging suite.
Borehole images of the ocean crust: case histories from the Ocean Drilling Program
Authors: Brewer T. S. , Harvey P. K. , Haggas S. , Pezard P. A. , Goldberg D. 
Published: April 2008

Abstract
Downhole logging is an integral part of the Ocean Drilling Program (ODP), although the choice of tool deployment is primarily a function of the scientific objectives of an individual leg. Following the successful deployment of the Formation Microscanner (FMS) during Leg 126, FMS images have been used to constrain a variety of sedimentary, igneous, metamorphic and tectonic questions in the ocean. However, it is only recently, that the full potential of FMS images and other logging data has been employed in the study of volcanology, which provides important constraints on the evolution of the volcanic pile when fully integrated with core based measurements. Furthermore, many of the holes drilled into the volcanics often have incomplete core recovery and here the logging results can be used to constrain the lithological, chemical and mineralogical variations in such intervals. Using the log based stratigraphy from crust created at slow (Hole 395A) and intermediate (Holes 504B and 896A) spreading centres, it is evident that the proportions of volcanic rock types (pillows/flows/breccias) correlate with the spreading rate. This relationship is suggested from submersible observations, but the ODP data provide additional data to test such hypotheses and to also extended and test it within the third dimension.
A reassessment of Manx Group acritarchs, Isle of Man
Authors: Molyneux S. G. 
Published: April 2008

Abstract
The biostratigraphy of acritarch assemblages from the Manx Group, Isle of Man, has been reassessed in the light of evidence from the Skiddaw Group, rocks in the English Lake District that are the Manx Group’s equivalents in terms of both age and lithofacies. Assemblages from the Santon Formation (formerly the Lonan Flags) and the Glen Dhoo Unit (formerly the Glen Dhoo Flags) are considered to be of early Arenig rather than the previously suggested latest Tremadoc age, and indicate that these two formations probably correlate with each other, and with the Hope Beck Formation of the Skiddaw Group. An acritarch assemblage associated with volcanic rocks at Peel is reassessed as being of early Arenig age, rather than late Arenig as previously thought. The age of an assemblage from the Glen Rushen Formation (formerly the Maughold Banded Group) is now considered to be of mid-Arenig age and to indicate correlation with the Loweswater Formation of the Skiddaw Group, while that from the Lady Port Formation is regarded as being an upper Arenig assemblage indicating correlation with the Kirk Stile Formation. An assemblage from Glenfaba Brickworks was previously assigned to the Niarbyl (Flags) Formation, but is now considered to be from undifferentiated Manx Group rocks. It is a poor assemblage that is not younger than early Arenig, but could be as old as Late Cambrian, although its proximity to the Peel locality makes an early Ordovician age more likely.
Macrofauna and ichnofauna of the Manx Group (early Ordovician), Isle of Man
Authors: Orr P. J. , Howe M. P. A. 
Published: April 2008

Abstract

Within the Manx Group, the key elements of the limited macrofauna include a
Rhabdinopora
-like graptoloid from Cronk Sumark and a didymograptid-dichograptid fauna from Baltic Rock. The ichnofaunal assemblage is dominated by fodinichnia (mainly examples of
Phycodes
). This is atypical of Phanerozoic deep-marine environments as a whole, but is a feature of other early Ordovician deep-marine ichnofaunal assemblages, notably that within the Skiddaw Group of the English Lake District.
Dictyodora zimmermani
and
Glockerichnus radiatus
occur within the Manx Group; these ichnotaxa are present in other ichnofaunal assemblages of early Ordovician age which were also emplaced at high southerly palaeolatitudes.
Revised lithostratigraphy of the Manx Group, Isle of Man
Authors: Woodcock N. H. , Morris J. H. , Quirk D. G. , Barnes R. P. , Burnett D. J. , Fitches W. R. , Kennan P. S. , Power G. M. 
Published: April 2008

Abstract
The existing lithostratigraphy of the Manx Group (lower Ordovician) of the Isle of Man is formalized as far as is possible given a paucity of biostratigraphical and structural control. Coherent packages of strata can be recognized within northeast striking structural tracts. Some tract boundaries are faulted but poor exposure leaves doubt about the nature of others. Some structural repetition of successions is likely. However, the long-held equivalence of the sandstone units on either side of the island can no longer be maintained, because the Niarbyl Formation in the west is now known to be of Silurian age. Repetition of Manx Group units across a syncline along the axis of the island is therefore in doubt. Different outcrops of superficially similar units are accordingly named separately on each flank of the island. The stratigraphy of part of the northern Manx Group is left unrevised awaiting further work.
The southeastern, sandstone-dominated units of the Manx Group comprise three tracts divided into the Lonan and Santon (lower Arenig) Formations, the Port Erin and Mull Hill Formations, and the Ny Garvain and Creg Agneash Formations. The Creg Agneash Formation is stratigraphically overlain by the mudstone-dominated Maughold Formation. The next two tracts to the northwest both contain a black mudstone unit, the possibly correlative Barrule and Glen Rushen (middle Arenig) Formations, each structurally overlain by laminated silty mudstone of the Injebreck Formation. A further unit of laminated siltstone and mudstone, the Creggan Mooar Formation, is defined in tract 6, west of which an enigmatic unit contains lowest Arenig fragmental volcanic rocks. In the most northwesterly tract, the Lady Port Formation is a varied assemblage of black mudstone, turbidites, pebbly mudstone and quartz arenite. Lithological correlation of these different Manx Group successions is attempted, but is constrained by only four biostratigraphical control points.
The Manx Group stratigraphy has long been correlated with that of the Skiddaw Group of the Lake District. A tentative correlation of events on this part of the early Ordovician margin of Gondwana can be made assuming some synchroneity of Early Arenig lowstand turbidite fans, of a mid-Arenig transgression, and of a late Arenig mass-wasting event.
Lithofacies of Lower Palaeozoic deep-marine sediments in the Isle of Man: a new map and stratigraphic model of the Manx Group
Authors: Quirk D. G. , Burnett D. J. 
Published: April 2008

Abstract
A classification scheme for lithofacies in the Lower Palaeozoic Manx Group has been designed based on a simple assessment of the sandstone:mudstone ratio, bed thickness and sedimentary structures. The scheme was used to acquire high-resolution, standardized field data over areas of good exposure on the Isle of Man. These data were then correlated in order to produce a lithostratigraphic framework and a simplified geological map. Overall, the succession appears to young northwestwards from early Arenig, sand-rich sediments on the southeast coast to mud-rich sediments of mid-late Arenig age inland and on the northwest coast. A number of alternative structural reconstructions have been made which fit to a greater or lesser degree with limited biostratigraphic data. The favoured model involves a compromise between inferred duplication of stratigraphic units by reverse faults and repetition of similar depositional cycles or sequences within the succession. This model implies that the Manx Group is between 5400 and 9250 m thick and contains within it both a lateral facies change (from proximal to distal character east-west) and an overall fining-upwards stratigraphic signature. The sediments are interpreted to have been rapidly deposited on the west dipping margin of a basin situated between the Isle of Man and southeast Ireland, which forms an embayment on the northwest edge of Eastern Avalonia. The main depositional processes were turbidity currents and debris flows, with evidence of possible current deflection or reworking of the upper parts of turbidites by northwards flowing contour currents. During the Caledonian orogeny, the basin was inverted with the development of northeast-southwest trending thrusts and east-west dextral faults. Tentative evidence also exists for the presence of an older north-northeast-south-southwest normal fault trend, although whether it was active during the Arenig is uncertain. It is recommended that future stratigraphic work should concentrate on testing possible correlations between and within the mixed sand-mud Lonan, Port Erin, Injebreck and Creggan Mooar Formations.
An early Ordovician turbidite system on the Gondwana margin: the southeastern Manx Group, Isle of Man
Authors: Woodcock N. H. , Barnes R. P. 
Published: April 2008

Abstract
The southeastern part of the Manx Group comprises sandstone-rich deep-marine turbidites of Arenig (early Ordovician) age, deposited on the Avalonian segment of the Gondwana margin. The main area comprises a 2 km thick succession from thin-bedded wacke sandstone and mudstone of the Lonan Formation up into medium-bedded wacke and arenite of the Santon Formation. This succession is interpreted as the distal part of a mixed mud-sand ramp overlain by a major distributary channel and lobe system. The Keristal Member is a unit of thick-bedded quartz arenite within the Lonan Formation recording a short-lived incised channel system with small terminal sand lobes.
Flutes and scours in the Lonan and Santon Formations show west-southwest directed transport, contrasting with north-northwest directed estimates from ripple cross-lamination. Constraint by margin topography may have caused the higher concentration components of the flows to run along-margin, whilst flow-stripping of the lower concentration flow-tops allowed them to collapse down the regional north-northwest facing palaeoslope.
The southwestern and northeastern areas contain fault-bounded successions that can be correlated only tentatively with the main area. In the southwest, thin-bedded wackes and mudstones of the Port Erin Formation pass up into the quartzose Mull Hill Formation, which shows the thickening-up motif of a fan lobe. In the northeast, the Creg Agneash Formation resembles the Mull Hill Formation, and probably overlies the quartzose wackes of the Ny Garvain Formation.
The contrast of arenite and wacke sandstones in the Manx Group may have resulted partly from the intrabasinal separation of sand and mud, e.g. by flow stripping. However, the major factor was the availability on the basin margin of both clean and muddy sediment. The quartz arenite sands were probably sourced from the widespread Armorican quartzite facies of Gondwana, constraining the rifting of Avalonia from its parent continent to mid-Arenig time or later.
Debris flows on the Ordovician margin of Avalonia: Lady Port Formation, Manx Group, Isle of Man
Authors: Woodcock N. H. , Morris J. H. 
Published: April 2008

Abstract
The Lady Port Formation (Arenig, Lower Ordovician) occurs in a fault-bounded tract on the northwestern coast of the Isle of Man. It forms part of the Manx Group, deposited on the outboard edge of the Avalonian margin of Gondwana. The formation is dominated by laminated siltstones and mudstones deposited from low-concentration turbidity flows, and rare manganiferous ironstones. This facies is overlain in places by thin-bedded sand-based turbidites with conspicuously bioturbated mud tops. These sands are quartzose wackes and contrast with a third facies of quartzose arenite turbidites that punctuate the laminated mudstones. This arenite facies suggests a discrete inboard source of clean sand which was occasionally diverted into this part of a predominantly mud-prone basin.
The Lady Port Formation also features units of pebbly mudstone and associated intervals of quartz arenite or mudstone showing strongly disrupted bedding. The pebbly mudstones are the products of cohesive debris flows. Clast compositions distinguish debrites derived from the bedded facies with which they are now intercalated from debrites that contain further travelled, but still intrabasinal, clasts. The disrupted facies preserves a spectrum of soft-sediment fragmentation of bedding, culminating in bed fragments being incorporated into the base of pebbly mudstone units. The facies is interpreted as the product either of downslope slumping, the possible precursor to debris flows, or of deformation ahead of and below advancing debris flows.
The local derivation of slumps and debrites implies an actively forming topography in this part of the Manx Group basin. The slumps and debrites of the Lady Port Formation are matched in other, less well-exposed, parts of the northwestern Manx Group. The available biostratigraphic control suggests that the formation is of late Arenig (Fennian) age and contemporaneous with the Buttermere olistostrome and pebbly mudstones in the Kirk Stile Formation of the Skiddaw Group, Lake District. A widespead mass wastage event is indicated on the Gondwana margin, perhaps coeval with the rifting from Gondwana of the Avalonian microcontinent.
The Silurian fauna (graptolite and nautiloid) of the Niarbyl Formation, Isle of Man
Authors: Howe M. P. A. 
Published: April 2008

Abstract

The discovery of a mid-late Wenlock (Silurian) graptolite and orthoconic nautiloid fauna at Traie Dullish Quarry, Peel Hill, in the Niarbyl Formation (Dalby Group) of the Isle of Man, disproves all earlier correlations between the Niarbyl and Lonan Flags on the west and east coasts of the island, respectively. All previous structural hypotheses require re-examination. The graptolites comprise
Cyrtograptus
cf.
lundgreni, Monograptus flemingii
cf.
warreni
and
Monograptus
ex gr.
flemingii
. They suggest, but do not prove, a
lundgreni
Biozone age, thus indicating a possible correlation between the Niarbyl Formation and the Birk Riggs Formation of the English Lake District, and the Denhamstown Formation of the Balbriggan Inlier, Southern Ireland.
Palaeomagnetism of (Palaeozoic) Peel Sandstones and Langness Conglomerate Formation, Isle of Man: implications for the age and regional diagenesis of Manx red beds
Authors: Piper J. D. A. , Crowley S. F. 
Published: April 2008

Abstract

The Peel Sandstones are a sequence of fault-bounded fluvially deposited red beds of uncertain age exposed on the western coast of the Isle of Man. Palaeomagnetic study identifies partial preservation of an A component pre-dating deformation at four of eight sampled sites; the presence of both polarities in this remanence defines a positive class C reversal test. This component adjusted for tilt is
D/I
= 356.9/−47.1° (48 samples, α
95
= 5.6°) and is interpreted to be a post-depositional detrial remanence. The palaeolatitude (29° S) corresponds to the position of Britain during Late Silurian-Early Devonian times and implies that these sediments are correlative with Lower Old Red Sandstone molasse from elsewhere in the British Caledonides; a post-mid-Carboniferous age is excluded. Palaeomagnetic and geological evidence are used to constrain an age of
c.
410–400 Ma for the Peel Sandstones, whilst a declination contrast of 40–50° is interpreted to reflect either: (a) tectonic emplacement of a unit including the Peel Sandstone outcrop; or (b) wider post-Early Devonian and pre-Late Carboniferous counterclockwise rotation between the Isle of Man and the mainland during final shaping of the Caledonides. A post-folding B component of uniform reversed polarity (
D/I
= 195.6/−30.8°, 45 samples, α
95
= 4.8°) is present at all sites and was acquired during diagenesis at
c.
250 Ma.

Red sandstones within the Langness Conglomerate Formation, near the base of the Lower Carboniferous (Chadian-Arundian) succession exposed in the southeast of the Isle of Man, have a uniform reversed magnetization (
D/I
= 209.7/−24.2°, 20 samples, α
95
= 6.8°). Like the B magnetization in the Peel Sandstones, this was acquired by diagenesis in Early Permian times (
c.
250 Ma) and during the Permo-Carboniferous Reversed Superchron. It is temporally related to early extensional tectonism in the Irish Sea region.
Crustal magnetic structure of the Irish Sea region: evidence for a major basement boundary beneath the Isle of Man
Authors: Kimbell G. S. , Quirk D. G. 
Published: April 2008

Abstract
Imaging and modelling of regional aeromagnetic data indicate a significant change in crustal magnetization across a boundary which extends northeast-southwest across the Irish Sea. A concealed magnetic basement is interpreted to underlie the area to the southeast of the boundary at mid-crustal levels, whereas relatively non-magnetic rocks lie at these levels to the northwest. The boundary does not coincide with the Iapetus Suture as defined by seismic evidence in the Irish Sea and palaeontological evidence on the east coast of Ireland. Instead, it appears to extend towards the northern margin of the Precambrian rocks of southeast Ireland. Its orientation swings sharply in the vicinity of the Isle of Man from north-northeast-south-southwest in the south to east-northeast-west-southwest in the northeast. There is an apparent correlation between the magnetic basement structure and an overlying, shallow, anomalous zone along the axis of the island which is revealed by gravity and high-resolution aeromagnetic data. Modelling indicates that shallow and deep structures may be related if both are assumed to dip to the northwest, a dip direction supported by seismic reflection data acquired immediately to the south of the island. The preferred interpretation is that the mid-crustal magnetic block is of Precambrian age and represents the northern part of an Avalonian basement which was assembled in late Precambrian-early Cambrian times. The geometry of the boundary beneath the Isle of Man may have been inherited from the pre-existing Avalonian basement architecture. Planes of weakness could have been reactivated as major, early Palaeozoic extensional structures and subsequently been activeunder a compressional regime during the closure of the Iapetus Ocean and the Acadian Orogeny.
Shallow geophysical and geological evidence for a regional-scale fault duplex in the Lower Palaeozoic of the Isle of Man
Authors: Quirk D. G. , Burnett D. J. , Kimbell G. S. , Murphy C. A. , Varley J. S. 
Published: April 2008

Abstract

A distinctive set of linear anomalies is seen on potential field data crossing the Isle of Man in a northeast-southwest belt, 5–6 km wide. The lineaments occur in an imbricate pattern with three constituent trends: northeast-southwest, east-west (to east-northeast-west-southwest) and north-south. The belt can be traced into the offshore where it ties with a northwest dipping set of anomalous high-amplitude seismic reflections interpreted as fluid-filled fractures or intrusions along fractures. In the field, the lineaments coincide with northeast-southwest reverse faults, east-west dextral strike slip faults and north-south sinistral strike slip faults interpreted to have formed during northwest-southeast compression in the late Caledonian. Several of the strike-slip faults were later sites of mineralization. In addition, there is limited kinematic evidence for an earlier period of sinistral transpression on east-west ductile shear zones. A tentative model is proposed where the Manx Group is located on the eastern side of an inverted Lower Palaeozoic basin (the Manannan Basin) forming an embayment on the northwest margin of Eastern Avalonia. During closure of Iapetus, the direction of maximum principal stress (σ
1
) rotated from north-northeast-south-southwest to northwest-southeast as Eastern Avalonia docked and then locked against Laurentia. The imbricate belt developed as a duplex at the eastern edge of the basin during the later stages of contraction. The implications of the model is that the stratigraphy of the Manx Group is telescoped.