bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and geodynamics of the Uralian orogen
Authors: Puchkov V. N. 
Published: April 2008

Abstract
The Urals are a Late Palaeozoic orogenic belt. The relicts of earlier orogens are traced in its basement. In particular, the Late Vendian pre-Uralian orogen is reconstructed and identified as a part of the Late Precambrian Cadomian orogen. The Uralian orogeny was preceded by Late Cambrian-Early Ordovician epicontinental rifting and formation of the Paleo-Uralian ocean whose remnants are Palaeozoic ophiolites. Calc-alkaline volcanites and plutons, typical of active margins, are widely developed in the eastern Urals. The Uralian foldbelt results from oblique collision between the East European (Laurussia) passive margin and the active margin on the Kazakhstanian continent. Collision began in the south of the Urals and moved, wave-like, to the north. The eastern and northern parts of the Urals have been affected by the Middle Jurassic Cimmerian intracontinental (intra-Pangaea) shortening. The Uralian-Cimmerian mountain belt was eroded and partially inundated by seas in the Late Jurassic-Early Cretaceous times and has been reactivated since the Oligocene in response to a recent intracontinental shortening.
History of exploration in the southern North Sea
Authors: Glennie K. W. 
Published: April 2008

Abstract
Exploration history in the Southern North Sea Basin extends back to 1858 in Germany, which was the centre of Europe’s oil industry for about a century, with a resurgence in oil discoveries from 1934 to 1945. This changed dramatically in 1963 with the realization of the immense size of the Dutch Groningen gas field. Core data indicated that the Rotliegend reservoir extended westward into the southern North Sea. Between December 1965 and October 1966, five major gas discoveries totalled reserves of almost 20 tcf, sufficient to saturate the UK monopoly market. By 1969, with cheaper seismic ships and a billion barrel oil field in Norwegian waters, UK exploration activity shifted to the central and northern North Sea. The UK southern North Sea became a backwater until about 1981 when, with a pending shortage, British Gas encouraged renewed activity by increasing the price for new gas, the Carboniferous soon becoming an exploration target. Meanwhile, exploration in the Dutch land and offshore, and German land areas resulted in a steady stream of gas discoveries and some oil derived from Liassic source rocks, both enhanced by the later use of 3D seismic data.
Compartmentalization of Rotliegendes gas reservoirs by sealing faults, Jupiter Fields area, southern North Sea
Authors: Leveille Gregory P. , Knipe Rob , More Colin , Ellis Dave , Dudley Graham , Jones Greg , Fisher Quentin J. , Allinson Gareth 
Published: April 2008

Abstract
Rotliegendes gas reservoirs in the Jupiter Fields are compartmentalized by sealing faults. Significant variations in free water levels (i.e. gas-water contacts corrected for capillary pressure effects), hydrocarbon composition and pressure exist between sealed fault blocks. Displacements on many of the sealing faults are low, resulting in ‘clean’, porous and permeable Rotliegendes sandstones being juxtaposed across the faults. Characteristics that are important in determining the sealing potential of intra-Rotliegendes faults include (i) fault-rock cement types and volumes, (ii) intensity of cataclasis, (iii) three-dimensional continuity of the fault and associated damage zone, (iv) authigenic clay content at the time of faulting, and (v) relative orientation, timing and magnitude of later deformational events.
Detailed analysis of fault rocks from core indicates cementation is the most effective fault sealing mechanism in the Jupiter Fields. Volumetrically significant cements include salt, anhydrite and quartz. Cataclasis and deformation induced mixing of authigenic clay with fragments of framework grains also contribute to the sealing potential of some faults. Permeabilities in cemented and cataclastic fault rocks are reduced by two or more orders of magnitude compared to undeformed sandstones.
3D seismic mapping indicates NNE-SSW-trending fault zones have the highest along-strike continuity, followed by NW-SE- and E-W-trending fault zones. The NNE-SSW-trending faults also appear to have had the simplest deformational history, with NW-SE- and E-W-trending faults exhibiting evidence of movement during multiple deformational events. Static reservoir data indicate that some NNE-SSW- and NW-SE-trending faults seal over geological time, and it is expected other faults will act as seals or baffles during reservoir depletion.
Diagenetic controls on reservoir quality in Permian Rotliegendes sandstones, Jupiter Fields area, southern North Sea
Authors: Leveille Gregory P. , Primmer Tim J. , Dudley Graham , Ellis David , Allinson Gareth J. 
Published: April 2008

Abstract
Reservoir quality in Lower Permian Rotliegendes Group sandstones in the Jupiter Fields varies considerably between fault blocks due to differing degrees of diagenetic alteration. Average porosities in individual fault blocks range from 12 to 21%, and geometric mean permeabilities vary between 2 and 200 md. Rotliegendes stratigraphy and sedimentology varies little across the area, and therefore does not strongly influence reservoir quality.
The two most important diagenetic processes were the formation of authigenic illite and burial compaction. Illite growth mainly occurred during the Middle Jurassic to Early Cretaceous, coincident with maximum burial of the Rotliegendes. Fault blocks with good reservoir quality generally contain (1) relatively low illite abundances, (2) low-potassium illite, (3) increasing illite abundances with depth, (4) illite ages that decrease with depth and (5) comparatively low amounts of burial compaction. Fault blocks with poor reservoir quality all exhibit (1) high illite abundances, (2) high-potassium illite, (3) no consistent trend in illite abundances or age with depth and (4) high amounts of burial compaction. These observations are believed to indicate that reservoir quality was preferentially preserved in fault blocks that were structurally high during the main phase of illite growth. Factors contributing to the preservation of reservoir quality in structurally high fault blocks included differences in pore fluid chemistry, less burial compaction, and, in places, early hydrocarbon charging. Reservoir quality in undrilled fault blocks can be predicted by reconstructing the structural geometries present during the Mid-Jurassic to Early Cretaceous.
Probing the lower limits of a fairway: further pre-Permian potential in the southern North Sea
Authors: Cameron Nick , Ziegler Tom 
Published: April 2008

Abstract
Although the southern North Sea has become a major centre of hydrocarbon production, the lower limit of the fairway has not been established. We show, using a review of the pre-Permian source-rock potential of the southern North Sea, that the regional geology will permit exploration below the present base of the fairway. Seismic mapping indicates that this portion of the stratigraphic column is associated with multiple objectives. Two very different examples demonstrate the range of opportunities. The first example is a conventional structural trap located on the northeast flank of the London-Brabant Ridge in Quadrant 53. Reservoirs are the Westphalian to Devonian succession. Source-rocks are lacustrine horizons within the local Westphalian succession and the Carboniferous to Devonian section to the northeast of the South Hewett Fault. The second example presents a new objective, a stratigraphic trap to the ESE of a high located in Quadrants 42 and 43 and identified for the first time by this study. The anticipated reservoir is Dinantian carbonate progradational wedge derived from the adjacent high. Namurian and Dinantian source-rocks are predicted. Until opportunities of these types are evaluated, the lower limit of the Southern North Sea fairway will remain undefined and ultimate reserves estimates will continue to be poorly constrained.
The structure of the Westphalian in the northern part of the southern North Sea
Authors: Quirk David G. , Aitken John F. 
Published: April 2008

Abstract
A clear understanding of the tectonic framework of the Westphalian in the northern part of the southern North Sea has improved confidence during seismic interpretation and offers the possibility of finding new exploration targets within structures that have already been drilled. Two aspects of the tectonic framework are crucial. Firstly, Westphalian strata were deposited within a major foreland basin; consequently, thickness variations on a local scale are minimal. Secondly, the area was affected by a phase of rifting, known as the Saalian event, during the early Permian. This rifting event led to the formation of major E-W and NW-SE normal faults that tilt and offset Westphalian strata. The Upper Rotliegend, which lies unconformably on top of the Westphalian, was deposited during thermal sag after rifting ceased. Identifying where Westphalian reservoirs are present within structure requires careful mapping of both intra-Westphalian and base Rotliegend levels.
Sequence stratigraphy of the Westphalian in the northern part of the Southern North Sea
Authors: Quirk D. G. 
Published: April 2008

Abstract

A series of stacked fluvio-lacustrine sequences in the Westphalian of the northern part of the Southern North Sea can be correlated over areas of greater than 2500 km
2
. Each sequence is similar in terms of thickness (100–300 m) and the internal arrangement of lithofacies but they differ in colour and in the amount of sandstone and coal that they contain. A typical sequence consists of a sand-rich lower unit, a mud-dominated middle unit which fines upwards towards its top and a mud-dominated upper unit which generally coarsens upwards. The main reservoir-prone intervals are confined to the lower-middle parts of sand-rich units and consist of coarse-grained braided or low-sinuousity channel deposits. These fluvial sandstones are laterally extensive and are neither typical of incised valley fills (in terms of stratal geometries) nor of progradational systems tracts (in terms of facies distribution). Instead they appear to have been deposited during periods of widespread fluvial aggradation caused by transgression as a result of relative lake-level rise. Each lower sand-rich unit is overlain by a dark mudstone with a high gamma ray expression which is interpreted as an initial (lake) flooding surface marking the onset of predominantly lacustrine and mire sedimentation associated with the development of the fining-upwards mud-dominated unit. The top of each fining-upwards unit is marked by a maximum gamma ray peak interpreted as a maximum flooding surface which defines the end of lake transgression. Above the maximum flooding surface, each coarsening-upwards mud-dominated unit shows increasing deltaic influence upwards associated with a slowing in the rate of relative lake level rise. The tops of some of these units are eroded suggesting that in some case deltaic progradation was followed by a relative fall in lake level; in other cases the boundary with the overlying transgressive sand-rich unit in the next sequence is wholly conformable. Coal mires developed in coastal areas, particularly during transgression when coarse-grained sediment was trapped up-dip on the coeval alluvial plain. Relative changes in lake level had a periodicity of 1.5 Ma or less indicating that they may be related to third order eustatic cycles.
Lower crustal structure of the East Irish Sea from deep seismic reflection data
Authors: England R. W. , Soper N. J. 
Published: April 2008

Abstract
Deep near-normal incidence reflection profiles across the East Irish Sea show that the middle and lower crust are dominated by dipping reflectors with a NE-SW strike. The northward dipping Iapetus suture can be traced and contoured beneath the Solway Firth where it projects upward beneath the Peel and Solway Firth basins. South of the suture there are both northward and southward dipping reflectors. These are considered to be related to Early Devonian (Acadian) deformation. Although the Carboniferous was deposited in basins with a broadly NE-SW trend there is no clear evidence of reactivation of earlier structures during either Carboniferous sedimentation or Variscan inversion. The faults that controlled Permian and Mesozoic basin development in the East Irish Sea are at a high angle to Caledonian and Acadian trends and are considered to be juvenile structures which developed in the late Westphalian.
The geology and hydrocarbon prospectivity of the North Channel Basin
Authors: Maddox Steven J. , Blow Richard A. , O’Brien Sean R. 
Published: April 2008

Abstract
The geology and hydrocarbon prospectivity of the offshore North Channel has been evaluated, integrating data from a number of onshore wells with seismic, gravity, magnetic and onshore outcrop studies. Interpretation of these data suggest that the North Channel can be divided into two sub-basins, separated by the offshore extension of the Southern Uplands Fault Zone (SUFZ). The narrow, southern, Portpatrick sub-basin has a NNW-SSE trend and consists of a series of simple tilted fault-blocks which dip east, towards the basin-bounding Portpatrick Fault. The northern sub-basin widens considerably into the Larne-Firth of Clyde basin complex, which has a predominantly Caledonide (NE-SW) orientation and is an extension of the Scottish Midland Valley. This sub-basin is characterised by westerly dipping fault blocks, the reversal in basin polarity apparently accommodated along the SUFZ.
The primary reservoir interval is expected to occur in the Lower Triassic Sherwood Sandstone Group, although secondary targets may exist in the Permian and Carboniferous. Shallow coring and seismic facies analysis suggests that the Mercia Mudstone Group subcrops Quaternary-Recent deposits at sea bed and overlies the Sherwood Sandstone. Halites and shales within the Mercia Mudstone Group should provide an effective regional top-seal, except in areas where the Sherwood Sandstone is close to the surface. Large tilted-fault block and rollover anticline traps have been identified on seismic data, although the Carboniferous source rock potential and burial history are poorly understood and exploration risk is high. Regional outcrop patterns and the compaction state of the Mesozoic strata, together with vitrinite measurements suggest the basin was uplifted in the early Tertiary. In common with the East Irish Sea, maturity was probably reached prior to the end of the Cretaceous. This implies that source rocks within the basin will not currently be generating hydrocarbons, having effectively been ‘switched’ off by Tertiary uplift. Charge mechanics are uncertain but must involve early pre-uplift migration or remigration.
Structural evolution of the Isle of Man and central part of the Irish Sea
Authors: Quirk D. G. , Kimbell G. S. 
Published: April 2008

Abstract
Gravity, aeromagnetic, seismic, borehole and outcrop data from the Isle of Man area have been used to study the structural framework and tectonic evolution of the central part of the Irish Sea since the Ordovician. The area has been affected by two major compressional events (Caledonian and Variscan), three rifting events (early Carboniferous, early Permian and ?late Jurassic) and a period of thermal uplift (early Tertiary). A large part of the Isle of Man consists of early Ordovician turbidites (‘basement’) interpreted to have been deposited in a back arc or fore arc basin that was inverted during the Caledonian orogeny. Major NE-SW and subsidiary NW-SE strike-slip faults were initiated at this time, some of which were later reactivated to form important basin controlling faults in the Irish Sea. Post-Caledonian basin subsidence was initiated in the early Carboniferous with a period of NW-SE directed extension followed by thermal sag which ceased at the end of the Carboniferous as a result of Variscan compression. E-W extension in the early Permian led to the development of new extensional faults which have influenced the thickness of the Collyhurst Sandstone in the offshore. Post-rift thermal sag continued throughout the late Permian and the Triassic. A late Jurassic period of extension has been proposed in order to explain post-Triassic offset across major normal faults east of the Isle of Man although direct evidence of syn-rift or post-rift strata has been removed by erosion during uplift in the early Tertiary. This uplift was due to thermal doming of the crust, an event which was associated with the intrusion of a large number of dolerite dykes. The structural evolution of the Isle of Man has also been influenced by a major NW-SE trending basement fracture known as the ‘Central Valley Lineament’ which extends into the offshore to the SE and NW of the island. The lineament appears to be important in defining areas of different hydrocarbon prospectivity in the Irish Sea.
The occurrence and correlation of oils and Namurian source rocks in the Liverpool Bay-North Wales area
Authors: Armstrong James P. , Smith Janet , D’Elia Victor A. A. , Trueblood Stephen P. 
Published: April 2008

Abstract

Along the northeast coast of Wales, the Holywell Shale is a significant lithological unit of about 150 m thickness. In the field, the Holywell Shale appears to be lithologically fairly uniform. Geochemical analysis of field samples has demonstrated highly variable features within the Holywell Shale. These pertain to organic richness and hydrocarbon source potential. Some samples exhibit good to rich potential for oil and gas, with extractable hydrocarbons akin to those of a light or medium gravity crude oil. Richer examples also exhibit higher hydrogen indices. These data point to oil-prone sources which have realised some of their potential. By contrast, the other samples taken from the section, whilst not poor in organic carbon, have low S
1
and S
2
and HI signatures. It is anticipated, from the data collected that cyclicity is present within the Holywell Shale sediments.

The isotope geochemical data also highlights another, more gradual variation. Sources towards the base of the Holywell Shale formation have generated hydrocarbons which are isotopically lighter than those from the middle and upper sections of the formation. This is attributed to middle/upper sections being more proximal to land and consequently, having higher proportions of terrestrially derived organic matter.
Two oils (110/13–10 and 110/15–6) from the Douglas and Lennox fields discovered within the Liverpool Bay area have been analysed. Although the two oils are isotopically similar, chromatography analyses reveal that one oil comprises two hydrocarbon phases whereas the other oil has three envelopes. Extracts taken from the Lower Holywell Shale sources and Holywell bitumen are isotopically similar to both oils. Organically rich sources from higher up in the Holywell Shale formation yield more condensate-like hydrocarbons upon extraction and are isotopically heavier than the oils.
Challenging the ‘sheetflood’ myth: the role of water-table-controlled sabkha deposits in redefining the depositional model for the Ormskirk Sandstone Formation (Lower Triassic), East Irish Sea Basin
Authors: Herries Robert D. , Cowan Greig 
Published: April 2008

Abstract
Two distinct units can be recognized in the Lower Triassic Ormskirk Sandstone Formation in the East Irish Sea Basin. Perennial fluvial channel, lacustrine and minor aeolian sandstones dominate the upper part, but the lower is characterized by thick (tens of metres) enigmatic wavy bedded deposits interbedded with aeolian and minor fluvial channel sandstones. Previous interpretations that invoked an overbank ‘sheetflood’ or ‘sandflat’ origin for the wavy bedding are difficult to reconcile with the sedimentary structures, which are more consistent with algal and evaporitic processes in modern sabkhas. These deposits contain widespread (km) ‘drying upward’ patterns 2–10 m thick, reflecting a sabkha to more aeolian dominated setting. Such thicknesses are consistent with an origin related to 23 000 year Milankovitch cyclicity.
The lower, wavy bedded portion of the Ormskirk Sandstone Formation is regionally truncated by fluvial channel-belt sandstones. Their extent reflects a combination of high sediment supply, uniform subsidence and low basinal relief. Lacustrine units near the top of the formation can be correlated regionally, with one passing southward into a major aeolian unit that thickens to 60 m in the south of the basin. This transition demonstrates the diachroneity of the Mercia Mudstone Group transgression. The key to correlating the Ormskirk Sandstone Formation lies in identifying intervals dominated by fluvial, lacustrine or sabkha-aeolian deposits. Correlation of water-table-controlled ‘drying upward’ patterns within sabkha-aeolian deposits allows finer scale subdivision, and provides an estimate for the degree of fluvial truncation at the top of the unit.
Early Dinantian evaporites of the Easton-1 well, Solway Basin, onshore, Cumbria, England
Authors: Ward Jim 
Published: April 2008

Abstract
An early Viséan, anhydrite-rich, carbonate-clastic succession, of vertical thickness 3784 feet (no base) was found in 1990 at the Easton-1 well in the Solway Basin, onshore Cumbria. The succession is stratigraphically located in the Lower Border Group where only traces of evaporites had been found at outcrop. It is proposed to name the succession the ‘Easton Anhydrite Facies of the Lower Border Group’, abbreviated to ‘EA Beds’.

The EA Beds are divided into three units. Unit 1 at the top, about 400 feet thick, contains two sequences of upwardly thickening anhydrite beds within mixed lithologies. Unit 2, about 2100 feet thick, consists of nine cyclic sequences of limestones, shales and sandstones with numerous interbeds of anhydrite. Overall similarity of several of the sequences suggests similar origins. Unit 2 sequences are grouped into three megacycles, two of approximately 750 feet and one 590 feet thick. Deposition is interpreted to have taken place in arid or partly arid climatic conditions, within a shallow and rapidly, but uniformly subsiding basin with glacio-eustatically controlled rise and fall of sea level. Many of the Unit 2 anhydrite beds are interpreted to be of subaqueous origin. Unit 3, about 1500 feet thick, displays complex patterns of cyclicity with sedimentation apparently responding directly to solar insolation under orbitally induced control within Milankovitch periodicities of 100 000 and 400 000 years. Seismic interpretation indicates that the regional extent of the EA Beds is greater than 1000 km
2
.