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Monaghan A.a. - One of the best experts on this subject based on the ideXlab platform.
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Organic geochemistry of Palaeozoic Source Rocks of the Irish Sea, UK
British Geological Survey, 2016Co-Authors: Vane C.h., Uguna C., Kim A.w., Monaghan A.a.Abstract:The East Irish Sea gas and oil fields (Triassic reservoir e.g. Morecambe, Lennox) are believed to be sourced from the underlying Carboniferous strata (e.g. Armstrong et al., 1997; Quirk et al. 1999 and references therein). This study undertook a systematic screening of Rock-Eval and vitrinite reflectance data extracted from released legacy well reports with the aim of providing a data based, regional overview of Carboniferous source rock intervals and their levels of maturity in the wider Irish Sea study area. The method and description of calculated parameters used are given in Vane et al. (2015). The Palaeozoic stratigraphy of the region is described in Wakefield et al. (2016b) and the regional petroleum systems analysis in Pharaoh et al. (2016). Released geochemical data from the Palaeozoic of the Irish Sea is sparse and a variety of stratigraphical units have been sampled, mostly from units other than the likely main source rock interval (Bowland Shale Formation and equivalents). Nine wells were evaluated: 110/02b-10, 110/07-2, 110/07b-6, 110/09a-2, 111/25-1A, 113/27-1, 113/27-2 and 113/27-3. Well 110/12a-1 was not assessed due to the absence of key maturity information. In these wells, the Pennine Lower Coal Measures, Millstone Grit Group and Bowland Shale Formation are mainly gas-prone strata of poor-fair generative potential remaining and mature to the gas window at the sampled intervals in Quadrants 110 and 113 (Figure 1). Within the limited well sample set examined, high Total Organic Carbon (TOC) coal intervals have the best generative potential remaining. The Cumbrian Coastal Group, Appleby Group and Carboniferous Limestone Supergroup present in two wells in Quadrant 111 are at oil to gas window maturity levels, but have low TOC and low residual hydrocarbon generative potential
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Seismic interpretation and generation of depth surfaces for Late Palaeozoic strata in the Irish Sea Region
British Geological Survey, 2016Co-Authors: Pharaoh T.c., Kirk K., Quinn M., Sankey M., Monaghan A.a.Abstract:This report describes the methodology and results of a regional seismic interpretation of the basins of the Irish Sea. It does not review the basins of the Celtic Sea. The aim of the interpretation was to map the distribution of Palaeozoic basins and highs, interpreting the key Devonian-Carboniferous surfaces and main structural elements of the area. About 40,000 km of 2D seismic reflection data have been interpreted and tied to key released wells in the project area. The seismic and well data were augmented by donated reports from sponsor companies. A set of 8 depth structure maps of key horizons have been produced for the pre-Permian succession. These maps provide a key dataset to aid assessment of the petroleum systems of the Palaeozoic strata within the study area. The surfaces, supplied digitally at a grid spacing of 5000 m, give a regional view of the topography of the horizons, and comprise: ‘UVAR’ (Variscan Unconformity) beneath Permian and Triassic strata Base Warwickshire Group (late Westphalian - ?Stephanian) Top Namurian (Base Pennine Coal Measures Group) Top Intra-Namurian (Top Bowland Shale in south, Base Millstone Grit elsewhere) Top Visean (Lower Carboniferous) Intra-Visean (amalgamated with Top Middle Border Group in north) Base Carboniferous (amalgamated with Base Clyde Plateau lavas in the North Channel to South-West Arran Sub-Basin) ‘UCAL’ Acadian (Caledonian) Unconformity) It is important to note that the variable data quality and sparsity of deep wells leads to a seismic interpretation which is strongly driven by regional geological models, themselves heavily dependent on inference from the onshore area. This is particularly the case with the deeper Carboniferous horizons which are not penetrated by any well and which may be only weakly reflective. In such cases, picks from better quality data may be interpolated through areas with poor quality data, as a modelled surface, to ensure a continuous surface for gridding. The well dataset has been re-interpreted (Wakefield et al., 2016) before integration with the seismic interpretation. The following general observations are made: The present study has confirmed the Permian-Mesozoic structural framework for the region established by Jackson and Mulholland (1993) and Jackson et al. (1995, 1996, 1997). The basin recognised in Quadrant 109 by Jackson and co-workers (op. cit.) is reinterpreted as a major Carboniferous half-graben structure controlled by a syndepositional fault on its NW side. It continues beneath thin Permo-Triassic cover into the Eubonia Basin and Ogham Platform, preserving a thick Westphalian succession, including inferred Warwickshire Group strata. It is inferred to have continued eastward into the Lagman Basin prior to its tectonic dissection by a combination of Variscan inversion and Permo-Mesozoic graben development along the Keys Fault. A belt of Variscan fold/thrust inversion structures on the Godred Croven Platform is correlated with structures on the Formby Platform and Ribblesdale Foldbelt onshore. CR/16/041 Last modified: 2016/05/30 09:37 10 The area of Carboniferous (undivided) subcrop depicted on mapping by BGS (1994) to north and west of the Isle of Man has been reclassified into Visean and Namurian elements. The presence of significant thicknesses of Carboniferous strata in the southern part of the North Channel is regarded as doubtful, but farther north, in the Larne, Rathlin and South-West Arran Sub-basins, greater thicknesses may be present. A detailed description of tectono-stratigraphic development based on the seismic interpretation is given in Pharaoh et al. (2016b), integrated with the petroleum system analysis
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Devonian and Carboniferous stratigraphical correlation and interpretation in the Central North Sea, Quadrants 25 – 44
British Geological Survey, 2015Co-Authors: Kearsey T., Ellen R., Millward D., Monaghan A.a.Abstract:This report details the stratigraphy and palaeogeography of Devonian and Carboniferous rocks of the UK Central North Sea for the 21CXRM Palaeozoic project. The 21CXRM Palaeozoic project results are delivered as a series of reports and digital datasets for each area. This report describes the stratigraphical correlation of Devonian and Carboniferous strata south of, and over, the Mid North Sea High (Quadrants 25-44) using both well and seismic data. It builds on the work of Cameron (1993a) and others, and uses lithostratigraphy to understand how facies vary across the area. A major outcome of this work is the detailed description of the Cleveland Group, the basinal correlative of the Scremerston, Yoredale and Millstone Grit formations within the offshore extension of the Cleveland Basin
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Palaeozoic petroleum systems of the central North Sea/Mid North Sea High
British Geological Survey, 2015Co-Authors: Monaghan A.a., Ellen R., Hannis S., Gent C., Arsenikos S., Callaghan E., Henderson A., Leslie G., Johnson K., Kassyk M.Abstract:This report synthesises the results of the 21CXRM Palaeozoic project to describe the Carboniferous and Devonian petroleum systems of the Central North Sea/Mid North Sea High area (Quadrants 25–44). Focusing on frontier areas to the north of the Southern North Sea gas fields and west of the Auk-Flora ridge, integration of a large volume of seismic, well, geophysical, organic geochemistry, maturity and reservoir property data at regional scale has established: Extensional to strike-slip Devonian and Carboniferous basins cutting across the Mid North Sea High on orientations strongly controlled by basement inheritance, granites and a complex Palaeozoic stress field. Varsican orogenic transpression and inversion was superimposed resulting in a variety of structural trapping styles and burial/uplift histories, and a complicated pre-Permian subcrop map. A widespread spatial and temporal extent of oil and gas mature source rock intervals within the Carboniferous succession particularly; o lower Carboniferous (Visean) coals and mudstones of the Scremerston Formation, dominantly fluvio-deltaic and lacustrine with some marine influence, dominantly gas prone. Gas mature in Quadrant 41 and central-southern Quadrants 42-44 and oil mature in the Forth Approaches and North Dogger Basin o lower-mid Carboniferous (Visean-Namurian) coals and mudstones of the Yoredale and Millstone Grit formations in fluvio-deltaic to marine cycles, gas prone with oil prone intervals. Gas mature in central Quadrant 41 and southern Quadrants 42-43, oil mature across northern Quadrants 41-44, Quadrant 36, 38 and 39. o Lower-mid Carboniferous (Visean-Namurian) mudstones and siltstones of the Cleveland Group, over 1 km thick, deposited in dominantly marine environments. Gas mature to overmature in southern Quadrants 41-44 and modelled as having generated oil and gas. Potentially widespread reservoir intervals of varying reservoir quality. Favourable intervals include the Upper Devonian sandstone of the Buchan Formation expecially where fractured, channels within the fluvio-deltaic lower-mid Carboniferous (Visean-Namurian) Scremerston, Yoredale and Millstone Grit formations, the laterally extensive, high net:gross Fell Sandstone Formation, and possibly turbidites or shoreface sands within marine mudstones/siltstones in southern Quadrants 41-44 (likely tight gas unless early hydrocarbon charged) Widespread opportunities for structural (fault/fold/dip) traps utilising a Silverpit mudstone, or Zechstein evaporite seal as in the Breagh Field. Intraformational Carboniferous seals are documented widely in onshore Carboniferous fields and in some offshore fields and should be further investigated, particularly in mudstone/siltstone-dominated basinal successions with modelled Carboniferous and recent hydrocarbon generation, along with possibilities for stratigraphic traps. Basin modelling predicts oil and gas generation at a variety of times (Carboniferous, Mesozoic and Cenozoic dependent on the well) from lower-mid Carbonferous (Visean-Namurian) strata in Quadrants 41-44. In the Forth Approaches, Quadrant 29/North Dogger basins and on the poorly constrained Devonian-Carboniferous Mid North Sea High, oil window maturity levels are modelled at selected wells in a largely gas-prone sequence, though basinwards gas maturity may be achieved. It is recommended that the contribution and volumetrics of relatively thin oil-prone intervals within the Carboniferous succession be further investigated
Gary J Hampson - One of the best experts on this subject based on the ideXlab platform.
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sequence stratigraphy of the upper Millstone Grit yeadonian namurian north wales
Geological Journal, 2007Co-Authors: Rhodri M Jerrett, Gary J HampsonAbstract:The upper Millstone Grit strata (Yeadonian, Namurian) of North Wales have been studied using sedimentological facies analysis and sequence stratigraphy. These strata comprise two cyclothems, each containing prodelta shales (Holywell Shale) that pass gradationally upwards into delta-front and delta-plain deposits (Gwespyr Sandstone Formation). The deltas formed in shallow water (<100 m), were fluvial-dominated, had elongate and/or sheet geometries and are assigned to highstand systems tracts. Two delta complexes with distinctive sandstone petrographies are identified: (1) a southerly derived, quartzose delta complex sourced locally from the Wales-Brabant Massif, and (2) a feldspathic delta complex fed by a regional source(s) to the north and/or west. The feldspathic delta complex extended further south in the younger cyclothem. A multistorey braided-fluvial complex (Aqueduct Grit, c. 25 m thick) is assigned to a lowstand systems tract, and occupies an incised valley that was eroded into the highstand feldspathic delta complex in the younger cyclothem. A candidate incised valley cut into the highstand feldspathic delta complex in the older cyclothem is also tentatively identified. Transgressive systems tracts are thin (<5 m) and contain condensed fossiliferous shales (marine bands). The high-resolution sequence stratigraphic framework interpreted for North Wales can be readily traced northwards into the Central Province Basin (‘Pennine Basin’), supporting the notion that high-frequency, high-magnitude sea-level changes were the dominant control on stratigraphic architecture. Copyright © 2007 John Wiley & Sons, Ltd.
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evidence for relative sea level falls during deposition of the upper carboniferous Millstone Grit south wales
Geological Journal, 1998Co-Authors: Gary J HampsonAbstract:Detailed sedimentological facies analysis of the fluvio-deltaic Millstone Grit succession (Upper Carboniferous) of South Wales reveals that a number of cyclothems bounded by marine flooding surfaces (marine bands) in these strata exhibit facies architectures that represent erosion, non-deposition and/or deposition during periods of falling relative sea-level. A major fluvial complex below the Subcrenatum Marine Band, the Farewell Rock, lies within an incised valley, with a regional unconformity (sequence boundary) at its base. This unconformity is marked by deep erosional relief, an identifiable time gap and an angular discordance in bedding. The Cumbriense Quartzite, a correlative unit containing several mature palaeosols, records a depositional hiatus on a terrace-like interfluve that lay beyond the margins of the coeval Farewell Rock valley. Cyclothems in the underlying Middle Shales contain additional surfaces and units of subtler character. Beneath the Cancellatum Marine Band, a thin (15 cm), calcareous siltstone bed (the ‘Amroth Granule Bed’) that directly overlies prodelta shales contains reworked bioclasts, bored phosphorite clasts and quartz granules. Quartz granules in this bed are interpreted to represent relict lowstand, fluviatile? deposits, which were reworked during later transgression. Three further cyclothems contain sharp-based, storm-reworked mouth bars that record an abrupt lowering of wave base, most probably during periods of falling relative sea-level. One of these cyclothems also contains a distributary channel complex, which records an abrupt influx of coarse-grained sediment of ambiguous origin. The significance of these subtle surfaces and units for intracyclothem stratigraphy has rarely been considered; their prevalence in the Middle Shales provides evidence for numerous, high-frequency relative sea-level falls, which were previously unrecognized. These relative sea-level falls appear to alternate coherently with the widespread sea-level rises recorded by the marine bands, suggesting that glacio-eustasy is their most likely driving mechanism. The notion of glacio-eustatic sea-level falls is supported by the correlation of the basal Farewell Rock sequence boundary with sequence boundaries documented in adjacent basins. The angular unconformity and a change in sediment provenance at the base of the Farewell Rock, however, suggest an additional tectonic control on stratigraphic architecture here, namely a short-lived phase of rifting or inversion prior to widespread fluvial incision. Copyright © 1998 John Wiley & Sons, Ltd.
David Banks - One of the best experts on this subject based on the ideXlab platform.
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hydrogeochemistry of Millstone Grit and coal measures groundwaters south yorkshire and north derbyshire uk
Quarterly Journal of Engineering Geology and Hydrogeology, 1997Co-Authors: David BanksAbstract:Abstract A pilot study has been performed to ascertain the baseline hydrochemistry of both shallow (springs) and deep (borehole) groundwaters of the Millstone Grit and Coal Measures. In terms of major ion composition the majority of the shallow groundwaters in the two formations are rather similar (typically Ca/Mg-SO 4 2- /HCO 3 - ). The deep groundwaters show more variability. In some boreholes, marked seasonal temperature fluctuations and chemical compositions similar to shallow groundwaters indicate short residence times. In contrast, several boreholes in the Coal Measures indicate highly reducing conditions, evidenced by sulphate reduction and spectacular methane exsolution at two sites in Sheffield. Some deep Coal Measures groundwaters show elevated chloride concentrations compared with shallow waters, which may indicate the influence of deep formation brines, while others yield sodium bicarbonate waters indicative of cation exchange. At the other extreme, highly oxidizing conditions, e.g. in broken ground at the Mam Tor landslip, promote pyrite oxidation and yield acidic, ferruginous waters with high contents of heavy metals including uranium and thorium. At three sites in the Coal Measures, sampling of radon was feasible, yielding values in the range 8–32 Bq/l.
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Hydrogeochemistry of Millstone Grit and Coal Measures groundwaters, south Yorkshire and north
1997Co-Authors: David BanksAbstract:A pilot study has been performed to ascertain the baseline hydrochemistry of both shallow (springs) and deep (borehole) groundwaters of the Millstone Grit and Coal Measures. In terms of major ion composition the majority of the shallow groundwaters in the two formations are rather similar (typically Ca/Mg-SO42-/HCO3-). The deep groundwaters show more variability. In some boreholes, marked seasonal temperature fluctuations and chemical compositions similar to shallow groundwaters indicate short residence times. In contrast, several boreholes inthe Coal Measures indicate highly reducing conditions, evidenced by sulphate reduction and spectacular methane xsolution at two sites in Sheffield. Some deep Coal Measures groundwaters show elevated chloride concentrations compared with shallow waters, which may indicate the influ-ence of deep formation brines, while others yield sodium bicarbonate waters indicative of cation exchange. At the other extreme, highly oxidizing conditions, e.g. in broken ground at the Mare Tor landslip, promote pyrite oxidation and yield acidic, ferruginous waters with high contents of heavy metals including uranium and thorium. At three sites in the Coal Measures, sampling of radon was feasible, yielding values in the range 8-32 Bq/1
Stuart Handysides - One of the best experts on this subject based on the ideXlab platform.
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bjgp library the Millstone Grit smoothed off after 50 years
British Journal of General Practice, 2017Co-Authors: Stuart HandysidesAbstract:The Millstone Margaret Drabble Penguin, 2016 (first published 1965), PB, 176pp, £8.99, 978-0241979174 The Millstone , Margaret Drabble’s mid-1960s tale of unmarried motherhood, isn’t quite the kitchen-sink drama I was expecting. Its narrator’s exposure to NHS medicine depicts an overburdened service (no change there) in which a person’s class and connections affect the care they receive. The narrator, Rosie, is a postgraduate student from a well-off socialist family, living in a large flat near Marylebone; her parents are away in Africa. Her friends are writers and the man she sleeps with — just once, and decides not to tell — is a BBC announcer. Rosie’s first reaction to her pregnancy is to induce miscarriage with a bottle of gin and a hot bath, but her friends turn up and share the bottle. Another friend …
B A Thomas - One of the best experts on this subject based on the ideXlab platform.
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lepidostrobus haslingdenensis a new species from the lancashire Millstone Grit
Geological Journal, 2007Co-Authors: B A Thomas, Alicja DytkoAbstract:A collection of microsporangiate cones is described from the topmost Namurian of Rossendale, Lancashire. The microspores are closely comparable with the dispersed spore species Lycospora noctuina, being of a type that has not been previously recorded from a fructification.
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Millstone Grit of the central province
1996Co-Authors: C J Cleal, B A ThomasAbstract:The Central Province refers to the complex of depositional basins lying between the Wales-Brabant Barrier to the south and the Askrigg Block to the north (Figure 9.1). It is the thickest development of Millstone Grit in Britain, with a maximum thickness of over 180 m near Burnley and Skipton, and outcrops over an area of more than 4000 m. Much of the strata is relatively resistant to erosion, resulting in rugged scenery most typically represented by the moorland and hills of the High Peak between Sheffield and Manchester; names such as Kinder Scout and Edale are as well known to the hiker and rock-climber as they are to the geologist. Such scenery is well suited to producing good outcrop, and has attracted many geologists to the area. Furthermore, fossils occur abundantly, particularly in the marine bands which have yielded biostratigraphically sensitive ammonoids and conodonts.