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- Volume 6, Issue 4, 2000
Petroleum Geoscience - Volume 6, Issue 4, 2000
Volume 6, Issue 4, 2000
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Organic geochemistry of petroleum seepages within the Jurassic Bencliff Grit, Osmington Mills, Dorset, UK
Authors D. F. Watson, A. D. Hindle and P. FarrimondOccurrences of oil within the Bencliff Grit at Osmington Mills were studied through an integration of organic geochemistry and a consideration of the geological setting. Oil-stained sandstones dominate the cliff outcrop with localized regions of particularly concentrated oil impregnation. A second ‘live’ seep of oil occurs where the Bencliff Grit beds pass below high tide level at Bran Point. Organic geochemical analyses showed both oils to be at least moderately biodegraded, with the oils in the cliff outcrop showing enrichment in polar constituents compared with the active seep. Multivariate statistical analysis of the molecular composition identified an enrichment in diasterane biomarkers in the oils of the live seep; this difference is ascribed to source and/or maturity differences. The oil within the outcrop is considered to represent the residual staining of an unroofed oil field, whilst the live seepage at Bran Point represents a migration pathway towards the eroded anticline.
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Thermal buffering of sedimentary basins by basement rocks: implications arising from numerical simulations
Authors Guichang Lin, Jeffrey A. Nunn and David DemingThe Earth’s crust releases or absorbs heat energy in response to changes in the thermal regime. Numerical simulations of basin-scale heat transport which use the sediment–basement interface as a thermal boundary assume that near-surface temperature changes have no effect on basement rocks and vice versa (unbuffered model). We test this assumption by comparing numerical models of transient fluid flow and heat transport in the Arkoma foreland basin with and without thermal buffering by basement rocks. Thermal buffering by basement rocks reduces cooling (by fresh water recharge) of deep basin sediments near the fold–thrust belt and reduces warming (by upward fluid discharge) of basin margin sediments. The unbuffered model predicts a temporary warming of basin margin sediments which is largely an artefact of the model thermal boundary conditions. In all cases, the buffered model produces no significant thermal transient. Exaggerated temperature predictions also can occur in numerical simulations of uplift and erosion or heat refraction.
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Lower Cretaceous turbidites of the Moray Firth: sequence stratigraphical framework and reservoir distribution
More LessLower Cretaceous depositional systems of the Moray Firth are influenced by eustatic sea-level oscillations which have been dramatically overprinted by two major phases of pulsed tectonism, the Late Cimmerian and Austrian. The biostratigraphical resolution obtained has allowed the timing and differentiation of distinct tectonic/sequence boundaries, some of which are utilized as important seismo-stratigraphic markers. The construction of detailed facies maps for individual sequences has, in parallel, allowed an insight into the tectonic history of the main source areas during the Early Cretaceous.
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Britannia Field, UK North Sea: petrographic constraints on Lower Cretaceous provenance, facies and the origin of slurry-flow deposits
Authors G. A. Blackbourn and M. E. ThomsonDeep-water sandstones of the Early Cretaceous Britannia reservoir are rich in ‘muddy’ material, with the development of unusual ‘slurry-flow’ deposits (sensu Lowe & Guy 2000 ), including banded facies. The banding comprises couplets of pale sandstone containing microporous detrital chlorite and other clays, retaining substantial porosity, and dark sandstone in which biotite (now altered to chlorite) has promoted quartz pressure solution that has largely destroyed porosity. The main source of the abundant chlorite and biotite is the Jurassic Forties Igneous Province, underlying and surrounding the Britannia Field. Altered alkali basalts and other lithologies here are known to be rich in both minerals.
Grain-size distributions have been examined using image analysis. The banded facies are generally finer grained than the high-density turbidite and unbanded slurry-flow sandstones, and may be a distal equivalent. Dark bands in some cases contain no more fine clays than associated light bands, indicating that Lowe & Guy’s model for dark-band formation, invoking a cohesive sublayer, is incomplete. Gelation of chlorite-rich clays within each banded couplet is proposed as an alternative mechanism. These microporous pore-filling chlorites have restricted the precipitation of quartz overgrowths and other non-porous cements, although their presence inhibits permeability.
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An Early Cretaceous lithostratigraphic and biostratigraphic framework for the Britannia Field reservoir (Late Barremian–Late Aptian), UK North Sea
Authors N. R. Ainsworth, L. A. Riley and L. T. GallagherA Lower Barremian–Upper Aptian lithostratigraphic scheme applicable to the Britannia Field (Blocks 15/29, 15/30, 16/26 and 16/27) is presented. The Britannia Sandstone Formation reservoir is formally subdivided into three members (type well 15/30-9); the Lapworth (Late Barremian to Early Aptian), Kilda (Late Aptian) and Bosun (latest Aptian) members. The Lapworth Member is subdivided into three units, Lapworth ‘A’ (Late Barremian), the intra-Fischschiefer Lapworth ‘B’ (intra-Early Aptian) and Lapworth ‘C’ (Early Aptian).
The Early Barremian to Early Aptian upper Valhall Formation is subdivided into seven units: ‘V3A’ the Hauptblatterton, ‘V3B’, ‘V3C’, ‘V3D’, Fischschiefer Bed, and ‘V4’. The overlying Sola and Rodby Formations are subdivided into Units ‘S1’ and ‘S2’ of the ‘Lower’ Sola Formation (Late Aptian), plus Units ‘S3’ and ‘S4’ of the ‘Upper’ Sola Formation (Early Albian). The Rodby Formation (Middle? to Late Albian) is subdivided into three units: ‘R2’, ‘R3’ and ‘R4’.
A high resolution biostratigraphic zonal scheme is defined for the Early Barremian to earliest Albian interval, utilizing calcareous nannoplankton, micropalaeontology and palynology. Within this, 49 zones and 38 subzones (12 microfaunal zones and 4 subzones, 23 palynological zones and 19 subzones, and 14 nannoplankton zones and 15 subzones) are recognized. Of these, 5 micropalaeontological zones (and 4 subzones), 11 palynological zones (and 15 subzones) and 7 calcareous nannoplank-ton zones (and 10 subzones) are directly applicable to the Britannia reservoir section.
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Sediment transport and dispersal pathways in the Lower Cretaceous sands of the Britannia Field, derived from magnetic anisotropy
Authors Ernie Hailwood and Fung DingSediment transport directions and dispersal patterns in the Lower Cretaceous sands of the Britannia Field have been investigated, using magnetic anisotropy and palaeomagnetic core re-orientation methods, to aid understanding of the geometry and architecture of the reservoir sand units. The results indicate that sands were sourced mainly from the north. This applies both to the massive sand bodies with lobate geometry in the lower reservoir zones in the western part of the field and to the laminated slurried beds with tabular geometry in the upper zones in the eastern part. Thus, sediment in this part of the Outer Moray Firth play appears to have been derived largely from a discrete point source to the north rather than from axial flow along the Witch Ground Graben.
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Volumes & issues
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Volume 30 (2024)
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Volume 29 (2023)
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Volume 28 (2022)
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Volume 27 (2021)
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Volume 26 (2020)
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Volume 25 (2019)
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Volume 24 (2018)
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Volume 23 (2017)
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Volume 22 (2016)
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Volume 21 (2015)
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Volume 20 (2014)
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Volume 19 (2013)
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Volume 18 (2012)
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Volume 17 (2011)
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Volume 16 (2010)
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Volume 15 (2009)
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Volume 14 (2008)
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Volume 13 (2007)
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Volume 12 (2006)
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Volume 11 (2005)
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Volume 10 (2004)
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Volume 9 (2003)
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Volume 8 (2002)
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Volume 7 (2001)
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Volume 6 (2000)
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Volume 5 (1999)
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Volume 4 (1998)
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Volume 3 (1997)
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Volume 2 (1996)
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Volume 1 (1995)