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Structural evolution of a complex 3D fault array in the Cretaceous and Tertiary of the Porcupine Basin, offshore Ireland

By
Greg Jones
Greg Jones
Rock Deformation Research Ltd, School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK (e-mail: g.jones@rdr.leeds.ac.uk)
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L. S. Williams
L. S. Williams
Chevron Europe, 93, Wigmore Street, London WW IHH, UK (current address: PanAfrican Energy UK Ltd, Sheridan House, 40-43 Jewry St., Winchester, Hampshire S023 8RY, UK)
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R. J. Knipe
R. J. Knipe
Rock Deformation Research Ltd, School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK (e-mail: g.jones@rdr.leeds.ac.uk)
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Published:
January 01, 2004

Abstract

A high-quality 3D seismic survey, located in the northwest Porcupine Basin (Irish Atlantic Margin), has been used to investigate the geometry and origin of pervasively developed and complexly distributed linked extensional fault arrays, present within Late Cretaceous and Early Tertiary sequences. The faults show a downwards transition from relatively simple, planar fault segment geometries (~N-S-trending) within younger Early Eocene sand-dominated clastic sequences, into complex conjugate arrays in the underlying older Early Eocene to Late Cretaceous shale-dominated sequences. Rectilinear to polygonal structural configurations are developed at the deeper levels. Most of the fault array ultimately terminates downwards into the Late Cretaceous, where structural accommodation may have taken place by localized or more regional bedding plane slip and/or by volume changes resulting from compaction of fine-grained sequences. Locally, reactivated Jurassic syn-rift extensional faults are locally seen to link upwards into the shallow fault array and appear to have controlled both the intensity and facing direction of the shallower faults on a km scale. The seismic data also clearly show that early upslope-throwing faults are cross-cut by later, downslope-throwing faults. Such geometries are comparable to those formed in sandbox models where gravitational collapse of a tilted sequence is the dominant process controlling fault development. Overall, the fault array geometries seen in the Cretaceous and lower Tertiary successions in this area are interpreted to have resulted from gravitational collapse processes during basin subsidence and sediment compaction, and where the main deformation mechanism was non-rigid block rotation. Differential compaction of Cretaceous and lower Tertiary sediments over pre-Cretaceous rift topography and selective reactivation of the Jurassic fault array are also considered important influences on the resultant fault distribution in 3D.

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Contents

Geological Society, London, Memoirs

3D Seismic Technology: Application to the Exploration of Sedimentary Basins

Richard J. Davies
Richard J. Davies
Cardiff University, UK
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Joseph A. Cartwright
Joseph A. Cartwright
Cardiff University, UK
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Simon A. Stewart
Simon A. Stewart
BP, Azerbaijan
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Mark Lappin
Mark Lappin
ExxonMobil Exploration Company, USA
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John R. Underhill
John R. Underhill
The University of Edinburgh, UK
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Geological Society of London
Volume
29
ISBN electronic:
9781862394049
Publication date:
January 01, 2004

GeoRef

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