Structural evolution of a complex 3D fault array in the Cretaceous and Tertiary of the Porcupine Basin, offshore Ireland
Greg Jones, L. S. Williams, R. J. Knipe, 2004. "Structural evolution of a complex 3D fault array in the Cretaceous and Tertiary of the Porcupine Basin, offshore Ireland", 3D Seismic Technology: Application to the Exploration of Sedimentary Basins, Richard J. Davies, Joseph A. Cartwright, Simon A. Stewart, Mark Lappin, John R. Underhill
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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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3D Seismic Technology: Application to the Exploration of Sedimentary Basins
A ‘new age’ of subsurface geological mapping that is just as far ranging in scope as the frontier source geological mapping campaigns of the past two centuries in emerging. It is the direct result of the advent of 2D, and subsequently 3D, seismic data paralleled by advances in seismic acquisition and processing over the past three decades. Subsurface mapping is fuelled by the economic drive to explore and recover hydrocarbons but inevitably it will lead to major conceptual advances in Earth sciences, across a broader range of disciplines than those made during the 2D seismic revolution of the 1970s. Now that 3D seismic data coverage has increased and the technology is widely available we are poised to mine the full intellectual and economic benefits. This book illustrates how 3D seismic technology is being used to understand depositional systems and stratigraphy, structural and igneous geology, in developing and producing from hydrocarbon reservoirs and also what recent technological advances have been made. This technological journey is a fast-moving one where the remaining scientific potential still far exceeds the scope of the advances made thus far. This book explores the breadth of the opportunities that lie ahead as well as the inevitable accompanying challeges.