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AAPG Bulletin, V.
The influence of fault array evolution on synrift sedimentation patterns: Controls on deposition in the Strathspey-Brent-Statfjord half graben, northern North Sea
1Department of Geology and Geophysics, University of Edinburgh, Grant Institute, King's Buildings, West Mains Road, Edinburgh, EH9 3JW, Scotland, United Kingdom; current address: Earth Resources Laboratory, Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 42 Carleton Street E34-554, Cambridge, Massachusetts, 02142-1324; email: [email protected]
2Department of Geology and Geophysics, University of Edinburgh, Grant Institute, King's Buildings, West Mains Road, Edinburgh, EH9 3JW, Scotland, United Kingdom; email: [email protected]
3Department of Geology and Geophysics, University of Edinburgh, Grant Institute, King's Buildings, West Mains Road, Edinburgh, EH9 3JW, Scotland, United Kingdom; current address: Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, England, United Kingdom; email: [email protected]
4Department of Geology and Geophysics, University of Edinburgh, Grant Institute, King's Buildings, West Mains Road, Edinburgh, EH9 3JW, Scotland, United Kingdom; current address: Department of Geology, Tulane University, New Orleans, Louisiana, 70118; email: [email protected]
Aileen McLeod is currently a postdoctoral research fellow in the Earth Resources Laboratory at Massachusetts Institute of Technology (MIT) working on the sedimentation and tectonics of the west African continental margin. The work presented in this article was undertaken at the University of Edinburgh as part of an integrated research project studying the effects of normal fault array evolution on Late Jurassic synrift sediment dispersal and deposition in the North Sea. Aileen received a B.Sc. degree in geology from the University of Glasgow and an M.Res. degree and Ph.D. from the University of Edinburgh. She spent a year as a postdoctoral researcher in Edinburgh before moving to Boston.
John Underhill has been a professor of stratigraphy at the University of Edinburgh since 1998. Prior to joining the faculty at Edinburgh in 1989, John worked for Shell International in The Hague and London as an exploration geoscientist. He was an AAPG Distinguished Lecturer in 1999 and was awarded their prestigious Matson Award for excellence in presentation in 1992. John has also been the recipient of the Geological Society's President's Award in 1990 and their Wollaston Fund in 1999. He was the European Association of Petroleum Geoscientists' Distinguished Lecturer in 1989 and 1992. In his spare time, John is a professional soccer referee and officiates in international (FIFA and UEFA) and Scottish Premier League competitions.
Sarah Davies is a lecturer in the Department of Geology at the University of Leicester. She holds a B.Sc. degree in geology from the University of Leeds and a Ph.D. from the University of Leicester. Prior to moving to Leicester, Sarah undertook postdoctoral research at Liverpool University and held a temporary lectureship at the University of Edinburgh.
Nancye Dawers earned a B.S. degree from the University of Kentucky, an M.S. degree from the University of Illinois at Urbana-Champaign, and an M.Phil. degree and Ph.D. from the Lamont-Doherty Earth Observatory of Columbia University. During 1996-1999, she held a research associate position at the University of Edinburgh. Nancye joined Tulane University in 2000, where she is currently an assistant professor. Her interests include fault growth, scaling in fault populations, neotectonics, and basin analysis.
We gratefully acknowledge Esso, Norsk Hydro, Shell, Statoil, and Texaco (and their partners) for access to proprietary 3-D seismic and well data. In particular, we thank Tim Juett, Winfried Leopoldt, Erik Lundin, Gunn Mangerud, Steve Taylor, and Alistair Welbon for facilitating data release and funding. Seismic interpretation facilities at the University of Edinburgh, using Schlumberger GeoQuest IESX software, were supported by the Center for Marine and Petroleum Technology, Esso, Norsk Hydro, and Shell. Computing support was provided by Chung-Lun Lau and James Jarvis. This study benefited from discussions with Iain Armstrong, Rob Gawthorpe, Ruth Gilpin, Sanjeev Gupta, Jon Turner, and Mike Young, and this manuscript benefited from reviews by Patience Cowie and Bruce Trudgill. McLeod was supported by a Natural Environmental Research Council (NERC) Industrial CASE studentship, GT19/96/7/ICS, with partners the Cambridge Arctic Shelf Program (CASP), Oryx Energy (now Kerr McGee), Shell/Esso, Statoil, and Texaco. Underhill acknowledges Norsk Hydro for supporting his academic position during the period of this study. Dawers was funded by NERC under the Realizing Our Potential Award scheme, GR3/R9521.
The dispersal and deposition of sediments in a rift basin are controlled by the sediment supply and the generation of accommodation space; hence, for the facies mosaic and depositional architecture of synrift sediments to be understood, both these variables must be constrained. Subsurface data sets, comprising three-dimensional (3-D) seismic and well data, provide the opportunity to quantify the rates of sediment supply and accommodation generation for the duration of the extensional event and over an area of regional extent.
In this article, we address the controls on synrift sedimentation through detailed analysis of a high-resolution subsurface data set from the Late Jurassic northern North Sea rift basin. The sedimentation history in the study basin comprises four discrete stages intimately linked to the growth of the normal fault population. The earliest stage of rifting is characterized by a distributed fault population comprising a large number of faults with low slip rates. Sediment supply outpaced tectonic subsidence at this time, and rising eustatic sea level was the primary control on sedimentation. As rifting progressed, strain was localized onto a smaller number of active structures with higher displacement rates. The basin developed a grabenlike geometry, and the lateral propagation and linkage of fault strands controlled accommodation generation. Although the basin was flooded, the rate of sediment supply remained high and largely kept pace with the rate of tectonic subsidence. During the final two stages, the fully linked, half-graben bounding fault was the only active structure in the basin; the rate of sediment supply at this time was greatly exceeded by the rate of tectonic subsidence, and the basin became underfilled. Significantly, the final stage of the sedimentation history is characterized by large-scale fault interactions that changed the fault-controlled basin floor topography; hence, modified sediment dispersal and deposition.
We conclude that sediment dynamics and facies distribution in a rift can only be understood in the context of the coevally active fault population. As the faults active at the close of a rift event are very different in location and character to those active during the initiation of rifting, this further emphasizes the need to integrate structural, sedimentary, and stratigraphic studies in rift basins.
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