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Original Article |
1 1Amerada Hess Corporation, 6688 North Central Expressway, Suite 1400, Dallas, TX 75206-3925, USA (e-mail: john.argent@hess.com)
2 2BP, Azerbaijan, Chertsey Road, Sunbury on Thames, MIddlesex TW16 7LN, UK
3 3Geotrack International Pty Ltd, 37 Melville Road, West Brunswick, Vic. 3055, Australia
4 4Department of Geology and Geophysics, University of Edinburgh, Grant Institute, King's Buildings, West Mains Road, Edinburgh EH9 3JW, UK
Integration of regional seismic interpretation, sonic velocity, vitrinite reflectance and apatite fission-track analysis (AFTA®) studies has demonstrated that the western region of the Moray Firth rift arm (UK North Sea) experienced pronounced exhumation during the Cenozoic. Although this basin is usually considered to have experienced regionally uniform exhumation, interpretation of new seismic data has revealed the presence of a major system of post-Jurassic normal faults, with throws commonly in the range of 10–300 m and locally exceeding 1 km. New, high-quality seismic data are used in combination with AFTA and vitrinite reflectance data to investigate the role of extensional faulting during exhumation of this basin. Results of this interpretation not only confirm the offsets across major faults, but also show that greater exhumation and erosion occurred on their footwalls than on their hanging walls. We conclude that the localized, differential exhumation is the result of superposition of local or short-spatial-wavelength extensional tectonics upon regional, long-spatial-wavelength exhumation. These results suggest that differential exhumation might be characteristic of unroofed rift basins where normal faults subcrop the exhumation-related unconformity and that, in such cases, thermal histories from footwall locations may yield inaccurate predictions of the burial history of hanging-wall depocentres. Inaccurate burial histories will lead to a misrepresentation of the thermal history, with an impact on the estimation of hydrocarbon source rock maturity for petroleum basins.
Key Words: Moray Firth • exhumation • inversion tectonics • AFTA • source rocks
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