3D seismic analysis of the structure and evolution of a salt-influenced normal fault zone: A test of competing fault growth models |
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| Institution: | 1. Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, England, UK;2. Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway;1. Dipartimento di Scienze della, Terra Università La Sapienza di Roma, Roma, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia Roma, Italy;3. Dipartimento di Scienze della Terra Università degli Studi di Siena, Italy;4. Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Italy;1. Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713-8924, USA;2. Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK;1. Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College, Prince Consort Road, London SW7 2BP, United Kingdom;2. Department of Earth Science, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway;3. Statoil ASA, Sandslivegen 90, 5254 Sandsli, Norway;1. Centre for Integrated Petroleum Research, University of Bergen, Allégaten 41, 5007 Bergen, Norway;2. Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway;3. Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK;1. Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK;2. Department of Earth Science, University of Bergen, Allegaten 41, 5007 Bergen, Norway;3. Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK;4. Statoil ASA, Sandslivegen 90, 5254 Sandsli, Norway |
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| Abstract: | In this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3D seismic reflection dataset from the Suez Rift, Egypt. Our analysis indicates that the October Fault Zone is composed of two fault systems that are locally decoupled across a salt-bearing interval of Late Miocene (Messinian) age. The sub-salt system offsets pre-rift crystalline basement, and was active during the Late Oligocene-early Middle Miocene. It is composed of four, planar, NW–SE-striking segments that are hard- linked by N–S-striking segments, and up to 2 km of displacement occurs at top basement, suggesting that this fault system nucleated at or, more likely, below this structural level. The supra-salt system was active during the Pliocene-Holocene, and is composed of four, NW–SE-striking, listric fault segments, which are soft-linked by unbreached relay zones. Segments in the supra-salt fault system nucleated within Pliocene strata and have maximum throws of up to 482 m. Locally, the segments of the supra-salt fault system breach the Messinian salt to hard-link downwards with the underlying, sub-salt fault system, thus forming the upper part of a fault zone composed of: (i) a single, amalgamated fault system below the salt and (ii) a fault system composed of multiple soft-linked segments above the salt. Analysis of throw-distance (T-x) and throw-depth (T-z) plots for the supra-salt fault system, isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history. The fault tips were then effectively ‘pinned’ and the faults accumulated displacement via predominantly downward propagation. We interpret that the October Fault Zone had the following evolutionary trend; (i) growth of the sub-salt fault system during the Oligocene-to-early Middle Miocene; (ii) cessation of activity on the sub-salt fault system during the Middle Miocene-to-?Early Pliocene; (iii) stretching of the sub- and supra-salt intervals during Pliocene regional extension, which resulted in mild reactivation of the sub-salt fault system and nucleation of the segmented supra-salt fault system, which at this time was geometrically decoupled from the sub-salt fault system; and (iv) Pliocene-to-Holocene growth of the supra-salt fault system by downwards vertical tip line propagation, which resulted in downward breaching of the salt and dip-linkage with the sub-salt fault system. The structure of the October Fault Zone and the rapid establishment of supra-salt fault lengths are compatible with the predictions of the coherent fault model, although we note that individual segments in the supra-salt array grew in accordance with the isolated fault model. Our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre-scale, basin-bounding faults. Furthermore, we highlight the role that fault reactivation and dip-linkage in mechanically layered sequences can play in controlling the three-dimensional geometry of normal faults. |
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| Keywords: | Normal fault Salt Extension Suez rift Fault growth |
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