3D seismic analysis of gravity-driven and basement influenced normal fault growth in the deepwater Otway Basin,Australia |
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Affiliation: | 1. Centre for Tectonics Resources and Exploration (TRaX), Department of Physical Sciences, University of Adelaide, Adelaide, 5005, South Australia, Australia;2. Australian School of Petroleum, Santos Building, University of Adelaide, Adelaide, 5005, South Australia, Australia;1. Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, 78712, USA;2. Department of Geology, Washington and Lee University, Lexington, VA, 24450, USA;1. Memorial University of Newfoundland, Department of Earth Sciences, St. John''s, A1B3X5, Canada;2. Pertamina EP, asset-5, Exploitation Section, Jakarta, JKS, 12930, Indonesia;3. Louisiana State University, Department of Geology and Geophysics and Coastal Studies Institute, Baton Rouge, LA, 70808, USA;4. Rice University, Department of Earth Sciences, Houston, TX, 77005, USA;1. Graduate School of Science and Technology, Shizuoka University, Shizuoka 422–8529, Japan;2. Center of Integrated Research and Education of Natural Hazards, Shizuoka University, Shizuoka 422–8529, Japan;3. Department of Applied Science and Technology (DISAT), Politecnico di Torino, 10129 Torino, Italy;4. Institute of Geosciences, Shizuoka University, Shizuoka 422–8529, Japan;5. Graduate School of Environmental Studies, Tohoku University, Sendai 980–8579, Japan |
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Abstract: | We use three-dimensional (3D) seismic reflection data to analyse the structural style and growth of a normal fault array located at the present-day shelf-edge break and into the deepwater province of the Otway Basin, southern Australia. The Otway Basin is a Late Jurassic to Cenozoic, rift-to-passive margin basin. The seismic reflection data images a NW-SE (128–308) striking, normal fault array, located within Upper Cretaceous clastic sediments and which consists of ten fault segments. The fault array contains two hard-linked fault assemblages, separated by only 2 km in the dip direction. The gravity-driven, down-dip fault assemblage is entirely contained within the 3D seismic survey, is located over a basement plateau and displays growth commencing and terminating during the Campanian-Maastrichtian, with up to 1.45 km of accumulated throw (vertical displacement). The up-dip normal fault assemblage penetrates deeper than the base of the seismic survey, but is interpreted to be partially linked along strike at depth to major basement-involved normal faults that can be observed on regional 2D seismic lines. This fault assemblage displays growth initiating in the Turonian-Santonian and has accumulated up to 1.74 km of throw.Our detailed analysis of the 3D seismic data constraints post-Cenomanian fault growth of both fault assemblages into four evolutionary stages: [1] Turonian-Santonian basement reactivation during crustal extension between Australia and Antarctica. This either caused the upward propagation of basement-involved normal faults or the nucleation of a vertically isolated normal fault array in shallow cover sediments directly above the reactivated basement-involved faults; [2] continued Campanian-Maastrichtian crustal extension and sediment loading eventually created gravitational instability on the basement plateau, nucleating a second, vertically isolated normal fault array in the cover sediments; [3] eventual hard-linkage of fault segments in both fault arrays to form two along-strike, NW-SE striking fault assemblages, and; [4] termination of fault growth in the latest Maastrichtian. We document high variability of throw along-strike and down-dip for both fault assemblages, thereby providing evidence for lateral and vertical segment linkage. Our results highlight the complexities involved in the growth of both gravity-driven normal fault arrays (such as those present in the Niger Delta and Gulf of Mexico) and basement-linked normal fault arrays (such as those present in the North Sea and Suez Rift) with the interaction of an underlying and reactivating basement framework. This study provides an excellent example of spatial variability in growth of two normal fault assemblages over relatively short spatial scales (∼2 km separation down-dip). |
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Keywords: | Normal fault Extension Structural evolution Otway Basin Southern margin 3D seismic data |
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