Salt tectonics at passive margins: Geology versus models – Reply |
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| Institution: | 1. Géosciences Rennes, Rennes, France;2. G.O. Logical Consulting, Rennes, France;1. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China;2. Key Laboratory of Urban Security and Disaster Engineering (Beijing University of Technology), Ministry of Education, Beijing 100124, China;1. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, Hubei, China;2. McDougall School of Petroleum Engineering, University of Tulsa, OK, USA;3. Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, NV, USA |
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| Abstract: | Rowan et al. (2012) vehemently argue that salt tectonics is entirely driven by differential sedimentary loading and refute all the results of our work (Brun and Fort, 2011) showing that salt tectonics on passive margins is dominated by gliding, which we referred to in our paper as “dominant gliding”; in other words the deformation is controlled by salt flowing down the regional dip of these margins. We point out that “pure spreading” would be driven by differential sedimentary loading only if margins could remain strictly horizontal (i.e. not tilted), whereas “dominant gliding”, which combines spreading and gliding, affects sedimentary successions above salt layers on passive margins as soon as these are titled. Our work shows that the fundamental dynamic difference between the two processes is that in “pure spreading” salt resists deformation whereas in “dominant gliding” salt drives deformation. In “dominant gliding”, even in absence of sediments, salt flows down dip with a component of spreading, demonstrating that differential sedimentary loading is not a necessary condition of salt tectonics and that spreading – i.e. layer parallel stretching- does not require sedimentation to occur. Rowan et al. (2012) put forward arguments, related to thrust mechanics and deduced from some “pure spreading” sand and silicon box models, to backup their claims about “pure spreading” but none of them is applicable to salt basins at margin-scale. The objections made by Rowan et al. (2012) about shelf break migration and slope deformation in the Gulf of Mexico are not substantiated nor justified by verifiable and validated data. Using an adequately scaled laboratory sand-silicone box experiment, in which sedimentary progradation is oblique to silicone (salt) flow, we show that transfer zones develop with directions close to silicone (salt) flow and define patterns directly comparable to those observed in the northern Gulf of Mexico. This paper documents the results of a review of all the arguments and statements contradicting the results of our work put forward in Rowan et al. (2012), and suggests that none of them is valid. |
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