Shear-enhanced compaction bands formed at shallow burial conditions; implications for fluid flow (Provence,France) |
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Institution: | 1. Swiss Federal Institute of Technology, Zurich, Institute of Geology, Engineering Geology, Sonneggstrasse 5, 8092 Zurich, Switzerland;2. RWTH Aachen, Chair of Engineering Geology, Lochnerstrasse 4-20, 52064 Aachen, Germany;1. Dept. de Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain;2. Géosciences Montpellier, Université de Montpellier-CNRS, 34095 Montpellier, France;3. Depto. de Geología, Universidad de Salamanca, 3700 Salamanca, Spain;4. Aix-Marseille Univ., CNRS, IRD, Coll de France, CEREGE, Aix en Provence, France;5. Géosciences Environnement Toulouse, Observatoire Midi-Pyrénées-CNRS, 31400 Toulouse, France;6. Géosciences Rennes, Université de Rennes 1-CNRS, 35042 Rennes, France |
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Abstract: | Field observations of highly porous and permeable sandstone in the Orange area (S-E Basin, France) show that networks of shear-enhanced compaction bands can form in a contractional regime at burial depths of about 400 m ± 100 m. These bands show equal compaction and shear displacements, are organized in conjugate and densely distributed networks, and are restricted to the coarse-grained (mean grain diameter of 0.6 ± 0.1 mm) and less porous (porosity of 26 ± 2%) sand layers. The bands are crush microbreccia with limited grain comminution and high grain microfracture density. They show reductions of permeability (mD) ranging from 0 to little more than 1 order of magnitude. They show no control on the alteration products related to meteoric water flow, which suggests that these shear-enhanced compaction bands have no or only negligible influence on subsurface fluid flow. Their selective occurrence and small (20%) reduction in transmissibility in densely populated layers prevented them from compartmentalizing the sandstone reservoirs. A comparison with compaction-band populations in the Navajo and Aztec sandtsones (western U.S.) emphasizes the role of burial depth and the presence of chemical compaction processes for the sealing potential of deformation bands. |
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