Polygonal deformation bands |
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| Institution: | 1. Alma Mater University of Bologna, Department of Biological Geological and Environmental Sciences, Via Zamboni 67, 40126 Bologna BO Italy;2. Department of Geosciences and Engineering, Technical University Delft, Stevinweg 1, 2628 CN Delft, The Netherlands;1. Material and Structural Systems Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;2. Institute for Superhard Materials, National Academy of Science of Ukraine, 2 Avtozavodskaya Street, 04074 Kyiv, Ukraine;1. Géosciences Montpellier, UMR 5243, Université de Montpellier-CNRS, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France;2. TOTAL EP, CSTJF, Av. Larribau, 64018 Pau, France;1. Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA;2. Geosciences Environnement Toulouse (GET), IRD-CNRS-Université de Toulouse, 14, av. Edouard Belin, 31400 Toulouse, France;1. Department of Earth and Environmental Sciences, KU Leuven, Celestijnenlaan 200E Box 2410, B-3001 Heverlee, Belgium;2. Department of Earth Sciences, Utrecht University, Budapestlaan 4 Box 80021, N-3508 Utrecht, The Netherlands;1. School of Geography, Environment & Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand;2. Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand |
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| Abstract: | We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1–5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes. |
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| Keywords: | Polygonal faults Fault propagation and interaction Deformation bands Porous sandstone Strain hardening Homogeneous strain Arches National Park (Utah USA) |
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