The unusual 3D interplay of basement fault reactivation and fault-propagation-fold development: A case study of the Laramide-age Stillwell anticline,west Texas (USA) |
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| Affiliation: | 1. School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC, 3800, Australia;2. Instituto Geonorte, National University of Salta, INENCO-CONICET, Av. Bolivia 5150, 4400, Salta, Argentina;3. Centre for Lithospheric Research, Czech Geological Survey, Klárov 3, 118 21, Prague 1, Czech Republic;1. Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Spain;2. Université Lille, CNRS UMR 8187, Laboratoire d''Océanologie et de Géosciences, France;3. Instituto Geológico y Minero de España, Unidad de Zaragoza, Spain;1. Dipartimento di Scienze della Terra, Università di Napoli Federico II, Naples, Italy;2. Dipartimento di Scienze della Terra e dell''Ambiente, Università di Pavia, Via Ferrata, 1, Pavia, Italy;1. Department of Geoscience, Aarhus University, 8000 Aarhus C, Denmark;2. Maersk Oil Copenhagen, Denmark;3. dGB Earth Sciences, Houston, USA;1. ChronoEnvironnement, UMR 6249, Université de Franche Comté, 16 route de Gray, 25030 Besançon, France;2. Géosciences Montpellier, UMR 5243, Université Montpellier 2, 34095 Montpellier, France;3. DNO International ASA, Bryggegata 9, 0250 Oslo, Norway;4. Total, Jean Feger Scientific and Technical Center, Avenue Larribau, 64018 Pau, France;1. School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA 70504, USA;2. Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA;3. Biodiversity and Climate Research Centre and Senckenberg, Frankfurt am Main, Germany;4. Department of Geosciences, Goethe University Frankfurt, 60438 Frankfurt, Germany;5. Department of Geosciences, University of Wisconsin, Madison, WI 53706, USA;6. Institute of Mineralogy and Geochemistry, University of Lausanne, Lausanne, Switzerland;7. New Mexico Bureau of Geology and Mineral Resources, New Mexico, Institute of Mining and Technology, Socorro, NM, USA |
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| Abstract: | Subsurface fault geometries have a systematic influence on folds formed above those faults. We use the extraordinarily well-exposed fold geometries of the Laramide-age Stillwell anticline in west Texas (USA) to develop a strain-predictive model of fault-propagation fold formation. The anticline is a 10-km long, NW-trending, NE-vergent, asymmetric fold system with an axis that displays a map-view left-stepping, en echelon pattern. We integrated field observations, geologic and structural data, cross-sections, and 2D kinematic modeling to establish an unusual 3D two-stage model of contractional fold formation, including: 1) reverse reactivation of a pre-existing, NW-striking, SW-dipping, left-stepping, en echelon normal fault system in Paleozoic basement rocks to generate monoclinal flexures in overlying layered Cretaceous carbonate rocks; and 2) the formation of a subsequent flat-ramp fault system that propagated horizontally along a mechanically-weak, clay-rich Cretaceous unit before ramping up at the hinge of the pre-existing monocline system. Strain is focused within the forelimb of the system, in front of the propagating fault tip, and is accommodated by a combination of interlayer slip, flat-ramp faulting, and fracturing proximal to planes of slip. This strain predictive model can be applied to similar, less-well-exposed contractional systems worldwide and provides a new, unusual example of Laramide-age contractional deformation. |
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| Keywords: | Stillwell anticline Fault reactivation Fault-propagation fold En echelon Kinematic modeling |
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