Polygonal faults in chalk: Insights from extensive exposures of the Khoman Formation, Western Desert, Egypt

Abstract

Research Article| June 01, 2014 Polygonal faults in chalk: Insights from extensive exposures of the Khoman Formation, Western Desert, Egypt Barbara J. Tewksbury; Barbara J. Tewksbury 1Department of Geosciences, Hamilton College, Clinton, New York 13323, USA Search for other works by this author on: GSW Google Scholar John P. Hogan; John P. Hogan 2Geology and Geophysics Program, Missouri University of Science and Technology, Rolla, Missouri 65409, USA Search for other works by this author on: GSW Google Scholar Simon A. Kattenhorn; Simon A. Kattenhorn 3Department of Geological Sciences, University of Idaho, Moscow, Idaho 83844, USA Search for other works by this author on: GSW Google Scholar Charlotte J. Mehrtens; Charlotte J. Mehrtens 4Department of Geology, University of Vermont, Burlington, Vermont 05405, USA Search for other works by this author on: GSW Google Scholar Elhamy A. Tarabees Elhamy A. Tarabees 5Department of Geology, Damanhour University, Damanhour 22516, Egypt Search for other works by this author on: GSW Google Scholar Author and Article Information Barbara J. Tewksbury 1Department of Geosciences, Hamilton College, Clinton, New York 13323, USA John P. Hogan 2Geology and Geophysics Program, Missouri University of Science and Technology, Rolla, Missouri 65409, USA Simon A. Kattenhorn 3Department of Geological Sciences, University of Idaho, Moscow, Idaho 83844, USA Charlotte J. Mehrtens 4Department of Geology, University of Vermont, Burlington, Vermont 05405, USA Elhamy A. Tarabees 5Department of Geology, Damanhour University, Damanhour 22516, Egypt Publisher: Geological Society of America Received: 08 Dec 2013 Revision Received: 02 Mar 2014 Accepted: 04 Mar 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2014 Geological Society of America Geology (2014) 42 (6): 479–482. https://doi.org/10.1130/G35362.1 Article history Received: 08 Dec 2013 Revision Received: 02 Mar 2014 Accepted: 04 Mar 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Barbara J. Tewksbury, John P. Hogan, Simon A. Kattenhorn, Charlotte J. Mehrtens, Elhamy A. Tarabees; Polygonal faults in chalk: Insights from extensive exposures of the Khoman Formation, Western Desert, Egypt. Geology 2014;; 42 (6): 479–482. doi: https://doi.org/10.1130/G35362.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Although polygonal fault systems and related features are common in fine-grained sediments in modern submarine basins and have been studied in basins worldwide using three-dimensional (3-D) seismic data, extensive on-land exposures have remained elusive. We report here on the discovery of a polygonal fault system occurring in nearly continuous surface exposure over ∼900 km2 in chalk of the Cretaceous Khoman Formation near Farafra Oasis, Egypt. Field exposures reveal polygon boundaries defined by clusters of dozens of normal faults with strongly grooved fault surfaces and coarse calcite veins along faults with evidence for multiple fluid flow events. Geometric patterns and fault intersections reveal that mechanically interacting normal faults with multiple orientations were active contemporaneously in a horizontal strain field that was essentially isotropic and extensional. We interpret the very steep dips (∼80°) to reflect fault initiation in response to elevated pore fluid pressures. In the uppermost part of the Khoman Formation, a terrain of isolated circular structures displaying shallow inward dips overlies the polygonal fault network. The spatial relationship to the underlying faults is consistent with these small circular basins having formed as fluid escape structures as the polygonal fault system evolved. Outcrops in the Khoman Formation provide an unprecedented look into the 3-D geometry of a polygonal fault system, providing context for the analysis of analogous systems in marine basins and other on-land exposures. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.