Cataclasis and deformation-band formation in unconsolidated marine terrace sand, Humboldt County, California

Research Article| February 01, 2000 Cataclasis and deformation-band formation in unconsolidated marine terrace sand, Humboldt County, California Sue Cashman; Sue Cashman 1Department of Geology, Humboldt State University, Arcata, California 95521, USA Search for other works by this author on: GSW Google Scholar Kathy Cashman Kathy Cashman 2Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Sue Cashman 1Department of Geology, Humboldt State University, Arcata, California 95521, USA Kathy Cashman 2Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Publisher: Geological Society of America Received: 21 May 1999 Revision Received: 27 Sep 1999 Accepted: 21 Oct 1999 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2000) 28 (2): 111–114. https://doi.org/10.1130/0091-7613(2000)28<111:CADFIU>2.0.CO;2 Article history Received: 21 May 1999 Revision Received: 27 Sep 1999 Accepted: 21 Oct 1999 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Sue Cashman, Kathy Cashman; Cataclasis and deformation-band formation in unconsolidated marine terrace sand, Humboldt County, California. Geology 2000;; 28 (2): 111–114. doi: https://doi.org/10.1130/0091-7613(2000)28<111:CADFIU>2.0.CO;2 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 Zones of deformation bands occur in unconsolidated late Pleistocene marine terrace sand in the footwall of the active McKinleyville thrust fault in Humboldt County, California. Individual deformation-band shear zones are as much as 8 cm wide and accommodate ∼50 cm of reverse-dip separation. Like deformation bands described in Mesozoic sandstone of the Colorado Plateau, these structures formed in fine-grained, well-sorted, porous sand. We assessed the relative importance of compaction, grain breakage, and grain rotation during shear-zone development by measuring grain size, grain shape, grain orientation, porosity, and bulk strain both within and outside deformation-band shear zones. Sand grains within shear zones are smaller, more compacted, and have stronger preferred orientations and more elongate shapes than grains outside of deformation-band shear zones. Bulk strain analyses of sand within shear zones give strain ellipses that are compatible with dextral shear strains of ∼0.1–0.5 and volume loss of 5%–15%. On the basis of these observations, we conclude that compaction, grain rotation, and extensive cataclasis all contribute to deformation-band shear-zone formation in these unconsolidated sands, despite very low confining pressures. In addition, the position of these deformation-band shear zones adjacent to an active fault with a history of episodic slip during large earthquakes suggests that they may form in conjunction with slip events. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.