Displacive Widening of Calcite Veins in Shale: Insights Into the Force of Crystallization

Abstract

Research Article| March 20, 2018 Displacive Widening of Calcite Veins in Shale: Insights Into the Force of Crystallization Qingfeng Meng; Qingfeng Meng Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, U.K. Search for other works by this author on: GSW Google Scholar John Hooker; John Hooker Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, U.K. Search for other works by this author on: GSW Google Scholar Joe Cartwright Joe Cartwright Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, U.K. Search for other works by this author on: GSW Google Scholar Author and Article Information Qingfeng Meng Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, U.K. John Hooker Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, U.K. Joe Cartwright Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, U.K. e-mail: meng.qingfeng@hotmail.com Publisher: SEPM Society for Sedimentary Geology First Online: 26 Mar 2018 Online Issn: 1938-3681 Print Issn: 1527-1404 Copyright © 2018, SEPM (Society for Sedimentary Geology) Journal of Sedimentary Research (2018) 88 (3): 327–343. https://doi.org/10.2110/jsr.2018.18 Article history First Online: 26 Mar 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Qingfeng Meng, John Hooker, Joe Cartwright; Displacive Widening of Calcite Veins in Shale: Insights Into the Force of Crystallization. Journal of Sedimentary Research 2018;; 88 (3): 327–343. doi: https://doi.org/10.2110/jsr.2018.18 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 SocietyJournal of Sedimentary Research Search Advanced Search Abstract The geometry, microtextures, and c-axis fabrics of calcite “beef” veins in the Lower Jurassic black shales (Wessex Basin, UK) were characterized to investigate the mechanism responsible for widening following fracture propagation. Isolated beef veins exhibit planar tapering tips, whereas closely spaced veins are characterized by blunt tips. Vein surfaces are generally smooth and flat; however, circular ridges appear on vein surfaces that protrude into the host clays where there are solid inclusions below or above the ridges. Fossils with well-preserved morphologies, which are separated by subvertical calcite fibers, are observed on both the lower and upper surfaces of single veins. The shale laminations around beef veins are folded and parallel to vein margins. The beef veins commonly contain blocky zones of small, equant calcite crystals, pyrite, and organic matter. The fibers exhibit a preferred subvertical c-axis orientation, whilst crystals in the median zones and blocky zones have random c-axis orientations. The different crystal sizes, morphologies, and c-axis orientations of the fibers from the blocky crystals suggest that the fibers grew without competition with each other under a nonhydrostatic stress field. The displacive widening of calcite beef veins, which is evident from vein interactions and deformation of individual fossil skeletons, demonstrates that fibers grew incrementally because the crystallization pressure of calcite exceeded the overburden load. The force of crystallization is suggested to be responsible for the c-axis orientations of calcite fibers, whereby crystals with free surfaces normal to c-axis orientations grew preferentially. The present study suggests that the fibrous widening of calcite veins in shale postdates their initiation and may result from displacive crystallization rather than fluid overpressure. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.