DOCSLIB.ORG

Introduction to Structural Geology

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Introduction to Structural Geology Contents i GEOL 326 Cornell University Introduction to Structural Geology Spring 1999 by Richard W. Allmendinger Department of Geological Sciences Snee Hall Cornell University, Ithaca, NY 14853-1504 USA [email protected] R. W. Allmendinger © 1999 Contents ii Contents Lecture 1—Introduction, Scale, & Basic Terminology...............................................1 1.1 Introduction.................................................................................................................................. 1 1.2 Levels of Structural Study............................................................................................................ 2 1.3 Types of Structural Study............................................................................................................. 2 1.4 Importance of Scale..................................................................................................................... 3 1.4.1 Scale Terms.................................................................................................................... 3 1.4.2 Scale Invariance, Fractals...............................................................................................4 Lecture 2 —Coordinate Systems, etc....................................................................... 8 2.1 Introduction.................................................................................................................................. 8 2.2 Three types of physical entities.................................................................................................... 8 2.3 Coordinate Systems..................................................................................................................... 9 2.3.1 Spherical versus Cartesian Coordinate Systems..........................................................10 2.3.2 Right-handed and Left-handed Coordinate Systems.................................................... 10 2.3.3 Cartesian Coordinate Systems in Geology................................................................... 11 2.4 Vectors.......................................................................................................................................12 2.4.1 Vectors vs. Axes ........................................................................................................... 12 2.4.2 Basic Properties of Vectors...........................................................................................12 2.4.3 Geologic Features as Vectors.......................................................................................14 2.4.4 Simple Vector Operations............................................................................................. 17 2.4.5 Dot Product and Cross Product .................................................................................... 18 Lecture 3 — Descriptive Geometry: Seismic Reflection..........................................21 3.1 Echo Sounding...........................................................................................................................21 3.2 Common Depth Point (CDP) Method......................................................................................... 23 3.3 Migration .................................................................................................................................... 25 3.4 Resolution of Seismic Reflection Data.......................................................................................26 3.4.1 Vertical Resolution ........................................................................................................26 3.4.2 Horizontal Resolution....................................................................................................27 3.5 Diffractions.................................................................................................................................28 3.6 Artifacts...................................................................................................................................... 29 Contents iii 3.6.1 Velocity Pullup/pulldown ...............................................................................................29 3.6.2 Multiples........................................................................................................................ 29 3.6.3 Sideswipe......................................................................................................................30 3.6.4 Buried Focus.................................................................................................................31 3.6.5 Others ...........................................................................................................................32 Lecture 4 — Introduction to Deformation & Strain..................................................33 4.1 Introduction................................................................................................................................33 4.2 Kinematics .................................................................................................................................33 4.2.1 Rigid Body Deformations .............................................................................................. 33 4.2.2 Strain (Non-rigid Body Deformation).............................................................................34 4.2.3 Continuum Mechanics...................................................................................................36 4.2.4 Four Aspects of a Deforming Rock System: ................................................................. 37 4.3 Measurement of Strain............................................................................................................... 38 4.3.1 Change in Line Length:................................................................................................. 39 4.3.2 Changes in Angles:.......................................................................................................40 4.3.3 Changes in Volume (Dilation): ......................................................................................41 Lecture 5 — Strain II: The Strain Ellipsoid ............................................................42 5.1 Motivation for General 3-D Strain Relations ..............................................................................42 5.2 Equations for Finite Strain.......................................................................................................... 43 5.3 Extension of a Line .................................................................................................................... 43 5.4 Shear Strain...............................................................................................................................45 Lecture 6 — Strain III: Mohr on the Strain Ellipsoid...............................................47 6.1 Introduction................................................................................................................................47 6.2 Mohr’s Circle For Finite Strain ...................................................................................................47 6.3 Principal Axes of Strain..............................................................................................................48 6.4 Maximum Angular Shear ........................................................................................................... 49 6.5 Ellipticity.....................................................................................................................................50 6.6 Rotation of Any Line During Deformation ..................................................................................50 6.7 Lines of No Finite Elongation.....................................................................................................51 Lecture 7 — Strain IV: Finite vs. Infinitesimal Strain.............................................53 7.1 Coaxial and Non-coaxial Deformation .......................................................................................54 Contents iv 7.2 Two Types of Rotation............................................................................................................... 55 7.3 Deformation Paths .....................................................................................................................55 7.4 Superposed Strains & Non-commutability .................................................................................58 7.5 Plane Strain & 3-D Strain........................................................................................................... 58 Lecture 8—Stress I: Introduction ..........................................................................60 8.1 Force and Stress........................................................................................................................ 60 8.2 Units Of Stress...........................................................................................................................61 8.3 Sign Conventions:......................................................................................................................61 8.4 Stress on a Plane; Stress at a Point ..........................................................................................62 8.5 Principal Stresses ......................................................................................................................63 8.6 The Stress Tensor .....................................................................................................................64
Load more

Recommended publications
  • Faults and Joints
    133 JOINTS Joints (also termed extensional fractures) are planes of separation on which no or undetectable shear displacement has taken place. The two walls of the resulting tiny opening typically remain in tight (matching) contact. Joints may result from regional tectonics (i.e. the compressive stresses in front of a mountain belt), folding (due to curvature of bedding), faulting, or internal stress release during uplift or cooling. They often form under high fluid pressure (i.e. low effective stress), perpendicular to the smallest principal stress. The aperture of a joint is the space between its two walls measured perpendicularly to the mean plane. Apertures can be open (resulting in permeability enhancement) or occluded by mineral cement (resulting in permeability reduction). A joint with a large aperture (> few mm) is a fissure. The mechanical layer thickness of the deforming rock controls joint growth. If present in sufficient number, open joints may provide adequate porosity and permeability such that an otherwise impermeable rock may become a productive fractured reservoir. In quarrying, the largest block size depends on joint frequency; abundant fractures are desirable for quarrying crushed rock and gravel. Joint sets and systems Joints are ubiquitous features of rock exposures and often form families of straight to curviplanar fractures typically perpendicular to the layer boundaries in sedimentary rocks. A set is a group of joints with similar orientation and morphology. Several sets usually occur at the same place with no apparent interaction, giving exposures a blocky or fragmented appearance. Two or more sets of joints present together in an exposure compose a joint system.
    [Show full text]
  • Pressure Solution and Hydraulic Fracturing by a Lastair Beach
    C H E M ！C A L P R O C E S S E S IN D E F O R M A T IO N A T L O W M E T A M O R P H IC G R A D E S Pressure Solution and Hydraulic Fracturing by A lastair Beach Pressure solution has long been recognized as an im portant m echanism of de和rm ation, particularly in sedim entary rocks at low m etam orphic grade. G eologists have tended to study only the m ost easily m anaged aspect of pressure solution structures 一their geom etry as a record of rock deform ation. A t the sam e tim e the m ost co m m on pressure solution structures, such as stylolites in lim estones, clearly evolve th rough com plex chem ical processes, as do cleavage stripes and associa ted syntectonic veins w hich are abundant in terrigenous sedim entary rocks that have been d e form ed under lo w grade m etam orphic conditions. This review 和cusses on stripes and veins, draw ing together those concepts that need integrated study in o rd e r to r e a c h a b e t te r understanding a厂pressure solution. G eological Setting s m a lle r s c a le in s la t e s a n d t h e d e fin it io n o f c h e m ic a l a n d m ineralogical changes associated w ith cleavage developm ent Spaced cleavage stripes are the w idespread result of defor- (K nipe, 1982).
    [Show full text]
  • The Role of Pressure Solution Seam and Joint Assemblages In
    THE ROLE OF PRESSURE SOLUTION SEAM AND JOINT ASSEMBLAGES IN THE FORMATION OF STRIKE-SLIP AND THRUST FAULTS IN A COMPRESSIVE TECTONIC SETTING; THE VARISCAN OF SOUTHWESTERN IRELAND Filippo Nenna and Atilla Aydin Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 e-mail: [email protected] scale such as strike-slip faults and thrust-cored folds in Abstract various stages of their development. In this study we focus on the initiation and development of strike-slip The Ross Sandstone in County Clare, Ireland, was faults by shearing of the initial JVs and PSSs and deformed by an approximately north-south compression formation of thrust faults by exploiting weak shale during the end-Carboniferous Variscan orogeny. horizons and the strike-parallel PSSs in the adjacent Orthogonal sets of fundamental structures form the sandstone intervals. initial assemblage; mutually abutting arrays of 170˚ Development of faults from shearing of initial oriented set 1 joints/veins (JVs) and approximately 75˚ fundamental structural elements with either opening or pressure solution seams (PSSs) that formed under the closing modes in a wide range of structural settings has same stress conditions. Orientations of set 2 (splay) JVs been extensively reported. Segall and Pollard (1983), and PSSs suggest a clockwise remote stress rotation of Martel and Pollard (1989) and Martel (1990) have about 35˚ responsible for the contemporaneous described strike-slip faults formed by shearing of shearing of the set 1 arrays. Prominent strike-slip faults thermal fractures in granitic rocks. Myers and Aydin are sub-parallel to set 1 JVs and form by the linkage of (2004) and Flodin and Aydin (2004) reported strike-slip en-echelon segments with broad damage zones faulting formed by shearing of joints formed by an responsible for strike-slip offsets of hundreds of metres.
    [Show full text]
  • Deformation in Moffat Shale Detachment Zones in the Western Part of the Scottish Southern Uplands
    This is a repository copy of Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/1246/ Article: Needham, D.T. (2004) Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands. Geological Magazine, 141 (4). pp. 441-453. ISSN 0016-7568 https://doi.org/10.1017/S0016756804009203 Reuse See Attached Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Geol. Mag. 141 (4), 2004, pp. 441–453. c 2004 Cambridge University Press 441 DOI: 10.1017/S0016756804009203 Printed in the United Kingdom Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands D. T. NEEDHAM* Rock Deformation Research, School of Earth Sciences, The University, Leeds LS2 9JT, UK (Received 17 June 2003; accepted 23 February 2004) Abstract – A study of the decollement´ zones in the Moffat Shale Group in the Ordovician Northern Belt of the Southern Uplands of Scotland reveals a progressive sequence of deformation and increased channelization of fluid flow. The study concentrates on exposures of imbricated Moffat Shale on the western coast of the Rhins of Galloway. Initial deformation occurred in partially lithified sediments and involved stratal disruption and shearing of the shales. Deformation then became more localized in narrower fault zones characterized by polyphase hydrothermal fluid flow/veining events.
    [Show full text]
  • Fracture Cleavage'' in the Duluth Complex, Northeastern Minnesota
    Downloaded from gsabulletin.gsapubs.org on August 9, 2013 Geological Society of America Bulletin ''Fracture cleavage'' in the Duluth Complex, northeastern Minnesota M. E. FOSTER and P. J. HUDLESTON Geological Society of America Bulletin 1986;97, no. 1;85-96 doi: 10.1130/0016-7606(1986)97<85:FCITDC>2.0.CO;2 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes Geological Society of America Downloaded from gsabulletin.gsapubs.org on August 9, 2013 "Fracture cleavage" in the Duluth Complex, northeastern Minnesota M.
    [Show full text]
  • Accommodation of Penetrative Strain During Deformation Above a Ductile Décollement
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Earth and Atmospheric Sciences, Department Papers in the Earth and Atmospheric Sciences of 2016 Accommodation of penetrative strain during deformation above a ductile décollement Bailey A. Lathrop Caroline M. Burberry Follow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences Commons This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Accommodation of penetrative strain during deformation above a ductile décollement Bailey A. Lathrop* and Caroline M. Burberry* DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES, UNIVERSITY OF NEBRASKA-LINCOLN, 214 BESSEY HALL, LINCOLN, NEBRASKA 68588, USA ABSTRACT The accommodation of shortening by penetrative strain is widely considered as an important process during contraction, but the distribu- tion and magnitude of penetrative strain in a contractional system with a ductile décollement are not well understood. Penetrative strain constitutes the proportion of the total shortening across an orogen that is not accommodated by the development of macroscale structures, such as folds and thrusts. In order to create a framework for understanding penetrative strain in a brittle system above a ductile décollement, eight analog models, each with the same initial configuration, were shortened to different amounts in a deformation apparatus. Models consisted of a silicon polymer base layer overlain by three fine-grained sand layers. A grid was imprinted on the surface to track penetra- tive strain during shortening.
    [Show full text]
  • Stylolites: a Review
    Stylolites: a review Toussaint R.1,2,3*, Aharonov E.4, Koehn, D.5, Gratier, J.-P.6, Ebner, M.7, Baud, P.1, Rolland, A.1, and Renard, F.6,8 1Institut de Physique du Globe de Strasbourg, CNRS, University of Strasbourg, 5 rue Descartes, F- 67084 Strasbourg Cedex, France. Phone : +33 673142994. email : [email protected] 2 International Associate Laboratory D-FFRACT, Deformation, Flow and Fracture of Disordered Materials, France-Norway. 3SFF PoreLab, The Njord Centre, Department of Physics, University of Oslo, Norway. 4Institute of Earth Sciences, The Hebrew University, Jerusalem, 91904, Israel 5School of Geographical and Earth Sciences, University of Glasgow, UK 6University Grenoble Alpes, ISTerre, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, 38000 Grenoble, France 7OMV Exploration & Production GmbH Trabrennstrasse 6-8, 1020 Vienna, Austria 8 The Njord Centre,PGP, Department of Geosciences, University of Oslo, Norway *corresponding author Highlights: . Stylolite formation depends on rock composition and structure, stress and fluids. Stylolite geometry, fractal and self-affine properties, network structure, are investigated. The experiments and physics-based numerical models for their formation are reviewed. Stylolites can be used as markers of strain, paleostress orientation and magnitude. Stylolites impact transport properties, as function of maturity and flow direction. Abstract Stylolites are ubiquitous geo-patterns observed in rocks in the upper crust, from geological reservoirs in sedimentary rocks to deformation zones, in folds, faults, and shear zones. These rough surfaces play a major role in the dissolution of rocks around stressed contacts, the transport of dissolved material and the precipitation in surrounding pores. Consequently, they 1 play an active role in the evolution of rock microstructures and rheological properties in the Earth’s crust.
    [Show full text]
  • The Role of Pressure Solution Creep in the Ductility of the Earth's
    The role of pressure solution creep in the ductility of the earth’s upper crust Jean-Pierre Gratier, Dag Dysthe, Francois Renard To cite this version: Jean-Pierre Gratier, Dag Dysthe, Francois Renard. The role of pressure solution creep in the ductility of the earth’s upper crust. Advances in Geophysics, Elsevier, 2013, 54, pp.47-179. 10.1016/B978-0- 12-380940-7.00002-0. insu-00799131 HAL Id: insu-00799131 https://hal-insu.archives-ouvertes.fr/insu-00799131 Submitted on 11 Mar 2013 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 1 The role of pressure solution creep in the ductility of the Earth’s upper crust Jean-Pierre Gratier1, Dag K. Dysthe2,3, and François Renard1,2 1Institut des Sciences de la Terre, Observatoire, CNRS, Université Joseph Fourier-Grenoble I, BP 53, 38041 Grenoble, France 2Physics of Geological Processes, University of Oslo, Norway 3Laboratoire Interdisciplinaire de Physique, BP 87, 38041 Grenoble, France The aim of this review is to characterize the role of pressure solution creep in the ductility of the Earth’s upper crust and to describe how this creep mechanism competes and interacts with other deformation mechanisms.
    [Show full text]
  • Stylolites and Stylolite Networks As Primary Controls on the Geometry and Distribution of Carbonate Diagenetic Alterations
    Stylolites and stylolite networks as primary controls on the geometry and distribution of carbonate diagenetic alterations Enrique Gomez-Rivas1,*, Juan Diego Martín-Martín1, Paul D. Bons2,3, Daniel Koehn4, Albert Griera5, Anna Travé1, Maria-Gema Llorens6, Elliot Humphrey7 and Joyce Neilson7 1 Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain, e.gomez- [email protected], [email protected], [email protected] 2 Department of Geosciences, Eberhard Karls University of Tübingen, Wilhelmstr. 56, 72074 Tübingen, Germany, [email protected] 3 School of Earth Science and Resources, China University of Geosciences, Xueyuan Road 29, Haidian district, 100083 Beijing, China. 4 GeoZentrum Nordbayern, University Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany, [email protected] 5 Departament de Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra (Cerdanyola del Vallès), Barcelona, Spain, [email protected] 6 Geosciences Barcelona - CSIC, 08028 Barcelona, Spain, [email protected] 7 School of Geosciences, University of Aberdeen, King’s College AB24 3UE Aberdeen, Scotland, UK, [email protected], [email protected] * Corresponding author: [email protected] This paper is a non-peer reviewed preprint submitted to EarthArXiv. This preprint has been submitted for publication in a scientific journal on 14th July 2021. 1 Stylolites and stylolite networks as primary controls on the geometry and distribution of carbonate diagenetic alterations Enrique Gomez-Rivas1,*, Juan Diego Martín-Martín1, Paul D. Bons2,3, Daniel Koehn4, Albert Griera5, Anna Travé1, Maria-Gema Llorens6, Elliot Humphrey7 and Joyce Neilson7 1 Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain 2 Department of Geosciences, Eberhard Karls University of Tübingen, Wilhelmstr.
    [Show full text]
  • MECHANICAL ENGINEERING Syllabus
    SYLLABUS OF MASTER OF MECHANICAL ENGINEERING First semester Category:- Departmental / Specialization Basket PAPER-I PG / ME / T/ 111A-Theory of Elasticity Stress and strain tensors, equations of equilibrium and compatibility in rectangular and curvilinear coordinates, Cauchy’s formula, stress transformation, principal stresses, Lame’s stress ellipsoid, Cauchy stress quadratic, octahedral stress, stress- strain relations, basic equations of elasticity, Boundary value problem, Uniqueness of solutions, Torsion of non-circular sections, St. Venant’s theory of torsion, Scalar and Vector potentials, Strain potentials. Plane state of stress and strain, Airy’s stress function for problems, Representation of biharmonic function using complex variables, kolosoff-Mushkelishvili method. Thermal stress, Applications to problems of curved beam, thick cylinder and rotating disc, stress concentration. Introduction to numerical methods in elasticity. PG / ME / T / 111B-Continuum Mechanics: Introductory concepts and mathematics- ideas of vector calculus, elements of tensor algebra, calculus of variations, orthogonal curvilinear co-ordinates. Theory of deformation- concepts of normal and shear strain, physical significance of terms of €-matrix, principal strains, rotation of volume element, its relation to displacement gradient, affine deformation, homogeneous deformation, kinematics of deformable media, compatibility relations, discussions on curvilinear co-ordinates and in general co-ordinate systems. Theory of stresses- definition, tensoral character, principal stresses, mean, deviatoric, octahedral stresses, differential equations of motion in orthogonal curvilinear co- ordinates. Three dimensional equations- Elastic/non-elastic response of a body, intrinsic energy density function, generalized Hook’s law, equations of thermoelasticity, differential equation of heat conduction, stress-strain temperature relations, spherico-symmetric stress distribution, energy principles- its applications to a deformable media (Navier- stokes equations), non-linear constitutive relations.
    [Show full text]
  • Formation of the Frontal Thrust Zone of Accretionary Wedges Jonathan Weiss, Garrett Ito, Benjamin Brooks, Jean-Arthur Olive, Gregory Moore, James Foster
    Formation of the frontal thrust zone of accretionary wedges Jonathan Weiss, Garrett Ito, Benjamin Brooks, Jean-Arthur Olive, Gregory Moore, James Foster To cite this version: Jonathan Weiss, Garrett Ito, Benjamin Brooks, Jean-Arthur Olive, Gregory Moore, et al.. Formation of the frontal thrust zone of accretionary wedges. Earth and Planetary Science Letters, Elsevier, 2018, 495, pp.87-100. 10.1016/j.epsl.2018.05.010. hal-02329642 HAL Id: hal-02329642 https://hal.archives-ouvertes.fr/hal-02329642 Submitted on 17 Nov 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 1 Formation of the frontal thrust zone of accretionary wedges 2 3 Jonathan R. Weiss1,2, Garrett Ito1, Benjamin A. Brooks3, Jean-Arthur Olive4, Gregory F. Moore2, 4 and James H. Foster5 5 6 1. COMET, School of Earth and Environment, University of Leeds, Leeds, United Kingdom 7 2. Department of Geology and Geophysics, University of Hawai‘i, Honolulu, HI, USA. 8 3. U.S. Geological Survey Earthquake Science Center, Menlo Park, California, USA. 9 4. Laboratoire de Géologie, Ecole Normale Supérieure / CNRS UMR 8538, PSL Research 10 University, Paris, France. 11 5.
    [Show full text]
  • Stylolites in Limestones: Barriers to Fluid Flow?
    Stylolites in limestones: Barriers to fl uid fl ow? Michael J. Heap1, Patrick Baud1, Thierry Reuschlé1, and Philip G. Meredith2 1École et Observatoire des Sciences de la Terre, Université de Strasbourg (UMR 7516 Centre National de la Recherche Scientifi que), F-67084 Strasbourg cedex, France 2Department of Earth Sciences, University College London, London WC1E 6BT, UK ABSTRACT MATERIALS AND METHODS Stylolites—products of intergranular pressure-solution—are lat- The materials of this study were taken from vertical boreholes drilled erally extensive, planar features. They are a common strain localiza- around the ANDRA Underground Research Laboratory near Bure, France. tion feature in sedimentary rocks. Their potential impact on regional We selected four lithologies to sample (Fig. 1), three within the Oxford- fl uid fl ow has interested geoscientists for almost a century. Prevalent ian stage (Late Jurassic) and one within the Middle Jurassic “Dogger” views are that they act as permeability barriers, although laboratory series. We selected these lithologies based on their differences in porosity studies are extremely rare. Here we report on a systematic laboratory and texture. Macroscopically there is no systematic difference in stylolite study of the infl uence of stylolites on permeability in limestone. Our density or thickness (50–200 µm) between the limestone units, although data demonstrate that, contrary to conventional wisdom, the studied occasional thicker stylolites (1500–3000 µm) are observed in the Dogger stylolites do not act as barriers to fl uid fl ow. In detail, when a stylolite limestone. In this study we chose to focus on bedding-parallel sedimenta- occurs perpendicular to the direction of fl ow, the permeability simply ry stylolites; subvertical stylolites of tectonic origin are also present within follows the same power law permeability-porosity trend as the stylo- these formations (Rolland et al., 2013), but only occur rarely in borehole lite-free material.
    [Show full text]