A new conceptual fold-fracture model including prefolding joints, based on the Emigrant Gap anticline, Wyoming

Research Article| March 01, 2004 A new conceptual fold-fracture model including prefolding joints, based on the Emigrant Gap anticline, Wyoming Stephan Bergbauer; Stephan Bergbauer 1Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar David D. Pollard David D. Pollard 1Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2004) 116 (3-4): 294–307. https://doi.org/10.1130/B25225.1 Article history received: 31 Jul 2002 rev-recd: 17 Dec 2002 accepted: 12 Mar 2003 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Stephan Bergbauer, David D. Pollard; A new conceptual fold-fracture model including prefolding joints, based on the Emigrant Gap anticline, Wyoming. GSA Bulletin 2004;; 116 (3-4): 294–307. doi: https://doi.org/10.1130/B25225.1 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 SocietyGSA Bulletin Search Advanced Search Abstract Symmetric relations between synfolding fractures and fold geometry have been used to explain the formation of fractures in folded sedimentary rocks. Based on field observations at the Emigrant Gap, a Laramide anticline located near Casper, Wyoming, we propose that the orientation of synfolding fractures was influenced dominantly by two tectonic joint sets, J1 and J2, which developed prior to folding. Rotations appropriate for unfolding the strata reorient most fractures such that they strike sub-parallel to one or the other of the two joint sets and oblique to the fold hinge line. On the fold limbs, these prefolding joints apparently propagated along strike and infilled during folding to form a denser network of joints bedding perpendicularly with spacing ∼1/5 to 1/10 that of the same joint set in nearby unfolded outcrops of the same formation. With proximity to the hinge line of the anticline, where bending of strata and surface curvature are elevated, the style of deformation is different. Whereas most J2-parallel fractures still are joints, fractures in the J1 orientation include sheared prefolding joints and bedding-inclined shear fractures. Apparent normal offsets of bedding by these shear fractures are an order of magnitude larger than offsets observed across sheared joints on the fold limbs. The proposed model of fracture-fold relationships differs from existing conceptual models because it postulates that folding-related fracture orientations are controlled by the orientations of prefolding fractures. For the Emigrant Gap anticline, these fractures are not oriented symmetrically with respect to the fold hinge line. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.