Sedimentology and provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains, Alaska: Bearings on the accretionary tectonic history of the Wrangellia composite terrane

Abstract

Research Article| May 01, 2005 Sedimentology and provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains, Alaska: Bearings on the accretionary tectonic history of the Wrangellia composite terrane Jeffrey M. Tropaff; Jeffrey M. Tropaff 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Search for other works by this author on: GSW Google Scholar Darren A. Szuch; Darren A. Szuch 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Search for other works by this author on: GSW Google Scholar Matthew Rioux; Matthew Rioux 2Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Robert B. Blodgett Robert B. Blodgett 3U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Jeffrey M. Tropaff 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Darren A. Szuch 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Matthew Rioux 2Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA Robert B. Blodgett 3U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508, USA Publisher: Geological Society of America Received: 24 Jan 2004 Revision Received: 30 Jun 2004 Accepted: 10 Sep 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2005) 117 (5-6): 570–588. https://doi.org/10.1130/B25575.1 Article history Received: 24 Jan 2004 Revision Received: 30 Jun 2004 Accepted: 10 Sep 2004 First Online: 02 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 Jeffrey M. Tropaff, Darren A. Szuch, Matthew Rioux, Robert B. Blodgett; Sedimentology and provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains, Alaska: Bearings on the accretionary tectonic history of the Wrangellia composite terrane. GSA Bulletin 2005;; 117 (5-6): 570–588. doi: https://doi.org/10.1130/B25575.1 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 Analysis of the Upper Jurassic Naknek Formation in the Talkeetna Mountains, Alaska, documents synorogenic sedimentation in a forearc basin along the outboard (southern) margin of the allochthonous Peninsular terrane during accretion to the western North American continental margin. New geochronologic, sedimentologic, and compositional data define a two-part stratigraphy for the Naknek Formation. Microfossil, megafossil, and U-Pb clast ages document early Oxfordian to early Kimmeridgian deposition of the lower 690 m of the Naknek Formation and early Kimmeridgian to early Tithonian deposition of the upper 225 m of the Naknek Formation. Lithofacies and paleocurrent data from the lower Naknek Formation demonstrate initial deposition on a high-gradient, southward-dipping basin floor. Submarine mass flows deposited poorly sorted, cobbl-boulder conglomerate in proximal fan-delta environments. Gravelly mass flows transformed downslope into sandy turbidity currents on a muddy pro-delta slope. During early Kimmeridgian to early Tithonian time, fan-delta environments were replaced by lower gradient marine shelf environments characterized by deposition of cross-stratified sandstone and bioturbated mudstone. Sourc-diagnostic clasts, feldspathic sandstone compositions, southward-directed paleocurrent indicators, and U-Pb zircon ages of plutonic clasts (167.6 ± 0.3 Ma; 166.5 ± 0.2 Ma, 164–159 Ma, 156.2 ± 0.4 Ma) indicate that the Naknek Formation was derived primarily from volcanic and plutonic source terranes exposed along the northern basin margin in the southern Talkeetna Mountains. Geologic mapping documents the Little Oshetna fault, a newly identified northward-dipping reverse fault that bounds the northern margin of the Naknek Formation in the Talkeetna Mountains. The concentration of boulder-rich mass-flow deposits in the foot-wall of the fault in combination with geochronologic and compositional data suggest that sedimentation was coeval with Late Jurassic shortening along the fault and exhumation of plutonic source terranes exposed in the hanging wall of the fault. From a regional perspective, coars-grained forearc sedimentation and pluton exhumation along the outboard (southern) segment of the Peninsular terrane were coeval with crustal-scale shortening and synorogenic sedimentation in retroarc basins along the inboard (northern) margin of the Wrangellia terrane (Kahiltna, Nutzotin, and Wrangell Mountains basins). We interpret the regional and synchronous nature of Late Jurassic crustal-scale deformation and synorogenic sedimentation in south-central Alaska as reflecting either initial collision of the Wrangellia and Peninsular terranes with the former continental margin of western North America or amalgamation of the two terranes prior to collision. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.