A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation

Abstract

Research Article| March 01, 2004 A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation Ben Kneller; Ben Kneller 1School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Juan Pablo Milana; Juan Pablo Milana 2CONICET e Instituto de Geología, Universidad Nacional de San Juan, San Juan, Argentina Search for other works by this author on: GSW Google Scholar Clare Buckee; Clare Buckee 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Omar al Ja'aidi Omar al Ja'aidi 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar GSA Bulletin (2004) 116 (3-4): 348–367. https://doi.org/10.1130/B25242.1 Article history received: 15 Aug 2002 rev-recd: 18 Feb 2003 accepted: 14 Apr 2003 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 Ben Kneller, Juan Pablo Milana, Clare Buckee, Omar al Ja'aidi; A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation. GSA Bulletin 2004;; 116 (3-4): 348–367. doi: https://doi.org/10.1130/B25242.1 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 The combination of high sediment supply rates and ample accommodation within fjords provides high-resolution records of deglaciation. Ancient fjord fills provide the potential for three-dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process. We describe the fill (Jejenes Formation) of a well-exposed Late Carboniferous (Pennsylvanian) glacial valley and its tributaries; these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments. The geometry of the valley and its tributaries is controlled by the underlying lower Paleozoic lithologies: a deep valley with steep sides exists where the bedrock is massive limestones, and a broader, shallower valley exists where the bedrock is generally a fine-grained olistostrome. The valleys are locally floored with diamictites, including both in situ tillites and remobilized diamictites. In the trunk valley these are locally overlain by a small, shallow-water delta. The major part of the valley fill consists of a ≤150-m-thick mudstone-dominated succession (probably generated by plumes of glacial outwash) containing numerous dropstones that decrease in abundance down the fjord. The mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys, each of which has a distinctive clast suite related to the local subcrop. The entire succession is overlain by >300 m of sandy turbidites, of which the upper part includes large mass-transport complexes.Intercalated within the succession in the trunk valley are structureless, graded, silty mudstones lacking dropstones but with abundant large wood fragments. Close to the steep western margin of the trunk valley, each of these massive mudstones is underlain by a slump or debris flow, locally containing meter-scale blocks of Ordovician limestone from the valley side. We interpret these as a consequence of rockfalls from the steeper valley sides, triggering debris flows on the subaqueous fjord slopes. We suggest that large solitary waves were generated as the rockfalls entered the water, traveling along the fjord and stripping vegetation from the shoreline. Large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds. These deposits, and other mass-flow deposits within the succession, emphasize the potential importance of catastrophic sedimentation within deglacial successions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.