Synthesis of the 780–740 Ma Chuar, Uinta Mountain, and Pahrump (ChUMP) groups, western USA: Implications for Laurentia-wide cratonic marine basins

Abstract

Research Article| May 01, 2017 Synthesis of the 780–740 Ma Chuar, Uinta Mountain, and Pahrump (ChUMP) groups, western USA: Implications for Laurentia-wide cratonic marine basins Carol Dehler; Carol Dehler † 1Department of Geology, Utah State University, 4505 Old Main Hill, Logan, Utah 84322-4505, USA †[e-mail] Search for other works by this author on: GSW Google Scholar George Gehrels; George Gehrels 2Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Susannah Porter; Susannah Porter 3Department of Earth Science, University of California at Santa Barbara, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Matt Heizler; Matt Heizler 4New Mexico Bureau of Geology & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801-4796, USA Search for other works by this author on: GSW Google Scholar Karl Karlstrom; Karl Karlstrom 5Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 871311, USA Search for other works by this author on: GSW Google Scholar Grant Cox; Grant Cox 6Department of Applied Geology, Western Australian School of Mines, Kent Street, Bentley, Perth, Western Australia 6102, Australia7Centre for Tectonics Resources and Exploration (TRaX), Department of Earth Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia Search for other works by this author on: GSW Google Scholar Laura Crossey; Laura Crossey 5Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 871311, USA Search for other works by this author on: GSW Google Scholar Mike Timmons Mike Timmons 4New Mexico Bureau of Geology & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801-4796, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Carol Dehler † 1Department of Geology, Utah State University, 4505 Old Main Hill, Logan, Utah 84322-4505, USA George Gehrels 2Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA Susannah Porter 3Department of Earth Science, University of California at Santa Barbara, Santa Barbara, California 93106, USA Matt Heizler 4New Mexico Bureau of Geology & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801-4796, USA Karl Karlstrom 5Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 871311, USA Grant Cox 6Department of Applied Geology, Western Australian School of Mines, Kent Street, Bentley, Perth, Western Australia 6102, Australia7Centre for Tectonics Resources and Exploration (TRaX), Department of Earth Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia Laura Crossey 5Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 871311, USA Mike Timmons 4New Mexico Bureau of Geology & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801-4796, USA †[e-mail] Publisher: Geological Society of America Received: 11 Mar 2016 Revision Received: 09 Sep 2016 Accepted: 29 Nov 2016 First Online: 06 Jul 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2017 Geological Society of America GSA Bulletin (2017) 129 (5-6): 607–624. https://doi.org/10.1130/B31532.1 Article history Received: 11 Mar 2016 Revision Received: 09 Sep 2016 Accepted: 29 Nov 2016 First Online: 06 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Carol Dehler, George Gehrels, Susannah Porter, Matt Heizler, Karl Karlstrom, Grant Cox, Laura Crossey, Mike Timmons; Synthesis of the 780–740 Ma Chuar, Uinta Mountain, and Pahrump (ChUMP) groups, western USA: Implications for Laurentia-wide cratonic marine basins. GSA Bulletin 2017;; 129 (5-6): 607–624. doi: https://doi.org/10.1130/B31532.1 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 upper Tonian Chuar, Uinta Mountain, and middle Pahrump (ChUMP) groups of present-day western Laurentia collectively record the early breakup of Rodinia, large-scale perturbations in the carbon cycle, and eukaryotic evolution, all of which preceded the onset of global glaciation by tens of millions of years. The spectacularly preserved and shale-rich Chuar Group of the Grand Canyon Supergroup stands out as one of the best global records of this time period, particularly for paleobiology. A new U-Pb age of 782 Ma on detrital zircons (n = 14 young grains) from the underlying Nankoweap Formation refines the Chuar Group's maximum depositional age to younger than 782 Ma. A new 40Ar/39Ar age of 764 ± 16 Ma (2σ) from K-feldspar within early diagenetic marcasite nodules from the upper Chuar Group (Awatubi Member) helps calibrate the rich Chuar microfossil record and constrain the large-magnitude shift in δ13Corg (up to 18‰; referred to here as the Awatubi positive carbon-isotope excursion or APCIE) to between ca. 764 and ca. 742 Ma, the date of an ash near the top of the Chuar Group.In addition to the maximum depositional age of ca. 782 Ma, U-Pb detrital zircon analyses (n = 826 grains) on sandstone beds from the underlying Nankoweap Formation indicate the presence of multiple older Laurentian age peaks. The similarity of detrital zircon populations and sedimentary character to that of the overlying Chuar Group (n = 764 grains) suggests that the Nankoweap Formation should be included as the lowermost unit in the Chuar Group. This revised geochronological framework indicates a 300 Ma unconformity between the Chuar Group (including the Nankoweap Formation) and the underlying 1.1 Ga Cardenas Basalt of the Unkar Group.Chuar Group detrital zircon populations share similarities with those of the Uinta Mountain Group and especially the middle Pahrump Group, including ca. 780 Ma grains. Biostratigraphic correlation using microfossils enhances the ChUMP connection and shows a trend of higher acritarch diversity in the lower Chuar and Uinta Mountain groups, and the presence of vase-shaped microfossils in the upper intervals of all three ChUMP units. Comparisons of δ13Corg and δ13Ccarb among ChUMP successions suggest a combination of local and regional controls. Thus, ChUMP successions are coeval within the 780–740 Ma range, show similar fossil and C-isotope trends, and derived sediments from similar Laurentian sources or source types.In light of recent age constraints and compiled paleontology in other Neoproterozoic basins, our high-resolution correlation of ChUMP successions can be extended to the Callison Lake dolostone of NW Canada and the Akademikerbreen-Polarisbreen groups of Svalbard.Biostratigraphic correlation with poorly age-constrained strata such as the Akademikerbreen-Polarisbreen groups and, farther afield, the Visingsö Group of Baltica suggests that ChUMP units record continentwide—and perhaps global—evolutionary patterns. The δ13Corg and δ13Ccarb values in the Chuar Group and its equivalents in Canada and Svalbard show broadly similar trends, including the APCIE, suggesting that δ13Corg values from organic-rich shale record variations in the C-isotope composition of late Tonian oceans. Intracratonic basins and contiguous rift margins of ChUMP age are inferred to have been important locations for microbial productivity and significant organic carbon burial that induced large positive shifts in δ13C and changes in global carbon balance prior to the onset of snowball Earth. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.