title: Chuar Group of the Grand Canyon: record of breakup of Rodinia, associated change in the global carbon cycle, and ecosystem expansion by 740 Ma.
abstract: The Chuar Group (approximately 1600 m thick) preserves a record of extensional tectonism, ocean-chemistry fluctuations, and biological diversification during the late Neoproterozoic Era. An ash layer from the top of the section has a U-Pb zircon age of 742 +/- 6 Ma. The Chuar Group was deposited at low latitudes during extension on the north-trending Butte fault system and is inferred to record rifting during the breakup of Rodinia. Shallow-marine deposition is documented by tide- and wave-generated sedimentary structures, facies associations, and fossils. C isotopes in organic carbon show large stratigraphic variations, apparently recording incipient stages of the marked C isotopic fluctuations that characterize later Neoproterozoic time. Upper Chuar rocks preserve a rich biota that includes not only cyanobacteria and algae, but also heterotrophic protists that document increased food web complexity in Neoproterozoic ecosystems. The Chuar Group thus provides a well-dated, high-resolution record of early events in the sequence of linked tectonic, biogeochemical, environmental, and biological changes that collectively ushered in the Phanerozoic Eon.
authors.affiliation: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque 87131, USA. kek1@unm.edu
authors.forename: K E
authors.initials: KE
authors.lastname: Karlstrom
authors.forename: S A
authors.initials: SA
authors.lastname: Bowring
authors.forename: C M
authors.initials: CM
authors.lastname: Dehler
authors.forename: A H
authors.initials: AH
authors.lastname: Knoll
authors.forename: S M
authors.initials: SM
authors.lastname: Porter
authors.forename: D J
authors.initials: DJ
authors.lastname: Des Marais
authors.forename: A B
authors.initials: AB
authors.lastname: Weil
authors.forename: Z D
authors.initials: ZD
authors.lastname: Sharp
authors.forename: J W
authors.initials: JW
authors.lastname: Geissman
authors.forename: M B
authors.initials: MB
authors.lastname: Elrick
authors.forename: J M
authors.initials: JM
authors.lastname: Timmons
authors.forename: L J
authors.initials: LJ
authors.lastname: Crossey
authors.forename: K L
authors.initials: KL
authors.lastname: Davidek
mesh_terms: D000818:Animals; D001130:Arizona; D005075:Biological Evolution; D002244:Carbon / Q000737:chemistry*; D002247:Carbon Isotopes; D000458:Cyanobacteria; D018534:Earth, Planet; D017753:Ecosystem; D056890:Eukaryota; D019419:Evolution, Planetary; D018559:Exobiology; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis* / Q000382:microbiology; D008280:Magnetics; D009792:Oceans and Seas; D014871:Water Microbiology
chemical_list: D002247:Carbon Isotopes; D002244:Carbon