Chuar Group of the Grand Canyon: record of breakup of Rodinia, associated change in the global carbon cycle, and ecosystem expansion by 740 Ma.
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.
Karlstrom
K E
KE
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque 87131, USA. kek1@unm.edu
Bowring
S A
SA
Dehler
C M
CM
Knoll
A H
AH
Porter
S M
SM
Des Marais
D J
DJ
Weil
A B
AB
Sharp
Z D
ZD
Geissman
J W
JW
Elrick
M B
MB
Timmons
J M
JM
Crossey
L J
LJ
Davidek
K L
KL
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
D002247:Carbon Isotopes; D002244:Carbon