- journal_title：Geology
- Contributor：Karl E. Karlstrom ; Samuel A. Bowring ; Carol M. Dehler ; Andrew H. Knoll ; Susannah M. Porter ; David J. Des Marais ; Arlo B. Weil ; Zachary D. Sharp ; John W. Geissman ; Maya B. Elrick ; J. Michael Timmons ; Laura J. Crossey ; Kathleen L. Davidek
- Publisher：Geological Society of America
- Date：2000-
- Format：text/html
- Language：en
- Identifier：10.1130/0091-7613(2000)28<619:CGOTGC>2.0.CO;2
- journal_abbrev：Geology
- issn：0091-7613
- volume：28
- issue：7
- firstpage：619
d="p-1">The Chuar Group (∼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.