2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 3-2
Presentation Time: 8:15 AM


LANDING, Ed, New York State Museum, 222 Madison Avenue, Albany, NY 12230, KOUCHINSKY, Artem, Dept. of Palaeozoology, Swedish Museum of Natural History, Box 50007, Stockholm, SE-104 05, Sweden, WESTROP, Stephen R., Oklahoma Museum of Natural History and School of Geology & Geophysics, Univ of Oklahoma, Norman, OK 73072, GEYER, Gerd, Institut für Geographie und Geologie, Universität Würzburg, Am Hubland, Würzburg, 97074, Germany and BOWRING, Samuel A., Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, ed.landing@nysed.gov

Mollusk-rich assemblages with Watsonella crosbyi with or without Aldanella spp. represent a temporally problematical, earliest Cambrian interval. Although frequently regarded as Tommotian-equivalents (upper Terreneuvian), new biotic and carbon isotope data demonstrate a pre-Tommotian (middle Terreneuvian) age for early W. crosbyi-A. spp. assemblages. Both W. crosbyi and A. spp. occur below the I’ carbon isotope excursion in the Siberian “Manykayan/Nemakit-Daldynian” Stage. Roughly coeval (pre-Tommotian) W. crosbyi-bearing faunas with A. attleborensis (=A. yanjiaheensis) occur below a distinctive, positive δ13C excursion in the middle Meishucunian Stage (China; L4, P3, ZHUCE excursions) and correlatives (middle Chapel Island Formation, Avalonia; upper Bayan Gol Formation, Mongolia). Heraultia Limestone (Gondwanan France) faunas are also pre-Tommotian-equivalents. The δ13C excursion above early W. crosbyi-bearing faunas is a reliable Stage 2 basal marker that is older (ca. 530 Ma) than earliest Tommotian (ca. 525.5 Ma). Benthic faunas with W. crosbyi and A. spp. record a ca. 10 m.y. “slow down” in the Cambrian Evolutionary Radiation. A Stage 2 base defined by W. crosbyi or A. attleborensis FADs is discouraged; these FADs are diachronous; W. crosbyi Zone taxa also appear with exceptionally early Cambrian acritarchs (Baltica), and their ranges are bracketed by lithofacies changes and unconformities (SE Siberia, South China, Avalonia, France).
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