%0 Journal Article %J Canadian Journal of Earth Science %D 1998 %T Duration of the Early Cambrian: U-Pb Ages of Volcanic Ashes from Avalon and Gondwana %A E. Landing %A Bowring, S. A. %A Davidek, K. L. %A Westrop, S. R. %A G. Geyer %A Heldmaier , W. %K trilobites %K upper Lower Cambrian %K Volcanic zircons %X

Volcanic zircons from three ashes give a U-Pb date of 511 ± 1 Ma on trilobite-bearing, upper Lower Cambrian (upper Branchian Series) strata of southern New Brunswick that correlate into the Siberian middle Botomian - Toyonian Stage interval. This very young age on the late, but not latest, Early Cambrian of Avalon is consistent both with a 519 ± 1 Ma age on the older Caerfai Bay Shales of south Wales that are tentatively correlated into strata with the oldest Avalonian trilobites (lower Branchian) and with a 517 ± 1.5 Ma age on the Antatlasia gutta-pluviae Zone (trilobites) of Morocco. Determination of a 522 ± 2 Ma zircon age on the Moroccan subtrilobitic Lower Cambrian Lie de vin Formation is consistent with an earlier reported 521 ± 7 Ma age from the Lie de vin but suggests that a 526 ± 4 Ma age on Australian trilobite-bearing Lower Cambrian rocks may be too old. A 33+ Ma duration of the Avalonian Early Cambrian and an 8+ Ma length of the Avalonian trilobite-bearing Lower Cambrian support proposals that most Cambrian time was Early Cambrian and the majority of the Early Cambrian was pretrilobitic.

%B Canadian Journal of Earth Science %V 35 %P 329-338 %G eng %U http://www.nrcresearchpress.com/doi/abs/10.1139/e97-107#.VgRN3ZeOUg4 %R 10.1139/e97-107