01868nas a2200217 4500008004100000245008900041210006900130300001200199490000700211520119000218653001501408653002501423653002101448100001601469700002001485700002001505700002001525700001401545700001801559856007301577 1998 eng d00aDuration of the Early Cambrian: U-Pb Ages of Volcanic Ashes from Avalon and Gondwana0 aDuration of the Early Cambrian UPb Ages of Volcanic Ashes from A a329-3380 v353 a

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.

10atrilobites10aupper Lower Cambrian10aVolcanic zircons1 aLanding, E.1 aBowring, S., A.1 aDavidek, K., L.1 aWestrop, S., R.1 aGeyer, G.1 aHeldmaier, W. uhttp://www.nrcresearchpress.com/doi/abs/10.1139/e97-107#.VgRN3ZeOUg4