01809nas a2200169 4500008004100000245011000041210006900151300001200220490000700232520127500239653001201514100001601526700002001542700001901562700002001581856003801601 1997 eng d00aU-Pb Zircon Date from Avalonian Cape Breton Island and Geochronologic Calibration of the Early Ordovician0 aUPb Zircon Date from Avalonian Cape Breton Island and Geochronol a724-7300 v343 a

A U–Pb zircon date of 483 ± 1 Ma is recorded from an uppermost Tremadoc K-bentonite from the Chesley Drive Group on McLeod Brook, eastern Cape Breton Island. The associated fauna, with the trilobite Peltocare rotundifrons, is also known from the Reversing Falls section in Saint John, New Brunswick, and the traditional reference of the latter section to the Arenig is incorrect. A 483 ± 1 Ma age is significantly older than a U – Pb zircon age reported from the classical base of the Arenig Series in north Wales and about 10 Ma older than strata regarded herein as upper Arenig in central Newfoundland. If the global standard for the base of the Arenig is defined at the Tetragraptus approximatus Zone base, then the base of the type Arenig in Wales is younger than the latter horizon. The McLeod Brook occurrence is from an uppermost Tremadoc (Hunnebergian Stage) interval that has been removed below the unconformity in north Wales. The age of the Tremadoc –Arenig series boundary remains uncertain; however, a tentative estimate that it is significantly younger than 483 Ma is suggested by fossil evidence.

10ageology1 aLanding, E.1 aBowring, S., A.1 aFortey, R., A.1 aDavidek, K., L. uhttp://dx.doi.org/10.1139/e17-059