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U-Pb zircon date from Avalonian Cape Breton Island and geochronologic calibration of the early Ordovician

January 1, 1997

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.

Citation Information

Publication Year 1997
Title U-Pb zircon date from Avalonian Cape Breton Island and geochronologic calibration of the early Ordovician
Authors E. Landing, S.A. Bowring, R.A. Fortey, K.L. Davidek
Publication Type Article
Publication Subtype Journal Article
Series Title Canadian Journal of Earth Sciences
Index ID 70019793
Record Source USGS Publications Warehouse