Early Ordovician CA-IDTIMS U–Pb zircon dating and conodont biostratigraphy, Canning Basin, Western Australia

Abstract

ABSTRACTA continuously cored section of more than 300 m through the Nambeet Formation and the basal part of the conformably overlying Willara Formation in the Olympic 1 petroleum well, drilled in the Canning Basin of northern Western Australia, yields valuable information that increases by more than 40% the number of precise isotopic ages available to constrain the Ordovician Period. New CA-IDTIMS U–Pb zircon ages for seven bentonite layers in the Olympic 1 core are integrated into a new conodont biostratigraphic framework for the Early Ordovician comprising four biozones recognised in this well. The weighted mean U–Pb dates range from 479.37 ± 0.16 Ma within the late Tremadocian Paroistodus proteus conodont Biozone, to 470.18 ± 0.13 Ma near the boundary between the Floian and Dapingian stages within the Jumudontus gananda conodont Biozone. The intervening Prioniodus oepiki–Serratognathus bilobatus conodont Biozone (early Floian) and succeeding Oepikodus communis conodont Biozone (middle Floian) are similarly well constrained by isotopic dates centred on ca 477 Ma for the early Floian and by three ages of 473–471 Ma for the middle Floian. The seven new isotopic dates significantly increase the precision of dating for the Early Ordovician, where previously only two ages with limited or imprecise biostratigraphic control were known globally.