A U-Pb age for the Cambrian Taylor Formation, Antarctica:: Implications for the Cambrian time scale

Isotopic ages for the Middle Cambrian-Late Cambrian are few because formations of the appropriate age combining diagnostic fossils and rocks datable by precise isotopic techniques are not common. The Taylor Formation in Antarctica includes carbonate units that host trilobites, indicating an early late Middle Cambrian age. Volcanics below and above the trilobite-bearing horizon yielded zircons that date the horizon at 505.1 +/- 1.3 Ma. This age suggests that the Middle-Late Cambrian boundary is less than 505 Ma, consistent with a similar to 500 Ma boundary and a duration of similar to 10 m.yr. each for the Middle and Late Cambrian.