Zircon U-Pb ages for the Early Cambrian time-scale
Abstract
Single zircons from two Early Cambrian volcanic horizons have been analysed using the SHRIMP ion microprobe. Full details of the analytical procedures and data reduction are given. Zircons from tuff within the Lie de Vin Formation, near Tiout, Morocco, show little spread in U-Pb age and have a mean value of 521 ± 7 Ma (2σ). Those from a bentonite within unit 5 of the Meishucun section near Kunming, southern China, show relatively dispersed U-Pb ages, revealing the presence of both detrital or xenocrystic grains as well as areas within grains that have lost radiogenic Pb. The main population has a mean age of 525 ± 7 Ma, but a mean ^(207)Pb/^(206)Pb age of 539 ± 34 Ma which is a maximum estimate for the bentonite age. These results conflict with previous Rb-Sr whole rock ages of c. 580 Ma for overlying Cambrian shales at Meishucun, and c. 570 Ma for Atdabanian shales from the E. Yangtse Gorges area.
Additional Information
© 1992 Geological Society of London. Received 29 May 1991; revised typescript accepted 15 October 1991. This work is a contribution to IGCP project no. 29 on the Precambrian-Cambrian Boundary, and is dedicated to the memory of the late Richard L. Armstrong. We thank A. Latham, R. Riding, A. Bensald and M. Dahamani for assistance with the field sampling, and R.J. Pankhurst, N.J. Snelling, G.S. Odin and W. B. Harland for valuable reviews of the manuscript.Additional details
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- CaltechAUTHORS:20130130-085827823
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2013-01-30Created from EPrint's datestamp field
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2021-11-09Created from EPrint's last_modified field