POTASSIUM-ARGON AGE OF THE OBISPO FORMATION WITH PECTEN LOMPOCENSIS ARNOLD, SOUTHERN COAST RANGES, CALIFORNIA

1 January 1966

journal article
Published by Geological Society of America in GSA Bulletin

Vol. 77 (4) , 443-446
https://doi.org/10.1130/0016-7606(1966)77[443:paotof]2.0.co;2

Abstract

Fossil pelecypods, Pecten (Amusium) lompocensis Arnold and Pecten (Lyropecten) crassicardo Conrad, were discovered in rhyohtic tuff and breccia of the Obispo Formation, San Luis Obispo County, California. The potassium-argon age of plagioclase obtained from the middle of the tuff is 20.9 ± 1.5 × 10⁶ years. The age of plagioclase in the Morro Rock andesite-dacite volcanic neck is 23.5 ± 1.8 × 10⁶ years.

Keywords

ANDESITE
LUIS
ARNOLD
ARGON AGE
LYROPECTEN
LOMPOCENSIS
OBISPO FORMATION

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