Abstract

Strontium isotope ratios (87Sr/86Sr) calculated from three samples of benthic foraminifers and one mollusc indicate an age range from 23.8 to 27.0 Ma for the Nuwok Member of the Sagavanirktok Formation, eastern North Slope, Alaska. Previous correlations derived paleontologically (foraminifers, ostracodes, and molluscs) for the Nuwork beds have differed greatly (Oligocene to Pliocene), but strontium isotope ratios substantiate the late Oligocene age determined from benthic foraminifers. The results constitute an important test case, illustrating the effectiveness of the strontium isotope method in correlating high-latitude carbonate samples to the standard Oligocene chronostratigraphy. In addition, a sample from the Kugmallit sequence in the Beaufort Sea Edlok N-56 well provided a strontium isotope age estimate of 30.7 Ma. The Edlok sample was paleontologically correlated to just below the early/late Oligocene boundary (30.0 Ma).

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