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January 1, 1977Geological Magazine

Radiometric age of the Monograptus cyphus graptolite zone in Southeastern Alaska — an estimate of the age of the Ordovician—Silurian boundary

Marvin A. Lanphere M. Churkin G. Donald Eberlein

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Abstract

Summary K—Ar age measurements on Esquibel Island, southeastern Alaska yield a minimum age of about 433±3 Ma for the Zone of Monograptus cyphus of the Lower Silurian. An age of approximately 435—437 Ma is estimated for the Ordovician—Silurian boundary.

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Lanphere et al. (1977) studied this question.

synapsesocial.com/papers/6a86675469f19aa1782fd041 https://doi.org/10.1017/s0016756800043387

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