Abstract

The Albian–Cenomanian of Orphan Knoll yielded unrecrystallized, unheated, autochthonous glauconite. K/Ar ages for the Lower Cenomanian samples are 100, 91, and 105 Ma (average 99), and the K/Ar age for one Upper Albian (Vraconian) sample is 96 Ma. The non-sequential results do not allow for great confidence in a precise boundary age. However, the data can be read to support the widely used assumption of −100 Ma as the age for the Albian-Cenomanian = Early-Late Cretaceous boundary.

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