A late Oligocene or earliest Miocene molluscan fauna from Sitkinak Island, Alaska

Abstract

TheN arrow Cape Formation of Sitkinak Island, in the western Gulf of Alaska, contains a marine molluscan fauna of late Oligocene or earliest Miocene age that represents the Juanian Stage [= Echinophoria apta Zone] of the Pacific Northwest (Washington and Oregon) provincial molluscan chronology. The Narrow Cape Formation on Sitkinak Island is older than the type Narrow Cape Formation on Kodiak Island, which contains mollusks referable to the Newportian Stage. The fauna of the Narrow Cape Formation of Sitkinak Island lived in the outer neritic zone in a cool-temperate marine climate. The co-occurrence of taxa with Asiatic, North American, and high-latitude North Pacific zoogeographic affinities makes this fauna especially important for the development of circum-North Pacific chronostratigraphic correlations.