Studies of large collections of mollusks from numerous measured stratigraphic sections in the Gulf of Alaska Tertiary province permit recognition of eleven molluscan zones within the Poul Creek and Yakataga Formations. Correlation of these zones throughout the province illustrates the time-transgressive nature of the boundary of the two formations--a transgression across four molluscan zones between Kayak Island to the west and the Lituya district to the east. The age variation of the base of the Yakataga Formation is from earliest early Miocene to late Miocene. The use of these molluscan zones elucidates the disconformable relation between the two formations and the local absence of entire zones.

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