Age of the Fishcreekian transgression

The Fishcreekian transgression is one of a sequence of late Cenozoic marine transgressions recognized on the Alaskan Arctic Coastal Plain. The Fish Creek beds of northern Alaska, which were designated as the type section for this transgression (Carter and Galloway, 1985), contain fossils interpreted as Pliocene in age (2.48 Ma, Repenning et al., 1987; 2.41-2.14 Ma, Brigham-Grette and Carter, 1992). Analysis of the benthic foraminifers in the Fish Creek beds, however, indicates that deposition occurred in the latest Pliocene and early Pleistocene between 1.7 and 1.2 Ma during a "warm" interval which was characterized by climatic conditions similar to the present or slightly warmer where temperatures shifted within a relatively narrow range. The late Pliocene to early Pleistocene benthic foraminiferal fauna is distinctive and can be traced throughout the circum-Arctic region. This fauna is dominated by elphidiums and elphidiellids, particularly E. hannai, E. rolfi, and E. ustulatum. Paleomagnetics, geochemical analyses, and world-wide climatic conditions support the latest Pliocene and early Pleistocene age interpretation for these deposits. Examination of the basis for the older age interpretation and the age of the diagnostic vertebrate, ostracode, molluscan, spore, and pollen species shows that the latest Pliocene and early Pleistocene age for the transgression is well within the limitations imposed by these fossil groups.