ABSTRACT: Paleobiogeographic Implications of Middle and Late Cretaceous Molluskan Assemblages from Alaska
ELDER, WILLIAM P., U.S. Geological Survey, Menlo Park, CA
Cretaceous assemblages of Albian and younger age occur widely in Alaskan basins postdating Early Cretaceous arc accretion in western Alaska and contractional deformation in the Brooks Range of northern Alaska. These fossils are used to interpret timing of marine deposition and development of migration corridors. Comparisons are hampered, however, by the general lack of synchronous marine deposition between basins. For example, marine deposition in the Yukon-Koyukuk basin ceased in the late Albian to early Cenomanian and ended in the Santonian, and deposition on the Alaska Peninsula ceased in the late Albian and resumed in the late Santonian.
North Slope assemblages resemble those of the Western Interior of North America. Many components of these assemblages also are
present in Albian rocks of the Yukon-Koyukuk basin, but are lacking from Cenomanian rocks of the Kuskokwim basin. This suggests closure of a migration corridor between the north Pacific and the Arctic Oceans between these ages. Assemblages of the Kuskokwim basin contain fossils characteristic of the North Pacific with the occasional addition of some north Atlantic forms. Assemblages elsewhere in southern Alaska contain predominantly North Pacific taxa also found to the south along the west coast of North America. However, Alaskan assemblages are more depauperate than those to the south, suggesting a temperature related shift in biota between southern Alaska and the Great Valley-type assemblages found from Vancouver Island to southern California.