Foraminiferal sequence biostratigraphy and seismic stratigraphy of a tectonically active margin; the Yakataga Formation, northeastern Gulf of Alaska

Abstract

Upper Miocene through Recent glacial-marine deposits of the Yakataga Formation, which underlie the northern Gulf of Alaska continental shelf, are the focus of an integrated study to understand the depositional and climatic history of the upper Cenozoic Gulf of Alaska. Biostratigraphic, lithologie, and multichannel seismic data were integrated in a sequence stratigraphic analysis of the Yakataga continental margin. A paleontologically based approach to sequence stratigraphy, known as sequence biostratigraphy, was used to define eight seismic stratigraphic sequences on this tectonically active, glaciated continental margin. Foraminifera provide information on the age, paleoenvironments, and paleoclimates of strata within these eight sequences. Lithologic evidence is used to infer the presence and influence of tidewater glaciers.The three oldest sequences, arbitrarily labeled Brown, Red, and Orange (early Pliocene, mid-Pliocene, late Pliocene, respectively), were deposited in mainly outer neritic through upper bathyal environments. Planktic foraminiferal assemblages show that sea surface temperatures during deposition of these sequences were mainly cool temperate in the Gulf of Alaska at this time, yet benthic assemblages indicate cold bottom waters and dropstones indicate glacial-marine sedimentation during the late Pliocene.The five youngest sequences (labeled Yellow, Green, Aqua, Blue, Violet), which are Pleistocene to Recent in age, were deposited in deeper environments on average (upper bathyal to middle bathyal) than the older sequences. Glacial-marine sedimentation was common during deposition of these sequences (abundant dropstones) and foraminiferal assemblages indicate both cold sea surface and bottom water temperatures.