Paleoenvironmental significance of foraminiferal biofacies in the glaciomarine Yakataga Formation, Middleton Island, Gulf of Alaska

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Abstract
The 5-km thick Yakataga Formation contains a 6 m.y. record of late Cenozoic, high northern latitude, climatic and glacial history. Formaminiferal biofacies analysis of a 1.25-km section of Pleistocene Yakataga Formation on Middleton Island yields insights into relationships among climate history, paleobathymetry, and specific glaciomarine facies. The biofacies analysis includes a re-analysis of foraminiferal biofacies trends in the modern Gulf of Alaska. The Middleton Island samples contain four major biofacies comparable to the modern ones: 1) Elphidium excavatum clavatum biofacies (inner neritic); 2) Cassidulina norcrossi s.l. biofacies (outer neritic); 3) Uvigerina juncea biofacies (outermost neritic/upper bathyal); and 4) Cassidulina californica biofacies (neritic environments with firm/hard substrates and no net sediment accumulation). Biofacies trends within the Middleton Island sections define distinct paleobathymetric fluctuations with an amplitude of about 100 m. Prominent coquina horizons and boulder pavements within the Yakataga formation contain the Cassidulina californica biofacires, indicating their formation during periods of sediment starvation and winnowing. The deepest (upper bathyal) facies in the Middleton Island sections are normal marine mudstones containing planktonic foraminiferal assemblages with predominantly dextral Neogloboquadrina be associated with climatic warming.