Foraminiferal Biofacies Analysis of the Yakataga Formation, Icy Bay, Alaska: Insights into Pliocene Glaciomarine Paleoenvironments of the Gulf of Alaska

Abstract

The Upper Miocene to Pleistocene Yakataga Formation of the Gulf of Alaska provides a 5 km thick record of episodic glacially-influenced marine sedimentation. The Pliocene Yakataga Fm. is exposed along western Icy Bay and records the return of glaciomarine deposition in the Gulf of Alaska, after the initiation of glaciation in the Late Miocene, and the onset of major northern hemisphere glaciation by the Late Pliocene. Analysis of foraminifera found in the Yakataga Fm. provides the basis for the interpretation of paleobathymetry and depositional environments from these rocks. Quantitative analysis is used to define eight paleoenvironmentally significant biofacies: (1) Elphidium excavatum clavatum biofacies (inner neritic), (2) Haplophragmoides spp. biofacies (outer neritic--mudline), (3) Cassidulina cf. C. teretis biofacies (outer neritic), (4) Uvigerina juncea biofacies (uppermost bathyal), (5) Elphidiella hannai biofacies (innermost neritic), (6) Epistominella pacifica biofacies (upper bathyal), (7) Cassidulina cf. C. limbata biofacies (outer neritic), (8) Nonionella miocenica biofacies (outer neritic). Paleobathymetric zones defined by these biofacies, which are constrained by modern Gulf of Alaska faunal relationships, indicate bathymetric fluctuations on the order of 100 m in the Icy Bay section. Mixing of biofacies due to downslope transport is common. Analyses of paleobathymetry, benthic formaminiferal biofacies, and sedimentology are usedmore » to interpret depositional environments ranging from innermost neritic to upper bathyal for these rocks.« less