Sedimentation patterns and facies geometries on a temperate glacially-influenced continental shelf: the Yakataga Formation, Middleton Island, Alaska

The 5 km thick Yakataga Formation of the Gulf of Alaska provides the longest and most accessible record of late Cenozoic glaciation in the world. The formation consists of interbedded marine and glacimarine sediments of late Miocene to Holocene age and is well exposed on offshore islands and in the coastal mountain ranges as a result of the convergent margin setting of the Gulf. About 1.3 km of early Pleistocene Yakataga Formation sediments are exposed on extensive intertidal platforms around Middleton Island which is sited close to the modern continental shelf edge. Variably graded gravels and sands at the base of the Middleton Island succession were deposited by sediment gravity flows and represent the fill of a large submarine channel. The remainder of the succession is dominated by thick (up to 100 m) planar tabular units of fossiliferous diamict containing a series of striated boulder pavements and shell-rich beds (coquinas). The Yakataga Formation on Middleton Island contains a rich record of changing palaeobathymetry and ice volumes in the Gulf of Alaska. -from Authors