Quaternary paleoecology and stratigraphy of the sea cliffs, western Olympic Peninsula, Washington

Abstract

The sea cliffs of the western Olympic Peninsula are composed chiefly of discontinuous beds of unconsolidated gravel, sand, silt, and peat of Pleistocene age. Two lower stratigraphic units, the “Steamboat Creek gravel” and “Joe Creek silt”, were deposited probably during the Puyallup Interglaciation; the upper unit, the “Kalaloch silt”, was deposited during an interval that extends from Salmon Springs Glaciation through Fraser Glaciation. Radiocarbon dates of the Kalaloch silt range from about 17,000 to > 48,000 BP. Pollen analysis and stratigraphic correlation of the sea cliff sediments indicate that the present vegetation of the Olympic Peninsula has existed in this part of western Washington since the Puyallup Interglacial. During the Puyallup, the low elevation Tsuga heterophylla-Picea forest or its seral stages were predominant. During subsequent glaciations the low elevation forest was replaced by montane or alpine plant communities in areas near the ice front. At sites farther removed from glacial termini, low elevation forest apparently persisted, thriving in centers from which constituent species spread during interstadials.