Palynology of Quaternary deposits of the lower Bogachiel River area, Olympic Peninsula, Washington

Abstract

The palynology and radiocarbon chronology of an interstadial peat exposure and a bog located in the lower Bogachiel River drainage area provide further basis for the reconstruction of Quaternary vegetation and environments of the western Olympic Peninsula. The interstadial peat with a finite age of 59 600 ± 700 a BP at the top is overlain by till, and the bog situated distally in relation to an end moraine was formed before 30 000 ± 800 a BP following emplacement of the moraine. Pollen spectra of the interstadial peat are of subalpine forest species succeeded by tundra – park tundra types. The pollen record of the bog shows rising proportions of arboreal species in the lower part consisting of mountain hemlock and pine at the beginning and later of western hemlock. Subsequently, there follows in sequence a return of mountain hemlock and pine, culminating around 20 000 a BP, domination by tundra – park tundra types, and finally a rise of Sitka spruce to a maximum in association with alder. After about 10 000 a BP, alder reaches peak proportions and is followed by a succession of lowland arboreal species characterized chiefly by western hemlock. The pollen stratigraphy of these deposits correlates with a previously established biostratigraphic scheme for Quaternary deposits in western Washington. Data indicate one or more glacier advances predating 30 000 and postdating 59 600 a BP in the lower Bogachiel Valley.