A palynologic study of the lower part of the Samish Bay section of the Chuckanut Formation in northwestern Washington has been made to determine the age of these rocks and to interpret the nature of the source flora and environment of deposition.

The Chuckanut Formation is a series of strongly folded, terrestrial sandstones and shales. On the basis of plant megafossils, this formation has previously been assigned an age of Late Cretaceous to early Eocene. Only the lower 5100 feet of the approximately 9500-foot section of the Chuckanut Formation along Samish Bay are adequately represented by the 22 samples reported on in this study.

Seventy-nine palynomorphs are illustrated here. Of these, 19 have been used to zone the lower 5100 feet of strata into three parts. This zonation is based on changes in relative frequency and the stratigraphic ranges of these palynomorphs. It is demonstrated that these changes were brought about by changing environmental conditions during the deposition of the sediments.

An age of late Late Cretaceous to early Eocene is indicated for the lower 5100 feet of the Chuckanut section exposed along Samish Bay, on the basis of analysis of the palynomorphs.