Late Pleistocene Littoral Deposits in the Deming Sand at Bellingham Bay, Washington, and Their Implications for Relative Sea…

Recent mass wasting of sea cliffs along Bellingham Bay in Northwest Washington has exposed late Pleistocene littoral deposits in the Deming sand, which is underlain by Kulshan glaciomarine drift (gmd) and overlain by Bellingham glaciomarine drift (Easterbrook 1963). Marine shells in the Kulshan gmd were dated at 12,210 ± 80 14C-yrs B. P. and marine shells in the Deming sand were dated at 11,760 ± 85 and 11,685 ± 85 14C-yrs B. P. Marine shells in the Bellingham gmd were dated at 12,150 + 210 14C-yrs B. P. Fossiliferous Kulshan glaciomarine drift is overlain by 11.5 m of well-sorted, medium-grained, horizontally bedded and cross-bedded sand and sandy gravel with two silt and clay interbeds 0.57 m and 0.88 m thick. Evidence for a littoral environment includes (1) many cross-bedded, pebbly-sand beds containing abundant, abraded shells, abraded worm tubes, and shell fragments, (2) armored mud balls, (3) thin layers of concentrated garnet/magnetite sand common to beaches and 4) thick, well-indurated silt and clay characteristic of tidal flat deposits. All of these features mirror those in a shallow marine environment undergoing tidal phases and shoreline processes. Fossiliferous Bellingham glaciomarine drift approximately 11 meters thick caps the section. The exposure of Deming sand between the Kulshan and Bellingham gmds at Bellingham Bay mimics the stratigraphic order at the Everson type locality ca. 45 km to the east, which corroborates Easterbrook's (1963) hypothesis that the Deming sand throughout Whatcom County is fluvial in origin. This relationship plays a central role in the complex history of relative sea level changes. The Deming sand fixes relative sea level at approximately 10-20 m above present sea level, and because the Bellingham and Kulshan gmds occur at present elevations of ~ 100 and 200 m, that means relative sea levels must have fluctuated by at least approximately 100 m from the Kulshan to the Deming, and at least 200 m from the Deming to the Bellingham. Thus, the inference that sedimentation at the Everson type section was solely glacial (Croll, 1980; Dragovitch et al., 1997) with no fluctuations of local relative sea level is challenged.