MICROFOSSIL ANALYSIS OF LATE PLEISTOCENE PUGET LOWLANDS, WHATCOM COUNTY, WASHINGTON

The regional geology of the Pacific Northwest has been shaped by the growth and decay of the Cordilleran ice sheet throughout the Pleistocene. Characterizing the behavior of the ice sheet and pinpointing the timing of each glacial advance and retreat is complex, and glaciologists have relied on a combination of sedimentological and geomorphic analyses to piece together the geologic history of the region. In this ongoing study, we are using microfossil analysis to help resolve some of these outstanding biostratigraphic and paleoenvironmental questions. Microfossils can be used as paleoenvironmental proxies (i.e., identifying marine, estuarine or terrestrial environments) and can be used to measure changes in sea level and ocean chemistry.

Our analysis included field mapping and sample collection at two late Pleistocene Puget Lowlands localities in Whatcom County, WA and laboratory analysis of the microfossil assemblages preserved at each locality. Localities included Semiahmoo Peninsula in Blaine, WA and Locust Beach in Bellingham, WA, both of which are comprised of a collection of glacial and non-glacial sediments from periods of glaciation and interglaciation.

At each locality, we measured and logged a detailed stratigraphic section and then sampled sediment systematically in predetermined volumes in order to avoid over representation of any one type of microfossil as well as to make the most of the limited sediment volume. Sediment samples were processed and microfossils were isolated, identified, and counted. Subsamples intended for the study of carbonate microfossils, including foraminifera, ostracods, and pteropods, were prepared primarily utilizing filters and sieves. Subsamples intended for the study of calcareous microfossils, including coccoliths, prepared primarily utilizing an ultrasonic bath for the disintegration and deflocculation of the sediment. Subsamples intended for the study of siliceous microfossils, including diatoms, chrysophytes, and dinoflagellates, prepared primarily utilizing chemical dissolution. Upon completion of this study, we hope to provide a greater understanding of the glacial and interglacial environments of the Puget Lowlands during this important time period.