Advance and Retreat of Cordilleran Ice Sheets in Washington, U.S.A.

Abstract

Cordilleran Ice Sheet glaciations show characteristic patterns of advance and retreat, consisting of (1) advance out outwash, (2) glacial scouring, (3) deposition of till, (4) deposition of recessional outwash south of Seattle in the southern Puget Lowland, glaciomarine drift in the northern lowland, and eskers, kames, and small moraines on the Columbia Plateau. Radiocarbon dates show that the Puget and Juan de Fuca lobes advanced and retreated synchronously. The Puget lobe backwasted to Seattle by 13.4-14 ka yrs BP, where the thinning ice floated in seawater northward to Canada by 13 ka yrs BP depositing glaciomarine drift contemporaneously over 18,000 km2. Compelling evidence against the backwasting, calving, terminus model for the origin of the glaciomarine drift includes: 1) abundant 14C dates demonstrate simultaneous deposition of glaciomarine drift over the entire area; 2) stagnant-ice deposits closely related to glaciomarine drift are not consistent with an actively-calving, backwasting terminus; 3) irrefutable evidence for the nonmarine origin of Deming sand shows that Cordilleran ice was absent immediately prior to deposition of the overlying glaciomarine drift. The pattern of events in the northern Puget Lowland includes: 1) glacial loading under 1800 m of ice during the Vashon maximum; 2) rapid glacial thinning and floating of the ice deposited Kulshan glaciomarine drift 12-13 ka yrs BP; 3) emergence and deposition of fluvial Deming sand 11.5 ka yrs BP; 4) resubmer-gence and deposition of Bellingham glaciomarine drift up to -200 m, well beyond global eustatic sea level rise; 5) emergence 10.5-11.5 ka yrs BP and deposition of Sumas outwash on Bellingham glaciomarine drift; 6) Holocene eustatic sea level rise kept pace with isostatic rebound, thus, post-Sumas marine terraces are absent.

Contrasting Quaternary Histories in an Ecologically Divergent Sister Pair of Low-Dispersing Intertidal Fish (Xiphister) Revealed by Multilocus Dna Analysis

“…While it is suggested that X. atropurpureus persisted throughout its present range, this history is not necessarily supported by nongenetic evidence. For instance, the observed high level of endemic genetic diversity found within Strait of Georgia populations of X. atropurpureus (Orcas and Campbell River) is counter to evidence suggesting that the Strait of Georgia was completely glaciated at the LGM (Clague 1983;Pielou 1991;Easterbrook 1992). The control-region alleles found in the X. atropurpureus Orcas population make up a clade that is almost exclusively found in this inland waterway (with the exception of one allele found on the outer coast).…”

Habitat characterization of a tidal energy site using an ROV: Overcoming difficulties in a harsh environment

“…The northern Puget Lowland, where the turbine site is located, is an extensive topographic N-S oriented trough scoured by the ice. The Cordilleran Ice Sheet advanced into and retreated from or stagnated in western Washington six times or more during the Pleistocene (Easterbrook, 1992(Easterbrook, , 1994Fig. 1a).…”

Postglacial sediment budget of Chilliwack Valley, British Columbia

“…The Puget Lobe of the Cordilleran Ice Sheet reached its maximum extent 14 500-15 000 14 C yr ago (Easterbrook, 1992;Porter and Swanson, 1998;Booth et al, 2003). At that time, Chilliwack Valley was covered by about 2 km of glacier ice (Clague, 1989), and the terminus of the Cordilleran Ice Sheet in Puget Lowland was 250 km to the south-west.…”