SYNCHRONIETY OF MULTIPLE YOUNGER DRYAS AND ALLERøD MORAINES IN THE FRASER LOWLAND WITH LATE PLEISTOCENE MORAINES IN NORTH AMERICA, EUROPE, NEW ZEALAND, AND SOUTH AMERICA

Following emergence of the Fraser Lowland from Everson glaciomarine conditions (12,500-11,700 ¹⁴C yrs BP), a lobe of the Cordilleran Ice Sheet (CIS) advanced across the lowland from the Fraser Canyon to Bellingham during the Sumas Stade. At least eight end moraines were built successively across the lowland, each marking a position of ice advance or stillstand. The outermost of these moraines cut across multiple, well-defined marine shorelines 100-540 ft above sea level that lie upon Bellingham glaciomarine drift, conclusively proving that none of the Sumas moraines could possibly be lateral equivalents of Everson glaciomarine drift.

The age of end of the underlying Bellingham glaciomarine episode is well established by 23 dates from wood that average 11,729 ¹⁴C yrs BP and 18 dates from shells that average 11,726 ¹⁴C yrs BP, so all of the Sumas moraines are younger than that. A date of 11,413 ± 75 ¹⁴C yrs BP was obtained from the base of a bog on an intermediate Sumas outwash fan, so the oldest Sumas moraines must be between 11,700 and 11,400 ¹⁴C yrs BP. Dates of 11,113 ± 77, 11,080 ± 100, 10,815 ± 75, and 10,765 ¹⁴C yrs BP were obtained from basal peat in outwash channels of the Tenmile Creek moraine. A date of 10,980 ± 250 ¹⁴C yrs BP from basal peat limits the age of the Lynden outwash plain. Dates of 10,265 ± 65 and 10,245 ± 90 ¹⁴C yrs BP from basal peat in a kettle on outwash from the Clearbrook moraine indicate that the age of the youngest Sumas moraine is slightly older than that. Fluted topography southwest of the youngest Sumas moraine was made by glacial outburst floods when an ice-dammed lake in the Chilliwack Valley in Canada drained suddenly, releasing large volumes of water across the lowland.

The ¹⁴C chronology allows correlation of the Sumas moraines with moraines in the Cascade Range, Rocky Mts., Canada, Scandinavia, the European Alps, New Zealand, South America and elsewhere.