CGRG Bibliography of Canadian Geomorphology
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Author : Easterbrook, D.J; and Kovanen, D.J.
Date : 1998
Title : New radiocarbon evidence for the ages of two Sumas moraines of the Cordilleran Ice Sheet bween 10,000 and 11,300 14Cyrs B.P.
Publication : 1998 Annual Meeting, Geological Society of America, Toronto, October 26-29. Abstracts with Program.
Issue :
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Abstract
Thirty new 14C dates bracket the age of the outer of two Sumas moraines of the Cordilleran Ice Sheet between 11,300 and 11,000 14C-yrs BP and the inner moraine between10,500 and 10,000. Ice-contact drift of the outer Sumas moraine is younger than underlying glaciomarine drift dated at 11,300 14C-yrs. A 7-km-long, peat-filled, ice-marginal, outwash channel cuts through the outer moraine. Basal peat ~10 m deep in the channel yielded ages of 10,500 ± 80, 10,980 ± 250, and 11,037 ± 72, 14C-yrs BP. Peat deposition must have begun soon after abandonment of the channel, so ice must have retreated from the outer moraine close to 11,000 14C-yrs BP. Basal peat in another older Sumas outwash channel incised 33 m glaciomarine drift 20 km south of the US-Canadian border yielded 14C ages of 10,765 ± 70, 10,815 ± 75, 11,080 ±100, and 11,113 ± 77 14C-yrs BP, and basal peat 10m-deep in a kettle was dated at 10,400 ± 85 14C-yrs BP. Everson glaciomarine drift beneath outwash channel and kettle is younger than 11,500 14C-yrs BP. Thus, the older Sumas here is younger than 11,500 14C-yrs and had retreated by ~11,000 14C-yrs BP. The inner Sumas moraine lies ~15 km east of the outer Sumas moraine. Because the older Sumas readvance had retreated from its distal position by 10,500 14C-yrs BP., the inner moraine must be younger than 10,500. 14C dates of 10,245 ± 90, 10,265 ± 65, and 9,850 ± 75 14C-yrs BP from basal peat in a kettle left by ice buried by outwash from the younger Sumas moraine and dates of ~10,000 14C-yrs BP from meltwater channels originating from the inner Sumas moraine indicate that Sumas ice retreated from the inner moraine ~10,000 14C-yrs ago. Thus, the younger Sumas moraine was deposited during the Younger Dryas.
Bibliography of Canadian Geomorphology