THE DEGLACIATION CHRONOLOGY OF THE FORT MCMURRAY AREA, ALBERTA: IMPLICATIONS FOR MELTWATER DRAINAGE

New radiocarbon ages and analyses of DEM data from the Fort McMurray, Alberta area provides insight into deglaciation and meltwater drainage events in the area. From the analyses of DEM's and aerial views from a helicopter, a series or five ice margin positions have been identified and show a stair-step retreat pattern. Chronology is assigned to these ice margin positions from a network of 41 core sites from small lakes associated with moraines in the region. Five key sites document the retreat of an ice lobe emanating from the Lake Athabasca lowland. Preliminary radiocarbon dating results, pending additional analysis still in progress, indicate that deglaciation was later than originally supposed by Dyke et al., (2003) and Tarasov and Peltier (2005). Chronology of the moraines is presented from oldest (furthest to the southwest) to the youngest (northernmost). The oldest dated ice margin is from Don's Lake located on a moraine just south of the Birch Mountains and west of the Athabasca River, which indicates that this moraine formed prior to about 10,460 +/- 65 14C B.P. (ETH-30586). The next oldest ice margin, south of Fort McMurray, named the Stony Mountain Moraine has a minimum date of 10,030+/- 75 14C B.P (ETH-30177). The next ice margin with very lobate moraines just west of the Athabasca River, and is dated at 9,860 +/- 65 14C B.P. (ETH-30594) with a second date of 9,850 +/- 65 14C B.P. (ETH-30593) from a lake further up on the moraine. The next ice margin known informally as the Firebag Moraine, which also includes the Fort Hills, has a minimum date of 9,595 +/- 70 14C BP (ETH-30174). The youngest ice margin yields a date of 9,510 +/- 70 14C B.P (ETH-30587) from a lake located on the crest of the moraine. Ice margin recession in the study area consists of moraines spanning 1000 radiocarbon years. No evidence of a readvance was observed. The ice margin geometry when at the Firebag Moraine would have dammed the Athabasca valley, preventing any meltwater drainage through the Clearwater Spillway, catastrophic or otherwise until about 9,595 +/- 70 14C B.P. The well dated, sequential, ice margin chronology in northeast Alberta constrains the timing of potential meltwater drainage through the Clearwater Spillway, indicating that it is too late for it to be a source of freshwater to trigger the Younger Dryas cold period.