NO-MAN'S-LAND AND THE HISTORY OF NORTHWEST DRAINAGE FROM GLACIAL LAKE AGASSIZ

Viewed as the wild-card of drainage outlets from Lake Agassiz, numerous researchers have proposed that Lake Agassiz drained to the northwest, delivering meltwater to the Mackenzie River system across a sub-continental drainage divide in northern Saskatchewan, Canada. Reconstructions have been approached from two different directions. The first is by tracing strandlines and projecting water planes from the main, or ‘known’ Agassiz basin northwestwards into the upper Churchill River basin. The second is by using the well-developed Clearwater-lower Athabasca River spillway and catastrophic flood deposits within and along the upper edge of the spillway as evidence for a major flood, and then tracing strandlines at the head of the spillway southeastward towards the Lake Agassiz basin. The meeting point for these two approaches is a desolate location near the headwaters of the Churchill River on the Canadian Shield. In this general area are the Wycherely channels and boulder deposits recording flow from the east. Glaciolacustrine sediments and strandlines have been described from higher elevations adjacent to this area, but whether they record a local or regional glacial lake, or even glacial Lake Agassiz has remained conjectural. It is known that the Campbell Beach strandlines are the only strandlines from the Agassiz basin mapped into northern Saskatchewan, and that do project above the Wycherely channels. This opens the possibility that Lake Agassiz did drain to the northwest at about 9400 ¹⁴C yr BP (~10.5 ka cal), the age of the Upper Campbell Beach. The timing of deglaciation in north-central Saskatchewan is poorly known, but recent data from northwest Saskatchewan and northeast Alberta indicates deglaciation after the Younger Dryas chronozone, after which water could drain into the Mackenzie system. In summary, extant geomorphic and chronostratigraphic data from either side of the sub-continental drainage divide in northern Saskatchewan does not support possible northwest drainage from glacial Lake Agassiz until ~9400 ¹⁴C yr BP (10.5 ka cal).