CHRONOLOGY OF THE NORTHWESTERN OUTLET REGION OF GLACIAL LAKE AGASSIZ

Livingston and Vibracores were recovered from lakes in northwestern Saskatchewan that were either scour lakes or former basins associated with Lake Agassiz. Wycherley and Flatstone Lakes are just east of the Wycherley channels, a series of outlets that drained Lake Agassiz into Lake Wagtufro (composite of Wasekamio, Turnor & Frobisher Lakes in the upper Churchill River basin). Schmitt and Klap Lakes are scour channels between Lake Wagtufro and the Clearwater River (northwestern outlet spillway). All of the cores contained the target contact of organic muck (gyttja) overtop inorganic sand or rhythmites. Silty-clay rhythmites were recovered from the Wycherley1 and Flatstone Lake cores. About 50 pink rhythmites were counted near the top of the Flatstone core; all other rhythmites were gray or brownish gray in color. Below the rhythmites in the Flatstone core was 1.3m of sand interlaminated and interbedded with the clay. At the base of the core was 0.3m of thinner rhythmites. Beneath rhythmites in the Wycherley1 Lake core 0.4m of sand overlies 0.65m of diamicton. A subbottom acoustic survey of Wycherley Lake revealed little stratigraphy to tie the core stratigraphy to. Poor penetration is attributed to biogenic gas in the organic-rich sediments. Core stratigraphy in Schmitt and Klap Lakes consisted of gyttja over fine sand, with the contacts at 3.93m and 13.1m core depth, respectively. The depth of gyttja in Klap Lake is likely a result of sedimentation during the early Holocene when Wasekamio Lake drained north. Age models from the cores are based on linear sedimentation rates from radiocarbon dates. Dated material consisted of terrestrial macrofossil seeds and spruce needles concentrated over as much as 0.2m of core. The extrapolated 14C ages for the organic/inorganic contact are: 9220BP–Schmitt Lake and 9000BP–Wycherley Lake. These initial results are considered tentative without additional dates to more accurately determine rates of organic sedimentation. However, these results agree well with the previously published basal minimum date from nearby Long Lake of 9120 BP and suggest that the northwestern outlet of Lake Agassiz was abandoned by about 9200 14C BP, or approximately 200 years after the southern outlet.