Abandonment chronology of glacial Lake Agassiz's northwestern outlet

摘要

Spillway scour lakes and basins in northwestern Saskatchewan were cored to determine when the spillways were abandoned. The cores contained the target contact of organic muck (gyttja) overlying inorganic sand or silty-clay rhythinites New AMS radiocarbon dates on terrestrial macrofossils, in conjunction with previously published and unpublished data from the area, indicate that the spillways were abandoned between 9.07 and 9.59 C-14 kyr BP (10,220-10,8 10 cal yr BP). Of great interest is whether the channels are associated with northwestern drainage from glacial Lake Agassiz. The radiocarbon ages recording spillway abandonment are consistent with previous work, which clairns that overflow through the northwestern outlet ended similar to 9.5 C-14 kyr BP (10,700 cal yr BP); this is consistent with shifting drainage to the southern outlet at this time. The scarcity of dates from the northwestern outlets and other outlets of Lake Agassiz underscores the need to establish a tighter chronological control on outlet switching before outburst flooding frorn Lake Agassiz can be assuined to be the trigger for abrupt climate change. (c) 2006 Elsevier B.V All rights reserved.