Lake-level fluctuations and paleovegetation during the Houghton phase of glacial Lake Minong

The Houghton phase was a brief period of low water in the glacial Lake Minong (ancestral Lake Superior) basin during the early-mid Holocene. Previous lake-level reconstructions link the onset of the Houghton phase to the cessation of meltwater inflow and the formation of a stable lake level controlled by the St. Marys River bedrock sill. New stratigraphic evidence and radiocarbon dates from the Thunder Bay (Ontario, Canada) region point to a more complex paleohydrological history during this time. Specifically, we reconstruct a lowstand from > 9100 to 8900 cal yr BP that was followed by an increase in sedimentation and base level between ~ 8900 and 8700 cal yr BP, and a second low water period beginning ~ 8700 cal yr BP. Although in need of further testing, these rapid oscillations in the lake level likely reflect the varying contributions of meltwater inflow and high rates of evaporation to the water budget of glacial Lake Minong. Strandline evidence of the first lowstand may have been eroded or buried by the 8900 cal yr BP transgression, and the second lowstand was synchronous with closed basin conditions in the other Laurentian Great Lakes. Paleoecological (pollen, wood identification, plant macrofossil) analyses of organic deposits formed during the lowstands also yield exceptionally detailed ‘snapshots’ of the earliest biological communities that colonized the lake margin.