CGRG Bibliography of Canadian Geomorphology
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Author : Barnett, P.J.; and Delorme, L.D
Date : 2007.
Title : Record of late-glacial lake level fluctuations in the Lake Nipigon basin, northwestern Ontario, Canada.
Publication : Yellowknife 2007. Annual Conference of the Geological Association of Canada - Mineralogical Association of Canada. May 23-25, 2007. Yellowknife, Northwest Territories, Canada.
Issue :
Page(s) :
Abstract
River banks along the Little Jackfish River, north of Lake Nipigon, expose sediment sequences that record large fluctuations of lake level in the Lake Nipigon basin during ice-marginal recession of the Laurentide Ice Sheet. Two fining-upward cycles of rhythmically-bedded sediments are separated by a thin bed of marl. The lower part of the upper sequence, marl and upper part of the lower fining-upward sequence are fossil-bearing. Molluscs, ostracodes and oogonium and carbonate casts of the algae Chara occur in these sediments. Fourteen species of ostracodes were identified from a 105 cm interval that bracketed the marl bed. The silts of the uppermost part of the lower fining upward sequence contain ostracode assemblages that indicate the presence of a large cold-water lake environment. Subsequently, there was a decrease in water level, warming and an increase in the content of fluvial ostracode species that corresponds to the presence of Chara, a shallow water algae. The base of the upper fining-upward sequence contains ostracodes that indicate a renewed high-water stage of the lake. The sequence of sediments and the fossils indicate that a large ice-contact glacier-fed lake fronted the northward receding ice margin. The level of the proglacial lake lowered until very shallow water existed at the site until after marl formation. Water levels then rose rapidly flooding this locality. The sequence of lower sediments is believed to represent ice marginal retreat, to the Nakina I moraine (deep water event) and beyond, to uncover an eastern outlet (the Pic River via the Mullet outlet) that allowed for the bypass of Lake Agassiz waters via the Whiteclay Lake-Ogoki channel, a proposed outflow route. This resulted in the low water stage in the Nipigon basin. A readvance of the ice margin to the Nakina moraine II closed the eastward outlets and channel, once again raising the water level in the Nipigon basin; producing the upper fining-upward sediment sequence.
Bibliography of Canadian Geomorphology