Constraints on paleolake levels,spillways and glacial lake history,north-central Ontario,Canada |
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| Authors: | Shawn R Slattery Peter J Barnett Darrel G F Long |
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| Institution: | (1) Lake Simcoe Region Conservation Authority, 120 Bayview Parkway, Newmarket, ON, L3Y 4X1, Canada;(2) Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, ON, P3E 6B5, Canada;(3) Department of Earth Science, Laurentian University, Sudbury, ON, P3E 2C6, Canada |
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| Abstract: | The recognition of ice-marginal deltas constructed during the formation of the Nakina II moraine and a previously unrecognized
spillway, in the vicinity of Longlac, northern Ontario, indicates that existing concepts of ancestral lake level history and
drainage systems in the Lake Superior–Lake Nipigon region is inadequate. Based on isostatically corrected digital elevation
maps, ice-marginal deltas of the Nakina II moraine probably formed at the level of glacial Lake Minong, most likely Minong
III, and not glacial Lake Nakina as has been commonly suggested. In addition, the presence of a spillway near Longlac indicates
that lake water drained southward through the Mullet Outlet–Pic River system immediately following ice-marginal retreat from
the Nakina II moraine and not eastward as previously proposed. Architectural-element analysis of exposures within the spillway
indicates hyperconcentrated outbursts of meltwater produced thick channel-fill elements during flood conditions with peak-velocities
exceeding 3 m/s. Subsequent retreat of ice from the Pic River valley to the east, may have allowed waters of Lake Agassiz,
Lake Barlow–Ojibway, or both, to drain into post-Minong lake levels in the Lake Superior basin. These findings place major
constraints on previously proposed concepts of northeastern or eastern outlets of Lake Agassiz. |
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| Keywords: | Nakina moraines Lake Nakina Lake Minong Lake Agassiz Lake Ojibway Mullet Outlet Pic River |
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