Sub-bottom profiling and coring of sub-basins along the lower French River, Ontario: insights into depositional environments within the North Bay outlet |
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| Authors: | Gregory R Brooks Barbara E Medioli |
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| Institution: | (1) Geological Survey of Canada, Natural Resources Canada, 601 Booth Street, Ottawa, ON, K1A 0E8, Canada |
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| Abstract: | Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits
preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies
identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are
interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000
and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between
about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent
sedimentation within a ‘large’ lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression,
Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved
within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late
Mattawa-Stanley phase between 9,500–9,300 and 9,000–8,400 cal BP (~8,500–8,300 and ~8,000–7,600 BP), when the water surface
of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP),
the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the
base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the
cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough
low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower
French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold
had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake
occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits
marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional
sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved
pre-9,500 cal BP (~8,500 BP) post-glacial deposits. |
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