Spatially discontinuous modern sedimentation in Georgian Bay, Huron Basin, Great Lakes |
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Authors: | Francine M G McCarthy John H McAndrews Steve M Blasco Sarah H Tiffin |
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Institution: | (1) Department of Earth Sciences, Brock University, 500 Glenridge Ave., St. Catharines, ON, L2S 3A1, Canada;(2) Departments of Botany and Geology, University of Toronto, Toronto, ON, M5S 3B2, Canada;(3) GSC-Atlantic, Natural Resources Canada, Bedford Institute of Oceanography, Dartmouth, NS, B2Y 4A2, Canada;(4) Present address: School of Geography and Geology, McMaster University, Hamilton, ON, L8S 4M1, Canada |
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Abstract: | High-resolution seismic reflection profile data show that the modern sediment cover (over the last 150 years) in Georgian
Bay is thin and spatially discontinuous. Sediments rich in ragweed pollen, largely derived from siltation linked to land clearing
and European settlement, form a thin, discontinuous veneer on the lakebed. Much of the lakebed consists of exposed sediments
deposited during the late glacial or early postglacial. Accumulation rates of modern sediments range from < 0 mm/year (net
erosion) to ∼3.2 mm/year, often within a few hundred metres spatially. These rates are much lower than those reported for
the main basin of Lake Huron and the other Great Lakes, and are attributed to the low sediment supply. Only a few small rivers
flow into Georgian Bay, and most of the basin is surrounded by bedrock of Precambrian gneiss and granite to the east, and
Silurian dolostone, limestone and shale to the west. Thick deposits of Pleistocene drift, found on the Georgian Bay shoreline
only between Meaford and Port Severn, are the main sediment source for the entire basin at present. Holocene to modern sediments
are even absent from some deep basins of Georgian Bay. These findings have implications for the ultimate fate of anthropogenic
contaminants in Georgian Bay. While microfossil assemblages in the ragweed-rich sediments record increased eutrophication
over the last 150 years, most pollutants generated in the Georgian Bay catchment are not accumulating on the lakebed and are
probably exported from the Bay. |
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Keywords: | Great Lakes Georgian Bay/Lake Huron Sedimentation Siltation Pollen |
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