Geology and environmental significance of sediment distributions in an area of the submerged Niagara escarpment, Georgian Bay

Abstract

The study site covers a spur of the submerged Niagara escarpment and part of the Flowerpot basin of Georgian Bay. Bedrock outcrops occur on islands and shoals but much of the area is covered by glacial till (10–20 m thick). Glaciolacustrine clay occurs in thin patches on the spur; in the deepest parts of the area, however, it is nearly 70 m thick. The distributions of Recent sediments which comprise lag-gravels, sands and silty clays, reflect major postglacial lake level changes in the Huron — Georgian Bay basin.

Sediment geochemistry in Georgian Bay is similar to many other pans of the Great Lakes but calcium charbonate levels are lower than expected, except in some deposits of gaciolacustrine clay. There is little evidence of anthropogenic impact in the content of trace metals, although Pb likely includes a portion derived from atmospheric loading; Hg is usually present at very low levels but there arc anomalously high values in some deepwater modern muds.

In the bottom sediment habitat of modern benthos, the distribution of chironomids seems to reflect silt content. Oligochaetes are least in areas of thin Recent mud or exposed glaciolacustrine clay. Pontoporeia and sculpins are most numerous at depths between 50–110 m. Bottom tracks and other bed marks cover extensive areas of the deepwater lake sediments.