An investigation into the nature of the layering of deep-water sediments in two eastern Ontario lakes

The sediments deposited beneath the thermocline in certain lakes are finely banded with alternating dark and light bands. Most workers have assumed this banding to be an annual phenomenon, with the light bands representing summer deposits and the dark bands representing winter deposits. The microfossils contained in each layer, particularly pollen and diatoms, should represent the flora of the time of year at which the sediment was deposited. If this banding is annual, different species will be consistently associated with particular parts of a pair of layers.Pollen and diatom contents of individually separated dark and light layers from different depths of a core were analyzed. Pollen produced in late spring and early summer, and summer forms of diatoms, are associated with light layers whereas pollen produced early in the year, and winter diatoms, are associated with dark layers. The junction between layer types and the position of fossils in each layer were studied by observing sections cut from wax impregnated sediment blocks. The light layers contain much more calcareous material than the dark layers. From all evidence accumulated it is concluded that the layering is annual.