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Sedimentary
Geology, 47 (1986), 27-52
PLEISTOCENE
GLACIO-LACUSTRINE DELTAIC DEPOSITS OF THE SCARBOROUGH FORMATION, ONTARIO, CANADA
R.I.
KELLY and I.P. MARTINI
Department
of Land Resource Science, University of Guelph, Guelph, Ont. N1G 2W1 (Canada) ¡¡  The
late Pleistocene Scarborough Formation of the Lake Ontario Basin represents a
lacustrine-deltaic sequence strongly affected by a nearby glacier. It shows
gradual upward coarsening and thickening of layers from varve-like, clay-rich
rhythmites at the base to channelized cross-bedded sands at the top. Thick,
lensing, "massive" layers (Cm) of silty sand are found interstratified
with thin layers of silt and clay in the lower and middle parts of the sequence.
These" massive" layers were probably formed by subaqueous gravity
flows of material in part derived directly from a glacier. Absence of pebbles
and of other features such as glacial silt-pellets suggests dispersal away from
the foot of the glacier rather than deposition under floating ice. Varve-like
rhythmites, pollen and insect fauna indicate subarctic to arctic climatic
conditions at the time of sediment deposition. The large amount of sand in the
upper part of the formation is best explained as derived from active outwash
fans. Similar fans were formed during the last deglaciation in southern Ontario
and can be observed on the landscape.
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