Abstracts

was encountered in a single borehole. Multiple radiocarbon age determinations yield ages
range between >52 801 and 37 850 14 C yr BP. Distal bioturbated glaciolacustrine silt and
clay rhythmites passing upward into glacier-influenced rhythmites with interbedded sand
packages (SU5) drape the underlying deposits. This unit is composed of up to 3, possibly
correlatable, coarsening-upward successions up to 120 m thick. In places, there is abundant
ice-rafted debris and sedimentary structures are intensely deformed by subaquatic
slumping. Radiocarbon age determinations bracket SU5 between 37 850 and less than 28
060 14 C yr BP. The stratigraphy is erosively overlain by Late Wisconsin Newmarket Till.
The aforementioned succession is interpreted to record glacial advance during or prior
to the Illinois Episode (SU 1-3) followed by lengthy non-glacial conditions (Sangamon-
Early Wisconsin; SU4). The sharp transition from SU4 to SU5 records dramatic rises in
regional base levels to accommodate deposition of SU5 prior to overriding by glacier ice
during the Late Wisconsin. This succession is comparable to classic ‘type sections’ of Wisconsin
deposits exposed along the Scarborough bluffs.
Sands in SU5 represent significant local to sub-regional aquifers for domestic water supply.
SU4 deposits host significant amounts of groundwater, but commonly contain high levels
of methane and display poor overall water quality. Local coarse-grained units within the
lower glacial complex (SU1-3) host water suitable for domestic supply. Thick regional
aquitard units confine these water-bearing units except along the flanks of large surface
valley features where these strata are exposed.
288 - Geological and hydrogeological models of the ‘Yonge Street’
aquifer, south-central Ontario.
R. Gerber & S. Holysh
Oak Ridges Moraine Hydrogeology Program, Toronto, Ontario, Canada
H.A.J. Russell & D.R Sharpe
Geological Survey of Canada, Ottawa, Ontario, Canada
In the Aurora, Newmarket and Queensville areas of the Greater Toronto Area, south-central
Ontario, municipal water supply is obtained from the ‘Yonge Street aquifer’ (YSA), an informal
name long used to describe relatively deep sand and gravel deposits. These deposits were
previously described as discontinuous, perhaps channelized and possibly associated with buried
bedrock valleys, largely interpreted from data at a few municipal well fields. Despite much
historical and recent geological and hydrogeological work, including numerical groundwater
flow modelling, the fundamental geological and hydrogeological framework (i.e. conceptual
model) for the YSA has not been clearly developed and documented.
Based on high-quality geophysical and geological data (seismic profiles, continuously–
cored, sedimentologically-logged boreholes, downhole geophysics, geological mapping
and 3-D modeling) revised conceptual geological and hydrogeological models of the area
are presented. The data reveal a sedimentary succession (e.g., ~140 m thickness at Aurora)
that is truncated by a number of erosional unconformities characterized by deeply incised
channels, locally extending to bedrock, with a ~NS to NE-SW orientation, both beneath
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