Geological and geophysical studies of buried valleys and their fills near Elora and Rockwood, Ontario

Buried bedrock valleys are of economic interest for groundwater and engineering studies, and of scientific interest for the sedimentary sequences they may contain. Two buried valleys, about 60 m deep, north and northeast of Guelph, Ontario, are tributary to the major Dundas Valley southwest of Guelph. Located initially from water well data, their locations and geometry were refined with surface geophysics, including very low frequency resistivity, terrain conductivity, resistivity, transient electromagnetic, gravity, and seismic methods. Useful data are obtained roughly in proportion to cost. Cored and rotary holes in the two valleys were followed by geophysical downhole logging with normal electric, spontaneous potential, single-point resistance, calliper, neutron – epithermal neutron, gamma–gamma, and natural gamma methods. Cores revealed multi-till sequences in the upper parts of the holes and, together with geophysical logs and their interpreted electrofacies, indicate the presence of underlying uniform, pollen-bearing (pine and spruce dominate) lacustrine fills. These fills and the buried valleys containing them are interpreted to be perhaps as old as the last interglacial. Buried valleys are fruitful targets for the discovery of older Quaternary sequences.