A geophysical survey of the central basin of Lake Erie was carried out in 1960. The survey track consisted of 18 lines run normally to the lake's axis at five-mile intervals and two lines run parallel to the long axis of the lake. Sub-bottom reflection data show four reflecting horizons extensive enough to be mapped.
The lowest of these reflectors corresponds with Paleozoic bedrock and shows a trough whose axis is displaced somewhat to the south of the present lake's axis. A pronounced spur projecting eastward partially separates this trough from a deeper basin to the northeast.
The reflecting horizon immediately above the Paleozoic bedrock shows two principal topographic features: (1) a lobelike rise centered across the lake's axis, and (2) an elongate east-west trending basin lying to the east of the rise. The lobate rise and its position within the basin indicate a glacial origin during Lake Border time. The elongate basin appears to be an erosional feature. As such, it implies the existence during the Gary-Port Huron interval of a low–lake stage whose eastern outlet was downwarped at least 300 feet by ice loading.
The next highest reflector is widely distributed throughout the basin and generally gives a clear, strong reflection. Its topographic configuration shows a broad ENE-trending valley which leads into a partially closed basin. Within the sediments which fill this valley and basin is found the shallowest sub-bottom reflector. It is nearly level and is buried from 10 to 20 feet by Recent lake muds.
Reflection characteristics and configurations within the basin combined with other lake-study information identify these two horizons as a compact glaciolacustrine clay underlying shallow water deposits. Initiation of shallow water deposition occurred during the retreat of the Port Huron ice and coincided with the formation of Lake Iroquois in the Ontario basin. It was brought to a close as the water level rose in response to isostatic uplift of the eastern outlet at Niagara Falls.