Landforms and structures of the waterlain west end of St. Thomas moraine, SW Ontario, Canada

The western part of St. Thomas moraine was deposited by the Erie lobe terminating in Lake Maumee II during the Bruce stadial of the late Wisconsinan. The marginal 5 km wide zone of the Erie lobe became stagnant in the relatively shallow (15–20 m) part of the lake. Crevasse fillings, in the form of hundreds of slightly curved ridges were deposited as mesoforms upon the 5 km wide and 10 m high morainic macroform that consisted of Port Stanley basal till. Most crevasse fillings trend N-S, and consist of stratified pebbly sand deposited upon silty clay till, squeezed up by the load of the ice blocks from the macroform underneath. A couple of the till ridges were overthrusted eastward. This overthrusting was accomplished probably by wind-driven ice blocks at the time when lake level rose by about 7 m from Lake Maumee II to Lake Maumee III. The stagnant ice blocks did not melt out until after Lake Whittlesey time. of the southwestern end of the St. Thomas moraine at Wallacetown, the area is flat, without any morainic landforms, gently sloping for about 7 km as far as the Lake Erie bluffs. About 7 km south of Wallacetown natural exposures along creeks and lake bluffs reveal the northern edge of an erosional depression cut at least 20 m deep into the Port Stanley Drift and covered by glaciolacustrine sediments. Two small morainic ridges, each of them about 10 m high and about 1 km wide, are exposed in lake bluffs at the extension of the St. Thomas moraine on land. The lower one consists of Port Stanley basal till, the upper one of “waterlain till” and glaciotectonically deformed glaciolacustrine sediments. The erosional depression was cut probably by an ice stream that was more active than the rest of the Erie lobe, and the buried morainic ridges are probably contemporaneous with the St. Thomas moraine.