Supposed beach ridges in the Lake Agassiz Basin : a methodological approach to the study of their origins

Abstract

A study of two areas of supposed Lake Agassiz beach ridges was undertaken to ascertain the origin of the features and to establish criteria by which similar features might be recognized in the field. One ridge is at Ste. Anne, in Southern Manitoba, the other three ridges are at Ponton, in Northern Manitoba. This work was mainly achieved by a substantial study of the morphology and depositional elements of the ridges. The morphology was established, by means of air-photograph analysis and accurate surveying. Firstly, the stratigraphy was described. For gravel size particles, sphericity, roundness and long-axis orientation values were determined. Secondly, textual analyses and the percent heavy mineral determinations were used to charecterize the various deposits. Throughout the work, an attempt is made to compare the various aspects of the supposed beach ridges with other features, in the literature, whose origin is known. The ridges could conceivably be beach ridges, off-shore bars, berms, eskers, kames, drumlins, morainic features,or sand dunes. 0n the basis of morphology, statisticaL testing procedures, comparing these features with ones of known origin, indicated that because of the inequality of slopes, the Ste. Anne ridge and ridges l and 3 at Ponton may not be eskers or transverse dunes. Resemblances occur between these ridges and beaches, off-shore bars and berms. Ridge 2 at Ponton may be an esker....