RECENT AND  UPPER PLEISTOCENE COLD-TEMPERATE, COARSE-GRAINED BEACH DEPOSITS OF THE SOUTHERN GREAT LAKES, ONTARIO, CANADA

 V. PASCUCCI¹ , I.P. MARTINI² and A.L. ENDRES³

¹Dipartimento di Scienze della Terra, Universita' di Siena, via Laterina 8, 53100 Italy
²Department Land Resource Science, University of Guelph, ON, Canada
³Department of Geological Sciences, University of Waterloo, Waterloo, ON, Canada 

The sedimentary facies and facies architecture of two modern and one ancient (approximately 10,400-11,200 years old), cold-temperate, coarse-grained beach deposits have been studied in the southern Great Lakes of Ontario. In recent beaches, ice foot and ice-cementation develop during winter, but, differently from arctic beaches, no specific ice-related sedimentary features are preserved in the thawed deposits. The deposits retain typical characters reported in the literature for wave-dominated beaches; that is, they show  (a) an "infill zone" at the toe of the beachface, characterized by subspherical and rod-shaped clast accumulations with interstices filled to a various degree with finer pebbles and sand, (b) a swash zone ("sand run"), which is marked by isolated, outsized, flat clasts stranded on sand or finer subspherical to rod-shaped pebbles, (c) a fine to medium grained pebble "imbricated zone" of intermediate berms, (d) a coarse "flat-clast zone" of the top of the highest beach berm, and, in most cases, and except for shingle beaches (e) sandy "coastal dune" with variously developed soil profiles. These zones form a regular succession on the surface of modern beaches, however, they seldom occur as quasi-complete vertical successions in the Recent and Pleistocene deposits. The single or sets of components are most often juxtaposed through erosional contacts. Nevertheless, the lithofacies are sufficiently diagnostic to allow recognition of the various beach settings, and their lithofacies architectures allow deciphering important geological events, such as (a) local injection of fluvial material into the shoreface where it is partially reworked and moved onto the beachface, and (b) repeated rapid transgressions and regressions typical of glacial lakes precursors to the modern Great Lakes of North America.

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