RESOLVING THE ORIGIN OF STRATIFIED MORAINES IN SOUTHERN ONTARIO, CANADA

Stratified moraines not only contain information about past ice sheet dynamics and hydrology, they are also commonly targeted for groundwater resources in growing urban areas. A better understanding of their sedimentology and internal architecture is needed to better constrain deglacial histories and to manage groundwater resources effectively. Stratified moraines are deposited in a variety of ice-marginal settings. Depositional controls can include glaciofluvial, deltaic or subaquatic fans and deposits from these settings are often superimposed due to the dynamic nature of glacial environments. The resulting spatially highly-variable stratigraphy and the fact that dateable materials are often not preserved poses significant challenges in the analysis of these complex landforms.

Based on early 20th century mapping and landform analysis, the Waterloo Moraine has been described as a stratified interlobate feature that developed under the influence of the Georgian Bay, Huron, Erie and Ontario ice lobes of the Laurentide Ice Sheet. It consists primarily of stratified sand with local accumulations of gravel and discontinuous lenses of diamict and lacustrine muds (Maryhill drift). Recent subsurface mapping efforts have revealed a complex internal stratigraphy, which has confounded hydrogeological modelling efforts. Preliminary sedimentological analysis reveals a predominantly E-SE sediment source and antidunes, small to large cross-stratification, and simple and complex scour fills indicative of rapid sedimentation in glaciofluvial and glaciolacustrine fan settings as well as ice-walled conduits.

Deformation structures within these stratified moraines have received little attention to date. Several examples from stratified moraines in S. Ontario are given to illustrate the information that can be gained from such analysis. Systematic analysis of deformation structures in the Waterloo Moraine is being carried out to identify areas directly affected by ice, rapid sedimentation or subaqueous slumping. Integrated with regional subsurface mapping and sedimentological analysis, these data will help constrain the depositional origin and evolution of this stratified moraine.