Evidence for Early Pleistocene Glaciation from Borecore Stratigraphy in North-Central Alberta

Borecores collected from the east-central region of Alberta, Canada were sub-sampled and studied for paleomagnetic remanence characteristics. A magnetostratigraphy has been established for sediments previously assumed to represent multiple continental (Laurentide) glaciations, but for which no geochronology was available. Based on the Quaternary record elsewhere in Alberta and Saskatchewan, it was thought that some of these units might well be pre-late Wisconsin units.

The Quaternary sedimentary record is composed of till and lesser thicknesses of interbedded glacio-lacustrine and outwash sediments, which may be up to 300 m thick within buried valleys. Most of the sampled units are not accessible from outcrop and their sedimentology and stratigraphy is derived from core data only. In 4 of 16 borecores sampled to date, diamict that is located in a similar stratigraphic position as previously mapped Bronson Lake Formation till, is reversely magnetized, indicating it is at least Early Pleistocene in age. This formation is underlain by Empress Formation sediments and/or Colorado Group shales, and overlain by normally magnetized glacigenic sediments of the Bonnyville, Marie Creek and Grand Centre formations respectively.

This new record of Early Pleistocene glaciation in north-central Alberta places the westernmost extent of earliest Laurentide ice some 300 km farther westward from its previously established limit in the Saskatoon to Regina region of the western Canadian prairies, but still well short of the all-time limit and elevation established during the Late Wisconsin (Late Pleistocene) in the foothills of the Alberta and Montana Rocky Mountains.