ABSTRACT: The Quaternary history of the part of the Rocky Mountains, Foothills, Plains and western Porcupine Hills

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Abstract

The Quaternary deposits occurring approximately between the Porcupine Hills and the Continental Divide in southwestern Alberta were investigated and mapped in detail to determine the sequence of events. The program included lithological and fabric analysis. Pollen and faunal remains recovered from the nontill units aided in determining the ages of drift and climatic changes. There are three major glacial events of decreasing magnitude in the area, an event consisting of one Mountain and one Laurentide advance. The Albertan (oldest), Cowley (new name) and Gap (new name) tills were deposited by the Mountain glaciers. Advances of Laurentide ice deposited the Pincher (oldest), Maunsell and Beaver Creek tills. During each event, the Mountain glaciers reached their maxima and receded considerably prior to the advance of the Laurentide ice sheets. The Saskatchewan Sands and Gravels, consisting of preglacial boulders and an upper facies of proglacial sediments, underlie the oldest tills. These gravels are exposed a long major preglacial channels east of the Livingstone Range.The distribution of moraines in conjunction with pollen data indicates that 2 minor glaciations, subsequent to Event 3, occurred in the Mountains. The earlier advance led to the deposition of the Cache Creek till (new name) and the later, to cirque moraines. Proglacial lakes developed from local ponding by valley glaciers, or from extensive damming by Laurentide ice sheets. Sediments deposited in these lakes separate the tills or occur at the surface. Prominent terraces along the Oldman and Crowsnest Rivers in the Foothills were adjusted to the level of the last proglacial lake (event 3) to occupy the study area. Stratigraphic and palynologic evidence shows that there are 2 periods of preWisconsin and one of Early Wisconsin deposition to the east in the Lethbridge area. These are correlative with the Laurentide Pincher, Maunsell and Beaver Creek tills and the Albertan, Cowley and Gap drifts respectively. The Cache Creek advance is Classical Wisconsin based on aradiocarbon date (22,700±1,000 years B.P., GaK-2336) from bone underlying the outwash, and the Mazama tephra occurring upstream from the end moraines. Pollen data and the moraines in close proximity to cirques indicate that the last glacial event is correlative with the Neoglacial.The distribution and stratigraphy of drift sheets infers that the study area east of the Livingstone Range was ice-free during the Classical Wisconsin and Recent. A feature of the period was the deposition of gravels and alluvium along major streams in this zone. Pollen and mollusca recovered from bog and alluvial sediments indicate that prior to the Neoglacial(i,e., between ca. 5 to 1 1,000 years B.P.) the climate ameliorated. This interva1 is correlative with the Altithermal.

Bibliography of Canadian Geomorphology