Calcareous Glacial Drift and Plants, Fraserdale, Ontario, Canada

The composition of glacial drift has an influence on the types of plants that grow on that drift. For example, calcareous glacial drift would likely support plants that thrive on limy soil. In this note, I share an example of the influence of calcareous substrate on some types of plants present seen in the Fraserdale - Abitibi Canyon area, northeastern Ontario (Photo 1).

Location

Fraserdale and Abitibi Canyon are located about 130 kilometres (81 mi) north of Timmins and about 160 km (100 mi) south of James Bay, in Ontario, Canada (Photo 1). The area is located in the northern Boreal forest and lies about 30-50 km south of the boundary between the Boreal Forest and the James Bay lowland.

Brief Geology of the Area

From a geological perspective, the James Bay lowland is part of the larger Hudson Bay - James Bay Lowland (Photo 2). Calcareous, Paleozoic-aged rocks, consisting of limestone and dolostone, underlie the Hudson Bay - James Bay lowland. The limestone and dolostone rocks are in turn covered by clay, sand, and gravel deposits that were laid down at the end of the last ice age. That ice age, called the Wisconsin Glacial Episode or the Wisconsin glaciation for short, ended about 11,000 years ago in this area when the ice sheet began to melt. After the ice sheet melted away, extensive peat deposits formed on top of the clay, sand, and gravel glacial deposits. Check here for more details about the recent geological history of the lowlands.

The presence of limestone and dolostone rocks to the north of the Fraserdale area is important. During the last ice age, the glacier ground off rock flour and rock fragments from the calcareous, limestone and dolostone bedrock. Those materials were deposited as glacial till, at the base of the ice sheet (teal coloured area in Photo 3). The till is the oldest glacial deposit and it formed DURING the ice age. At the end of the ice age, when the ice sheet melted away, meltwater lakes and rivers were created with associated unconsolidated river, beach, delta, and lake bottom deposits (orange-, sandy-brown-, yellow-, and blue-coloured areas respectively on Photo 3). Geologists say these unconsolidated deposits are post-glacial in age - meaning they formed at the end of, and after, the ice age. Together, the undifferentiated glacial and post glacial surficial deposits are called glacial drift. The glacial drift lies on top of old Canadian Shield rocks that form the basement in the Fraserdale - Abitibi Canyon area (Photo 2). The most recent deposits, formed in modern times, consist of peat, muck and marl deposits that are shown in the mauve-grey-coloured areas on the surficial geology map (Photo 3).

For more insight about the local calcareous geology, check out: https://www.ontariobeneathourfeet.com/geological-sites#/fraserdale-glacial-drift .

Influence of Calcareous Drift

The calcareous drift supports calcicolous vegetation. Calcicolous vegetation is adapted to growing in limy conditions. In the literature and on websites, limy soil is sometimes referred to high pH bedrock or soil.

Examples of calcicolous plants observed in the Fraserdale area include: a) Marsh Grass of Parnassus (Parnassia palustris), growing on wet calcareous drift (Photo 4); b) Kalm's Lobelia (Lobelia kalmii), growing on moist calcareous drift (Photo 5); c) Sticky False Asphodel (Triantha glutinosa), which was fruiting and growing on moist calcareous drift (Photo 6); d) Hairy Goldenrod (Solidago hispida), which grows on a range of substrates, but which locally prefers calcareous substrate (Photo 7) and is very common in the Fraserdale area on calcareous drift; and e) Variegated horsetail (Equisetum variegatum), a calcicolous plant, is also growing in the moist calcareous soil with Kalm's Lobelia (Lobelia kalmii) and Marsh Grass of Parnassus (Parnassia palustris) (Photo 8).

Summary

Although this is a small sampling of plants, seen late in the flower season, it does illustrate that the local, calcareous glacial drift in the Fraserdale area, northeastern Ontario, does have an influence on the local flora. The limy nature of the glacial drift is a direct reflection of the geological history of the area, principally, the scraping off of rock flour and fragments from the limestone and dolostone rock that occurs in the James Bay lowlands, just to the north of the area. Geology does influence the location of plant types.

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Sept 8/21; Nov 15/21