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Archaeological Discovery in Organic Terrain in Canada – Page 3

– Page 3 –


The Nature and Origins of Peat

It is important to realize that, regardless of the technical descriptions of peat deposits, ‘peat’ is, essentially, an accumulation of any decayed, or partly decayed, plant material. So, the word ‘peat’ or ‘peaty’ is sometimes used in vernacular terms to describe the organic horizon of any tundra-like soil, or vegetation. For instance, the site record forms of the HjCl-1 and 2 sites, on Okak Island in coastal Labrador, state that they are located “on one of a series of peat-covered, sandy terraces which rise from the western shore”. Many site record forms from Newfoundland and Labrador list ‘peat’ where the site vegetation cover is described.

Photo: David Morrison, Gutchiak Site
Figure 1: Aerial view of the Gutchiak site excavation.
Photo: David Morrison, Canadian Museum of Civilization
Photo: David Morrison, 91-47 Photo: David Morrison, 91-64
Figure 2: Two views of a cross-section are presented.
Photos: David Morrison, Canadian Museum of Civilization

Sometimes peat development has been enhanced by past cultural activity and this archaeological peat might be said to have, in part, a bio-cultural origin. For instance, at the Gutchiak site (NhTn-1) (Figure 1), in the Inuvialuit lands of the Mackenzie Delta, the ‘dark humic soil’ (Morrison 2000: fig.7) (Figure 2), is essentially ‘peat’ – although it is not called it – because it is composed of decayed plant material that has been imported (leaves and twigs) (Figure 3) and grass that accumulated rapidly due to the nutrients derived from habitation waste and fish processing. A peaty matrix, such as at Gutchiak, is common to many habitation sites in arctic and subarctic Canada, and because it is less acidic than (natural) blanket peat, it creates ideal conditions for the preservation of artifacts made from organic materials – especially in the arctic where there is underlying permafrost – so that well-preserved artifacts (Figure 4) of wood, bark, antler have been collected from numerous sites – e.g. Gupuk (Arnold 1986); Kittegazuit (McGhee 1974); Kugaluk (Morrison 1988).

Photo: David Morrison Figure 3: The bio-cultural peat is partly formed from imported twigs, leaves and grass.
Photo: David Morrison,
Canadian Museum of Civilization
Figure 4: Well-preserved,
perishable, organic artifacts
in situ at the Gutchiak site.

Photo: David Morrison,
Canadian Museum of Civilization
Photo: David Morrison, 91-134

In scientific terms, however, two basic types of peat are recognized – bog peat and fen peat (Beuker 2002:13-14; Roberts 1989:125-128). Bog peat (also called a raised, or lenticular, bog, and blanket peat) develops in water rich depressions, when annual precipitation is 700-1150 ml and the temperature does not exceed a 10° C annual average. If the ground water is used up then the bog becomes dependant upon precipitation. Since sphagnum moss cells can store water, the water table of the bog can rise above surrounding ground-water table. Living raised bogs can spread rapidly under the right circumstances. Bog peat typically contains abundant micro and macro-scopic fossils and pollen and provides the raw data for regional palaeoecological studies. Raised or blanket peat bogs on gently sloping upland plateaus did not exist during the thermal optimum, but began to develop in the mid-Holocene because of a combination of climatic deterioration and soil maturation. The key factor is water logged soil and a fall in ph, so only acid and low nutrient tolerant plants like sphagnum or cotton grass can survive. Blanket peat covers wide areas of Newfoundland and Labrador, Nouveau Quebec, and the arctic Territories – wherever the average July temperature is less than 17° C. Lenticular, or raised, peat bogs also occur south of the 60th parallel, and in all the provinces west of Newfoundland and Labrador and some of these are very large and are located in, or near, densely populated centres. Examples include: Mer Bleue, in the City of Ottawa, Ontario; Burns Bog, in the City of Delta B.C.; and the Albert Bog, in southeastern Ontario.

The second type of peat – fen peat – is closely linked to topography, rather than climate, and is a common terrain feature of central and western Canada, called variously: marshlands, sloughs, fens, kettle lakes, swamps, or wetlands. Rich in nutrients, fen peat is composed of plants like cattail, reeds, rushes, water lilies, sorrel, sedge, etc. that accumulate around the edge of lakes and ponds. These small shallow wetlands often have a history of hydrosere succession from open water to fen, swamp, or peat bog or, when conditions permit, there may be a further succession of colonizing plants from shrubs (dogwood, alder) to water-tolerant trees (birch, spruce, ash, cedar, elm).


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