Parent Material

Surficial deposits are the parent materials from which soils develop. Because Vuntut National Park and the Old Crow Flats Special Management Area have not been glaciated, the parent materials tend to be weathered bedrock and rock debris, transported by rivers or wind and deposited in lakes in the lowlands (Hughes 1972). The nature of sediments is often described by the texture which is a result of the grain size: gravel is greater than 2 mm in diameter and thus holds no water, sand has grain size of 2 to 0.6 mm and allows water to drain well, silt has moderate grain size, and clay with very fine grain size, less than 0.004 mm, retains water giving it a sticky, clayey, nature. Loam is a combination of sand, silt and clay and is generally best for plant growth.

Welch and Smith (1993) state that soils formed over limestone tend to have alkaline reactions, high concentrations of base elements (Calcium, Magnesium, Sodium, Potassium), abundant clay, and often have significant surface accumulations of black organic matter. On the other hand, soils formed over quartzite or sandstone tend to be acidic in reaction, sandy or silt-textured, and lack base elements.

i) Lacustrine Deposits

The whole of the Old Crow Flats are shown as lacustrine (lake-formed) deposits on the surficial geology map. Hughes (1972) reports deposits of sand, gravel, silt and peat at least 60 m thick along the Old Crow River. These deposits extend below bedrock suggesting that the lowlands are not entirely erosional in nature; warping or faulting of the bedrock must have contributed to their formation. Glaciolacustrine sediments were deposited in a vast glacial lake formed when the Laurentide Ice Sheet blocked the east-flowing streams (see Geomorphology, Section 3Biiic, for further discussion). Drainage of the glacial lake through the Ramparts of the Porcupine was followed by incision (downward cutting) by rivers, local deposit of fluvial (river-borne) and shallow water lacustrine sediments, and widespread peat deposition (Hughes et al. 1989).

ii) Fluvial Deposits

Gravel, sand and silt make up the fluvial sediments being deposited along the rivers of the Old Crow Basin at present. Glaciofluvial sediments deposited by glacier meltwater streams also appear as stratified gravel, sand and silt. Both are in part covered with organic deposits.

iii) Colluvial Deposits

Slopewash, frost creep and solifluction (see below, and Geomorphology, section 3Ci) are processes which move sediment down slope and deposit it at the bottom of the slope. This redeposited or reworked material has no general characteristics. It can be mixed by frost action in frost creep. In lithified bedrock (solid stone) areas the deposit may consist of boulders.

iv) Organic Deposits

The other major source of parent material is organic matter. In arctic soils it can take the form of thick peat deposits or of peat layers between other parent materials. It is often mixed into the sediment by cryoturbation (mixing through freezing and thawing). It may also exist as a thin surface layer. The rate of decomposition of this organic matter is slow. This results in the characteristically low levels of available nutrients in arctic soils. In active wetlands the peat is generally fibric (undecomposed, individual plants can still be identified) to mesic (stage between fibric and decomposed).