Parent Material


In British Columbia as well as most of Canada, the majority of soils have developed from deposits left on the earth’s surface by the last glacial period that ended about 10,000 years ago. The nature of the parent material strongly influences soil properties such as texture, pH, fertility, and mineralogy. For example, coarse-grained, quartz-rich parent material such as glacial outwash generates soils that are often gravely and with a coarse (sandy) texture.

Soil parent material may be broadly grouped into the following classes:

  1. Residual or sedentary – developed in place (in situ) from the underlying rock. Typically it experienced long and intense weathering. Residual parent materials can be found overlying any rock type – provided that the landscape has been stable for a sufficient period of time for weathering to occur. This situation and type of parent material are uncommon in Canada.
  2. Transported – loose sediments or surficial materials (i.e., weathering products of rocks that are not cemented or consolidated) that have been transported and deposited by gravity, water, ice, or wind. These materials are classified on the basis of the agents responsible for their movement and deposition (see table below).
  3. Cumulose – organic deposits that have developed in place from plant residues and have been preserved by a high water table (or some other factor retarding decomposition). These deposits are widespread and not restricted to any climatic zone. Examples include peat (undecomposed or slightly decomposed organic matter) and muck (highly decomposed organic material).
Types of transported parent material and associated modes of transportation and deposition
Mode of Transport
Resulting Parent Material
Water
  • Alluvial or fluvial (deposited from flowing water)
  • Lacustrine (sediments in still water, especially lakes)
  • Marine (deposited in oceans or re-worked by oceans)
Water and Ice
  • Glacial-fluvial (sediments deposited by glacial meltwater in a floodplain environment)
  • Glacial-lacustrine (sediments deposited by glacial meltwater in lake environment)
  • Glacial-marine (sediments deposited by glacial metlwater in an ocean environment)
Ice
  • Till (sediment deposited directly by glacial ice)
Wind
  • Loess (sediment composed primarily of silt-sized particles)
  • Volcanic tephra (sediment composed of volcanic erecta in a range of particle sizes)
  • Eolian sand (sediment composed primarily of sand-sized particles)
Gravity
  • Colluvium (sediments found on steep slopes derived from local sources)

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