Soils NR 200
Formation of Soils
From Parent Materials
SOIL FORMING FACTORS
A. Parent Material origins
1) Igneous rock – ¼ of the earth’s surface
solidification of molten rock
a) Granite - intrusive
i. Quartz – weathers to form sand
ii. Feldspar biotite – form clays
b) Basalt - extrusive
2) Sedimentary Rocks – a great majority of the
earth’s surface, readily breaks down into soil.
Consolidation by silicates and carbonates
a) Limestone - organic marine animal
3) Metamorphic – rock that is heated under
pressure and changes-generally resists weathering.
d) Talc- which is ground into powder.
e) Graphite- used in pencils and lubricants.
14- Rocky Mountain
region all rock types
15- Mostly igneous rocks
loess in river basins
16- Great Basin gravels,
sands alluvial fans
igneous and sedimentary
18. Sierra and
Cascade mountains –
20. Glacial sediments
21. Great Valley –
C. Biota (Living Organisms)
* Accumulation can form peat bogs, Moss
Peat, Herbaceous peat, Woody peat and
* Animals turning the soil - pedoturbation
mater is formed
the material to
form peat bogs.
1) Moving soil by water and gravity
2) Low – accumulate salts, if saturated then reduced
3) Steep areas are never allowed to develop the soil
profile as the unconsolidated material leaves the
E. Time - allowing for the other factors to affect
Soil transportation modes.
If not transported, Residual
a) Glacial Ice - Moraine
b) Wind – Eolian
c) Water –
Lake - Lacustrine
Oceans - Marine
d) Gravity – Colluvium
A qualifier thapto- indicates the presence of a buried soil or
a buried horizon. This would be the case if a soil has a
surface mantel of new material that is 50 cm thick or more.
The surface mantel is named in the normal way (e.g. as a
Regosol, Andosol or Arenosol) and the buried soil would be
classified with a prefix qualifier `thapto-`.
If the surface mantle is less than 50 cm thick, it is ignored
in the soil name but the soil may be marked on the soil
map by a phase indicator.
2) Soil Formation processes
i) The physical and chemical changes that
occur in the soil
- Degradation of minerals while forming
- Degradation of OM and formation of
humus and organic acids
- Also the changing of aggregates
i) Movement of materials by water downward when in
abundance and upwards when the absence of surface
ii) Fine particles wind deposition
3) Soil Profile
a) O- organic layer
i) How is this formed??
ii) Sub classes i and a
b) A- topsoil – the most productive soil
i) With the addition of the acids from the higher
organic material leaching of the easily soluble
compounds calcium, calcite and gypsum will move
down into the lower horizons of the profile as far as
the water penetration will carry them.
ii) p -
c) E – an area where the greatest eluvation (removal of
clay, iron and OM) occurs, resistant materials such as
quartz, sand and silts remain usually light in color.
d) B – sub soil or zone of accumulation, illuviation usual location of hardpan
i) Where clay and/or silt concentration will increase
from transformation of particles weathering and
ii) m - cemented zone usually silicates or calcium
iii) g - strong gleying
e) C – Parent material
but broken down but not
subject to the soil
forming properties as the
above solum (A&B) and
not massive in structure
f) R- Rock
The subscript notes for each horizon and their meaning.