Geology Reference
In-Depth Information
Figure
4.14.
Location of the pedon of an orthic turbic cryosol in patterned ground (non-sorted
circle), together with typical cryosolic soil nomenclature. Legend to soil horizon: Ah
=
mineral
near-surface horizon (A) with zone of accumulation of organic matter (h); Bmy
mineral horizon
(B), slightly altered by hydrolysis, oxidation or solution (m), with broken (cryoturbated) layers (y);
Cz
=
mineral parent material (C) that is perennially frozen (z). See also Table 4.9. From Tarnocai
(2004a). Reproduced by permission of John Wiley & Sons Ltd.
=
4.9.2. Soil Micromorphology
Cryogenic processes result in distinctive soil-morphology patterns. These are described
by soil scientists (Brewer, 1976; Fox and Protz, 1981; Pawluk, 1988; van Vliet-Lanoë, 1982,
1998; van Vliet-Lanoë et al., 2004). The terminology associated with soil micromorphol-
ogy is complex.
Essentially, when material is displaced by freezing and thawing, coarse and clay-sized
minerals are realigned, aggregates and mineral particles are rotated, and coarse and fi ne
particles are sorted (Fox, 1994). If segregated ice lenses form during the freezing process,
the result is desiccation, compaction, and compression of the soil. Typically, this leads to
the formation of a platey or lamellar micro-structure. Under certain situations, hardpans
or indurated layers may result (Fitzpatrick, 1956; Nikiforoff, 1955). Planar voids and
cracks may also appear. The main factors that contribute to the evolution of cryosols are
waterlogging of the ground during spring and summer and frost desiccation during the
winter when soil is frozen. Because cryosuction potential at
20 °C can extract adsorbed
water from soil particles, the activity of the unfrozen water fi lm may be high. This may
explain the formation of iron coatings, rock varnish, and case hardening at the surface of
rocks. Likewise, a thermally-induced water potential may explain the migration of iron,
aluminum hydroxide, and silica ions to the permafrost table. Weak humifi cation is another
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