Soils with Lamellae - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 289

hyperthermic, thermic frigid, cryic (Fig. 24.3 ). It is of interest that none

of the 118 soil series in the USA with lamellae had an aquic soil-moisture regime,
which suggests that downward movement of water is essential for its formation and
that poor drainage conditions do not favor lamellae formation.

mesic

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24.6 Genesis of Lamellae

Lamellae may be of geological origin when they do not roughly parallel the surface,
occur as lenses rather than laminae, and lack argillans (Rawling 2000 ). Only 30 %
of the official soil series descriptions in the SSURGO database provided informa-
tion about clay films and bridges, and only 18 % gave estimates of the difference in
clay concentration between the E and Bt components of the E & Bt horizon
(Table 24.2 ). Clearly, this is insufficient to document the pedogenic origin of
lamellae.
It can be argued that lamellae, where they are pedogenic, are a precursor to the
argillic horizon. Indeed there are soils with thick lamellae that are classified in
Alfic, Ultic, or Argic subgroups. For example, the Montcalm series (coarse-loamy,
mixed, semiactive, frigid, Alfic Haplorthods), which occupies 188,000 ha in Mich-
igan, contains an E & Bt horizon from 84 to 152 cm with lamellae that exceed a
total thickness of 15 cm and is classified as part of an argillic horizon. However, the
notion that lamellae eventually coalesce and form continuous argillic horizons
needs further research.
Several laboratory experiments have been conducted to investigate the processes
involved in development of lamellae. Bond ( 1986 ) was able to produce a clay-
enriched lamella by leaching a fine sand containing 1 % clay. By alternately

leaching with percolate from a leaching column and drying with a water aspirator,
artificial clay skins were produced in “unweathered” loess material (Buol and Hole
1961 ). Dijkerman et al. ( 1967 ) conducted a series of experiments showing the
importance of drying, gravitation, and pore sieving on clay dispersion, movement,
and accumulation in sandy materials. Three mechanisms are important to form a
lamellic as well as an argillic horizon: dispersion, translocation, and accumulation
(Eswaran and Sys 1979 ). Dispersion involves the leaching of carbonates in calcar-
eous parent materials where lamellae may eventually form (Wurman et al. 1959 ;
Berg 1984 ). Translocation is reflected by the fact that lamellae are dominantly
found (89 %) in soils with udic and ustic soil-moisture regimes, because more water
is available for argilluviation (Fig. 24.3 ). Coatings on sand grains and bridging of
sand grains reflect accumulation of clay and other fine materials in the lamellae.
Wurman et al. ( 1959 ) suggested that clays moving downward in the profile may
accumulate as a result of drying induced by uptake of moisture by plants. However,
the wetting-front hypothesis may not explain multiple lamellae and lamellae occur-
ring to depths of nearly 500 cm. Several investigators have suggested that the bands
may be flocculated by Fe oxyhydroxides (Dijkerman et al. 1967 ;Berg 1984 ).

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