Geoscience Reference
In-Depth Information
Table 11.5 Genesis of argillic, natric, and kandic horizons (Bockheim and Hartemink
2013
)
Horizon
Argillic
Natric
Kandic
Mechanism
Dispersion
Dispersant
Decalcification
Dispersion by
abundant Na
Dispersion by organic matter,
oxyhydroxides
Sodium adsorption
ratio
Low
High
Low
Translocation
Soil moisture
regime
Aquic, udic, ustic,
xeric, aridic
a
Aquic, ustic,
xeric, aridic
a
Aquic, udic, ustic, xeric
Accumulation
Clay activity
High
High
Low
Common mineral-
ogy class
Mixed, smectitic
Mixed, smectitic Kaolinitic, siliceous, sesquic,
ferritic, ferruginous
Evidence
Depth-distribution of
clay
“Bulge” Bt
“Bulge” Bt
“Bulge” persists in C
Argillans
Common
Few or thin
Few or thin
Fine clay/total clay
ratio
Increase
Slight increase
Slight or no increase
Microfabric
Microstructure
Granular
Subangular blocky
Plasma fabric
Skel-masepic,
Ma-skelsepic
Argillasepic/silasepic
Related distribution Porphyroskelic
Open/close porphyric
Coefficient of linear
extensibility
High
High
Low
Other
Lamellae
Relative importance
Translocation from
eluvial
XX
XXX
X
Dust deposition and
translocation
XX (XXX
in aridic)
XX (XXX
in aridic)
X
Weathering in situ
XX
XX
XXX
Neoformation
XXX
XX
XX
a
Paleo-argillic; formed in moister SMR
commonly contain high-activity clays such as the smectites. Members of this
mineral group are readily broken down into fine clays, which can be readily
translocated through the soil; they have a high COLE. The argillic horizon is
manifested by a clay maximum or “bulge” when the depth-distribution of clay is
examined. Argillans are common in argillic horizons except in those of aridic
environments, where the clay skins may be destroyed by shrinking and swelling
(Gile and Grossman
1968
; Nettleton et al.
1969
; Khormali et al.
2003
). Similarly,
the upper part of argillic horizons in southeastern USA often lack evidence
of translocation because argillans are destroyed by weathering, and the clay
Search WWH ::
Custom Search