Geoscience Reference
In-Depth Information
authors who worked in the middle of the nineteenth century. The
system, revived a little later by Dokuchaev (§ 1.1.2) and his students, has
endured and has attained the status of a gradually refined international
coding system (Table 1.1). It still suffers from lack of universal acceptance
in some details. We turn to Tandarich
et al.
(1994) for the C and D
horizons.
Table 1.1
Codification of the major horizons.
O
L
, O
F
, O
H
Highly organic horizons of drained forest environments (with L for litter,
F for the fermenting layer of decomposition (fermentation), H for the
humifying layer); for the Americans, all these correspond to a 'folic' (with
leaves) horizon.
H
Highly organic horizons of wet environments (cf. histic horizons — see
Histosols).
A
Surface organo-mineral layer with living organisms and/or traces of
biological activity.
E
Almost totally mineral horizon depleted of iron and organic matter or clay,
often bleached ('E' for 'eluvial').
(
B) or S
Mineral horizon representing a stage of limited weathering compared to
the parent material of which some features are still seen (rock structure,
minerals, etc.); signs of evolution are: development of a specific colour
(expression of iron) and/or a structure of pedological, not geological origin
(prismatic, blocky, etc.).
B
Horizon in which components such as iron, clay, humus, salts or secondary
carbonates are accumulated, but from which primary carbonates have
disappeared.
C
Bottom horizon of the soil; it is already subject to the effects of atmospheric
agents; it shows cracking related to alternate wetting and drying cycles,
and partial or slight oxidation because of penetration of oxygen. On
the other hand, if not explicitly stated otherwise, it is devoid of the
accumulations typically seen in the B.
D
Parent material that has been altered but does not have the indications of
meteoric weathering seen in the C horizon; for example, granitic sand,
limestone scree, moraines (see 'regolith', Chap. 2).
R
Corresponds to the unweathered and unfragmented hard rock; it is called
'parent rock' when it is the source of the soil above it.
A given soil need not have the entire sequence of horizons described
above! For example, we find profiles of the AR or A(B)C type.
These horizon symbols can be qualified with suffixes that define
their nature better. For example, B
h
where h indicates the presence of
organic matter. Unfortunately there is no international accord regarding
these suffixes. If several horizons of the same type follow one another,
they are numbered in sequence, for example: A, B1, B2, C. If a given
