Dc. Bain et al., VARIATIONS IN WEATHERING PROCESSES AND RATES WITH TIME IN A CHRONOSEQUENCE OF SOILS FROM GLEN-FESHIE, SCOTLAND, Geoderma, 57(3), 1993, pp. 275-293
Chemical and mineralogical characteristics have been determined for a
chronosequence of six soil profiles ranging in age from 80-13,000 year
s BP developed on river terraces in the western Cairngorms of Scotland
. The C horizons are similar chemically and mineralogically, and the s
oils have similar pedogenetic histories. Exchangeable Ca and Mg decrea
se with time and base saturation decreases exponentially from 24.6% in
the Ah horizon of the youngest profile to 2.8% in the comparable hori
zon of the 10,000 year old profile according to the chronofunction y=3
.372+22.612 exp(-0.0007365t). Long-term weathering rates of base catio
ns, calculated from the loss of these cations relative to Zr, appear t
o decrease exponentially with time but this may be due to the method o
f calculation. The magnitude of loss of base cations decreases in the
sequence Na > K > Mg > Ca but when the relative mobilities of these el
ements are considered, the loss is in the order Mg > Na > Ca > K; this
reflects the dissolution of chlorite and loss of Mg, and the more rap
id weathering of plagioclase feldspar and loss of Na and Ca (particula
rly in the coarse sand fraction) than K-feldspar. The clay fractions,
although < 2% of all horizons, also show distinct patterns with age in
that chlorite and mica are less abundant in older soils and vermiculi
te is more abundant, the latter phase often having hydroxyaluminium po
lymers in the interlayer region. The chemical and mineralogical trends
in the soil sequence are closely associated and are induced by pedoge
nic weathering.