This paper discusses the relationship between the differentiation of
ferruginous accumulations and the variable water saturation of footslope
soil patterns. An analysis of the slope morphology of a typical hill in
the forest zone of southern Cameroon and a seasonal survey of the levels
of groundwaters, springs and rivers were considered in relation to the
petrology of different soil patterns. The study site is a tabular
hillock whose slopes present a progressive development from steep to
gentle slopes. The variable residence time of water within the soil,
creating an alternation of reducing and oxidizing conditions, affects
oil chemistry, structure and lateral extension of the soil patterns. The
ferruginous soil patterns, being formed on the footslopes, gradually
increase in extent with decreasing slope angle and the relative rise of
the groundwater level. The steep footslopes, where groundwater has a
shorter residence time, show a soft mottled clay pattern, restricted to
the bottom part of the slope. The moderate footslopes exhibit a deep
permanent and a temporary perched groundwater table. The latter, with
its regular capillary fringe, contributes to more reducing conditions
within isolated domains in the soil patterns, and thus to the
alternation with oxidizing conditions, generating a continuous hard soil
pattern (massive carapace). The more gently dipping footslopes exhibit
groundwater levels near the surface and also a significant amplitude of
groundwater fluctuation. Iron, previously accumulated in moderate
footslope patterns, is reduced, remobilized, and leached. The soil
patterns formed develop into a variegated carapace, more extended along
the slope, containing less iron, but nevertheless more hardened, due to
the important fluctuations of the groundwater table. These patterns are
limited to the zone of groundwater fluctuation and deteriorate as the
water fluctuation zone recedes. Copyright (c) 2005 John Wiley & Sons,
Ltd.