Regions under tropical rainforest cover, such as central Africa and Brazil are characterised by degradation and dismantling of old ferricrete structures. In southern Cameroon, these processes are relayed by present-day ferruginous accumulation soil
facies, situated on the middle and the lower part of hill slopes. These
facies become progressively harder towards the surface, containing from bottom to top, mainly
kaolinite,
kaolinite-
goethite and Al-rich
goethite-
hematite, and are discontinuous to the relictic
hematite-dominated ferricrete that exist in the upper part of the hill slope. These features were investigated in terms of geochemical differentiation of
trace elements. It appears that, in contrast to the old ferricrete
facies, the current ferruginous accumulations are enriched in transitional
trace elements (V, Cr, Co, Y, Sc) and Pb, while
alkali-earth elements are less differentiated. This recent chemical accumulation is controlled both by intense weathering of the
granodiorite bedrock and by mobilisation of elements previously accumulated in the old ferricrete. The observed processes are clearly linked to the present-day humid climate with rising groundwater tables. They slowly replace the old ferricretes formed during Cretaceous time under more seasonal climatic conditions, representing an instructive case of continuos global change.