Tertiary weathering profiles in central Nigeria as indicators of paleoenvironmental conditions

Abstract

In central Nigeria the Fluviovolcanic Series of the Jos Plateau are composed by deeply weathered volcanic rocks and sediments. The sequence is often capped by ferricretes. Ferricretes, remains of former soils, are also intercalated in the series. Profile sections between two ferricretes are deep (> 10 m). The repeated saprolite/solum sequence sometimes exceeds 100 m. It can be separated into a lower section without bauxitisation, but often with total bleaching of the saprolite, a middle section with bauxite and hematite in the saprolite and an upper kaolinitic section with hematite and goethite.Bleaching by total removal of Fe2+ and bauxitisation by total desilification are both indicators of wet and hot climates with a high biomass production. In the first case the groundwater was permanently high, in the latter a well drained fluctuating groundwater can be assumed. Changing groundwater conditions may be the result of plateau uplift.Paleoenvironmental changes are, thus, reflected in relatively datable paleosols. Undatable paleosoils with comparable characteristics on the planation surfaces of Central and Northeast Nigeria also result from paleoenvironmental conditions. Consequently, concepts of landscape evolution must take into account changing environments.