IRON GRAVEL LAYER FORMATION AND IRON DURI CRUST DEGRADATION IN THE SOILS OF HUMID CENTRAL-AFRICA

A mottled soft nodular ironcrust, which constitutes a transitory stage in the degradation in situ of a massive hematitic duricrust, is found in the forest region of southern Cameroon. Nodular volumes progressiv ely appear in the massive iron duricrust, while the nodules and the in ternodular matrix remain hematitic. In mottled soft ironcrust, the int ernodular matrix undergoes goethitization, but the initial framework o f the duricrust is conserved owing to internodular bridges, remnants o f the hematitic internodular matrix of the duricrust. The deferruginiz ation of these bridges causes the collapse of the initial structures o f the duricrust and leads lo the formation of a soft nodular material with a clayey matrix containing kaolinite and goethite.