FERRIFEROUS BACTERIAL ENCRUSTATIONS IN LATERITIC DURICRUSTS FROM SOUTHERN MALI (WEST-AFRICA)

In southern Mali, lateritic nodular duricrusts have been formed under subtropical climates. The duricrusts are massive and consist of nodule s set in a hematitic porous matrix. Ferriferous, coccoidal, filamentou s and rod-like, hollow encrustations were found in the matrix. Encrust ations are interpreted to be of bacterial origin, possibly replicas of the iron-bacteria Arthrobacter. Their genesis is explained schematica lly by an accumulation of ferric oxides on extracellular surfaces in a n environment with changing redox conditions created by seasonal fluct uation of the water table.