Abstract

Henri Demba* , Papiss J.A and Bouba J. Seck

Soils of the coastal region of West Africa present some specificities linked to the topography: they frequently occur in a well-defined and fairly regular sequence related to relief: the soil catena or toposequence. The objectives of this study were to (1) analyse kaolinite distribution on different landscape positions in the coastal area of the Saloum river Basin, west central Senegal, West Africa, in order to (2) demonstrate the influence of Continental Terminal (CT) sediments on local soil formation and mineral distribution. The described soils were distributed along the toposequence as Gleyic Hyposalic Solonchaks in the floodplain, Haplic Gleysols in the low terrace and Endogleyic Arenosols in the middle terrace. The middle terrace was characterized by a coarser soil texture (mainly sand) compared to the floodplain and the low terrace. The bulk mineralogy was dominated by quartz (SiO2). The clay fraction of the soils was dominated by kaolinite (≥ 70%), smectite (around 25%), illite (≤ 2%), and illite-smectite mixed layers (trace amounts). More detrital (eolian dust inputs) than pedogenic (in situ weathering) kaolinite was identified. The widespread distribution of kaolinite in the entire toposequence and the influence of CT sediments in such distribution trend is the main finding of this study.