# The origin of Vertisols and their relationship to Acid Sulfate Soils in the Senegal Valley

Barbiero, Laurent and Mohamedou, Abdallahi Ould and Roger, Lucien and Furian, Sonia and Aventurier, Alain and Remy, Jean Claude and Marlet, Serge (2005) The origin of Vertisols and their relationship to Acid Sulfate Soils in the Senegal Valley. In: Catena, 59 (1). pp. 93-116.

 PDF The_origin_of.pdf Restricted to Registered users only Download (1331Kb) | Request a copy

## Abstract

In the Senegal valley, it is commonly considered that the Acid Sulfate Soils of the delta are fossil soils overlain by more recent sediments, and that the Vertisols, which abruptly overlie a thick sandy horizon, result from a change in the sedimentation mode of the river. However, we show that both soils belong to the same pedological system extending from the delta to the limit of the last marine transgression. This conclusion is based on (1) the study of soil profiles intermediate between Acid Sulfate Soils and Vertisols along a 100-m sequence in the delta, (2) the mineralogy of the clay fraction $( < 2 \mu m)$ in a 200-km transect along the river, and (3) the similarity of the sand size distribution across the textural discontinuity between the horizons. The following processes are involved in the pedological transformations: (1) development of acidity by oxidation of pyrite, (2) neutralization of acidity initially by the carbonate in shell beds, and later by the hydrolysis of easily weatherable silicate clays. The slightly alkaline river water precipitates kaolinite and later smectite at the contact between the strongly acidic and slightly alkaline environments. This results in the formation of a superficial vertic clay horizon surmounting a sandy horizon. Therefore, we emphasize that the soil morphology results from development and control of acidity and not from changes in past climates.

Item Type: Journal Article The Copyright belongs to Elsevier. Acid Sulfate Soil;Vertisol;Soil genesis;Senegal valley;Senegal delta Division of Mechanical Sciences > Civil Engineering 28 Mar 2006 19 Sep 2010 04:24 http://eprints.iisc.ernet.in/id/eprint/5857