diedhiou, yankhoba université cheikh anta diop dakar - faculté des sciences et techniques - département de géologie, Sénégal , youm, cheikh ibrahima université cheikh anta diop dakar - faculté des sciences et techniques - département de géologie, Sénégal , sow, el hadji université cheikh anta diop dakar - faculté des sciences et techniques - département de géologie, Sénégal , sarr, raphaël université cheikh anta diop dakar - faculté des sciences et techniques - département de géologie, Sénégal , malou, raymond université cheikh anta diop dakar - faculté des sciences et techniques - département de géologie, Sénégal

Holocene shelly accumulations of the Retba lake (Senegal, West Africa): Faunal inventory, lithology and palaeoenvironment

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In order to reconstitute the history of post-nouakchottian inter-dune depressions of Western Senegal, the study of shellyaccumulations surrounding the lake Retba and subject of artisanal mining was conducted along five sections. A total of 12 species of gastropods, 11 species of bivalves and one species of echinoderm were inventoried. The stratigraphic study shows that the deposit is formed by an alternation of sandy, sandy shells or low sandy shells levels. Sedimentological, faunal and radiometric data allowed to identify three phases in the lake evolution: The first phase, characterized by a great diversity of the mollusc fauna with well preserved shells associated with a marine echinoderm and a predominantly sand sedimentation, corresponds to a stage of open marine gulf consecutive to the nouakchottian marine transgression (6800-4200 B. P.). The second phase post-nouakchottian corresponds to a little open marine gulf characterized by lower species diversity. The last phase corresponds to a semi-closed lagoon stage put in place between Sub-actual and the Current, distinguished by a specialized oligospecific fauna where Senilia senilis and Pelecyora isocardia are largely dominant. This part of the terrace is characterized by large shells of Senilia senilis subject of artisanal exploitation. Throughout the filing period, we meet in place brachish water species attesting freshwater goings on the south side of the lake.

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Molluscs , Nouakchottian age , sedimentology , marine gulf , Rebta lake , Senegal

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