Évolution des environnements de la Lagune de Tunis du Pléistocène moyen à l’Holocène

Abstract

The lake of Tunis, located in northern Tunisia, is part of the coastal wetlands sensitive to climatic and anthropic variations. This fragile ecosystem was an open bay 190 ka BP ago. Today, it is separated from the Mediterranean by a sandy barrier fed mainly by the Madjerda wadi. This study, based on a multidisciplinary geological approach, examines the evolution of the dynamics of the Tunis Lake, as well as the recent environmental changes that control the sedimentation. Two cores LN1 (55 m) and LS1 (40 m) were collected in the alluvial deposits, respectively in the North-East and South-East of the Lake. These cores have been studied in detail to determine the spatio-temporal distribution of the sedimentary stock. The data from this study complemented by those from previous work allowed us to refine and establish spatio-temporal correlation scenarios of the sediments filling the Tunis lagoon. These correlations are established between the LN1 core and the core taken at the SE (LS1). Spatial and temporal monitoring of sediment deposition in these cores has revealed a general regressive evolutionary trend, from a frankly marine environment to a lagoon environment more or less communicating with the sea, from the Middle Pleistocene (an age between 159 and 205 ka) to the present Holocene. The identification of ostracod associations typical of open marine or lagoon environments and of benthic foraminifera associations of lagoon environments has allowed us to trace the history of the Tunis Lake over the last two millennia. It begins with an open marine environment (around 2030 years BP) followed by an open lagoon environment around 1700 years BP.