Sedimentary Dynamic and Sea Level Variation Along Hachichina Coast (Sebkha Ras Younga, Gulf of Gabes, Tunisia) During Holocene: Response of Ostracods and Foraminifera Assemblages

Abstract

Several cores retrieved from Ras Younga Sebkha, (Hachichina coast, Gulf of Gabes), are subjected to a micropalaeontological and sedimentological study. The analysis of ostracods and foraminifera coupled with statistical approach (Correspondence analysis) are used in order to reconstruct the evolution of Holocene environment related to climatic and hydrodynamic forcing. The foraminifera and ostracods association present in the sediments core, allowed us to identify the different steps of the genesis of the Sebkha Ras Younga. Four major steps were distinguished: (i) the first one, corresponding to an estuarine lagoon, is characterized by the dominance of brackish ostracods association and reduced values of the diversity index (H) and (E); (ii) the second one, marked by the enrichment of marine, lagoonal, and shallow water ostracods and shallow water foraminifera and high values of (H) and (E) index, indicate the settlement of an opened lagoon toward 5105 a BP; (iii) the enhancement of lagoonal ostracods, associated to the increase of the individuals number mark the settlement of a closed lagoon related to the genesis of sand spit under the action of longshore currents; (iv) the last step, characterized by the absence of microfossil, corresponds to a more closed lagoon evolving into the current Sebkha.