HOLOCENE ENVIRONMENT CHANGES IN THE HACHICHINA WETLAND (GULF OF GABES, TUNISIA) EVIDENCED BY FORAMINIFERA AND OSTRACODA, GEOCHEMICAL PROXIES AND SEDIMENTOLOGICAL ANALYSES

Four sediment cores, drilled at Younga and Ouadrane Sebkhas (Hachichina wetland), were selected for micropalaeontological, sedimentological, geochronological and geochemical investigation coupled to hierarchical cluster and correspondence analysis. Our research aimed at reconstructing the past biodiversity, the Holocene palaeoenvironmental evolution and the responsible forcing. Subsurface sediments record four major phases: i) the first one is characterized by poorly to very poorly sorted silts, the dominance of the lagoonal/estuarine ostracod and the lagoonal/marine foraminifera and high values of terrestrial geochemical element ratios, such as K/Al and Fe/Al, which indicate an estuarine lagoon; ii) two major marine transgressions, TR1 and TR2, allowing the settlement of widely opened lagoons towards 7160-8680 and 5070-5520 cal yr BP, are marked by the enhancement of the marine/brackish ostracods and marine foraminifera, the improvement of species number, individuals number and H and E index values and of the marine element ratios such as Cl/Al and Sr/Al; iii) the opening of the lagoon is hampered by the action of drift currents allowing the genesis of sand spit and the settlement of a closed lagoon, towards 2610-3610 cal yr BP, characterized by the enhancement of lagoonal/estuarine ostracods and lagoonal/marine foraminifera and the increase of the individuals number; iv) the dominance of the lagoonal/estuarine ostracods and the lagoonal/marine foraminifera and the decline of the species number and density mark a brackish lagoon, also characterized by very poorly sorted silts transported by uniform suspension, which evolves to the actual sebkha. This evolution, within a global climate alteration context, from an estuarine environment to the present sebkha passing by an opened lagoon, is linked to the complex hydrographic setting of the sebkhas and of the Ouadrane Wadi outlet discharging in the Hachichina wetland

Geo mar. lett.

The present study investigates the history of the northern Sfax coast by means of subsurface sediments of the sebkhas El Merdessia and El Awebed through a multiproxy approach. Ostracod and mollusk assemblages, diversity index, sedimentological criteria, correspondence analysis, and radiocarbon datings together provide an overview of the development of this coast over the last 5000 years. Original data give evidence for periods of predominantly lagoonal and brackish water conditions. These data testify to the emersion of sebkha El Awebed during Holocene, while sebkha El Merdessia recorded three marine transgressions toward 4599, 2225, and 1396 years cal BP. These transgressions are indicated by the richness of sediments in lagoonal and marine ostracod assemblages coupled with marine mollusks and the high values of species richness and diversity index. Sandwiched between 2225 and 1396 years BP, a period of sea-level stability and buildup of sand barriers in front of the estuaries was evidenced. Toward 250 years cal BP, a tsunami event is evidenced by the deposition of a shelly bed containing angular and sharpened Cerithium vulgatum in coarser marine sands overlaid by silts and clays rich in charcoal particles and pottery fragments. The comparison between the proxies analyzed of the studied area and those of Skhira coast leads to the conclusion that the two coasts were subjected to the same factors. However, a time shift of sedimentation is due to the uplift of Sfax northern coast favored by the activity of the faults, unlike the southern Skhira subsidence

Evolution of the sebkha Dreîaa (South-Eastern Tunisia, Gulf of Gabes) during the Late Holocene: Response of ostracod assemblages

International audienc

Impact of relative sea level and extreme climate events on the Southern Skhira coastline (Gulf of Gabes, Tunisia) during Holocene times: Ostracodes and foraminifera associations' response

International audienc