Ostracods and mollusks in northern Sfax coast: reconstruction of Holocene paleoenvironmental changes and associated forcing

Abstract

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.