Reconstructing the Holocene depositional environments along the northern coast of Sfax (Tunisia): mineralogical and sedimentological approaches

This study aims to reconstruct the Holocene to modern depositional environments and the evolution over the main controls of the sedimentation along the northern coast of Sfax (Tunisia) using three sediment cores retrieved at 30 meters water depth by SEACNVS (Société d'Étude et d'Aménagement des Côtes Nord de la Ville de Sfax).

The identification of different types of depositional environments was mainly based on field work,mineralogical and sedimentological analyses of core sediments. Mineralogical analysis by X-ray diffraction have been done on bulk powder and on oriented aggregate of the clay < 2 microns fraction,particle size distribution,magnetic susceptibility was measured on opened cores with a Bartington MS2Epoint sensor and Loss-On-Ignition (LOI) was measured after 24h at 105°C (water content, density), after 4h at 550°C (organic matter content) and after 2h at 950°C (inorganic carbonate).The mineralogical composition is made by clay minerals, quartz, calcite, gypsum and K-feldspar.The mineralogy of <2μm clay fraction show a mixture of kaolinite,illite, smectite and palygorskite. As harp change in the magnetic susceptibility profiles records the transition from a marine to a continental depositional environment. The marine domain is characterized by lower magnetic susceptibility values and coarser sedimentary grain than the continental domain.

The vertical succession of depositional facies is made by two contrasted environments: a fluvial depositional environment (coastal plain) marked by channels and inundation plains at the in the lower section of all cores; a littoral marine environment characterized by fossil sand depositions in the upper section. The sand is rich in gastropods, lamellibranches, algæ and benthic fauna (Ammonia tepida, Ammonia beccarii, Elphidium crispum, Peneroplis pertususles Miliolidae, Peneroplis pertusus , Rosalina sp and Peneroplis planatus). This facies evolution indicates a relative sea-level rise which flooded the fluvial system at the coastal plain during the late Holocene. Results allowed the reconstruction of the Holocene shoreline variations along the northern coast of Sfax and complete the established records of sea-level fluctuations in southeast Tunisia during the last 10 000 years.