Contribution of the geochemical, physico-chemical, mineralogical, and statistical approaches to the reconstructing of the Holocene depositional environments along South-Eastern Tunisia

The characterization of organic matter (OM) composition, physico-chemical, geochemical, and mineralogical studies of sedimentary core can help to better understand the paleoclimates and the depositional environments. The purpose of this work is to identify the factors monitoring the mineralogical composition and the sedimentation of sebkha Mhabeul sediments (southeastern Tunisia), during the Holocene. A 100.5 cm core (Mh 1) collected from this sebkha was analyzed for the determination of chemical composition by X-ray fluorescence (XRF), carbonate content by Bernard calcimetry, grain-sized sediments by AFNOR sieves, OM content by Rock-Eval 6 Pyrolysis, and mineralogical composition by X-ray diffraction (XRD), scanning electronic microscope (SEM), and infrared spectroscopy (IR). The sedimentary fillings of this sebkha, constituted by fine fractions, are characterized by the dominance of the detrital minerals (72–96 %) with high quartz percentages (42.2–91.5 %). The mineralogical composition of the studied sediments included detrital minerals (clay minerals, quartz, and feldspars), carbonate minerals (ankerite, dolomite, and calcite), and evaporitic minerals (halite, bassanite). The clay minerals (11–14%) are composed of a mixture of kaolinite, illite and palygorskite. Fourier transform infrared (FTIR) absorption spectra of all sediment samples confirm the mineralogical composition obtained by XRD and the existence of OM, by defining the band assignments for OM and different minerals as quartz, feldspar, clay, and carbonate minerals. The Rock Eval pyrolysis shows that the OM is immature and has a mixed origin (terrestrial and aquatic). The statistical analyses prove the results of geochemical and mineralogical studies. Indeed, the principal component analysis (PCA) of geochemical and mineralogical data and the depth help to prove the relationships between minerals and chemical elements. Moreover, the negative correlation between the Rock Eval Pyrolysis parameters and the depth shows a homogenous statistical group.