Geochemistry and Mineralogy of Paleocene-Eocene Depositional Sequences in Oued Thelja Section, SW Gafsa, Tunisia

Abstract

The Paleocene-Eocene series associated with the Oued Thelja area is characterized with the diversity of depositional environment, evolving from sebkha to deep marine environment. This evolution is related to the occurrence of various rock types during the Paleocene-Eocene interval such as evaporates, carbonates, clays and phosphates. The mineralogical results reached by means of X-ray diffraction appear to reveal that marine transgression characterizing the El Haria and Chouabine Formations turns out to be dominated with clay minerals, carbonate-fluorapatite and calcite, which require the availability of a deep marine environment to precipitate. As for marine regression, it is represented essentially by gypsum and dolomite, indicating the existence of a shallow marine environment marking out the Thelja Formation. The geochemical results, as provided through X-ray fluorescence, appear to highlight an enrichment of SiO2, P2 O5 and CaO during marine transgression, and high amounts of SO3, CaO and MgO during decreasing sea level. The stratigraphic framework relevant to the studied section helps determine eleven third-order depositional sequences, each containing a set of sedimentary system tract. The geochemistry and mineralogy should explain the occurrence of depositional sequences and eustatic variations relevant to each sedimentary basin.