Abstract
This work deals with mineral and diatom contents of the lower Eocene (Ypresian) phosphatic pellets of the Gafsa-Metlaoui basin, using XRD and SEM method. Since, mineral composition and fossil diatoms are best indicators of the depositional environments and diatom content leads to understand the role of diatoms in the formation of siliceous rocks especially porcelanite of the interbedded facies. This study indicates that phosphate minerals (fluorapatite) are associated with opal CT, carbonate mineral (dolomite and calcite), pyrite, sphalerite, and clinoptilolite. This association corroborates with deposition of the Ypresian sediments of the Gafsa-Metlaoui basin in alkaline and anoxic to suboxic marine environments under sulfate-reducing conditions. On the other hand, the exogangue is roughly free from diatoms except some highly dissolved diatom frustules. Endogangue displays some preserved diatom frustules, which allow the determination of three species: Paralia sulcata, Stephanopyxis sp. and Aulacoseira sp. Aulacoseira sp occurs at the eastern part of the Gafsa-Metlaoui basin (M’Zinda section) and it is known as a freshwater diatom. Stephanopyxis sp. and P. sulcata are both indicative of warm shallow marine water. They occur at Metlaoui Table and Kef Eddour sections, respectively.
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