Sedimentology and Geochemistry of the Chouabine Phosphate Succession (Upper Paleocene-Lower Ypresian) in El Guettar Area (Gafsa Region, Central Tunisia)

Abstract

This work is set out to conduct a sedimentological and geochemical study of the phosphate series in Oued Tarfa section in El Guettar area (east Gafsa region) in order to characterize the phosphate deposits and reconstruct the phosphatogenesis environment. The studied phosphate series corresponds to the Chouabine Formation (Upper Paleocene–Lower Eocene) which is underlain by the uppermost dolomitic bed of the Selja Formation (Lower Paleocene). It is also and overlain by the carbonate cliff of the Kef Eddour Formation (Lower Eocene). The series mainly includes nine phosphate layers alternating with limestones and marls. The latter intercalations are themselves intercepted with 5–10 cm-thick phosphate horizons. The total rock major element contents show an alternation of phosphate layers relatively rich in MgO and Na2O with low concentrations of Fe2O3 and SiO2 that may be related to transgressive open-marine environment and sandy phosphate layers rather poor in MgO and Na2O with significant concentrations of Fe2O3 and SiO2 that may have been developed in regressive progradinglittoral environment. The open marine phosphates are richer in P2O5 than the littoral sandy ones.