Paleocene–Eocene palaeoenvironmental conditions of the main phosphorite deposits (Chouabine Formation) in the Gafsa Basin, Tunisia

•We investigated a phosphate rich Paleocene–Eocene succession in Tunisia.•Various diagenetic features are observed on calcareous microfossils.•Diagenesis is clearly dominated by processes related to phosphorite formation.•Negative δ13C shift is observed in marl dominated beds along the series.•Despite local factors, this shift is related to either the onset of PETM or pre-PETM global record.