Despite the large number of studies on the Paleocene–Eocene thermal maximum (PETM), the knowledge of
environmental and biotic responses in shallow marine environments remains quite poor. Benthic foraminiferal
assemblages of the Sidi Nasseur and Wadi Mezaz sections in Tunisia were studied quantitatively and the
paleoecologic interpretations provide new insights into the complex relationship between PETM global
warming and perturbations of shallow marine settings. These sections expose upper Paleocene to lower
Eocene shales and marls of the El Haria Formation up to the phosphate layers of the Chouabine Formation
underlying the El Garia limestones. The Sidi Nasseur section contains a more complete and expanded
Paleocene–Eocene boundary interval compared to Wadi Mezaz, although being truncated at the top.
The Wadi Mezaz section contains a more complete post-PETM interval. The studied interval can be subdivided
into a sequence of 4 biofacies, representing respectively a latest Paleocene biofacies, two PETM
biofacies and one post-PETM Eocene biofacies.
The latest Paleocene biofacies 1 consists of numerous calcareous benthic foraminifera (e.g. Anomalinoides
midwayensis, Frondicularia aff. phosphatica and various Bulimina and Lenticulina species), abundant noncalcareous
taxa (Haplophragmoides) and rare planktic foraminifera, indicating a slightly hypersaline eutrophic
inner neritic to coastal environment, regularly interrupted by oxygen deficiency (moderate dysoxia).
During the latest Paleocene, this highly productive environment shallowed as indicated by the increasing
abundances of A. midwayensis. The variable dominance of non-calcareous agglutinated taxa in biofacies 1
indicates post-mortem dissolution effects. The TOC δ13Corg record reveals a sharp negative excursion,
marking the base of the Eocene. In general, the absence of lithologic changes, an increasing sedimentation
rate and absence of reworking indicate that the initial part of the PETM is complete and expanded in the
Sidi Nasseur section. A sharp faunal turnover coincides with this negative δ13Corg excursion and is characterized
by the disappearance or diminution of common Paleocene taxa in this area. During the PETM, benthic
foraminifera are less abundant and consist of opportunistic non-calcareous taxa together with deeper
dwelling (middle neritic) lagenids and buliminids (biofacies 2 and 3). Planktic foraminifera, dominated by
flat-spired Acarinina (mainly A. multicamerata), become more abundant, as observed in many open marine
sequences worldwide. All these faunal parameters suggest more stressed probably severe dysoxic sea floor
conditions within a transgressive phase during the onset of the PETM. An estimation of the total duration
of the Sidi Nasseur PETM interval is difficult to establish, yet the lack of recovery carbon isotope values suggests
that the preserved PETM interval reflects only a part of the CIE “core”. The top of the PETM interval is
truncated due to local (?) erosion during the early Eocene. The Eocene recovery fauna is mainly composed
of Lenticulina and Stainforthia species (biofacies 4), indicating restricted coastal to hyposaline lagoonal
eutrophic conditions, distinctly different from earlier environmental conditions.