Trace fossils from Permian mixed siliciclastic/carbonate shallow-marine deposits of Southern Tunisia: implications for sedimentary environment interpretation

The marine middle-upper Permian exposed in southern Tunisia represents a typical example of a mixed siliciclastic-carbonate shelf system. These deposits contain a diverse assemblage of trace fossils-21 ichnogenera in total-representing the highest known diversity in marine Permian worldwide. The ichnofossils are typical of the Cruziana ichnofacies, with its possible variants. In the thinly bedded fine-grained sandstones of the offshore-transition environment, the presence of ?Nereites, Protovirgularia, and Psammichnites, and other horizontal traces represent the archetypal to distal variants of the Cruziana ichnofacies. Lower shoreface sandstones are characterized by trace fossils such as Archaeonassa, Palaeophycus, Parataenidium, and Siphonichnus, while the upper shoreface and foreshore sandstones yield a more diverse suite, including ?Ancorichnus, Cruziana, ?Diplocraterion, Halopoa, ?Helminthopsis, Palaeophycus, Parataenidium, Psammichnites, Planolites, and Siphonichnus. Atypically, these collectively reflect signals of the proximal to archetypal Cruziana ichnofacies, where the Skolithos ichnofacies should already be present. This is explained by less energetic conditions related to possible morphological protection and the influence of tides. Of particular significance is the identification of Cruziana for the first time in the same stratigraphic unit where the only known Tunisian specimen of the trilobite Pseudophillipsia sumatrensis (Roemer) group has been found-likely the trace maker. Inter-reef tidal channel sandstones also preserve ichnofossils such as Planolites, Phycodes, Parataenidium, Protovirgularia, and ?Gyrophyllites, which are attributed to the archetypal Cruziana ichnofacies.