New insights on the Permian mixed siliciclastic and carbonate deposits of southern Tunisia: Facies, ichnofacies and depositional environments

The present study investigates the Permian mixed siliciclastic-carbonate system of southern Tunisia and describes the trace fossils recorded within the siliciclastic intervals. The carbonate facies represent a spectrum of depositional environments ranging from the outer shelf (CF1), through the shelf margin (CF2), to the middle to inner shelf (CF3 to CF6) settings, while CF7 corresponds to conglomeratic facies resulting from reef destruction. The siliciclastic facies (SF1 to SF9) developed on a ramp profile, while the latest Permian facies (SF10 to SF14) belong to a dominantly meandering fluvial system with flood plain red-beds. This work provides the first comprehensive review of trace fossils in this region. Seventeen ichnogenera produced by bivalves, trilobites, crustaceans, and vermiform organisms have been identified. In addition to being very common, facies-crossing ichnogenera, such as Planolites or Palaeophycus , Psammichnites , Protovirgularia , Parataenidium , Thalassinoides , and Taenidium appear to be more specific components of the Permian Cruziana ichnofacies. The combination of facies analysis and ichnofacies distribution demonstrates that the sedimentary evolution encompasses the alternation of two dominant depositional regimes represented by mixed siliciclastic-carbonate ramp sedimentation and rimmed carbonate platforms dominated by reefal development. The vertical transition from ramp to rimmed carbonate platform and vice versa reflects periodic variations in carbonate sedimentation rates, primarily controlled by sea-level fluctuations, subsidence, and resulting accommodation space, and climatic and palaeoecological conditions. Surface-to-subsurface stratigraphic correlation indicates that the subsidence played an important role in shaping the basin configuration comprising a shelf margin domain (Tebaga outcrops) separating a wide middle to inner shelf to the south from a rapidly subsiding depocenter to the north. The latter interpreted as a foredeep setting, accumulated over 4000 m of sediment, including thin turbiditic sandstones, carbonate breccias, and conglomerates derived from the adjacent rimmed platform.