Ichnofossils and body fossils from the Permian of the Sorgue Valley (Saint-Affrique Basin, southern France): palaeoenvironmental implications

We report a new palaeontological assemblage from the Sakmarian (Early Permian) of Moulin de Latour in the Saint-Affrique Basin (southern France). Pelitic beds show the co-occurrence of arthropod (Diplopodichnus biformis) and tetrapod (Batrachichnus salamandroides and Dromopus lacertoides) tracks with jellyfishes (Medusina atava). Ichnofossils also include some swimming tracks of fishes. They show several morphologies, including Undichna quadrisulcata and three morphotypes of Undichna isp. The content of the palaeontological assemblage as well as the lithological features of the fossiliferous levels suggest that the depositional environment was a lake/playa system periodically flooded. Terrestrial plants (Autunia conferta) show that this environment was bordered by a pteridosperm-dominated flora. The dense accumulation of jellyfishes observed in some surfaces is interpreted as mass mortality events in lakes during dry periods. The significance of this discovery is threefold: (1) The swimming trails of fishes are the first ones to be reported from the Saint-Affrique Basin, and they are extremely rare in Permian deposits from France; (2) The co-occurrence of Undichna with tetrapod tracks is not common in Permian deposits worldwide; and (3) The recurrent occurrence of jellyfishes in Permian freshwater environments suggests a peculiar ‘taphonomic window’ for that time interval.