Article: Ichnofabric from the Upper Jurassic lithographic limestone of Cerin, southeast France
The upper Kimmeridgian lithographic limestones of Cerin, France, are lagoonal deposits, remarkable for the local occurrence of invertebrate burrows. Burrows are rare in the lower, well-laminated lithographic limestones, attesting to the absence of autochtonous benthic animals and, therefore, to the unfavourable life conditions on the lagoon floor. However, burrows are frequent in the upper lithographic limestones, the most abundant being Tubularina lithographica. These burrows are small, partly filled by pellets and were probably inhabited by intertidal polychaete worms. They are similar to Recent burrows restricted to the intertidal area of the lagoon of Aldabra (Seychelles). T. lithographica is fossilized as an 'open burrow', attesting to the drying-out of the lagoon and the onset of lithification. Other trace fossils, dominated by Thalassinoides and Rhizocorallium, are restricted to certain intermediate levels between the lower and upper lithographic limestones. The resulting ichnosequence may be the result of increasing periods of emersion in the lagoon. Compared with other well known lithographic limestones (e.g. Solnhofen, Canjuers, Montsec), this rich and unique ichnofabric clearly reflects the coastal location of the Cerin site.