Use of Trace Fossils for Interpretation of Triassic Depositional Environments, Northeast Border of French Massif, Central France: ABSTRACT

Abstract

A variety of trace fossils occur in Triassic sediments of the northeast border area of the French massif as follows: 1. Vertebrate tracks: numerous species (approx. 30) that point to the existence of: (a) numerous large herbivorous reptiles (Isochirotherium) accompanied by small ones (Rhynchosauroides, Rotodactylus); rare carnivorous reptiles of relatively small size (Coelurosaurichnus, Sphingopus, Anchisauripus); common omnivorous or necrophagous reptiles (Brachychirotherium); (b) very small insectivorous or herbivorous reptiles or amphibians (small Rhynchosauroides, Prolophonichnium, Platipes, Furcapes). 2. Invertebrate trace fossils: Isopodichnus, Planolites, Cochlichnus. 3. Plant imprints: Voltzia sp. 4. Associated primary sedimentary structures: ripple End_Page 697------------------------------ marks, mud cracks, salt-pseudomorphs, and groove marks accompanied by vertebrate footprints on the same slab. The set of trace fossils and associated sedimentary structures indicates an origin at the fringes of aquatic areas and at the borders of vegetation zones. These large areas were used by the ruling reptiles as pathways between the water and the vegetation where they found resting, breeding, and feeding places. The smaller vertebrates were living in habitats near the vegetation or at the borders of small channels. The invertebrate traces point out the proximity of water and the fluctuation of water level. The primary sedimentary structures suggest variable water levels and the salt-pseudomorphs suggest marine water. The assemblage of traces suggests very large sandy areas between the sea or lagoons and zones of dense vegetation which favored proliferation of the mobile Archosaurs. End_of_Article - Last_Page 698------------