RE-EVALUATUION OF THE ORIGINAL ICHNOASSEMBLAGE OF THE “ENTRADAICHNUS ICHNOFACIES,” JURASSIC OF UTAH

The original ichnoassemblage of the “Entradaichnus ichnofacies” was described from Jurassic eolianites in southeastern Utah in 1985. A review of this ichnoassemblage based on collections at the University of Utah and at the two original localities reveals that the three ichnotaxa named are invalid and that the originally reported stratigraphic position of these localities was in error. Entradaichnus is a taphotaxon, a synonym of Taenidium based on specimens of unlined, unbranched, sinuous, cylindrical burrows with mensicate backfill preserved in coarse sandstone. Pustulichnus similarly is a taphotaxon based on specimens of relatively short, unbranched, unornamented, cylinders perpendicular to bedding of Skolithos preserved in coarse sandstone. Digitichnus, however, is not a biogenic structure but instead a cylindrical weathering feature (small, sandstone-filled pipe) in thinly laminated sandstone. Both original localities of the “Entradaichnus ichnofacies” are south of Moab, Utah, and were reported to be in the Middle Jurassic Entrada Sandstone, but they are actually in the upper part of the Lower Jurassic Navajo Sandstone, a few meters below the base of the overlying Carmel Formation. The “Entradaichnus ichnofacies” is supposedly characterized by an ichnofauna of Planolites, Palaeophycus, Skolithos, Arenicolites and Taenidium, and ichnoassemblages that contain one or more of these ichnogenera are characteristic of interdunal facies in Permian-Jurasssic eolianites of the American Southwest, although they can occur in what must have been moist dunal settings. However, the “Entradaichnus ichnofacies” is not a distinctive ichnofacies but simply a synonym of the Scoyenia ichnofacies. The distinctive invertebrate ichnofacies of eolian paleoenvironments is the Octopodichnus ichnofacies, recognized by low diversity ichnofaunas of arthropod walking traces (Octopodichnus, Paleohelcura, etc.) and usually associated with footprints of the Chelichnus tetrapod ichnofacies.