Three ichnogenera are described from a 50 to 500 m thick shallow-water sandstone-shale sequence (Sierra Albarrana Quartzites). The ichnofauna consists of the burrows of worm-like animals (Arenicolites, Monocraterion, and Skolithos). The age of this formation, previously considered to be Precambrian or Palaeozoic, has been the subject of discussions. We may now assign it an Early Phanerozoic age, in agreement with the known stratigraphic distribution of the ichnofossils found.