Trace fossils from the Barrancos and Colorada formations, Ordovician, Ossa-Morena Zone, Portugal and Spain

The record of Ordovician trace fossils in the Portuguese-Spanish border region of Barrancos-to-Oliva de la Frontera, Ossa-Morena Zone, is briefly reviewed. Here the Lower-Middle Ordovician Barrancos Formation and the Upper Ordovician Colorada Formation provide contrasting sedimentary facies and trace fossil associations. The upper part of the Barrancos Formation (also known as the Xistos com Phyllodocites Formation) is a finely laminated, mudrock-dominated, unit with trace fossils that include Dictyodora, Nereites, “scribbling” traces, delicate Oldhamia like traces, and shallow arthropod-type traces. Although it has figured in the literature as an example of a moderately diverse lower Palaeozoic deepmarine trace fossil assemblage, deposition probably took place on a (distal?) shelf rather than a true deep-water setting. By contrast, the Colorada Formation is a sandstone-dominated, often heavily bioturbated, near-shore unit, with Skolithos, stellate trace fossils (?Stellascolites), Cruziana and unusual Rusophycus.