Trace Fossils Assemblages from the Cenozoic “Flysch Units” of the Campo de Gibraltar Complex (Southern Spain)

Ichnological analysis of deep-sea trace fossil assemblages from the Cenozoic turbiditic succession of the Campo de Gibraltar Complex (Cádiz Province, southern Spain) is presented. A relatively diverse and abundant trace fossil assemblage is recognized, with 20 ichnogenera belonging to the nongraphoglyptid assemblage and 12 to the graphoglyptid assemblage. Nongraphoglyptid traces are dominated by Chondrites, Halopoa, Helminthopsis, Lophoctenium, Nereites, Ophiomorpha, Phycosiphon, Planolites, Scolicia, Thalassinoides and Zoophycos, while Gordia and Tubotomaculum are common, and Cladichnus, Gyrophyllites, Polykampton, Rotundusichnium, Rutichnus, Spirophycus and Stelloglyphus are scarce or rare. Except for Helminthopsis and Spirophycus, all ichnotaxa are post-depositional structures, with feeding forms (pacichnia and fodinichnia) dominant. The graphoglyptid assemblage consists of agrichnia, predepositional trace fossils, with abundant Desmograpton, and Paleodictyon; in turn, Helminthorhaphe, Megagrapton and Urohelminthoida are common, and the rest, including Belorhaphe, Cosmorhaphe, Glockerichnus, Helicolithus, Lorenzinia, Paleomeandron and Spirorhaphe, are scarce or rare. Trace fossil assemblages can be attributed to the Nereites ichnofacies, with dominance of the Nereites ichnosubfacies, but the Ophiomorpha rudis ichnosubfacies and the Paleodictyon ichnosubfacies could be associated to different depositional settings into the deep-marine basin-floor and the deep-sea fan. Together with the tectonic activity and climate, variations in the petrology of the source area, inducing differences in clay mineral composition, may influence the input and deposition of organic matter, affecting graphoglyptid composition. The graphoglyptid assemblage is dominated by winding and meandering structures, some branched, as well as networks; while radial structures and spiral structures are scarce and little diversified. The studied successions are of special interest for interpreting paleoenvironmental and evolutionary changes affecting graphoglyptid assemblages from Paleocene to Miocene in the Campo de Gibraltar Complex.