Deep-Sea Fans

Turbiditic depositional systems are characterized by diverse, pre- and post-depositional trace fossils dominated by pascichnia, fodinichnia, agrichnia, and chemichnia. They belong mostly to the Nereites Ichnofacies, which includes the Nereites subichnofacies (mostly in shale-dominated facies), the Paleodictyon subichnofacies (mostly in thin- to medium-bedded turbidites), and the Ophiomorpha rudis subichnofacies (mostly in thick-bedded sandstones). Individual turbiditic beds are first colonized by opportunistic pascichnia, later by stationary fodinichnia and agrichnia, while oxygen and food content within the sediment decrease. Changes of oxygenation, food content, sedimentation rate, and other factors can influence the trace-fossil diversity and ichnofabric over longer time intervals. The Nereites Ichnofacies assemblages evolved since their appearance in the Early Ordovician. Their diversity decreased since the Late Carboniferous through the Permian/Triassic boundary crisis, increased during the Triassic and Jurassic and dropped during Early Cretaceous. Then diversity reached a maximum during the Eocene, showing a high diversification of agrichnia.