Ordovician Bathyal Trace Fossils From Metasiliciclastics in Central Norway and Their Sedimentological and Paleogeographical Implications

Numerous trace fossils are recognized in metasiliciclastic rocks of the Lower-Middle Ordovician Lower Hovin Group, Upper Ordovician Ekne Group and on roofing slates from an unknown locality (probably Ordovician) from the Trondheim region, central Norway. The trace fossil assemblages are dominated by meandering pascichnial forms, i.e., Helminthoidichnites in the Lower Hovin Group and Helminthoidichnites and Nereites in the slates. Protovirgularia, Dictyodora, ?Planolites and ?Palaeophycus are less common. Alcyonidiopsis, ?Trichophycus, Chondrites, cf. Chondrites, Gordia, ?Phycodes, ?Helminthopsis, cf. Naviculichnium, Treptichnus, Saerichnites, Megagrapton and ?Paleodictyon (Squamodictyon) are rare. The trace fossils were collected or observed at 17 different localities and represent assemblages belonging to the Nereites ichnofacies (deep-sea flysch deposits with thinly bedded turbidites). They reflect a distal Nereites subfacies (fan-fringe or basin-plain deposits) transitional to a Nereites/Paleodictyon subfacies (proximal fan facies). The trace fossil assemblages indicate an opportunistic style of colonization related to fluctuations in food supply introduced by turbidity currents.