Trace fossils and paleoenvironments of a Late Silurian marginal-marine/alluvial system: The Ringerike Group (Lower Old Red Sandstone), Oslo region, Norway

The Late Silurian Ringerike Group of southern Norway is a lower Old Red Sandstone megasequence that marks the regressive culmination of Cambro-Silurian marine deposition in the Oslo Region. The basal Sunduollen Formation represents deposition in a number of sub-environments of a broad, muddy coastal-plain setting, and is succeeded by fluvial deposition of the Stubdal and Store Aroya Formations. The terminal formation of the Ringerike Group, the Holmestrand Formation, represents deposition in sub-environments of a sandy beach setting. Both the marginal-marine Sundvollen and Holmestrand formations contain a wide variety of trace fossils (Arenicolites, Cruziana, Didymaulichnus, Diplichnites gouldi, Diplocraterion, Gordia marina, Margaritichnus, 'Merostomichnites, Oniscoidichnus, Paleohelcura, Palmichnium stoermeri, ?Polarichnus garnierensis, Rusophycus, Siskemia bipediculus, Skolithos, Steinsfiordichnus brutoni, Taenidium) that are discussed and analyzed, comprising the first complete Late Silurian study from the Baltic area. The trace fossils, which occur in facies-controlled assemblages, are combined with sedimentologic evidence to perform a high-resolution paleoenvironmental analysis of the Ringerike Group. Multivariate cluster analysis of the bulk Ringerike ichnofauna with similar-aged ichnofaunas from other paleocontinents supports the hypothesis that localized environmental factors outweighed provincialism as the dominant control on the composition of arthropod-trackway-dominated trace-fossil assemblages during the Siluro-Devonian.