The stratigraphy of the Dyvikvågen Group, Stord : a revision.

Abstract

A revision of the stratigraphy of the Upper Ordovician to Lower Silurian Dyvikvågen Group is presented. This group of sediments rests with primary stratigraphic unconfirmity upon a substrate of basaltic greenstones cut by basic dykes (Nonshaug Formation) and underlying gabbros and serpentinites. Thismagmatic complex, which is inferred to represent a dismembered ophiolite fragment, was deformed and eroded prior to Upper Ordovician (Ashgill) times. From base to top of the Dyvikvågen Group contains: the Limbuvik Formation (local basal conglomerates, sandstones, siltstones, limestones and calcareous phyllites), The Vikanes Formation (graptolitic shales) and the Utslettfjell Formation (polymict conglomerates). The revised stratigraphy of the Dyvikvågen Group and substrate is briefly discussed in terms of the association of obducted and deformed ophiolite fragments with a unconformably overlying Upper Ordovician to Lower Silurian cover sequence, a common feature in the allochthonous Caledonides of western Norway.