Relict Ordovician brachiopod faunas in the Lower Silurian of Asker, Oslo Region, Norway

The diverse brachiopod fauna of the lowest part of the Solvik Forrnation (Lower Llandovery) in the Asker area of the Oslo Region is a well-organised association overwhelmingly dominated by relict genera more typical of the Ordovician. These taxa appear to have survived the extinction events of the late Ordovician in deep water facies in or adjacent to the central Oslo Region. The gradual disappearance of Ordovician elements through the sequence is considered to have resulted from unsuccessful competition with immigrant stocks of Silurian aspect that may have originated around the shelves of archipelagos created during the late Ordovician regression. Thus competition is suggested to account for the final pulse of fauna) extinction above the Ordovician-Silurian boundary.