Stratigraphy and biota across the Ordovician-Silurian boundary in Hadeland, Norway

The uppermost Ordovician and lowest Silurian succession in Hadeland is divided into three formations with both lithofacies and biota reftecting changes in sediment supply and sea level. The lowest unit studied, the Kalvsjøen Formation, comprises nodular limestones and shales which are the host sediments for at !east five debris ftow deposits. The overlying Klinkenberg Formation (new name) is a mixed carbonate·siliciclastic unit characterised by its heterogeneity and is broadly Himantian in age. It is overlain by the dominantly siliciclastic Sælabonn Formation which contains the trilobite Acemaspis elliptifrons near its base suggesting that the lower formational boundary is dose to the base of the Silurian. The Klinkenberg and Sælabonn formations together comprise the Skøyen Group. Low stands in sea leve! are marked by karst surfaces at or near the tops of the Kalvsjøen and Klinkenberg formations. A major sea leve! rise is reftected in the rapidly deposited sediments of the Sælabonn Formation.