The paper deals with the Middle Ordovician stage 4b in the drift covered area around Lunner railway station. The sequence studied has a thickness of more than 170 m, and almost 160 m of this belongs to stage 4b. Lithologically it consists of alternating beds of biomicrite and silty shale. The percentages of the two rock types differ from level to level, and the biomicrite beds show a highly variable development. The beds are generally poorly fossiliferous, and few index fossils have been found. Faunal and lithological comparisons with the Oslo-Asker district (type district of the Oslo Region stages) is difficult because of the local development of the facies. The only lithological comparison possible is with substage 4b?), where the similarity to the Oslo-Asker district is clear.
The Middle Ordovician of the Oslo Region, Norway. 24. Stage 4b at Lunner, Hadeland