KJØRRVEN FORMATION
(Kjørrvenformasjonen)
(Owen 1978)
(Previously termed: 4d, 4c-α (pars), 4c-β-4d, Isotelus Shale).
Main Lithologies. Limestone, calcareous siltstone and shale.
Basal Stratotype. Hadeland: Track to Finnlaus, Grinda (Owen 1978 Fig. 9A) (NM 845 874).
Hypostratotype. Hadeland: Railway cuttings east of Kalvsjø (NM 876 853).
Definition. The Kjørrven Formation comprises beds of limestone and calcareous siltstone up to 20cm thick alternating with silty shales commonly less than 16cm thick but in some instances up to 60cm in thickness (Owen 1978 p. 18, Figs 9,10). The dark grey limestones decalcify to brown rottenstones and the grey shales become pale and friable on weathering. The base of the formation is transitional around Lunner but further north in the basal stratotype it marks an abrupt change from the shales of the Grinda Member of the Lunner Formation. Limestone horizons become more common towards the top of the Kjørrven Formation and the unit has a maximum thickness of about 1 00m.
Fauna and Age. The Kjørrven Formation contains a very diverse fauna of trilobites, brachiopods, corals, bryozoans, cephalopods, ostracods, echinoderms and conularids The trilobite fauna comprises at least 25 species (Owen 1981 pp.7-8, Tables 1, 2, Fig. 2) and although the association of genera is most similar to that of the type Cautleyan Stage, the species present most notably Sphaerocoryphe aff. kingi Ingham and Calymene (s.l.) holtedahli Størmer indicate a Rawthyan age. The same is also true for the brachiopods (pers. comm. D.A.T. Harper 1983).
(From Owen et al., 1990: The Ordovician Successions of the Oslo Region, Norway. NGU Special Publication 4. Figs. refer to the printed version.