KALVSJØEN FORMATION
(Kalvsjøformasjonen)
(Owen 1978)
(Previously termed: 5a, Gastropod kal ken, Gastropod Limestone).
Main Lithologies. Limestones Kalvsjøen Limestone, Kalvsjøkalken)
Basal Stratotype. Hadeland: Track to Finnlaus, Grinda (Owen 1978, Fig. 9A) (NM 845 872).
Definition. The Kalvsjøen Formation largely consists of nodular and bedded bioclastic limestones alternating with thin shales (Owen 1978 p. 18, Fig. 9; Heath 1989). The formation contains local accumulations of carbonate blocks, the best exposed being at Kalvsjø quarry where it is at least 20m thick. These are interpreted by Dr R.A.Heath of Aberdeen University as channel fill deposits (1989). The base of the Kalvsjøen Formation marks a fairly abrupt change to bedded limestones with thin shales. It overlies the Kjørrven Formation in the south, the Grinda Member of the Lunner Formation in the central part of its outcrop and the Gamme Formation in the north. The formation thickens southwards from approximately 60m at Grinda and Gammehaugen to about 80m around Lunner. It probably represents part of the same carbonate facies belt as the Langåra Formation in Oslo-Asker and Bønsnes Formation in Ringerike. It differs however in lacking thick shales (except very locally), in Palaeoporella limestones being very rare and in the development of local channel fill deposits.
Fauna and Age. Unlike the underlying units and equivalents in Oslo-Asker and Ringerike, trilobites are rare in the Kalvsjøen Formation (Owen 1981 p.8, Table 1). The occurrence of Amphilichas dalecarlicus in the lower part of the formation suggests a correlation with the Rawtheyan Bønsnes Formation in Ringerike. The only diverse trilobite fauna from the Kalvsjøen Formation is outlined by Owen & Heath (1990) and has a similar generic composition to faunas from the underlying Kjørrven Formation. Some of the echinoderms from the Kalvsjøen Formation have been described and include cystoids (Bockelie 1979, 1984), crinoids (Briskeby 1980) and a bothriocidarid echinoid (Bockelie & Briskeby 1980). Other elements of the biota include brachiopods, gastropods, corals, bryozoans, and (rarely) the calcareous alga Palaeoporella.
(From Owen et al., 1990: The Ordovician Successions of the Oslo Region, Norway. NGU Special Publication 4. Figs. refer to the printed version.