BØNSNES FORMATION
(Bønsnesformasjonen).
(Owen 1979)
(Previously termed: 5a Gastropodenkalk, Gastropod Limestone).
Main Lithologies. Limestone and calcareous shale Bønsnes Limestone, Bønsneskalken).
Basal Stratotype. Ringerike: West Frognøya (NM 653 577).
Definition. The base of this ca. 1 00m thick formation was taken by Owen (1979 p.255) at the first development of dark, platy limestones containing the alga Palaeoporella. These strata are overlain by lighter coloured limestones containing silicified corals. At Stamnestangen and on Store (=Vestre) Svartøya higher levels in the Bønsnes Formation include rubbly limestones with interbedded calcareous shales which have yielded the very diverse shelly faunas listed by Kiær (1897). The highest part of the formation comprises calcareous (>45cm thick) shales with scattered limestone nodules.
Fauna, Flora and Age. In addition to algae (Kiær 1922) and stromatoporoids (Kaljo et al. 1963), the Bønsnes Formation contains trilobites (Owen 1981; Bruton & Owen 1988), brachiopods (Kiær 1897; Holtehahl 1916; Hanken & Harper 1985; Harper in prep.), cephalopods (Strand 1933), gastropods and monoplacophorans (Koken 1925; Yochelson 1977), bryozoans (Brood 1980), corals (Bassler 1950; Hanken 1979a; Kaljo et al. 1963; (Kiær 1899, 1903, 1929; Neuman 1969, 1975; Scheffen 1933) and ostracods (Henningsmoen 1954). The trilobite fauna indicates a Rawtheyan age and includes species of Stenopareia Remopleurides, Eobronteus, Stygina, Holotrachelus, proetids, Erratencrinurus (Celtencrinurus), Atractopyge and Amphilichas.
(From Owen et al., 1990: The Ordovician Successions of the Oslo Region, Norway. NGU Special Publication 4. Figs. refer to the printed version.