SKOGERHOLMEN FORMATION

(Skogerholmformasjonen)

(New name)

(Previously termed: 4d; Isotelus beds)

Main Lithologies. Limestone, shale and siltstone.

Basal Stratotype. Oslo-Asker: Skogerholmen (Fig. 21) (NM 862 353).

Hypostratotypes. Oslo-Asker: Søndre Skjerholmen (NM 968 365), SW Hovedøya (Figs. 22, 23) (NM 968 409), Spannslokket (NM 855 358).

Definition. The Skogerholmen Formation and its two members were named by Owen (1981 Fig. 1) but not defined. The base of the formation marks a change to a limestone dominated succession from the largely shaly Skjerholmen Formation and is defined at the first continuous limestone horizon in the type (Skogerholmen) section (Fig. 21). The formation is 33.06m thick on Skogerholmen, about 43m on Hovedøya and about 39m on Skjerholmen.

Fauna and Age. The Skogerholmen Formation is generally poorly fossiliferous but shelly fossils, notably trilobites, brachiopods and cephalopods are known from various horizons, especially in the upper part, and indicate an Ashgill age.