Hukodden Member
(Hukoddleddet)
(New name)
(Previously termed: 3c-α , Der Megalaspiskalk, Megistaspiskalk, Megalaspis Limestone, Megistaspis Limestone).
Main Lithology. Limestone.
Basal Stratotype. Oslo-Asker: Huk (Fig. 7) (NM 938 410).
Hypostratotypes. Oslo-Asker: Engervik (NM 843 302) YP
(Fig. 6), Modum (Vikersund): Øvre Øren (NM 556 444). Eiker-Sandsvær Ringerike, Hadeland: as for formation.
Thickness variation. Oslo-Asker: Huk, Killingen, Engervik, Vekkerø (1.6m). Eiker-Sandsvær Råen Stablum (1.0m), Hals (1.07m). Modum (Vikersund): Øvre Øren (0.9m). Ringerike: Smeden (1.0m). Hadeland: Hovodden (1.56m), Granvollen (1.6m).
Definition. The Hukodden Member marks an abrupt change from the shales of the Tøyen Formation and is a light weathering, fine grained, limestone with thin shale laminae. Much of the limestone is dolomitic and accumulations of shelly material are commonly visible along irregular bedding planes/pressure solution seams.
Fauna and Age. Macrofossils are difficult to extract from the member but it has yielded trilobites including the asaphid Megistaspis (M) limbata limbata (e.g. Brøgger 1882, Jaanusson 1960, p.345) indicating a correlation with the Langevoja Substage. In contrast, Kohut (1972, pp.442-443) argued that the conodonts from the member belong within Lindström's (197.1) Paroistodus originalis Zone and thus indicate an older age for the member. Recent work by Stouge and Rasmussen (pers. comms. 1987 & 1989 and Rasmussen 1989) largely confirms Kohut's correlation and places the base of the P. originalis Zone above the base of the Hukodden Member and the base of the overlying Microzarkodina parva Zone also lies within the upper part of the member.
(From Owen et al., 1990: The Ordovician Successions of the Oslo Region, Norway. NGU Special Publication 4. Figs. refer to the printed version.