Sleipner Formation (new)
(From NPD Bulletin no. 3)
Recommended as Member in Norlex
Vestland Group
Name
From the Sleipner Field. Sleipner was Odin's eight-legged horse in Norse mythology. (Larsen and Jaarvik, 1981).
Well type section
Norwegian well 15/9-2
(Statoil) from 3657 m to 3699 m, coord N58°25'34.06", E01°42'28.2" (Fig. 26).
Well reference section
Norwegian well 15/12-1
(Statoil) from 3152 m to 3204 m, coord N 58°10'32.6", E01°44'23.6" (Fig. 27).
Thickness
42 m in the type well and 52 m in the reference well.
Lithology
The formation consists of a mixed sandstone and silty clay stone lithology with coal measures. The sandstones are non-calcareous, light to medium brown, fine to medium grained, with occasional coarse and pebbly layers. The sandstones show a moderate to poor sorting with sub-angular to sub-rounded grains. The silty claystones are medium to dark grey or greyish brown, micromicaceous, hard and slightly fissile. Coal fragments, fossil leaves and root hairs are commonly found. The coals are mature, black and massive, often with thin laminations of silty claystone.
Boundaries
The formation lies unconformably on erosional relics of lower Jurassic or
older rocks, and a break on dipmeter logs can frequently be observed.
Sandstones within the formation in general show lower interval velocites
than sandstones in the underlying formations. The upper boundary marks the
transition into the shales of the Viking Group or
the sandstones of the Hugin Formation. Where the
formation is overlain by the shales, clear breaks can be observed both on
sonic and gamma ray logs. Where the formation is overlain by the Hugin
Formation, the erratic sonic log pattern of the Sleipner Formation becomes
smoother when entering the overlying sandstones. On gamma ray logs the
sandstones of the Hugin Formation in general appear cleaner, more massive
and often thicker than in the Sleipner Formation.
Distribution
The formation is found in the southern Viking Graben between approximately 58° and 60°N. The Ness Formation in the East Shetland Basin is broadly equivalent to the Sleipner Formation. The name Sleipner Formation should be applied when the marine sandstones underlying the coaly sequence are absent. Non-marine sands, and associated strata, in the Central Graben and Norwegian-Danish Basin are referred to the Bryne Formation.
Depositional environment
The Sleipner Formation represents a continental fluviodeltaic coaly sequence.
Age
Usually Bajocian to Bathonian, but can locally be as young as Callovian (e.g. 15/12-1).
