Lark Formation

Hordaland Group

Members of Formation

Skade Member | Vade Member


English / Norwegian

Lark Formation / Larkformasjonen

Derivatio nominis

Named after the bird Lark.

Original definition

Knox, R.W.O.B. & Halloway, S. 1992. 1. Paleogene of the central and northern North Sea. In Knox, R.W.O.B. & Cordey, W.G. (eds.), Lithostratigraphic nomernclature of the UK North Sea. British Geological Survey, Nottingham.


The formation consists of brown-grey to grey-brown mudstone, silty in part, and locally grading upwards into sandstones of the Skade Member.


The Lark formation is 650 m in the type section well 21/10-4 . The formation reaches a maximum thickness of about 1000 m in the Central Graben (Knox & Holloway, 1992).

Geographical distribution

The Lark Formation is present over much of the Central and Northern North Sea.

Type well

Well name

UK 21/10-4

Interval of type section (m)

From 1217-1867 m in well 21/10-4.

Reference well

No reference well is presently defined.


Lower boundary (basal stratotype)

The lower boundary is marked by an upward change from a variable association of green- grey mudstone, grey silty mudstone, or sandstone of the Horda Formation, to grey-brown or brown-grey mudstone of the Lark Formation.

Upper boundary (characteristics)

The upper boundary of the Lark Formation is marked by an upward change from grey- brown to brown-grey mudstones of the Lark Formation to overlying green-grey, commonly glauconitic, silty mudstones or basal sandstones of the Nordland Group.

In the Central Trough, a zone occurs which has high gamma-ray readings and usually a slightly lower velocity than the underlying and overlying claystones. The upper boundary of the Hordaland Group is placed at the base of this zone.


Early Oligocene to early mid Miocene (Knox & Holloway, 1992).

Depositional environment

The mudstones of the Lark Formation were deposited in a distal shelf setting (Andrews et al., 1990; Knox & Holloway, 1992).


In blocks 2/2 and 2/3 the Lark Formation contains a unit of Upper Oligocene shallow marine sandstones assigned to the Vade Member.

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