Horda Formation

Hordaland Group

Members of Formation

Frigg Member | Grid Member>


English / Norwegian

Horda Formation / Hordaformasjonen

Derivatio nominis

From the Horda Platform. The formation is formally named by Knox & Holloway (1992), but the term has been widely used informally since 1987 where it first appeared in an unpublished report by RRI (now Simon Robertson Ltd.).

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 Horda Formation consists predominantly of grayish mudstone with subordinate sandstone.


The formation is 387.5 m in the UK type well 22/1-1A, and 504 m in the reference well 16/18-1, while the thickness is 808.5 m in reference well 9/4-1 and 158 m in reference well 21/22-1.

Geographical distribution

The Horda Formation is present over much of the Central and Northern North Sea, but passes laterally into the Mousa Formation along the eastern margin of the East Shetland Platform and in the west of the Outer Moray Firth (Knox & Holloway, 1992).

Type well

Well name

UK well 22/1-1A


WGS84 coordinates:
UTM coordinates:
UTM zone:

Drilling operator name

Completion date

Interval of type section (m)

1992-2379.5 m

Reference wells

Well names

UK wells 9/4-1, 16/18-1 and 21/22-1.


WGS84 coordinates:
UTM coordinates:
UTM zone:
WGS84 coordinates:
UTM coordinates:
UTM zone:
WGS84 coordinates:
UTM coordinates:
UTM zone:

Drilling operator name

Completion date

Interval of reference section (m)

UK 9/4-1: 1026.5-1835 m
UK 16/18-1: 1852.5-2356.5 m
UK 21/22-1: 1076-1234.5 m


Lower boundary (basal stratotype)

Over most of its areas, the Horda Formation rests on the Balder Formation, and the boundary is marked a upward change from dark grey, carbonaceous claystone to overlying variegated grayish mudstone and claystone. The lower boundary shows an increase in gamma-ray intensity and a decrease in velocity from the laminated tuffs of the Balder Formation into the claystones of the Hordaland Group (Fig. …..). Where the Frigg Member is present at the base of the Hordaland Group the lower boundary normally shows a decrease in gamma-ray response and an increase in velocity from the Balder Formation into the Frigg Member (Fig. …….)

Upper boundary (characteristics)

The upper boundary is placed at the contact with grey mudstones and claystones of the Horda Formation and the overlying brown mudstone of the Lark Formation. On wireline logs, the boundary is marked by a upward increase in gamma-ray readings.

"Reference" seismic sections

Location of section


Seismic section

[Colour figure]

Fossil events/zones dating the formation


Early Eocene to earliest Oligocene.



Depositional environment

The mudstones of the Horda Formation were deposited in an open marine environment, with pelagic sedimentation initially in water depths of several hundred metres (Knox & Holloway, 1992). The associated sandstones were deposited as submarine fans (Frigg Member), by gravity flows, or as open marine sands during a regressive period (Grid Member) (Isaksen & Tonstad, 1989).


The Horda Formation is here redefined to also include the Frigg and Grid members on the Norwegian sector.

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