Caithness Flagstone Group

The Caithness Flagstone Group is a Devonian lithostratigraphic group (a sequence of rock strata) in northern Scotland. The name is derived from the traditional county of Caithness where the strata are well exposed, especially in coastal cliffs.^[1]

Caithness Flagstone Group
Stratigraphic range: Eifelian (Devonian)
The Sandwick Fish Bed
Type	Group
Unit of	Old Red Sandstone Supergroup
Sub-units	Upper Stromness Flagstone Formation, Lower Stromness Flagstone Formation
Underlies	Eday Group
Overlies	Yesnaby Sandstone Group
Thickness	over 2,000 m (6,600 ft)
Lithology
Primary	Sandstone
Other	Mudstone, siltstone
Location
Region	Orkney, Shetland, Highland
Country	Scotland
Extent	Moray Firth to Shetland
Type section
Named for	Caithness

Outcrops

These rocks are exposed, along the Moray Firth and along the eastern side of Sutherland and throughout Caithness, across Orkney and, to a rather lesser extent, in Shetland.

Lithology and stratigraphy

The Group comprises the Upper Stromness Flagstone Formation and the Lower Stromness Flagstone Formation laid down in the lacustrine Orcadian Basin during the Eifelian Stage of the Devonian Period.

It contains numerous rhythmic sequences of mudstone, limestone, siltstone and sandstone of which there are 25 and 38 in the constituent lower and upper formations respectively. A conglomerate occurs at the base of the lower formation. A notable element is the Sandwick Fish Bed which defines the junction of the two formations and from which a diverse range of fish fossils have been recovered.^[2]