Laggantuin Cornstone Member

Laggantuin Cornstone Member (LGT), Isle of Arran, Carboniferous, Midland Valley of Scotland

The Laggantuin Cornstone Member is part of the Clyde Sandstone Formation.

Name

The member is named after Laggantuin on the north-east side of the Isle of Arran. See Paterson and Hall (1986); GSGB (1924); Tyrell (1928).

Lithology

Interbedded white sandstone and red claystone (shale) in fining-upwards cycles, with many small lenticular calcareous nodules (‘cornstone’) in the claystone. The upper beds recorded on the shore at Laggantuin have fairly good continuous pedogenic nodular limestones about 0.3–0.6 m thick. The overlying upper part of the member, comprising thick-bedded white sandstone and pebbly sandstone, is exposed north of Laggantuin.

Stratotype

The type section occurs in coastal exposures near Laggantuin on the north-east side of the Isle of Arran, Strathclyde (NS.0015.4855 to NR.9959.4914) (see Paterson and Hall, 1986).

Lower and upper boundaries

The lower boundary is mapped at the base of a white nodular limestone bed (‘cornstone’) that is approximately 0.6 m thick, overlying the alternating sequence of grey mudstone (shale), nodular limestone (‘cornstone’) and thin grey sandstone that comprises the Ballagan Formation (Figure 6, Column 1).

The upper boundary is conformably overlain by the pebbly coarse-grained white sandstone (grit) of the Millstone Point Sandstone Member. An occurrence of pebbly sandstone recorded as ‘Millstone Point Grits’ is exposed toward the northern part of the mapped extent of the Laggantuin Cornstone Member.

Thickness

Approximately 30 m. However, BGS (1987a) gave a generalised thickness of 50 m.

Distribution and regional correlation

The vicinity of Laggantuin, north-east coast of the Isle of Arran, Strathclyde.

Age

Tournaisian