Kinnesswood Formation

Kinnesswood Formation (KNW), Carboniferous, Midland Valley of Scotland

The Kinnesswood Formation is part of the Inverclyde Group.

Name

The name Kinnesswood Formation was introduced by Chisholm and Dean (1974) and has since been extended throughout the Midland Valley of Scotland and, by this report into the Northern England province (see section 6.3.1). it replaces the former term ‘Cornstone Beds’, a unit at the top of the ‘Upper Old Red Sandstone’.

Lithology

File:P593245.jpg

Cross bedding within the distinctive orange sandstone of the Kinnesswood Formation (Carboniferous) at Milton of Mathers. P593245

In the Midland Valley of Scotland the Kinnesswood Formation consists predominantly of purple-red, yellow, white and grey-purple, fine- to coarse-grained sandstones which are mostly cross-bedded and arranged in upward-fining units. Fine-grained, planar or poorly bedded sandstones, red mudstones and nodules and thin beds of concretionary carbonate (calcrete or ‘cornstone’) also occur. The cornstones range from immature, in which the sandstones have a partly carbonate matrix with ill-defined concretions, to mature, in which well-defined nodules (glaebules) are elongated in a vertical sense and are overlain by laminar and pisolitic structures. The laminar structures, which develop parallel to the bedding, may be brecciated and the carbonate replaced by chert. in the Northern England province the formation comprises mainly red sandstones, siltstones and conglomerates.

Genetic interpretation

In the Midland Valley of Scotland the Kinnesswood Formation was laid down in fluviatile environments. The cross-bedded sandstones were deposited in river channels and the fine-grained sandstones and mudstones represent overbank deposits formed on the associated floodplains. The cornstones, which characterise the formation, were developed in soil profiles on the floodplains and channel margins under the influence of a fluctuating water table in a semi-arid climate. in the Northern England province the original sediments were laid down in calcrete-rich (cornstone) alluvial fans that were deposited in a series of small, linked basins with internal drainage that developed during early stages of crustal extension (Chadwick et al., 1995). The beds are dominantly fluvial with a palaeocurrent towards the north-east.

Stratotype

The type section is the hillside to the east of the village of Kinnesswood at Kinnesswood Row, base of unit at (NO 1805 0363), top at (NO 1814 0362) (see Browne et al., 1999, fig. 1, col. 11). intra-Carboniferous erosion has removed the top part of the formation in the type area, but the BGS Glenrothes Borehole (BGS Registration Number NO20SE/385) (NO 25617 03144) provides a complete reference section from 362.4 to 449.3 m depth (see Browne et al., 1999, fig. 1, col. 12)

Lower and upper boundaries

In the Midland Valley of Scotland the transitional base of the Kinnesswood Formation is taken in the type area between strata with cornstones and the underlying aeolian sandstones without cornstones, the Knox Pulpit Formation (Stratheden Group). in most areas the top is conformable beneath the grey mudstone and siltstone with ferroan dolostones of the Ballagan Formation (Figure 6, Columns 1–3, 4B), but in the type area it is erosional beneath strata of the Strathclyde Group (Pathhead Formation).

In the Northern England province the base of the formation is typically unconformable upon Silurian strata of the Riccarton Group. In the Berwick-upon-Tweed area and Solway Basin, the Kelso volcanic and Birrenswark volcanic formations respectively, overlie it (Figure 8, Column 12; Figure 10, Columns 2,3)

Thickness

About 640 m (maximum) in the Edinburgh area (based on Mitchell and Mykura (1962, p. 31), and up to 200 m thick in the Northern England province. Generally, 40 m on Arran (BGS, 1987a), 68 m at Bute and Cowal, and 250 m in the Cumbrae Isles (BGS, 2008).

Distribution and regional correlation

Throughout the Midland Valley, on Arran, at Bute and Cowal and in the Cumbrae Isles. it is now extended across and south of the Southern Uplands from Eyemouth to Dalbeattie, where it crops out narrowly along the northern margin of the Northumberland Trough in the Langholm area (Lumsden et al., 1967) and west of the Cheviot Hills.

Age and biostratigraphical characterisation

In the Midland Valley of Scotland the formation is mostly early Carboniferous (Courceyan) in age, but the discovery of miospores of Tournaisian age (LN-PC biozones) from near the base of the formation (Smith, 1996) confirms that it may straddle the Devonian–Carboniferous boundary. In the Northern England province it is considered to be late Devonian (Famennian) to early Tournaisian (Courceyan) in age, Lumsden et al. (1967) and George et al. (1976) having postulated an early Carboniferous age for the upper part of the formation.

Formal subdivisions

Members of the Kinnesswood Formation, in ascending order, include:

Doughend Sandstone Member (DHS)

Foulport Mudstone Member (FMN)

West Bay Cornstone Member (WBC)

Kinnesswood Formation (KNW), Carboniferous, Northern England Province

Name

From the Kinnesswood Formation of the Midland Valley of Scotland. See above for definition. The following description is specific to the Northern England Province.

Lithology

The Kinnesswood Formation comprises red sandstones, siltstones and conglomerates.

Genetic interpretation

The original sediments were laid down in calcrete-rich (‘cornstone’) alluvial fans that were deposited in a series of small, linked basins with internal drainage that developed during early stages of crustal extension (Chadwick et al., 1995). The beds are dominantly fluvial with a palaeocurrent towards the north-east.

Stratotype

The type section is defined in the Midland Valley of Scotland (see above).

Lower and upper boundaries

The base of the formation is unconformable upon Silurian strata (grewackes and interbedded mudstones) of the Riccarton Group.

In the Berwick area and Solway Basin, the mainly basalts of the Kelso and Birrenswark volcanic formations overlie the formation conformably and irregularly respectively (Figure 8, Column 12; Figure 6, Column 7).

Thickness

Up to 200 m.

Distribution and regional correlation

The formation extends across and south of the Southern Uplands from Eyemouth to Dalbeattie, where it crops out narrowly along the northern margin of the Northumberland Trough in the Langholm area (Lumsden et al., 1967) and west of the Cheviot Hills.

Age

Late Devonian (Famennian) to early Tournaisian (Courceyan). Lumsden et al. (1967) and George et al. (1976) postulated an early Carboniferous age for the upper part of the formation.

Bibliography

Browne, M A E, Dean, M T, Hall, I H S, McAdam, A D and Monro, S K, 1995. A review of the lithostratigraphy of the Carboniferous rocks of the Midland Valley of Scotland. BGS Technical Report, WA/95/25R.

Paterson, I B and Hall, I H S, 1986. Lithostratigraphy of the late Devonian and early Carboniferous rocks in the Midland Valley of Scotland. British Geological Survey Report, 18/3.

Chisholm, J I and Dean, J M, 1974. The Upper Old Red Sandstone of Fife and Kinross: A fluviatile sequence with evidence of marine incursion. Scottish Journal of Geology, Vol. 10, 1-30.

Cameron, I B and Stephenson, D, 1985. The Midland Valley of Scotland. British Regional Geology, p.31.