Craigentimpin Lava Member
Craigentimpin Lava Member (CTLA), Campsie Block, Carboniferous, Midland Valley of Scotland
Craigentimpin Lava Member is part of the Clyde Plateau Volcanic Formation.
The Craigentimpin Lava Member consists of plagioclase-macrophyric basalt to trachybasalt (‘Markle’ type) characterised by large phenocrysts of calcic labradorite. Two lava flows are present in the Sloughmuclock area (NS 627 795). Elsewhere, it generally consits of only one lava.
The type area is the central Campsie Fells, north of Glasgow (NS 6316 8244 to NS 6224 8399) (Forsyth et al., 1996). A reference section is the Alvain Burn (NS 6180 8053 to NS 6179 8060) (Craig, 1980). The member is also well exposed in Craigentimpin Quarry (NS 616 802).
Lower and upper boundaries
The base is conformable or disconformable on the underlying plagioclase-microphyric trachybasalt (hawaiite) lava of the lower north Campsie lavas (Campsie Lava Member) in the north of its outcrop, and by plagioclase-microphyric trachybasalt (hawaiite) lavas of the lower north Campsie and lower south Campsie lavas (Campsie Lava Member) in the south of its outcrop.
The Craigentimpin Lava Member is overlain with apparent conformity by the upper north Campsie lavas (Campsie Lava Member) in the north of its outcrop and by the upper north Campsie and upper south Campsie lavas (Campsie Lava Member) in the south of its outcrop. The lithological change is to mostly plagioclase-microphyric basalt to trachybasalt (hawaiite) lavas (‘Jedburgh’ type).
Between 0 and about 30 m. The maximum thickness of the member is developed in the Sloughmuclock area (NS 627 795), but it thins out completely to the west.
Distribution and regional correlation
The member is restricted to the Campsie Block (Forsyth et al., 1996) and specifically to the central and eastern Campsie Fells, north of Glasgow. These rocks crop out north of the Campsie Fault in two areas. The southernmost of the two areas extends along the lower part of the escarpment north of the Campsie Fault, to the south-west of Lairs (NS 6424 7994), from west of Sloughneagh (NS 6532 7909) westwards to Craigentimpin Quarry (NS 616 802) and west to near Allanhead (NS 6070 8036). The northernmost of the two areas of outcrop is faulted and extends northwards, discontinuously, from the south side of Campsie Muir (NS 6316 8244), thence to its east and north, and to the eastern flanks of Dunbrach (NS 6224 8399). According to Whyte and MacDonald (1974) the orientation of the feldspar phenocrysts suggest that the source of the lava was the Waterhead Centre (‘Waterhead Central Volcanic-Complex’).
Mid Visean (Arundian to Asbian).
- Forsyth, I H, Hall, I H S, and McMillan, A A. 1996. Geology of the Airdrie district. Memoir of the British Geological Survey, Sheet 31W (Scotland)
- Hall, I H S, Browne, M A E, and Forsyth, I H. 1998. Geology of the Glasgow district. Memoir of the British Geological Survey, Sheet 30E (Scotland)
- Whyte, F, and Macdonald, J G. 1975. The lower Carboniferous rocks of the Campsie–Kilpatrick area. Scottish Journal of Geology. Vol. 11, 364–365
- Craig, P M. 1980. The volcanic geology of the Campsie Fells area, Stirlingshire. Unpublished PhD Thesis, University of Lancaster
- Whyte, F, and Macdonald, J G. 1974. Lower Carboniferous vulcanicity in the northern part of the Clyde plateau. Scottish Journal of Geology, Vol. 10, 187-198.