Tappetknowe Lava Member
Tappetknowe Lava Member (TKLA), Campsie Block, Carboniferous, Midland Valley of Scotland
Tappetknowe Lava Member is part of the Clyde Plateau Volcanic Formation.
Name
Previously named the Tappetknowe Lavas (Forsyth et al., 1996)[1].
Lithology
The Tappetknowe Lava Member consists of several lavas with a total thickness of approximately 40 m. These include, near Tappetknowe (NS 750 815), microporphyritic basaltic-trachyandesite (mugearite) and trachybasalt and rare plagioclase-macrophyric trachybasalt (‘Markle’ type). The rocks are intensely faulted and jointed and deeply weathered, and there are no good sections, exposure being limited to small crags.
Stratotype
The type area is the central Kilsyth Hills, north of Glasgow (NS 7176 8064 to NS 7622 8197) (Forsyth et al., 1996)[1].
Lower and upper boundaries
The lower boundary is conformable or locally disconformable on the underlying Laird’s Loup Lava Member, which comprises plagioclase-macrophyric trachybasalt, and is taken as the incoming of microporphyritic lavas (basaltic-trachyandesite to trachybasalt). The Tappetknowe Lava Member is overlain to the north-east of the Tak-ma-doon Fault (Craig, 1980)[2] by the Denny Muir Lava Member. The lithological change here is to massive, well-featured plagioclase-macrophyric basalt (of ‘Markle’ type), trachybasalt and rare basaltic-trachyandesite (mugearite).
To the south-west of the Tak-ma-doon Fault, the Tappetknowe Lava Member is overlain by the Kilsyth Hills Lava Member, and the lithological change is mainly to plagioclase-macrophyric basalts and trachybasalts (hawaiites of ‘Markle’ type).
Thickness
Some 40 m.
Distribution and regional correlation
The member is restricted to the southern part of the Campsie Block (Forsyth et al., 1996)[1] and specifically to the southern side of the central Kilsyth Hills, north-east of Glasgow. These rocks crop out in the escarpment on the southern side of the Kilsyth Hills, north-east of Kilsyth, from south of Tomtain (NS 7179 8062), eastward to the Tak-ma-doon Fault (Craig, 1980)[2], thence to the north and south of Doups (NS 7494 8138) and as far east as Tappetknowe (NS 7620 8196). Craig (1980)[2] inferred that the source of the lavas was near to the present outcrop.
Age
Mid Visean (Arundian to Asbian).
References
- ↑ 1.0 1.1 1.2 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).
- ↑ 2.0 2.1 2.2 Craig, P M. 1980. The volcanic geology of the Campsie Fells area, Stirlingshire. Unpublished PhD Thesis, University of Lancaster