Tappetknowe Lava Member

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Tappetknowe Lava Member (TKLA), Campsie Block, Carboniferous, Midland Valley of Scotland[edit]

Tappetknowe Lava Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

Previously named the Tappetknowe Lavas (Forsyth et al., 1996)[1].

Lithology[edit]

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[edit]

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[edit]

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[edit]

Some 40 m.

Distribution and regional correlation[edit]

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[edit]

Mid Visean (Arundian to Asbian).

References[edit]

  1. 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. 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