Denny Muir Lava Member

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Denny Muir Lava Member (DMLA), Campsie Block, Carboniferous, Midland Valley of Scotland[edit]

Denny Muir Lava Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

Previously named the Denny Muir Lavas (see Forsyth et al., 1996[1]).

Lithology[edit]

The Denny Muir Lava Member consists mostly of massive, well-featured plagioclase-macrophyric basalt or trachybasalt (‘Markle’ type), trachybasalt lavas and rare basaltic trachyandesite (mugearite) lavas. The basal lava east of Darrach Hill (NS 754 827) is composite, with intermingled components of plagioclase-macrophyric and plagioclase-microphyric basalt or trachybasalt (‘Markle’ and ‘Jedburgh’ types respectively). The remainder of the lavas are massive and well featured, for example west of Birns (NS 761 823). An intensely jointed and ‘slaggy’ basaltic-trachyandesite (mugearite) lava occurs in faulted ground in the headwaters of the Garvald Burn (NS 758 825).

Stratotype[edit]

The type area is the eastern Kilsyth Hills, north-east of Glasgow (NS 7406 8099 to NS 7584 8392) (Forsyth et al., 1996)[1]. A reference section is the crags west of Birns, eastern Kilsyth Hills (NS 7555 8228 to NS 7559 8228) (Craig, 1980)[2].

Lower and upper boundaries[edit]

To the north and east, the base, locally a composite lava, is conformable or disconformable on underlying plagioclase-microphyric trachybasalt lavas of the Campsie Lava Member, but towards the south-west, where these lavas are absent, the member rests directly on plagioclase-microphyric basaltic-trachyandesite and/or trachybasalt, of the Tappetknowe Lava Member, suggesting that the boundary is an unconformity.

The Denny Muir Lava Member occupies summit areas across its outcrop and the top of the member has been eroded.

Thickness[edit]

Up to 85 m.

Distribution and regional correlation[edit]

The member is restricted to the Campsie Block (Forsyth et al., 1996)[1] and specifically to the eastern Kilsyth Fells, north-east of Glasgow. These rocks crop out in high ground north of the Campsie Fault, and to the east of the Tak-ma-doon Fault (NS 7396 8109 to NS 7300 8196), across Denny Muir (NS 750 830), and around Darrach Hill (NS 7538 8275). In addition, there is a small outlier around the top of Tarduff Hill (NS 756 836). The lavas are essentially continuous with those of the Kilsyth Hills Lava Member which lie to the west of the Tak-ma-doon Fault (Craig, 1980)[2]. The lavas were thought by Craig (1980)[2] to have been derived from the Waterhead Centre (‘Waterhead Central Volcanic Complex’).

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