Burnhouse Lava Member

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Burnhouse Lava Member (BHLA), Campsie Block, Carboniferous, Midland Valley of Scotland[edit]

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

Name[edit]

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

Lithology[edit]

The Burnhouse Lava Member consists mainly of thin (2–3 m thick), ‘carbonated’ and relatively decomposed, heavily oxidised with much red veining, locally autobrecciated, plagioclase-macrophyric trachybasalt (hawaiite of ‘Markle’ type) and a few thin intercalated plagioclase-microphyric trachybasalt lavas (hawaiite of ‘Jedburgh’ type) and intercalated tuff. The lavas have proximal facies characteristics, are irregular in form, and commonly amygdaloidal. To the north-east, along the southern shores of the Carron Valley Reservoir (NS 705 830), the plagioclase-macrophyric lavas are more massive and the plagioclase phenocrysts vary in size and concentration. The microporphyritic trachybasalt lavas are exposed on the southern slopes of Haugh Hill (NS 680 832), in the Burnhouse area (NS 688 823), and in the March Burn (NS 709 830). The associated tuffs are also well exposed in the Burnhouse area and in the March Burn section where they comprise a series of well-stratified, red-weathered lapilli-tuffs and tuff-breccias with blocks and bombs, commonly up to 0.5 m in diameter and composed of various macroporphyritic and microporphyritic lava types. Scoria and cementstone blocks are also incorporated within the tuffs, which are typically cut by numerous small faults and intruded by dykes. Two possible source necks have been identified at (NS 682 825) and (NS 708 824) on the basis of the coarseness of the tuffs (Craig, 1980)[2].

Stratotype[edit]

The type area is the central Kilsyth Hills, north-east of Glasgow (NS 6852 8196 to NS 7084 8316) (Forsyth et al., 1996)[1]. A reference section is the Burnhouse Burn, central Kilsyth Hills, north-east of Glasgow (NS 6897 8251 to 6850 8199) (Craig, 1980)[2]. Here at (NS 687 822) the tuffs are so coarse as to suggest the proximity of a source vent. The lavas are also well exposed at this locality, although they are subordinate to the tuffs.

Lower and upper boundaries[edit]

The basal plagioclase-macrophyric trachybasalt of the Burnhouse Lava Member is unconformable on sandstone of the underlying Clyde Sandstone Formation (Inverclyde Group).

The Burnhouse Lava Member is overlain conformably, or disconformably, by the Campsie Lava Member. The change in lithology is to mainly plagioclase-microphyric basalt lavas (‘Jedburgh’ type).

Thickness[edit]

Some 20 m.

Distribution and regional correlation[edit]

The member is restricted to the central part of the Campsie Block (Forsyth et al., 1996)[1] and specifically to the central Kilsyth Hills, north-east of Glasgow. The largest area of outcrop is to the south-west of the Carron Valley Reservoir, from Burnhouse Burn area (NS 6852 8196) north towards Haugh Hill (NS 6800 8357) and east to beyond the March Burn (NS 7120 8304). The other area of outcrop lies to the north of Garrel Hill (NS 7036 8228 to NS 7122 8204).

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 Craig, P M. 1980. The volcanic geology of the Campsie Fells area, Stirlingshire. Unpublished PhD Thesis, University of Lancaster