Laird’s Loup Lava Member

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Laird’s Loup Lava Member (LDLL), Campsie Block, Carboniferous, Midland Valley of Scotland[edit]

Laird’s Loup Lava Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

Previously named the Laird’s Loup Lavas (Forsyth et al., 1996)[1].

Lithology[edit]

The Laird’s Loup Lava Member consists of plagioclase-macrophyric trachybasalt lavas (‘Markle’ type). Individual lavas range in thickness from 6–15 m. The lavas are massive, and there is a lack of significant tuff between the lavas, suggesting that the flows are relatively distal. The lavas are variably altered and some are characterised by an ophitic texture. No specific source vent has been identified for the lavas, although the vent at Craigdouffie is a possible source (Craig, 1980)[2], since the neck of the vent is infilled with breccia of similar material and exposures of the member near to the vent show proximal-facies characteristics.

Stratotype[edit]

The type area is the south-central Kilsyth Hills, north-east of Glasgow (NS 6920 7974 to NS 7224 8068) (Forsyth et al., 1996)[1]. A reference section, 50 m thick, occurs in the Laird’s Loup area of the Garrel Burn, south-central Kilsyth Hills (NS 7032 8025 to NS 6992 8059) (Craig, 1980)[2]. Here, at least six lava flows are well exposed, and whilst the base of the member is not exposed, the topmost lava is.

Lower and upper boundaries[edit]

The basal trachybasalt of the Laird’s Loup Lava Member appears to be either conformable or disconformable on the underlying microporphyritic basalt lava of the Drumnessie Lava Member.

At the western end of its outcrop, the Laird’s Loup Lava Member is overlain by the Campsie Lava Member. The lithological change is to mostly plagioclase-microphyric basalt to trachybasalt (basalt to hawaiite of ‘Jedburgh’ type). At the eastern end of its outcrop, the member is overlain by the Tappetknowe Lava Member, the lithological change being to microporphyritic basaltic-trachyandesite (mugearite) and trachybasalt and rare plagioclase-macrophyric trachybasalt (‘Markle’ type).

Thickness[edit]

Some 65 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 along the escarpment on the southern side of the Kilsyth Hills, north of Kilsyth, from the southern flank of Laird’s Hill (NS 6920 7974), eastwards to Green Bank (NS 7224 8068). A further small area of outcrop in the Craigdouffie Burn (NS 7424 8088 to NS 7437 8073) is tentatively correlated with the member.

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.