Carron Bridge Lava Member

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Carron Bridge Lava Member (CBRL), Campsie Block, Carboniferous, Midland Valley of Scotland[edit]

Carron Bridge Lava Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

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

Lithology[edit]

The Carron Bridge Lava Member consists predominantly of plagioclase-macrophyric trachybasalt lava (transitional from basalt to hawaiite of ‘Markle’ type). The principal exposure of the member is in the River Carron, above and below the bridge (NS 734 837 to NS 748 838), in the Faughlin area to the south (NS 735 827), and near Langhill (NS 775 844). The lavas are relatively thick, some flows being in excess of 15 m, although in the Langhill area, they are comparatively thinner, with about five lavas being present in the approximately 40 m thick succession. All of the lavas are massive, moderately altered, and in the Carron Bridge and Faughlin areas, have particularly high concentrations of plagioclase phenocrysts, which tend to be elongate, up to 6 mm in length, and aligned in the presumed direction of flow. Fairly large pseudomorphed olivine phenocrysts are also present, but are less common than the plagioclase phenocrysts. Craig (1980)[2] regarded these lavas as having distal-facies characterisitics. There is no indication of the source of the lavas.

Stratotype[edit]

The type area is in the eastern Kilsyth Hills, north-east of Glasgow (NS 7346 8254 to NS 7484 8384) (Forsyth et al., 1996)[1]. A reference section is the River Carron, above and below the bridge, north-west Kilsyth Hills, north-east of Glasgow (NS 7348 8375 to NS 7480 8380) (Craig, 1980)[2].

Lower and upper boundaries[edit]

The base has not been seen but is likely to be unconformable on sedimentary rocks of the Inverclyde Group.

In the section of the River Carron, below the bridge (NS 748 838), and in the Faughlin area to the south (NS 735 827), the Carron Bridge Lava Member is overlain, apparently conformably, or disconformably, by the Faughlin Lava Member. The lithological change is to tuff and agglomerate and basaltic-trachyandesite (mugearite). However, in the Carron River section above the bridge, and on its southern bank, the Faughlin Lava Member is absent, and the Carron Bridge Lava Member is overlain, disconformably or unconformably, by the Campsie Lava Member.

Thickness[edit]

More than 50 m, base not seen.

Distribution and regional correlation[edit]

The member is restricted to the eastern part of the Campsie Block (Forsyth et al., 1996)[1], specifically to the eastern Kilsyth Hills, north-east of Glasgow. These rocks crop out in inliers: in, and around, the Faughlin Burn (NS 734 825 to NS 737 828); in the River Carron (NS 7348 8375 to NS 748 838), and along the Faughlin Burn south to Faughlin Reservoir (NS 7411 8295) and south-east to a locality at (NS 7446 8248); and east of Langhill (NS 7705 8300) to the River Carron (NS 778 841), where the outcrop is truncated by the Carron Glen Fault (Craig, 1980)[2].

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.