Laird’s Hill Lava Member

From Earthwise
Revision as of 15:53, 26 July 2021 by Dbk (talk | contribs) (1 revision imported)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

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

Laird's Hill Lava Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

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

Lithology[edit]

The Laird’s Hill Lava Member consists of only one or two lavas. In the stream sections to the north and west of Corrie Reservoir (NS 674 791) it is represented by a single flow of plagioclase-macrophyric basalt (‘Markle’ type), which is not shown on 1:50 000 scale Sheet 31W (BGS, 1992)[2]. Farther north-east it consists of a similar flow, underlain by a basaltic-trachyandesite (mugearite) lava, both of which crop out near the summit of Laird’s Hill (NS 696 801) (the boundaries of the member here are difficult to delineate on both 1:50.000 and 1:10.000 scale maps). The two flows are also seen in various stream headwaters draining northwards to Loch Carron, although relationships here are less clear due to poor exposure, and it is possible that there is interdigitation with other members. The source of the lavas is uncertain.

Stratotype[edit]

The type area is the central Kilsyth Hills, north-east of Glasgow (NS 6670 7913 to NS 7042 8158) (Forsyth et al., 1996)[1]. A reference section is the Birken Burn, central Kilsyth Hills (NS 6900 8046 to NS 6867 8051) (Craig, 1980)[3]. Here, good exposures of the lavas are found in the stream section.

Lower and upper boundaries[edit]

The basal plagioclase-macrophyric basalt, or locally basaltic-trachyandesite (mugearite), of the member is conformable or disconformable in the south on the underlying microporhyritic trachybasalt lava of the lower south Campsie lavas (Campsie Lava Member), and in the north, on the undivided microporphyritic trachybasalt lavas of the lower north Campsie and lower south Campsie lavas (Campsie Lava Member).

The Laird’s Hill Lava Member is overlain in the north by the undivided upper north Campsie and upper south Campsie lavas (Campsie Lava Member) and the lithological change is to microporphyritic trachybasalt. However, in the south, the Campsie Lava Member is absent due to erosion prior to deposition of the Lower Lecket Hill Lava Member, and the Laird’s Hill Lava Member is overlain unconformably by basaltic-trachyandesite of the Lower Lecket Hill Lava Member. Locally also, in the south, the Laird’s Hill Lava Member is absent, presumably due to erosion prior to deposition of the Lower Lecket Hill Lava Member.

Thickness[edit]

Some 20 m.

Distribution and regional correlation[edit]

The member is restricted to the Campsie Block (Forsyth et al., 1996)[1] and specifically to the central part of the Kilsyth Hills, north-east of Glasgow. These rocks crop out in two main areas. One, on the northern side of the Campsie Fault extends eastwards from the east flank of Brown Hill (NS 6670 7913). It is locally absent on the south-west flank of Laird’s Hill from (NS 6844 7964 to NS 6938 7996), but reappears on the south-east, east and north flanks of Laird’s Hill (NS 6957 8018). The member is absent on Plea Muir (NS 6934 8076). The second area of outcrop extends from the north flank of Barrel Hill (NS 7042 8158) westwards as far as the Burnhouse Burn on the south-east side of Meikle Bin (NS 6746 8194).

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. British Geological Survey. 1992. Airdrie. Scotland Sheet 31W. Solid Geology. 1:50.000. (Southampton: Ordnance Survey for British Geological Survey.)
  3. Craig, P M. 1980. The volcanic geology of the Campsie Fells area, Stirlingshire. Unpublished PhD Thesis, University of Lancaster