Largs Lava Member

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Largs Lava Member (LGLA), Renfrewshire Hills, Carboniferous, Midland Valley of Scotland[edit]

The Largs Lava Member is part of the Clyde Plateau Volcanic Formation.

Name[edit]

Previously named the Largs Lavas (Paterson et al. 1990[1]; Monro 1999[2]), part of the ‘Lower Group’ of Richey (1928)[3], and part of ‘unit 2’ of Johnstone (1965)[4].

Lithology[edit]

Olivine-microphyric basalt lavas (‘Dalmeny’ type) with a few flows of clinopyroxene-olivine-microphyric basalt (‘Hillhouse’ type). Some clinopyroxene-olivine-macrophyric basalts or basanites are intercalated in the upper part of sequence.

Stratotype[edit]

The type area of the member occurs as a major scarp on the east side of Noddsdale, to the south of the Muirshiel Fault, which can be traced northwards along the east side of Noddsdale Water to the Rotten Burn (NS 252 682).

Lower and upper boundaries[edit]

The Largs Lava Member overlies the Noddsdale Volcaniclastic Member. In the Largs Borehole (BGS Registration Number NS25NW/5) (NS 2158 5936) from about 8.2 to 107.4 m depth, the lavas of the Largs Lava Member overlie the volcanic detritus, silty mudstone and tuffaceous sandstone of the Noddsdale Volcaniclastic Member. South of Largs (NS 20 59) the Largs Lava Member is not exposed, but is inferred to occur beneath the Greeto Lava Member (Monro, 1999)[2].

Lavas of the Largs Lava Member are more mafic than those of the overlying Greeto Lava Member with the boundary defined by the petrographical change from olivine-microphyric basalts (‘Dalmeny’ type) of the Largs Lava Member, to the plagioclase-phyric basalts and hawaiites (‘Jedburgh’ and ‘Markle’ types) of the Greeto Lava Member.

Thickness[edit]

Up to 130 m.

Distribution and regional correlation[edit]

Renfrewshire and Kilbirnie hills: the member occurs as a scarp slope east of Noddsdale Water from Largs (NS 21 58) to the Murishiel Fault (NS 23 65), on the eastern side of Knockencorsan Hill (NS 24 67), and south of Largs on the lower slopes of Douglas Park as far as the A760 road (NS 21 57).

Age[edit]

Mid Visean (Arundian to Asbian).

References[edit]

  1. Paterson, I B, Hall, I H S, and Stephenson, D. 1990. Geology of the Greenock district. Memoir of the British Geological Survey, Sheet 30W part 29E (Scotland)
  2. 2.0 2.1 Monro, S K. 1999. Geology of the Irvine district. Memoir of the British Geological Survey, Sheet 22W, part 21E (Scotland)
  3. Richey, J E. 1928. The north Ayrshire sequence of Calciferous Sandstone volcanic rocks. Transactions of the Geological Society of Glasgow. Vol. 18, 247–255
  4. Johnstone, G S. 1965. The volcanic rocks of the Misty Law–Knockside Hills district, Renfrewshire. Bulletin of the Geological Survey of Great Britain, No. 22, 53–64