Kilbarchan Lava Member
The Kilbarchan Lava Member is part of the Clyde Plateau Volcanic Formation.
Microporphyritic mafic basalts; olivine-microphyric basalt (‘Dalmeny’ type) with rare flows of clinopyroxene-olivine-microphyric basalt (‘Hillhouse’ type). Around Castle Semple and at Gladstone (see below) a few isolated flows of olivine-pyroxene-macrophyric basalt (‘ankaramite’ or ‘Craiglockhart’ type) occur.
The unit crops out over a wide type area between Castle Semple Loch (NS 360 595) and Ranfurly (NS 395 650) (see Paterson et al., 1990).
Lower and upper boundaries
At the lower boundary, a marked petrographical change occurs from macroporphyric mafic basalts (‘Dunsapie’ and ‘Craiglockhart’ types) of the underlying Marshall Moor Lava Member to the microporphyric mafic basalts (mainly ‘Dalmeny’ type) of the overlying Kilbarchan Lava Member.
The Kilbarchan Lava Member is overlain across an erosional boundary by volcaniclastic sedimentary rocks of the Kirkwood Formation, which contain detrital material from the underlying lavas.
Up to 75 m.
Distribution and regional correlation
The member crops out over a wide area in the Renfrewshire and Beith–Barrhead hills, between Castle Semple Loch (NS 36 59) and Ranfurly (NS 39 65) and extends east to the town of Kilbarchan (NS 40 63). It continues northwards, somewhat thinned, to Barochan (NS 410 690) where the outcrop is terminated by a system of major east-north-east- and west-north-west-trending faults. In the south, outcrops of the Kilbarchan Lava Member are terminated by a major east–west fault system at Lochwinnoch (NS 36 59), but thin outliers occur at the top of the lava succession between Glenlora (NS 324 587) and south of Ladyland (NS 325 575).
Mid Visean (Arundian to Asbian).
- 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)
- Richey, J E. 1928. The north Ayrshire sequence of Calciferous Sandstone volcanic rocks. Transactions of the Geological Society of Glasgow. Vol. 18, 247–255
- 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