Gleniffer Lava Member
The Gleniffer Lava Member is part of the Clyde Plateau Volcanic Formation.
The member comprises distinctive olivine-bearing plagioclase-macrophyric basalts (‘Markle’ type). Characterised by lavas with abundant, platy phenocrysts of plagioclase up to 25 mm long and microphenocrysts of red-brown olivine. A massive flow of plagioclase-microphyric basalt (‘Jedburgh’ type) forms the base of the member at Linn Well (NS 475 605). The lavas are interbedded with volcaniclastic sedimentary rocks at the base.
The Gleniffer Lava Member crops out in a prominent scarp in its type area along the north side of Gleniffer Braes to Brownside Braes (NS 450 607 to NS 485 605) (see Hall et al., 1998).
Lower and upper boundaries
The Gleniffer Lava Member is underlain by the sedimentary rocks of the Glenburn Volcaniclastic Member to the north and east of Brownside Braes (NS 485 605).
The member is overlain and may be cut out or overlapped, by the mafic basalts of the Sergeantlaw Lava Member around Sergeantlaw (NS 455 597) and to the east of Middleton (NS 445 579), and to the west of Barcraigs Reservoir (NS 39 57) and Walls Hill (NS 41 59).
The thickness is not stated.
Distribution and regional correlation
The Gleniffer Lava Member crops out in the Beith–Barrhead Hills to the east of Barcraigs Reservoir (NS 39 57) and is faulted against the Kirkwood Formation and Lawmuir Formation in the north, to the north of High Burnside (NS 42 60). It extends eastwards through Gleniffer Braes (NS 450 607) to Brownside Braes (NS 485 605). To the south the unit is faulted against the Upper Limestone Formation in Loch Libo (NS 435 556), and the Limestone Coal Formation by the Dusk Water Fault.
Mid Visean (Arundian to Asbian).
- Hall, I H S, Browne, M A E, and Forsyth, I H. 1998. Geology of the Glasgow district. Memoir of the British Geological Survey, Sheet 30E (Scotland)
- Monro, S K. 1999. Geology of the Irvine district. Memoir of the British Geological Survey, Sheet 22W, part 21E (Scotland)
- 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, Anderson, E M, and MacGregor, A G. 1930. The geology of north Ayrshire. Memoir of the Geological Survey of Great Britain, Sheet 22 (Scotland)