Carbeth Lava Member
Carbeth Lava Member (CBTL), Kilpatrick Hills, Carboniferous, Midland Valley of Scotland
The Carbeth Lava Member is part of the Clyde Plateau Volcanic Formation.
Name
Previously named the Carbeth Lavas (Hall et al., 1998)[1].
Lithology
Mainly plagioclase-macrophyric basalt (‘Markle’ type). There are also some plagioclase-microphyric basalts (‘Jedburgh’ type) and olivine-clinopyroxene-plagioclase-macrophyric basalts (‘Dunsapie’ type), as well as some mugearites near the base.
Stratotype
The lavas are well exposed in the type area around Carbeth (NS 527 796) and in the scarps around the Birny Hills (NS 495 770) (see Hall et al., 1998)[1]. A reference section was encountered in the Loch Humphrey Borehole (BGS Registration Number NS47NE/1) (NS 4582 7555) beneath the Greenside Volcaniclastic Member and above the Auchineden Lava Member. In the borehole, it is 20 m thick and consists of ‘Markle’ type lavas with some ‘Jedburgh’ type and some thin beds of tuff. A geological log is available.
Lower and upper boundaries
The Carbeth Lava Member overlies the plagioclase-microphyric basalts (‘Jedburgh’ type) of the Auchineden Lava Member.
The member is unconformably overlain by the Greenside Volcaniclastic Member. West of Loch Humphrey (NS 455 760) the member is reduced to one lava flow, which is preserved only in isolated patches below the volcaniclastic sedimentary rocks of the Greenside Volcaniclastic Member.
Thickness
Between 0 and 150 m. From the central part of the Kilpatrick Hills the member thins out towards the SW, partly due to erosion. It is some 80 m thick in the north-east of the region (Hall et al., 1998[1], table 5).
Distribution and regional correlation
The Carbeth Lava Member is geographically widespread in the Kilpatrick Hills, stretching from Strath Blane (NS 560 790) in the north-east to Brown Hill (NS 445 764) in the south-west. The member is well exposed around Carbeth and in the Birny Hills (see above).
Age
Mid Visean (Arundian to Asbian).