The BGS Lexicon of Named Rock Units — Result Details

Slackgun Volcaniclastic Member

Computer Code: SLAV Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Slackgun Volcaniclastic Member consists predominantly of bedded tuff and/or volcaniclastic sedimentary rock, with weathered basalt lava (including 'bole') and a local olivine-microphyric basalt lava.
Definition of Lower Boundary: The Slackgun Volcaniclastic Member unconformably overlies the Skiddaw Lava Member. The lithological change is from transitional plagioclase-macrophyric to plagioclase-microphyric basalt lava or composite basalt lava to a dull red 'bole' reflecting prolonged weathering of the underlying lavas.
Definition of Upper Boundary: The Slackgun Volcaniclastic member is overlain, conformably or disconformably, by the Spout of Ballochleam Lava Member. The lithological change is from tuff or volcaniclastic sedimentary rock to plagioclase-microphyric basalt lava (of 'Jedburgh' type).
Thickness: 0 to 80 m
Geographical Limits: The member is restricted to the northern Fintry Hills and the north-western Gargunnnock Hills, north-east of Glasgow. These rocks crop out from north-east of Spittalhill [NS 6521 8669] to the west-north-west to below Double Craigs [NS 631 875], north-north-west to below Stronend [NS 626 8955], and east-north-east to Black Craig [NS 6878 9241].
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Slackgun Interbasaltic Beds (-3682)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  In the northern, western and south-western Fintry Hills, and the north-western Gargunnock HIlls, north-east of Glasgow Francis et al, 1970 
Reference Section  Corrie-like scar, Slackgun, immediately north-west of Lees Hill, northern Fintry Hills, north-east of Glasgow Francis et al, 1970 
Reference(s):
Francis, E H, Forsyth, I H, Read, W A and Armstrong, M. 1970. The geology of the Stirling district. Memoir of the Geological Survey of Great Britain, Sheet 39 (Scotland). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S039