The BGS Lexicon of Named Rock Units — Result Details

Gargunnock Hills Lava Member

Computer Code: GHLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Gargunnock Hills Lava Member consists predominantly of plagioclase-macrophyric basalt (of 'Markle' type) and composite lavas, with subordinate plagioclase-microphyric basalt (of 'Jedburgh' type) and rare basaltic-trachyandesite (mugearite) lavas. Some lavas have weathered tops (dark red 'boles' with nodules of decomposed, slaggy basalt).
Definition of Lower Boundary: In the northern Gargunnock Hills, the basal plagioclase-macrophyric basalt of the member lies, apparently disconformably on trachybasalts of the Lees Hill Lava Member. In the northern Touch Hills, the Gargunnock Hills Lava Member interdigitates with the Lees Hill Lava Member and lies, probably disconformably, on microporphyritic basalts (of 'Jedburgh' type) of the Spout of Ballochleam Lava Member.
Definition of Upper Boundary: n the Gargunnock Hills and north-western Touch Hills, the member occupies the highest ground and its top is eroded. However, in the north-eastern and eastern Touch Hills, the member is overlain by the Black Mount Lava Member. The change in lithology is from plagioclase-macrophyric basalt to plagioclase-microphyric basalts and subordinate basaltic trachyandesite (mugearite).
Thickness: 91 m in the east, to more than 150 m in the west, where the top of the member is eroded
Geographical Limits: The member is restricted to the north-eastern Kilsyth Hills, and the Gargunnock and Touch hills, north-east of Glasgow.
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Gargunnock Hills Group (-4062)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Northern and eastern slopes of Scout Head, northern Touch Hills, north-east of Glasgow Francis et al, 1970 
Partial Type Section  In the gorge of the Touch Burn, downstream from Gilmour's Linn, northern Touch 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). 
Forsyth, I H, Hall, I H S and McMillan, A A. 1996. Geology of the Aidrie district. Memoir of the British Geological Survey, Sheet 31W (Scotland). 
Craig, P.M. 1980 The Volcanic Geology of the Campsie Fells area, Stirlingshire. Unpublished PhD thesis, University of Lancaster. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S039 S031