The BGS Lexicon of Named Rock Units — Result Details

Spout of Ballochleam Lava Member

Computer Code: SPBA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Spout of Ballochleam Lava Member consists predominantly of plagioclase-microphyric basalt lavas (of 'Jedburgh' type) with, near the base, rare olivine-microphyric basalt lavas (of 'Dalmeny' type) [NS 7061 9266], and higher within the member, isolated plagioclase-macrophyric basalt lavas (of 'Markle' type). Many of the basalt lavas are relatively coarse-grained and massive, with no clear distinction between the feldspar phenocrysts and the feldspars in the groundmass. The lavas are also variably, slaggy, vesiculose with amygdales, platy and occasionally columnar jointed, and spheroidally weathered. Dark red-weathered horizons ('boles'), some with nodules of decomposed lava are developed on the tops of some lavas.
Definition of Lower Boundary: n the northern Touch Hills and the north-eastern Gargunnnock Hills, the basal plagioclase- or olivine-microphyric basalt lava of the member lies unconformably on the eroded plagioclase-macrophyric lavas of the Baston Burn Lava Member, progressively overstepping them to the west. In the north-western Gargunnock Hills and the Fintry Hills, the member overlies conformably or disconformably, tuffs of the Slackgun Volcaniclastic Member.
Definition of Upper Boundary: In the north and west Fintry Hills, the member is overlain, apparently conformably or disconformably, by the Shelloch Burn Lava Member and the lithological change is to trachybasalt lava. In the northern Gargunnock Hills and north-western Touch Hills, however, the member is overlain, possibly disconformably, by trachybasalt lava of the Lees Hill Lava Member and in the north-eastern Touch Hills, possibly disconformably, by the Gargunnock Hills Lava Member. In the latter case, the lithogical change is to plagioclase-macrophyric basalt lava.
Thickness: 24 to 91m. The member is of varible thickness, but generally thickens to the west.
Geographical Limits: The member is restricted to the western and northern parts of the Fintry Hills, and the northern parts of the Gargunnock and Touch hills.
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Spout of Ballochleam Group (-1196)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Gully in steep cliffs, east end of Standmilane Craig, north-east Gargunnock Hills, north-east of Glasgow Francis et al, 1970 
Type Area  n the northern and western Fintry Hills, and the northern Gargunnock and 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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S039