The BGS Lexicon of Named Rock Units — Result Details

Fin Glen Lava Member

Computer Code: FGLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Fin Glen Lava Member consists of trachyte and plagioclase-microphyric varying to aphyric basaltic-trachyandesite (mugearite) transitional to trachybasalt (hawaiite) to basalt (of 'Jedburgh' type). The thickest development is on the east side of Finglen Burn [NS 581 816], but this area is faulted , and exposure is only sporadic. Significant thicknesses of basaltic scoria tuff-breccia and lapilli-tuff occur between most of the lavas. In all but the south-west and south-east, the base of the member is a phonolitic trachyte lava, characterised by well-developed planar jointing. This might be derived from a phonolite intrusion in the North Campsie Linear Vent-swarm near Fintry [NS 614 863] and is one of very few phonolitic lavas in the Carboniferous and Permian successions of Scotland (Upton et al., 2007). In the southern part of its outcrop, another trachyte lava occurs near the top of member. The wide variation in characteristics of the lavas and high degree of their interdigitation suggests individual lavas may have been erupted from different sources, some local and others more distant (Craig, 1980).
Definition of Lower Boundary: The basal phonolitic trachyte lava is conformable or disconformable on plagioclase-microphyric trachybasalt (hawaiite) lava of the upper north and south Campsie lavas (Campsie Lava Member).
Definition of Upper Boundary: The Fin Glen Lava Member is overlain by the Holehead Lava Member.The lithological change is to mostly to plagioclase-macrophyric olivine basalts and trachybasalts (basalts to hawaiites of 'Markle' type), characterised by the presence of variable amounts of generally small plagioclase macrophenocrysts.
Thickness: 60 to 110 m
Geographical Limits: The member is restricted to the Campsie Block and specifically to the western and central Campsie Fells, north of Glasgow. The thickest development is on the east side of Finglen Burn [NS 581 816].
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Fin Glen Lavas (-1538)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Aldessan Burn, central Campsie Fells, north of Glasgow Craig, 1980 
Type Area  Western and central Campsie Fells, north of Glasgow Forsyth et al, 1996, after Craig, 1980 
Reference(s):
Upton, B.G.J., Stephenson, D. and Ellam, R.M. 2007. Silica-undersaturated trachytic rocks of central Scotland. Scottish Journal of Geology, 43, 143-153.h Journal of Geology, Vol. 11, 364-365. 
Whyte, D. and MacDonald, J.G. 1975. The Lower Carboniferous rocks of the Campsie-Kilpatrick area. Scottish Journal of Geology, Vol. 11, 364-365. 
Craig, P.M. 1980 The Volcanic Geology of the Campsie Fells area, Stirlingshire. Unpublished PhD thesis, University of Lancaster. 
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). 
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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S031 S030