The BGS Lexicon of Named Rock Units — Result Details

Garvald Lava Member

Computer Code: GVLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Garvald Lava Member consists, from the top down, of plagioclase-microphyric basalts or trachybasalts (basalts or hawaiites of 'Jedburgh' type), an olivine-augite-plagioclase-macrophyric trachybasalt (hawaiite of 'Dunsapie' type), a prominently exposed microporphyritic basaltic trachyandesite (mugearite), two plagioclase-macrophyric trachybasalts (hawaiite of 'Markle' type), and a plagioclase-microphyric trachybasalt (hawaiite of 'Jedburgh' type) with pillow structures, indicating subaqueous emplacement. The source is thought to be local, either a neck exposed in the River Carron, north-east of Northshields [NS 779 840] or some other obscured source (Craig, 1980).
Definition of Lower Boundary: The base is not seen, due to faulting.
Definition of Upper Boundary: The Garvald Lava Member is overlain with angular unconformity by the Kirkwood Formation of the Strathclyde Group. In the Garvald Burn section [NS 781 838], the lithological change is from plagioclase-microphyric basalt or trachybasalt to volcaniclastic conglomerates and sandstones, which rest on progressively older lavas of the Garvald Lava Member towards the south
Thickness: More than 50 m
Geographical Limits: The member is restricted to the Campsie Block and specifically to the easternmost Kilsyth Hills, north-east of Glasgow.
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Garvald Lavas (-298)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The easternmost Kilsyth Hills, north-east of Glasgow Forsyth et al, 1996, after Craig, 1980 
Reference Section  Overton Burn, eastern Kilsyth Hills, north-east of Glasgow Craig, 1980 
Reference(s):
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 Unpublished PhD thesis, University of Lancaster. 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:
S031