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
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 
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 Unpublished PhD thesis, University of Lancaster.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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used: