The BGS Lexicon of Named Rock Units — Result Details

Overton Lava Member

Computer Code: OVLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Overton Lava Member consists of at least one plagioclase-macrophyric basalt lava (of 'Markle' type) overlying a basaltic-trachyandesite lava (mugearite). Several lavas, including trachybasalt, may be present and the best exposures are in the faulted River Carron section, to the north-west of Nicholswalls [NS 764 843] and in the Overton Burn, east of Overton [NS 772 834]. No source for the lavas has been identified.
Definition of Lower Boundary: The basal basaltic-trachyandesite (mugearite) lava of the member is conformable or disconformable in the north on the trachybasalt lavas of the undivided lower north and south Campsie lavas (Campsie Lava Member). Elsewhere the base is not seen.
Definition of Upper Boundary: The Overton Lava Member in the east is overlain conformably or disconformably by the undivided upper north and south Campsie lavas (Campsie Lava Member), and in the north, the member is overlain specifically by the upper north Campsie lavas. The transition is from plagioclase-macrophyric basalt lava to plagioclase-microphyric trachybasalt and some basalt lavas (basalt to hawaiite of 'Jedburgh' type) with scoriaceous agglomerates and tuffs.
Thickness: 35 m
Geographical Limits: The member is restricted to the Campsie Block and specifically to the eastern part of the Kilsyth Hills, north-east of Glasgow.
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Overton Lavas (-4240)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Overton Burn, east of Overton, eastern Kilsyth HIlls, north-east of Glasgow Craig, 1980 
Type Area  Eastern Kilsyth HIlls, north-east of Glasgow Forsyth et al., 1996, after 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 Unpublished PhD thesis, University of Lancaster. 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