The BGS Lexicon of Named Rock Units — Result Details

Slackdown Lava Member

Computer Code: SLLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Slackdown Lava Member consists of a varied assemblage of predominant trachybasalt, with plagioclase-macrophyric basalt lavas ('of 'Markle' type) and microporphyritic basalt lavas (of 'Jedburgh' type).
Definition of Lower Boundary: The basal basaltic-trachyandesite (mugearite) of the member unconformably overlies sedimentary rocks, including sandstone, siltstone and mudstone of the Clyde Sandstone Formation, of the Inverclyde Group.
Definition of Upper Boundary: The Slackdown Lava Member is overlain, conformably or disconformably by the Baston Burn Lava Member. The lithological change is from trachybasalt to plagioclase-macrophyric basalt (of 'Markle' type), except in the north-western Gargunnock HIlls, where the uppermost Slackdown Lava Member is represented by plagioclase-microphyric basalt (of Jedburgh' type).
Thickness: 30-79 m
Geographical Limits: The member is restricted to the northern Touch Hills and the north-eastern Gargunnnock Hills. These rocks crop out east-north-eastwards from the north of Lees Hill [NS 6576 9125] to the north side of Baston Burn [NS 7410 9372].
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Basal Group (-2427)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Crags north of Scout Head, northern Touch Hills, north-east of Glasgow Francis et al, 1970 
Type Area  In the northern Touch Hills, and the northern and north-eastern Gargunnock 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