| 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 [Obsolete Name and Code: Use SLLA]
(-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). |
| Dean, M T, Browne, M A E, Waters, C N and Powell, J H. 2011. A lithostratigraphical framework for the Carboniferous successions of northern Great Britain (onshore). British Geological Survey Research Report, RR/10/007. 165pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S039
|
