| 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 [Obsolete Name and Code: Use GVLA]
(-298)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
Overton Burn, eastern Kilsyth Hills, north-east of Glasgow. Craig, 1980. |
| Type Area |
The easternmost Kilsyth Hills, north-east of Glasgow. Forsyth et al., 1996, after Craig, 1980. |
| Reference(s): |
| Craig, P M. 1980. The Volcanic Geology of the Campsie Fells area, Stirlingshire. Unpublished Ph.D thesis, University of Lancaster. |
| 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. 165 pp. |
| Forsyth, I H, Hall, I H S, and McMillan, A A. 1996. Geology of the Airdrie district. Memoir of the British Geological Survey, Sheet 31W (Scotland). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S031
|
