The BGS Lexicon of Named Rock Units — Result Details

Campsie Lava Member

Computer Code: CMLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Campsie Lava Member has been divided stratigraphically into lower and upper sequences and geographically into northern and southern sequences that reflect petrographically their source vent-swarms (northern sequences from the North Campsie Linear Vent-swarm and the later Gonachan Glen and Dungoil linear vent-swarms; southern sequences from the South Campsie Linear Vent-swarm). Although the various sequences are distinctive in some areas, enabling their boundaries to be identified, elsewhere they interdigitate laterally and have no distinctive stratigraphical markers to separate them vertically. Hence it is not possible to draw continuous boundaries between them on a map and therefore they have all been assigned to a single formal member. The four sequences have been given informal names that have been widely used on maps and in literature (Craig, 1980; Forsyth et al., 1996; Hall et al., 1998). The informal sequences are the lower south Campsie lavas, the lower north Campsie lavas, the upper south Campsie lavas and the upper north Campsie lavas. The distinctive characteristic of the whole member is that it is composed almost entirely of plagioclase-microphyric basalt and trachybasalt (basaltic hawaiite and hawaiite) lavas (i.e. of 'Jedburgh' type). A few lavas are transitional to basaltic-trachyandesite (mugearite). Agglomerate and tuff occurs between many of the lavas. Within this restricted range there is considerable petrographical variation and there are systematic variations between the sequences. The south Campsie lavas contain significant amounts of clinopyroxene, whereas in the north Campsie lavas it is present only as small granules in the groundmass. The plagioclase microphenocrysts also differ, being labradorite to calcic andesine in the south but sodic andesine in the north. These variations reflect the whole-rock compositions, which are dominantly basalt to basaltic hawaiite in the south and hawaiite to mugearite in the north. The lower and upper Campsie lava sequences can be identified where they are separated locally by one of several other lava members of distinctly different petrography. These are the Craigentimpin Lava Member, the Loup of Fintry Lava Member, the Laird's Hill Lava Member and the Overton Lava Member. Since it is not certain if those four members are contemporaneous, the boundaries between the lower and upper Campsie lavas, where drawn, do not necessarily involve lavas of exactly the same age everywhere.
Definition of Lower Boundary: In the northern Campsie Fells, the lower boundary of the Campsie Lava Member is taken as the first appearance of basalt or trachybasalt lava above the underlying North Campsie Pyroclastic Member, and the contact appears to be conformable or disconformable. However, in the western and south-western Campsie Fells, the North Campsie Pyroclastic Member is absent and the Campsie Lava Member overlies the Clyde Sandstone Formation of the Inverclyde Group. Farther east in the southern Campsie Fells, between the Finglen Burn [NS 599 800] and the Forking Burn [NS 653 790], it rests directly, and unconformably, on mudstone, dolostone and sandstone of the older, Ballagan Formation of the Inverclyde Group, suggesting that the lower boundary is an unconformity, both there and maybe also in the northern Campsie Fells. To the east of the East Bachille Fault [NS 6915 7974] and west of the Chapmen's Graves Fault [NS 7063 8046], the lower boundary is taken as the first appearance of basalt or trachybasalt above the plagioclase-macrophyric trachybasalt (hawaiite) lavas of the Laird's Loup Lava Member.
Definition of Upper Boundary: In the central and western Campsie Fells, the Campsie Lava Member is overlain with apparent unconformity by the Fin Glen Lava Member. The lithological change is to trachyte, with basaltic trachyandesite (mugearite), trachybasalt (hawaiite) and basalt. In the eastern Campsie Fells and western Kilsyth Hills, the member is overlain variably disconformably to unconformably by the Lower Lecket Lava Member. In the north-eastern Kilsyth Hills, the Campsie Lava Member is overlain, probably unconformably by the lavas of the Gargunnock Hills Member, or in the south-east Kilsyth Hills, by the Kilsyth Lava Member.
Thickness: 80 to 265 m
Geographical Limits: The Campsie Lava Member accounts for over 30% of the outcrop of volcanic rocks in the structural Campsie Block, which comprises the Campsie Fells and Kilsyth Hills, north and east of Glasgow. It is present throughout the block with the exception of the southern escarpment between Garrel Hill [NS 704 805] and Tappetknowe [NS 761 819]. The lower south Campsie lavas are generally restricted to the southern part of the block and are developed along most of the length of the southern Campsie Fells and southern Kilsyth Hills. The extent to which they extend northwards across the central parts of the Campsie Fells and Kilsyth Hills is uncertain, but they are likely to be interdigitated with the lower north Campsie lavas across most of that area. The lower north Campsie lavas are generally restricted to the northern part of the Campsie Block and are developed along most of the length of the northern Campsie Fells and northern Kilsyth Hills. They are also interdigitated with and undivided from, the lower south Campsie lavas southwards across the central parts of the Campsie Fells and Kilsyth Hills. The upper south Campsie lavas are restricted to the southern part of the Campsie Block and are developed along most of the length of the southern Campsie Fells and southern Kilsyth Hills. The extent to which they extend northwards across the central parts of the Campsie Fells and Kilsyth Hills is uncertain, but they might be interdigitated with the upper north Campsie lavas across most of the area. The upper north Campsie lavas are generally restricted to the northern part of the Campsie Block and are developed along most of the length of the northern Campsie Fells and northern Kilsyth Hills. They also extend eastwards across the Kilsyth Hills, where they are interdigitated with the upper south Campsie lavas.
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Lower South and Lower North Campsie Lavas, Upper South and Upper North Campsie Lavas [Obsolete Name and Code: Use CMLA] (-143)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Campsie Fells and Kilsyth Hills, between Strathblane and the Carron Valley, north and north-east of Glasgow. Forsyth et al., 1996, after Craig, 1980. 
Reference Section  Because of the extensive nature of this member, both in terms of its outcrop area and its stratigraphical range, there is no section that can be representative of the member as a whole. Reference sections for the four informal divisions of the member are as follows (see Lithology section for details): For the lower south Campsie lavas: the southern escarpment of the south-western Kilsyth Hills between the Forking Burn [NS 653 790] and Burniebraes Burn [NS 661 788], notably the Red Cleuch Burn [NS 6569 7887 to NS 6572 7913]. For the lower north Campsie lavas: crags at Black Craig [NS 5573 8116 to NS 5587 8128], western escarpment of the Campsie Fells. For the upper south Campsie lavas: Goat Burn [NS 6368 7929 to NS 6371 7932], southern Kilsyth Hills. For the upper north Campsie lavas: Muir Toll Burn [NS 6311 8263 to NS 6260 8285], north-east Campsie Fells. Craig, 1980. 
Reference(s):
Hall, I H S, Browne, M A E and Forsyth, I H. 1998. Geology of the Glasgow district. Memoir of the British Geological Survey, Sheet 30E (Scotland). 
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). 
Craig, P M. 1980. The Volcanic Geology of the Campsie Fells area, Stirlingshire. Unpublished PhD 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. 165pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S031 S030