Kilsyth Hills Lava Member
Kilsyth Hills Lava Member (KHLA), Campsie Block, Carboniferous, Midland Valley of Scotland
Kilsyth Hills Lava Member is part of the Clyde Plateau Volcanic Formation.
Name
Previously named the Kilsyth Hills Lavas (Forsyth et al., 1996)[1].
Lithology
The Kilsyth Hills Lava Member consists predominantly of plagioclase-macrophyric basalts and trachybasalts (hawaiites of ‘Markle’ type). The lower of these lavas tend to have sparse and small plagioclase phenocrysts and are transitional to plagioclase-microphyric basalts and trachybasalts (hawaiites of ‘Jedburgh’ type). Some higher lavas in the sequence are olivine-augite-macrophyric basalts (of ‘Dunsapie’ type) although these are always subordinate to the plagioclase-phyric lavas. Also, there is a local intercalation of variably olivine- and olivine-augite-microphyric basalt lava (‘Jedburgh’ to ‘Dalmeny’ type).
Stratotype
The type area is in the central Kilsyth Hills, north-east of Glasgow (NS 6220 7992 to NS 7396 8109) (Forsyth et al., 1996)[1]. A reference section is the crags on the southern flanks of Tomtain Hill, central Kilsyth Hills (NS 7231 8072 to NS 7212 8140) (Craig, 1980)[2].
Lower and upper boundaries
Over most of its outcrop, the base is conformable or disconformable on basaltic-trachyandesite (mugearite) and/or trachybasalt (hawaiite) of the Upper Lecket Hill Lava Member. However, towards the south-east, the member rests unconformably on progressively older members until, in the Garrel Hill area (NS 698 810), it rests on basaltic-trachyandesite (mugearite) of the Lower Lecket Hill Lava Member. South of Garrel Hill (NS 750 806) it is directly underlain by plagioclase-microphyric trachybasalt (hawaiite) lava of the Campsie Lava Member, and to the south of Tomtain (NS 7179 8062) and as far east as the Tak-ma-doon Fault (NS 7396 8106) it is underlain by basaltic-trachyandesite (mugearite) and/or trachybasalt (hawaiite) of the Tappetknowe Lava Member.
The Kilsyth Hills Lava Member occupies summit areas across its outcrop and the top of the member has been eroded.
Thickness
The member is most thickly developed on Tomtain (NS 721 814), where its apparent thickness is 160 m. Top eroded.
Distribution and regional correlation
The member is restricted to the Campsie Block (Forsyth et al., 1996)[1] and specifically to the central Kilsyth Hills, north-east of Glasgow. The rocks crop out in the highest ground above the escarpment north of the Campsie Fault, to the west and around the summits of Lairs (NS 6424 7994), Cort-ma Law (NS 6515 7995) and Lecket Hill (NS 6445 8121). The member also crops out in a separate area extending from the west of Garrel Hill (NS 7044 8105), around its north and south flanks, and around those of Tomtain Hill (NS 721 814), as far east as the Tak-ma-doon Fault (NS 7396 8109 to NS 7300 8196). It is exposed in crags on high ground from Crighton’s Cairn (NS 625 799) and Lecket Hill (NS 645 812) eastwards to the Tak-ma-doon Fault (NS 7396 8109 to NS 7300 8196) (Craig, 1980)[2]. The member is equivalent laterally to the Denny Muir Lava Member which is recognised to the east of the Tak-ma-doon Fault. The lavas were thought by Craig (1980)[2] to have been derived from the Waterhead Centre (‘Waterhead Central Volcanic Complex’).
Age
Mid Visean (Arundian to Asbian).
References
- ↑ Jump up to: 1.0 1.1 1.2 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)
- ↑ Jump up to: 2.0 2.1 2.2 Craig, P M. 1980. The volcanic geology of the Campsie Fells area, Stirlingshire. Unpublished PhD Thesis, University of Lancaster