The BGS Lexicon of Named Rock Units — Result Details

Lower Lecket Hill Lava Member

Computer Code: LLHLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Lower Lecket HIll Lava Member consists of lavas of plagioclase-microphyric trachybasalt (hawaiite) (of 'Jedburgh' type) to basaltic-trachyandesite (mugearite) and trachyandesite (benmoreite). Basaltic tuff-breccia and lapilli-tuff are present between the lavas. Along the southern escarpment of the Campsie Fells, to the north of the Campsie Fault, south of Laird [NS 6424 7994], these are up to 4 thick, and incorporate large scoria bombs. Craig (1980) interpreted these deposits as indicating derivation of at least some of the Lower Lecket Hill Lava Member as being from eruptive sources associated with South Campsie Linear Vent-swarm.
Definition of Lower Boundary: Across the northern and north-western parts of its outcrop, the base of the Lower Lecket Hill Lava Member appears to be conformable or disconformable on the underlying Campsie Lava Member. However, in the southern and south-eastern parts of its outcrop [between NS 6489 7904 and 7034 8060] the base is unconformable on older members, including the Loup of Fintry Lava Member and the Laird's Hill Lava Member. The unconformity may also extend farther to the west to the western limit of outcrop [NS 6178 8000], where there appears to be thinning of the underlying upper north and upper south Campsie lavas (Campsie Lava Member).
Definition of Upper Boundary: The Lower Lecket Hill Lava Member is generally overlain with apparent conformity or disconformity by the Boyd's Burn Lava Member, whose geographical extent is similar to that of the Lower Lecket Hill Lava Member. The lithological change is to mostly to plagioclase-macrophyric hawaiite lavas (of 'Markle type'). However, in the Meikle Bin area [NS 667 822], lavas of the Lower Lecket Hill Lava Member pass directly upwards into the remnant of the tephra cone associated with the Meikle Bin Trachytic Vent (Waterhead Centre).
Thickness: 50 m
Geographical Limits: The member is restricted to the Campsie Block (Forsyth et al, 1996) and has a limited geographical extent in the eastern Campsie Fells and western Kilsyth HIlls, north of Glasgow.
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Lower Lecket Hiil Lavas (-3529)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The eastern Campsie Fells, and western Kilsyth Hills, north of Glasgow Forsyth et al, 1996, after Craig, 1980 
Reference Section  Alnwick Burn, western Kilsyth Hills, north-east of Glasgow. The thickest development of the member, 50 m; there are at least seven succesive lavas, transitional between trachybasalt (hawaiite) and basaltic-trachyandesite (mugearite). Craig, 1980 
Reference(s):
Craig, P.M. 1980 The Volcanic Geology of the Campsie Fells area, Stirlingshire. Unpublished PhD thesis, University of Lancaster. 
Forsyth, I H, Hall, I H S and McMillan, A A. 1996. Geology of the Aidrie 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