Fereneze Lava Member
Fereneze Lava Member (FZLA), Beith-Barrhead Hills, Carboniferous, Midland Valley of Scotland
The Fereneze Lava Member is part of the Clyde Plateau Volcanic Formation.
Name
Previously known as the ‘Fereneze Lavas’ (Hall et al., 1998[1]; Monro, 1999[2]; Paterson et al., 1990[3]) and equated with ‘Lower Group (c)’ (Richey et al., 1930)[4].
Lithology
Mainly plagioclase-macrophyric basalt (‘Markle’ type) and olivine-clinopyroxene-plagioclase macrophyric basalts (‘Dunsapie’ type). Several flows of mugearite are present, two were encountered in a borehole at Crummock Park (NS 350 540), Beith and three in Loanhead Quarry (NS 365 555) where a discontinuous bed of tuff is also seen. These flows are 15 m, 8 m and over 10 m thick and are separated by boles up to 0.5 m thick. The basalts are amygdaloidal with much hydrothermal alteration giving a range of secondary minerals such as calcite, prehnite, analcime, thomsonite, natrolite, bowlingite and heulandite. The quarry is well known for copper mineralisation with native copper, malachite and cuprite recorded.
Stratotype
The best exposure of the Fereneze Lava Member is in its type area on the north-west limb of the Beith Anticline, to the west of Barcraigs Reservoir (NS 38 57). Here flows of mainly olivine-basalts form good scarp and dip slope topography (‘trap features’). A reference section is the Crummock Park Borehole (NS 350 540) which penetrated 120 m of the Fereneze Lava Member, but no detailed geological log is available (see Monro, 1999)[2].
Lower and upper boundaries
The ‘Markle’ and ‘Dunsapie’ basalts of the Fereneze Lava Member appear to cut or overlap most of the underlying ‘Dalmeny’ and ‘Dunsapie’ basalts of the Sergeantlaw Lava Member in the area of the Fereneze Hills.
In the west of the Beith–Barrhead Hills, Bog Hall (NS 362 540) to Newton of Belltrees (NS 372 582), the Fereneze Lava Member is overlain by the olivine-microphyric basalts (‘Dalmeny’ type) of the Beith Lava Member. The upper boundary of the unit is not seen in the eastern Beith–Barrhead Hills.
Thickness
The maximum thickness is greater than 120 m.
Distribution and regional correlation
North-west limb of the Beith Anticline, to the west of Barcraigs Reservoir (NS 384 570) where the member forms good scarp and dip slope topography. It is faulted out in the south against the Blackhall Limestone and Lower Limestone Formation (Clackmannan Group) by the Dusk Water Fault to the south of Blaelochhead (NS 395 532). In the east (south-east limb of the Beith anticline), the member underlies the Fereneze Hills between Capellie Farm (NS 465 583) and the top of Boylestone Quarry (NS 495 597).
Age
Mid Visean (Arundian to Asbian).
References
- ↑ 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)
- ↑ 2.0 2.1 Monro, S K. 1999. Geology of the Irvine district. Memoir of the British Geological Survey, Sheet 22W, part 21E (Scotland)
- ↑ Paterson, I B, Hall, I H S, and Stephenson, D. 1990. Geology of the Greenock district. Memoir of the British Geological Survey, Sheet 30W part 29E (Scotland)
- ↑ Richey, J E, Anderson, E M, and MacGregor, A G. 1930. The geology of north Ayrshire. Memoir of the Geological Survey of Great Britain, Sheet 22 (Scotland)