The BGS Lexicon of Named Rock Units — Result Details

Kilbarchan Lava Member

Computer Code: KBLA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: Microporphyritic mafic basalts, commonly hard, fresh and blue: olivine-microphyric basalt (Dalmeny type) with rare flows of clinopyroxine-olivine-microphyric basalt (Hillhouse type). Around Castle Semple and at Gladstone a few isolated flows of olivine-pyroxene-macrophyric basalt (ankaramitic or Craiglockhart type).
Definition of Lower Boundary: A distinct petrographic change from macroporphyric mafic basalts (Dunsapie and Craiglockhart types) of the underlying Marshall Moor Lava Member to the microporphyric mafic basalts (mainly Dalmeny type) of the overlying Kilbarchan Lava Member.
Definition of Upper Boundary: The Kilbarchan Lava Member is overlain across an erosional boundary by volcaniclastic sedimentary rocks of the Kirkwood Formation which contain detrital material from the underlying lavas.
Thickness: Up to 75m.
Geographical Limits: On the eastern flanks of the Renfrewshire Hills, the unit crops out over a wide area between Castle Semple Loch [NS 36 59] and Ranfurly [NS 39 65] and extends east to the town of Kilbarchan [NS 40 63]. It continues northwards, somewhat thinned, to Barochan [NS 410 690] where the outcrop is terminated by a system of major ENE- and WNW-trending faults. In the south, outcrops of the Kilbarchan Lava Member are terminated by a major east-west fault system at Lochwinnoch [NS 36 59], but thin outliers occur at the top of the lava succession between Glenlora [NS 324 587] and south of Ladyland [NS 325 575].
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Kilbarchan Lavas (-4724)
Alternative Name(s): none recorded or not applicable
Type Area  The unit crops out over a wide area between Castle Semple Loch and Ranfurly. Paterson et al. 1990 
Johnstone, G S. 1965. The volcanic rocks of the Misty Law-Knockside Hills district, Renfrewshire. Bulletin of the Geological Survey of Great Britain. No. 22. pp 53-64. 
Paterson, I B, Hall, I H S & Stephenson, D. 1990. Geology of the Greenock district: Memoir for 1:50000 geological sheet 30W and part of sheet 29E (Scotland). 
Richey, J E. 1928. The north Ayrshire sequence of Calciferous Sandstone volcanic rocks. Transactions of the Geological Society of Glasgow. 18. pp 247-255. 
Monro, S K. 1999. Geology of the Irvine District. Memoir of the British Geological Survey, Sheet 22W and part of 21E (Scotland). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S022 S030