The BGS Lexicon of Named Rock Units — Result Details

Marshall Moor Lava Member

Computer Code: MALA Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: Macroporphyritic mafic basalts: olivine-clinopyroxene-plagioclase-macrophyric basalt (Dunsapie type) and olivine-bearing plagioclase-macrophyric basalt (Markle type) with some olivine-clinopyroxene macrophyric basalt (Craiglockhart type or ankaramite).
Definition of Lower Boundary: Lavas of the Marshall Moor Lava Member are considerably more mafic than those of the underlying Strathgryfe Lava Member. The abrupt change may imply a significant time interval between the two petrologically distinct volcanic episodes.
Definition of Upper Boundary: A distinct and obvious petrographic change distinguishes the macroporphyritic mafic basalts (Dunsapie and Craiglockhart types) of the Marshall Moor Lava Member from the overlying microporphyritic mafic basalts (mainly Dalmeny type) of the Kilbarchan Lava Member.
Thickness: Up to 75m
Geographical Limits: Restricted to the eastern part of the Renfrew shire Hills. The thickest development of the member occurs in the area between Peockstone [NS 357 610] and Bridge of Weir [NS 388 655] and it is well exposed around Marshall Moor [NS 375 625]. To the north it becomes discontinuous in faulted outcrops between Yonderton [NS 390 667] and Barochan [NS 420 693]. To the south, outliers occur around Lochwinnoch golf course [NS 344 597] and a single flow occurs beneath the Kilbarchan Lava Member between between Glenlora and the Maich Water [NS 324 587]. The most southerly outcrops are on the east side of the Maich Water around Ladyland [NS 325 578].
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Marshal Moor Lavas (-4178)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Thickest development of the member is between Peockstone [NS 357 610] and Bridge of Weir [NS 388 655]. Paterson et al. 1990 
Reference(s):
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). 
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). 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S022 S030