The BGS Lexicon of Named Rock Units — Result Details

Gowk Stane Member

Computer Code: GOWK Preferred Map Code: notEntered
Status Code: Full
Age range: Visean Stage (CV) — Visean Stage (CV)
Lithological Description: A mixed sequence of pyroclastic, epiclastic and volcaniclastic sedimentary rocks that are locally derived and mainly trachytic in composition (MacPherson and Phillips, 1997). There is a marked lateral variation in deposits within the unit. In the northern part of the crop, south of Eaglesham [NS 570 520] to the vicinity of Carrot Farm [NS 575 481], and north-east of Darvel the member consists of primary pyroclastic rocks with limited epiclastic reworking. These include rocks of trachytic and basaltic composition. The pyroclastic rocks are poorly sorted, grey to grey-green, fine- to coarse-grained lapilli tuff and/or agglomerate. Beds are generally less than 0.5 m thick and exhibit normal grading, either within the tuff mattrix or in the distribution of blocks in typically matrix-supported agglomerate. In the southern part of the crop, such as that exposed in Glen Water [NS 587 432] to [NS 579 413], the Gowk Stane Member is dominated by fluviatile volcaniclastic sedimentary rocks that were locally derived by penecontemporaneous weathering and erosion of the pyroclastic deposits and lavas (MacPherson and Phillips, 1997). This thickly bedded sedimentary sequence consists of interbedded mudstone, siltstone and tuffaceous sandstone with sporadic conglomerate units. The mudstones are pinkish-brown, the sandstones are greenish grey to buff and poorly to locally well sorted with fragments of volcanic rock. Cross-bedded channel and chaotic mass movement (lahar-type) deposits are recognized (MacPherson and Phillips, 1977).
Definition of Lower Boundary: The pyroclastic and volcaniclastic strata of the unit are inferred to overlie and be penecontemporaneous with the Eagelsham and Dumdruff Hill lavas within the Clyde Plateau Volcanic Formation (MacPherson and Phillips, 1997; MacPherson et al., 2000). Volcaniclastic and pyroclastic breccia of the Gowk Stane Member appears to overlie directly trachyandesite of the Dumdruff Hill lavas at East Revoch Farm [NS 569 508], although the contact is not exposed (MacPherson and Phillips, 1998).
Definition of Upper Boundary: Not seen, but is inferred to be overlain by the Upper Flow Moss Lava Member, within the Clyde Plateau Volcanic Formation (MacPherson and Phillips, 1997; MacPherson et al., 2000).
Thickness: At least 60m thick, from vertical section on British Geological Survey 1:10 000 Series Scotland sheet NS54SE (Whitelee Forest).
Geographical Limits: Between Eaglesham [NS 570 520] and Darvel [NS 565 375] in Strathclyde, Scotland.
Parent Unit: none recorded or not applicable
Previous Name(s): Gowkstane Member (-4069)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Exposures of volcaniclastic strata in the Glen Water river valley, near Laigh Overmuir Farm, 6 km northnortheast of Darvel, Strathclyde. MacPherson and Phillips, 1997; MacPherson et al., 2000. 
Type Section  Exposures of pyroclastic strata on a 20m-high, partially grassed, north-facing slope and in a small, disused quarry at the crest of the slope 600m north of East Revoch Farm [NS 569 508], 1.2km southsouthwest of Eaglesham, East Renfrewshire. MacPherson and Phillips, 1998. 
Reference(s):
MacPherson, K A T and Phillips, E R. 1997. The geology of the Clyde Plateau Volcanic Formation of the Kilmarnock district (Sheet 22E), central Scotland. British Geological Survey Report, WA/97/88. 
MacPherson, K A T and Phillips, E R. 1998. A welded pyroclastic deposit within the Dinantian Clyde Palteau Volcanic Formation, near Eaglesham, in the East Renfreshire Hills of the Midland Valley, Scottish Journal of Geology, Vol.34, 165-72. 
MacPherson, K A T, Smith, R A and Akhurst, M C. 2000. Geology of the Kilmarnock district. Sheet description of the British Geological Survey 1:50 000 Sheet 22E Kilmarnock (Scotland). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S022