Gowk Stane Volcaniclastic Member
Gowk Stane Volcaniclastic Member (GOWV), Dunlop-Eaglesham Block, Carboniferous, Midland Valley of Scotland
The Gowk Stane Volcaniclastic Member is part of the Clyde Plateau Volcanic Formation.
Mixed sequence of pyroclastic rocks and volcaniclastic sedimentary rocks, which are locally derived and mainly trachytic in composition (MacPherson and Phillips, 1997). There is a marked lateral variation in deposits within the Gowk Stane Volcaniclastic Member. In the northern part of the outcrop, 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 reworking. These include rocks of trachytic and basaltic composition. The pyroclastic rocks are poorly sorted, grey to grey-green, lapilli-tuff and/or agglomerate. Beds are generally less than 0.5 m thick and exhibit normal grading, either within the lapilli-tuff matrix or in the distribution of blocks in typically matrix-supported agglomerate. In the southern part of the outcrop, such as that exposed in Glen Water (NS 587 432 to NS 579 413), the Gowk Stane Volcaniclastic Member is dominated by volcaniclastic sedimentary rocks (MacPherson and Phillips, 1997). This thickly bedded sedimentary sequence consists of interbedded mudstone, siltstone and tuffaceous sandstone with sporadic conglomerate units. The mudstones and siltstones are pinkish brown, the sandstones are greenish grey to buff coloured and poorly to locally well sorted with fragments of volcanic rock.
In the northern part of the outcrop (see above) and north-east of Darvel, the member is dominated by primary pyroclastic deposition, but in the south (see above), fluviatile processes dominated. Here the volcaniclastic sedimentary rocks, locally derived by penecontemporaneous weathering and erosion of the pyroclastic deposits and lavas, include channel and chaotic mass movement (lahar-type) deposits (see MacPherson and Phillips, 1997).
The type section comprises exposures at (NS 5692 5092) of pyroclastic strata on an approximately 20 m high, partially grassed, north-facing slope, and in a small, disused quarry at the crest of the slope 600 m north of East Revoch Farm (NS 569 508), 1.2 km south-south-west of Eaglesham, East Renfrewshire (Macpherson and Phillips, 1998). A partial type section includes exposures of volcaniclastic strata in the Glen Water river valley, near Laigh Overmuir Farm, 6 km north-north-east of Darvel, Strathclyde (NS 5790 4140 to NS 5860 4320) (MacPherson and Phillips, 1997; MacPherson et al., 2000).
Lower and upper boundaries
The pyroclastic and volcaniclastic strata of the Gowk Stane Volcaniclastic Member are inferred to overlie and be penecontemporaneous with the Eaglesham Lava Member and Dumdruff Hill Lava Member within the Clyde Plateau Volcanic Formation (MacPherson and Phillips, 1997; Macpherson et al., 2000). Volcaniclastic sedimentary breccia and pyroclastic breccia of the Gowk Stane Volcaniclastic Member appear directly to overlie trachyandesite of the Dumdruff Hill Lava Member at East Revoch Farm (NS 569 508) although the contact is not exposed (MacPherson and Phillips, 1998).
The upper boundary of the Gowk Stane Volcaniclastic Member is 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).
Based on the vertical section on 1:10 000 scale Geological Sheet NS54SE (Whitelee Forest), the minimum thickness is 60 m.
Distribution and regional correlation
The type area is in the Dunlop–Eaglesham moors between Glasgow, Kilmarnock and Hamilton, specifically between Eaglesham (NS 570 520) and Darvel (NS 565 375).
Mid Visean (Arundian to Asbian).
- 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 Technical Report, WA/97/88
- MacPherson, K A T, Smith, R A, and Akhurst, M C. 2000. Geology of the Kilmarnock district. Sheet description of the British Geological Survey, Sheet 22E (Scotland)
- MacPherson, K A T, and Phillips, E R. 1998. A welded pyroclastic deposit within the Dinantian Clyde Plateau Volcanic Formation, near Eaglesham, in the East Renfrewshire Hills of the Midland Valley. Scottish Journal of Geology, Vol. 34, 165–172