The BGS Lexicon of Named Rock Units — Result Details

Stewartry Group

Computer Code: STEW Preferred Map Code: notEntered
Status Code: Full
Age range: Cisuralian Epoch (PLC) — Cisuralian Epoch (PLC)
Lithological Description: Thick and very thick sequences of red sandstone and sedimentary breccias, some with evidence of basaltic lavas at or near the base of the sequence, deposited within separate fault-defined or fault-controlled basins e.g. Stranraer [Stone, 1988]. Breccia formations may be present at the base of the Stewartry Group. They are either overlain by sandstone formations or breccia and sandstone formations occur in an intertonguing relationship. Basaltic lava may also be present at or near the base of the Group. The Stewarty Group sequences are thick, c.1400m in the Dumfries and Lochmaben basins, but cannot be correlated between the adjacent depositional basins. The Waterbeck and North-East Axial faults, that are aligned northeast and lie along the line of the Solway Firth, bound the southerly extent of the Stewarty Group. South of the Waterbeck and North-East Axial faults the sequences of Permian strata are relatively thin, around 500m in the Annan and Carlisle basins and up to 550m in west Cumbria, and lithostratgraphical units are laterally extensive and correlated between basins. Lithostratigraphical formations within the Appleby and Cumbrian Coast groups can be correlated from west Cumbria to the Carlisle Basin.
Definition of Lower Boundary: Unconformable, with basal lithologies of breccia or basaltic lava, overlying Carboniferous or Lower Palaeozoic rocks in south and west Scotland.
Definition of Upper Boundary: The upper boundaries are not seen; Triassic strata are not preserved in onshore basins in Scotland unlike Permian sequences in the adjacent Carlisle, Solway, Irish Sea and Larne basins. The preserved upper surface is the present day level of erosion and there is no evidence for the previous presence of Triassic strata.
Thickness: The proven preserved thickness of the Stewarty Group is up to 610m in the Mauchline Basin, 270m in the Thornhill Basin, and >98m in the Moffat Basin [BGS water borehole records]. Where the thickness is not proven by drilling or exposure, estimates of thickness have been derived from modelling of the Upper Palaeozoic strata from gravity anomaly data as being around 1400m in the Dumfries and Lochmaben basins and 1.5 to 2.0km in the Stranraer Basin.
Geographical Limits: In the isolated basins in south and west of Scotland [Stranraer, Mauchline, Thornhill, Dumfries, Lochmaben and Moffat basins and in the Sound of Islay] within the counties of Argyll, Ayrshire and the Dumfries and Galloway region and the eastern part of Borders region.
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Dumfries and Lochmaben basins, Galloway, Scotland. See also the second "Type Area" Description and Comments for how to locate more detail on the stratotypes of constituent formations within the component basins. 
Type Area  Basins in south and west Scotland. The NGR quoted is not specific (though it lies within the Stranraer area). See Comments for how to locate more detail on the stratotypes of constituent formations within the component basins. Stranraer Basin [see Park End Breccia, Corseclays and Loch Ryan formations]; Maucline Basin [see Mauchline Volcanic and Mauchline Sandstone formations]; Thornhill Basin [see Carron Basalt, Durisdeer Breccia. Locherben Breccia and Thornhill Sandstone formations]; Moffat Basin [see Hartfield Formation]; Sound of Islay [see Glas Eilean Lava Formation]; Kintyre [see Bellochantuy Bay Formation. Also present in the Lochmaben Basin [no current cross reference]. 
Reference(s):
Akhurst, M C, Chadwick, R A, Holliday, D W, McCormac, M, McMillan, A A, Millward, D, Young, B, Ambrose, K, Auton, C A, Barclay, W J, Barnes, R P, Beddoe-Stephens, B, James, J C W, Johnson, H, Jones, N S, Glover, B W, Hawkins, M P, Kimbell, G S, MacPherson, K A T, Merritt, J W, Milodowski, A E, Riley, N J, Robins, N S, Stone, P and Wingfield, R T R. 1997. The geology of the west Cumbria district. Memoir of the British Geological Survey, Sheets 28, 37 and 47 (England and Wales). 138pp. 
Holliday, D W, Warrington, G, Brookfield, M E, McMillan, A A and Holliday, S. 2001. Permo-Triassic rocks in boreholes in the Annan-Canonbie area, Dumfries and Galloway, southern Scotland. Scottish Journal of Geology, vol. 37, p.97-113. 
Williamson, I T. 2003. Howford Bridge, east Ayreshire. 166-169 in Stephenson, D, Loughlin, S C, Millward, D, Waters, C N and Williamson, I T, Carboniferous and Permian rocks of Great Britain north of the Variscan Front. Geological Conservation Review Series, No. 27, Joint Nature Conservation Committee, Peterborough. 
Geological Survey of Scotland. 1885. Sheet 10. [Ordnance Survey Office for Geological Survey of Scotland: Southampton]. 
Institute of Geological Sciences, 1978. Ayr. Scotland sheet 14W. Solid Geology, 1:50 000. [HMSO: Southampton for the Institute of Geological Sciences]. 
Jin, Y, Wardlaw, B R, Glenister, B F and Kotlyar, G V. 1997. Permian chronostratigraphic subdivisions. Episodes, Vol.20, 10-15. 
Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M and Roberts, D H. 2001. Geology of the Isle of Man and its offshore area. British Geological Survey Research Report, RR/01/06. 
Holliday, D W, Holloway, S, McMillan, A A, Jones, N S, Warrington, G and Akhurst, M C. 2004. The evolution of the Carlisle Basin, NW England and SW Scotland. Proceedings of the Yorkshire Geological Society, Vol.55, Pt.1, 1-19. 
McMillan, A A. 2002. Geology of the New Galloway and Thornhill District. 2002. Memoir of the British Geological Survey. Sheets 9W and 9E (Scotland). 
Smith, R A, Johnston, T P and Legg, I C. 1991. Geology of the country around Newtownards. 
Stone, P, 1995. Geology of the Rhins of Galloway district. Memoir of the British Geological Survey, Sheets 1 & 3 (Scotland). 
Wagner, R H. 1983. A lower Rotliegend flora from Ayrshire. Scottish Journal of Geology, Vol.19, 135-155. 
Upton, B G J, Fitton, G J and Macintyre, R M. 1987. The Glas Eilean lavas: evidence of a Lower Permian volcanotectonic basin between Islay and Jura, Inner Hebrides. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol.77, 289-293. 
Stone, P. 1988. The Permian successions at Ballantrae and Loch Ryan, south-west Scotland. Report of the British Geological Survey, Vol.19, No.2, 13-18. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S001 S003 S007 S009 S010 S014 S015 S016 S027 S028