The BGS Lexicon of Named Rock Units — Result Details

Balcreuchan Group

Computer Code: BCN Preferred Map Code: BCN
Status Code: Full
Age range: Tremadoc Series (O1) — Arenig Series (OR)
Lithological Description: An interbedded succession of basaltic pillow lava (some are boninitic) and breccia, agglomerate, volcaniclastic sandstone, tuff, siltstone, conglomerate and mudstone-supported melange, and hyaloclastite. Locally sheared and metamorphosed to amphibolitic schist and chlorite-epidote schist. The dominant lavas are contained in faulted, tectonic blocks and are not, for the most part, formally defined as formations. There is good stratigraphical correlation between some of the blocks, but connections are generally tenuous. A number of the more distinctive lithological units have been defined formally as formations.
Definition of Lower Boundary: Not seen. The probable oldest component, the Mains Hill Agglomerate Formation, has its base faulted out by the Stinchar Valley Fault.
Definition of Upper Boundary: The major unconformity at the base of the overlying Barr Group.
Thickness: 1.5 to 2km
Geographical Limits: Between Girvan and Ballantrae, Ayrshire, southwest Scotland.
Parent Unit: Ballantrae Ophiolite Complex (BX)
Previous Name(s): Knockdolian Spilitic Group (-3826)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Pinbain Hill and surrounding slopes Bluck, 1982. 
Type Section  Coast section, Games Loup and Port Vad, Bennane Head. Stone and Smellie, 1988; Owen and Rushton, 1999. 
Reference(s):
Smellie, J L and Stone, P. 1988. The Ballantrae area. Classical areas of British Geology. 
Cameron, I B, Stone, P and Smellie, J, 1986. Geology of the Country around Girvan. Explanation of 1:50 000 sheet. British Geological Survey, Sheet 7, Scotland. 
Stone, P and Rushton, A W A, 1983. Graptolite faunas from the Ballantrae Ophiolite Complex and their structural implications. Scottish Journal of Geology, Vol. 19, 297-310. 
Bluck, B J, 1982. Hyalotuff deltaic deposit in the Ballantrae Ophiolite of SW Scotland: evidence for the crustal position of the lava sequence. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol.72 (for 1981), 217-228. 
Bailey, E B and McCallien, W J, 1957. The Ballantrae Serpintine, Ayrshire. Transactions of the Edinburgh Geological Society, Vol.17, 33-53. 
Owen, A W and Rushton, A W A, 1999. Scotland: Ordovician of the Midland Valley terrane - Balcreuchan Rort to Bennane Head. 329-331 in Ruchton, A W A, Owen, A W, Owens, R M and Prigmore, J K: British Cambrian to Ordovician Stratigraphy. Geological Conservation Review, Vol.18. [Peterborough, JNCC.] 
Smellie, J L and Stone, P. 1988. The Balcreuchan Port Borehole, Ballantrae Complex: geochemical associations of the lava sequence. Report of the British Geological Survey, Vol.19, No.2, p.1-5. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S007 S008