The BGS Lexicon of Named Rock Units — Result Details

Crossbrae Gelifluctate Bed

Computer Code: CBGEL Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Gravelly, slightly clayey, silty sand diamicton. Variably coloured, dark brown to dark grey. Crudely medium-bedded, matrix supported, weakly to non-calcareous. Clasts are typically subangular to subrounded (with pelitic metasedimentary rocks commonly striated). Clast lithologies are dominated by quartzose and psammitic, and pelitic/semipelitic metasedimentary rocks, with less common red brown sandstone, felsite, grey granite, and mafic igneous rocks. Clast fabric orientations are typically normal to the present day ground topographic contours. The crude bedding of the diamicton is picked out by laminae of silty medium sand. Interpreted as periglacial gelifluctate deposits.
Definition of Lower Boundary: The lower boundary of the bed abruptly overlies dark brown diamicton of the Crossbrae Till Formation with a sharp, planar unconformity. Locally the basal boundary of the unit has also been observed to overlie abruptly an unnamed sand and gravel unit, which itself directly overlies the Crossbrae Farm Peat Bed.
Definition of Upper Boundary: The upper boundary of the bed is the present ground surface.
Thickness: Up to 2.5m observed
Geographical Limits: Buchan, northeast Scotland. The bed is only known from the vicinity of Crossbrae Farm, Turriff on Sheet 86E (Turriff).
Parent Unit: Crossbrae Till Formation (CBTIL)
Previous Name(s): Crossbrae Gelifluctate (-2057)
Crossbrae Gelifluctate Bed (CBGEL)
Crossbrae Head (-3280)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Geological test pit (Site B), near Crossbrae Farm, 3km northeast of Turriff, Buchan, northeast Scotland. Whittington et al. 1998. 
Partial Type Section  Temporary drainpipe trench (Site A', pit 1), near Crossbrae Farm, 3km northeast of Turriff, Buchan, northeast Scotland. Whittington et al. 1998. 
Reference(s):
Whittington, G. 1994. Bruckenthalia spicufolia (Salisb.). Reichemb. (Ericaceae), in the Late Quaternary of western Europe. Quaternary Science Reviews, Vol.13, 761-768. 
Merritt, J W, Connell, E R and Bridgland, D R (editors). 2000. The Quaternary of the Banffshire Coast and Buchan; Field Guide. (London: Quaternary Research Association.) 
Sutherland, D G. 1999. Scotland. 99-114 in Bowen D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. Special Report of The Geological Society of London, No.23. 
Whittington, G, Connell, E R, Coope, G R, Edwards, K J, Hall, A M, Hulme, P D and Jarvis, J. 1998. Devensian organic interstadial deposits and ice sheet extent in Buchan, Scotland. Journal of Quaternary Science, Vol.13, 309-324. 
Connell, E R and Hall, A M. 1987. The periglacial history of Buchan, Scotland. 277-285 in Boardman, J (Editor), Periglacial Processes and Landforms in Britain and Ireland. Periglacial processes in Britain and Ireland. Cambridge University Press, Cambridge. 
Hall, A M and Connell, E R. 1991. The glacial deposits of Buchan, northeast Scotland. 129-136 in Ehlers, J, Gibbard, P L and Rose, J (editors), Glacial Deposits in Great Britain and Ireland. (Rotterdam: Balkema.) 
Merritt, J W, Auton, C A, Connell, E R, Hall, A M and Peacock, J D. 2003. The Cainozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, Sheets 66E, 67, 76E, 77, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland) 
Hall, A M (Editor). 1984. Buchan Field Guide. Quaternary Research Association, Cambridge, 120pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable