The Border Group (Lumsden et al. 1967; Day, 1970) consists of two sedimentary formations corresponding to some extent to the geographically extended, former Lower and Middle Border groups of Day (1970; see also Waters et al., 2007). The lower, the Lyne Formation (which equates with the ‘Cementstones’ of older terminology in Northumberland) comprises strata of heterolithic clastic and nonmarine carbonate facies. The Fell Sandstone Formation, of fluviodeltaic (‘Millstone Grit’) facies, diachronously overlies the Lyne Formation. Thin olivine basalt lavas occur as the Kershopefoot basalts (Williamson in Stephenson et al., 2003).
Lower and upper boundaries
The base of the group is conformable where the interbedded sandstones, limestones, anhydrites, rootlet beds and thin coals of the Ballagan Formation (Inverclyde Group) pass upward into the cyclical sequences of sandstone, mudstone and thin limestone of the Lyne Formation. This is the presumption at Bewcastle and Kirkbean, and it has been proved in a borehole at Annandale. The base is also conformable at Brampton where the Ballagan Formation passes upwards into the sandstone-dominated Fell Sandstone Formation. However, in the north-east part of the Northumberland Trough the same boundary is unconformable; and within the central part of the trough, the base of the group has not been proved. The base of the Yoredale Group (mixed shelf carbonate and deltaic (‘Yoredale’) facies) defines the top of the Border Group.
Greater than 1350 m thick in the central part of the Northumberland Trough.
The Border Group is restricted in geographical extent to the Northumberland Trough and Solway Basin.
It is late Tournaisian to Holkerian in age.
- Lumsden, G I, Tulloch, W, Howells, M F, and Davies, A. 1967. The geology of the neighbourhood of Langholm.Memoir of the Geological Survey of Great Britain, Sheet 11 (Scotland).
- Day, J B W. 1970. Geology of the country around Bewcastle.Memoir of the Geological Survey of Great Britain, Sheet 12 (England and Wales).
- Waters, C N, Browne, M A E, Dean, M T, and Powell, J H. 2007. Lithostratigraphical framework for Carboniferous successions of Great Britain (Onshore).British Geological Survey Research Report, RR/07/01.
- Stephenson, D, Loughlin, S C, Millward, D, Waters, C N, and Williamson, I T.2003.Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front.Geological Conservation Review Series, No. 27. (Peterborough: Joint Nature Conservation Committee.)