The BGS Lexicon of Named Rock Units — Result Details

Branksome Sand Formation

Computer Code: BRKS Preferred Map Code: notEntered
Status Code: Full
Age range: Lutetian Age (GL) — Lutetian Age (GL)
Lithological Description: The Branksome Formation comprises mainly interbedded cross-bedded fine- to coarse-grained sand and heterolithic (mixed grain-size) sediments, with subordinate kaolinitic clay (‘pipeclay’), organic-rich clay and rooted lignites, mainly as lenticular units (a complex of white and yellow sands, laminated carbonaceous clays and loams, and thin impure pipe-clays, arranged for the most part in overlapping lenses).
Definition of Lower Boundary: On the mainland the formation rests on an erosion surface on the Parkstone Clay Member of the Poole Formation. In the Isle of Wight the formation rests on an erosion surface at the top of the Marsh Farm Formation of the Bracklesham Group.
Definition of Upper Boundary: The upper surface is a generally planar erosion surface representing a marine transgression cutting across the finely-interbedded sands and clays of the formation. This surface is overlain by fine-grained, well-sorted sand with bidirectional cross-bedding of the Boscombe Sand Formation.
Thickness: Up to 70m.
Geographical Limits: The Branksome Formation is represented mainly in the Bournemouth to Ringwood area of Hampshire and Dorset, with a possible outlier (Creechbarrow Outlier) south of Wareham. The formation is present in the western part of the Isle of Wight and is the lateral equivalent of the Selsey Sand Formation outcropping in the east of the island.
Parent Unit: Bracklesham Group (BRB)
Previous Name(s): Bournemouth Freshwater Beds (BRFR)
Bournemouth Marine Beds (BRMR)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Christchurch Borehole SZ29SW12. Bristow et al. (1991). 
Type Section  Cliffs between Poole Head and Boscombe Pier, Bournemouth where up to 70m of the formation is seen. The Formation is named after Branksome Chine [SZ 069 090]. The formation is well exposed in cliff sections where up to eight fining upward cycles of interbedded sediments. Can be seen. A typical cycle commences with very coarse-grained sand with clay clasts passing up into cross-bedded coarse- to medium-grained sands and into interbedded fine-grained sands and silty clays. Bristow et al. (1991). 
Reference(s):
Bristow, C R, Freshney, E C, and Penn, I E. 1991. Geology of the country around Bournemouth. Memoir for 1:50 000 geological sheet 329 (England and Wales). HMSO, London. 
Edwards, R A and Freshney, E C. 1987. Lithostratigraphical classification of the Hampshire Basin Palaeogene Deposits (Reading Formation to Headon Formation) Tertiary Research, Vol.8, 43-73. 
Curry, D, Adams, C G, Boulter, M C, Dilley, F C, Eames, F E, Funnell, B M, and Wells, M K. 1978. A Correlation of Tertiary rocks in the British Isles. Geological Society of London Special Publication, Vol. 12, 1-72. 
Plint, A G. 1983. Facies, Environments and Sedimentary Cycles in the Middle Eocene, Bracklesham Formation of the Hampshire Basin-Evidence for Global Sea-Level Changes. Sedimentology, Vol.30(5), 625-653. 
Plint, A G. 1988. Global eustacy and the Eocene sequence in the Hampshire Basin, England. Basin Research, Vol. 1, 11-22. 
Gardner, J S. 1879. Description and correlation of the Bournemouth Beds. Part II. Lower or Freshwater series. Quarterly Journal of the Geological Society, Vol. 38, 1-15. 
Costa, L I, Downie, C, and Eaton, G L. 1976. Palynostratigraphy of some Middle Eocene sections from the Hampshire Basin (England). Proceedings of the Geologists' Association, Vol. 87, 273-284. 
Hopson, P M, and Farrant A R. 2014. Geology of the Isle of Wight - a brief explanation of the Isle of Wight Special Geological Map Sheet. Sheet Explanation of the British Geological Survey. Parts of 1:50 0000 Sheets 330 (Lymington), 331 (Portsmouth), 344 (Chale) and 345 (Ventnor) (England and Wales) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E314 E329 E341 E342 E343