The BGS Lexicon of Named Rock Units — Result Details

Baulking Sand Member

Computer Code: BKGS Preferred Map Code: notEntered
Status Code: Full
Age range: Aptian Age (KP) — Aptian Age (KP)
Lithological Description: Fine- to medium-grained siltstone and sandy mudstone with horizons of fuller's earth. Locally the member is richly glauconitic, with some horizons of shelly sand. The lower part of the member is usually sandier, with horizons of fuller's earth and slumped beds. The upper part of the member is mostly dark grey, thin current-bedded mudstone, with ironstone locally developed in the lower part of the member. The mudstone contains white, fine-grained sandy and silty wisps and laminae.
Definition of Lower Boundary: The base of the member is the unconformable contact with Jurassic strata (Corallian Group limestones or Kimmeridge Clay Formation mudstones) or it lies conformably above the coarse, pebbly sandstones of the Faringdon Sponge Gravel Member.
Definition of Upper Boundary: The top of the formation is the unconformable contact with the Fernham Sand Member, marked by the sharp upward facies change from mudstone to ferruginous sandstone.
Thickness: Up to 48m in the Uffington Borehole SU38NW/1 [3065 8948] (Poole et al., 1971).
Geographical Limits: Baulking to Uffington area, Oxfordshire.
Parent Unit: Faringdon Sand Formation (FDNS)
Previous Name(s): Division 3 (Sandy Clays) (-1359)
Undivided Lower Greensand (-2612)
Alternative Name(s): none recorded or not applicable
Reference Section  The Fernham Boreholes (Nos 1 to 14; SU29SE 1 to 9 and SU39SW 13 to 17) and Baulking Boreholes (Nos 1 to 11; SU39SW 2 to 4 and 24 to 31) [SU 28 29 to SU 32 90] (see Poole and Kelk, 1971; Poole et al., 1971 for details). 
Type Area  In the vicinity of Baulking [SU 31 90] in Oxfordshire. 
Type Section  Laporte Earths Quarry [SU 323 912], at Baulking, Oxfordshire. Where the entire member is proven in boreholes and was seen during excavations. 
Wilkinson, I P. 2006. The Holostratigraphy of the Albian Stage (Lower Cretaceous) of the United Kingdom and its continental shelf. British Geological Survey Research Report, RR/06/01. 
Poole, E G and Kelk, B. 1971. Calcium montmorillonite (fuller's earth in the Lower Greensand of the Baulking area, Berkshire. Institute of Geological Sciences Report 71/4. 
Poole, E G, Kelk, B, Bain J A and Morgan, D J. 1971. Calcium montmorillonite (fuller's earth) in the Lower Greensand of the Fernham area, Berkshire. Report of the Institute of Geological Sciences, 71/12, 64pp. 
Arkell, W J. 1947. The Geology of Oxford. 267pp. [Oxford: Clarendon Press.] 
Casey, R, 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. 
Meyer, C J A. 1864. Three days at Faringdon. Geologist, Vol.7, 5-11. 
Rawson, P F, Curry, D, Dilley, F C, Hancock, J M, Kennedy, W J, Neale, J W, Wood, C J and Worrsam, B C. 1978. A correlation of Cretaceous rocks in the British Isles. Geological Society of London, Special Report No.9. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable