The BGS Lexicon of Named Rock Units — Result Details

Faringdon Sponge Gravel Formation

Computer Code: FSG Preferred Map Code: FSG
Status Code: Full
Age range: Aptian Age (KP) — Aptian Age (KP)
Lithological Description: The formation is composed of red and yellow sponge gravels, in the lower part of the unit, overlain by clayey sands and sandy clays and capped by ferruginous sands and sandstones. The sponge gravels are highly fossiliferous, with abundant sponges, and "the matrix is a coarse quartz sand with many small, smooth quartz and lydite pebbles" (Arkell, 1947). The "Red Gravel" shows ferruginous staining. Locally thers is a pebble bed at the base. Resting on an erosion surface, a pebble bed passes up into glauconitic sandy clays, clayey sands and silts. The clay minerals are dominantly calcium montmorillonite and illite with small amounts of Kaolinite and fuller's earth is well developed in two seams. Brown, ferruginous, cross-bedded, medium to coarse-grained sands and sandstones, resting on an erosion surface, occurs at the top of the formation. Scattered pebbles, bands of grit and cherty sandstones also occur in places. Fossil fragments are common. The top of the member is indurated to form a hard sandstone which caps a number of hills in the Abingdon district.
Definition of Lower Boundary: An erosion surface separates the sponge gravels from the underlying Jurassic Ampthill Clay and Coral Rag.
Definition of Upper Boundary: The upper boundary of the Faringdon Formation is rarely seen. In the Uffingham Borehole and some of the Baulking boreholes, mudstone of the Gault Formation is seen to rest disconformably on the sands of the Faringdon Formation.
Thickness: Up to an estimated 49m.
Geographical Limits: The Upper Aptian Faringdon Formation is preserved as an isolated deposit within the NW-SE orientated Faringdon Trough (Arkell, 1947), a fault controlled depression (Ruffell and Wignall, 1990) on the eroded Jurassic surface. The formation rests disconformably on the Late Jurassic between Faringdon, Fernham and Baulking (Arkell, 1947, Poole and Kelk, 1971; Poole et al., 1971).
Parent Unit: Not Entered (?)
Previous Name(s): The Sponge Gravels Of Farringdon (-916)
Faringdon Sponge Gravels (-263)
"Sands And Gravels Of Faringdon" (-4659)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Faringdon Pit Arkell, 1947; Krantz, 1972. 
Reference Section  Baulking No1 Borehole Poole & Kelk, 1971 
Reference Section  Baulking No.2 Borehole Poole & Kelk, 1971 
Reference Section  Little Coxwell Pit Meyer, 1864; Arkell, 1947; Krantz, 1972. 
Reference Section  Wicklesham Pit Meyer, 1864; Arkell, 1947; Krantz, 1972. 
Reference Section  Fernham No1 Borehole Poole et al., 1971 
Reference Section  Fernham Borehole No.13 Poole et al., 1971 
Reference Section  Baulking No.4 Borehole Poole & Kelk, 1971 
Reference(s):
Casey, R, 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. 
Golding, R, Layer, M G, Magyari, A, Palotas, K and Dexter, J. 1998. Facies variation in the Corallian Group (U. Jurassic) of the Faringdon-Shellingford area (Oxfordshire) and the rockground base to the Faringdon Sponge Gravels (L. Cretaceous). Proceedings of the Geologists' associatio;n, Vol. 109, p. 115-125. 
Krantz, R. 1972. Die Sponge-Gravels von Faringdon (England). Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen, 140, 207-231. 
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. 
Mantell, G 1839. The wonders of Geology, volume 2. 
Arkell, W J. 1947. The Geology of Oxford. 267pp. [Oxford: Clarendon Press.] 
Austen, R A C. 1850. On the age and position of the fossiliferous sand and gravel of Farringdon. Quarterly Journal of the Geological Society of London, Vol.6, 454-478. 
Sharpe, D 1854. On the age of the fossiliferous sands and gravels of Faringdon and its neighbourhood. Quarterly Journal of the Geological Society, London, 10, 176-198. 
Ruffell, A H and Wignall, P B. 1990. Depositional trends in the Upper Jurassic-Lower Cretaceous of the northern margin of the Wessex Basin. Proceedings of the Geologists' Association, Vol.101, 279-288. 
Meyer, C J A. 1864. Three days at Faringdon. Geologist, Vol.7, 5-11. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E253