The BGS Lexicon of Named Rock Units — Result Details

Seend Ironstone Formation

Computer Code: SEEI Preferred Map Code: notEntered
Status Code: Full
Age range: Aptian Age (KP) — Aptian Age (KP)
Lithological Description: Dark brown to red-brown, cross-bedded, highly ferruginous sandstone. The sandstone is generally poorly sorted and medium- to very coarse-grained or pebbly. At some localities there are veins of limonite, white chert pebbles and mudstone-rich partings. There is a rich marine macrofossil fauna dominated by brachiopods and molluscs, and including sporadic ammonites.
Definition of Lower Boundary: Known occurrences of the Seend Ironsand unconformably overlie mudstones of the Kimmeridge Clay Formation or finer-grained ferruginous sandstone of the Whitchurch Sand Formation. Possible equivalent strata described by Jukes-Browne (1905) from the Devizes district also unconformably overlie Portland Group sandstones. At Faringdon, strata apparently representing the Seend Ironstone Formation occur within the Faringdon Sand Formation (ie above the older term Faringdon Sponge Beds, now Member). Here the lower boundary of the Seend Ironstone equivalent (the Baulking Sand Member) is marked by the downward facies change from ferruginous sand to coarse, sponge-rich gravels.
Definition of Upper Boundary: The upper boundary of the Seend Ironstone is the unconformable base of the Carstone Formation, Gault Formation or Quaternary sediments. Where the cover units are absent, the base of the present day weathered zone marks the top of the formation.
Thickness: Estimated to be not more than 12.2m (Jukes-Browne, 1905).
Geographical Limits: Wiltshire, Oxfordshire, Buckinghamshire.
Parent Unit: Lower Greensand Group (LGS)
Previous Name(s): Iron Sands Of Seend (-3025)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Hogshaw Hill Farm [SP 746 218], 1.6km north of Quainton, Buckinghamshire. Considered to be preserved in a channel cut into the Whitchurch Sand Formation that shows a section of reddish brown very coarse-grained locally conglomeratic limonite-cemented sandstone. 
Type Section  Old ironstone workings [ST 938 608 to 937 610], near the village of Seend, Wiltshire. A number of small pits give a complete composite succession. 
Reference(s):
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. 
Casey, R and Bristow, C R. 1964. Notes on some ferruginous strata in Buckinghamshire and Wiltshire. Geological Magazine, Vol.101, 116-128. 
Hesselbo, S P, Coe, A L, Batten, D J and Wach, G D. 1990. Stratigraphic relations of the Lower Greensand (Lower Cretaceous) of the Calne area, Wiltshire. Proceedings of the Geologists' Association, Vol.101, 265-278. 
Cunnington, W. 1850. On a section of Lower Greensand near Devizes. Quarterly Journal of the Geological Society of London, Vol.6, 453-454. 
Jukes-Browne, A J. 1905. The geology of the country south and east of Devizes. Memoir of the Geological Survey. Sheet 282 (England and Wales). 
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