| Computer Code: |
FDNS |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Aptian Age (KP)
— Aptian Age (KP) |
| Lithological Description: |
The formation is now divided from the base into the Faringdon Sponge Gravel Member, Baulking Sand Member and the Fernham Sand Member. The Faringdon Sponge Gravel Member comprises cross-bedded pebbly sands and highly fossiliferous gravels composed predominantly of the remains of calcareous sponges, with brachiopods, echinoderms and bryozoa. Bored mudstone and limestone clasts and phosphatised fossils, derived from the underlying Kimmeridge Clay and Corallian Group strata, occur at the base of the formation and at higher levels within the succession. Two subdivisions,comprising lower "yellow gravel" and upper (iron-oxide stained) "red gravel", have previously been recognized, separated by a non-sequence. According to Poole et al. (1971), cross-bedding diminishes upwards from the "yellow gravel" into the "red gravel", and there is a change in current direction as indicated by apparent dips. The Baulking Member comprises fine- to medium-grained siltstone and sandy mudstone with horizons of fuller's earth. Locally richly glauconitic with some horizons of shelly sand. The lower part of the interval is usually sandier, with horizons of fuller's earth and slumped beds. The upper part of the formation is mostly dark grey, thin current-bedded mudstone, with ironstone locally developed in the lower part of the interval. The mudstone contains white, fine-grained sandy and silty wisps and laminae. The Ferham Sand Member comprises reddish-brown, ferruginous, cross-bedded, shell-fragmental, medium- to coarse-grained, clean sandstone. There are scattered pebbles, bands of conglomeratic grit and minor horizons of mudstone. |
| Definition of Lower Boundary: |
Unconformable, channelled, at the basal contact of the "yellow gravel" with underlying Kimmeridge Clay mudstones or, locally, Corallian Group limestones. |
| Definition of Upper Boundary: |
Not seen. The Fernham Sand Member occurs as hill-cappings in the Baulking area. The top of the member is locally defined by the depth of the present-day weathered zone. |
| Thickness: |
Variable depending on local superposition of constituent members that have maximum thicknesses of about 50 m (Faringdon Sponge Gravel Member), up to 48 m (Baulking Sand Member) and at least 24 m (Fernham Sand Member). |
| Geographical Limits: |
In the Faringdon, Baulking to Uffington areas, and around Little Coxwell and Fernham, Oxfordshire. |
| Parent Unit: |
Lower Greensand Group (LGS)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| 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). These contain together the full succession of the Fernham Sand and Baulking Sand members |
| Type Area |
In the vicinity of Furze Hill [SU 29 92] and Fernham [SU 293 919], Oxfordshire. Where the upper part of the succession is indicated within field brash and exposures. |
| Reference Section |
Furze Hill Borehole SU29SE/16 [2905 9281] and boreholes F10 (SU29SE/5 [2982 9242]), F12 (SU29SE/7 [2925 9288]) and F13 (SU29SE/8 [2950 9305]) described in Poole et al. (1971), all located near Fernham, Oxfordshire. The Furze Hill Borehole contains the thickest development of the Fernham Sand Member. |
| Reference Section |
Laporte Earths Quarry [SU 323 912], at Baulking, Oxfordshire. Exposes the Baulking Sand Member. |
| Partial Type Section |
Grid reference [SU 288 943] is for the pit labelled as "Faringdon Pit" by Arkell (1947). The formation is found in old gravel pits between Faringdon and Little Coxwell, Oxfordshire. At the Faringdon pit only the Sponge Gravel Member is seen. |
| Type Area |
In the vicinity of Baulking [SU 31 90], Oxfordshire. Where the upper part of the succession is indicated within field brash and exposures. |
| Reference(s): |
| 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. |
| Hopson, P M, Wilkinson, I P and Woods, M A. 2008. A stratigraphical framework for the Lower Cretaceous of England. British Geological Survey. British Geological Survey Research Report, RR/08/03. |
| Arkell, W J. 1947. The Geology of Oxford. 267pp. (Oxford: Clarendon Press.) |
| 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. |
| 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. |
| Meyer, C J A. 1864. Three days at Faringdon. Geologist, Vol.7, 5-11. |
| 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. |
| Casey, R, 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
