The BGS Lexicon of Named Rock Units — Result Details

Cambridge Greensand Member

Computer Code: CBG Preferred Map Code: CGS
Status Code: Full
Age range: Cenomanian Age (KE) — Cenomanian Age (KE)
Lithological Description: Glauconitic marl: Thin but distinctive condensed basement bed of pale greenish grey marl rich in phosphatic nodules (so called "coprolites") at base. Much dark green glauconite as sand-sized grains, disseminated or concentrated in pods and layers giving a sandy texture and hence name "greensand". Rare erratic pebbles at base. (Hawkes, 1943).
Definition of Lower Boundary: The lower boundary is a disconformity at a sharp contact; commonly burrowed on underlying grey Gault clay; glauconitic burrow infillings to 0.3m below junction.
Definition of Upper Boundary: The upper boundary is placed at the rapid upward transition to "Chalk Marl", West Melbury Marly Chalk Formation or Lower Chalk lacking distinctive glauconite grains and nodule concentrations.
Thickness: Typically 0.1 to 1.0m. Locally thicker developments infilling hollows on top of the Gault. 0.5 to 0.7m at Arlesey Brickpit [TL 188 347]. (Hopson, 1992).
Geographical Limits: Known from the north Hertfordshire and Cambridgeshire area within the Transitional Province.
Parent Unit: West Melbury Marly Chalk Formation (WMCH)
Previous Name(s): Cambridge Greensand [Obsolete Name And Code: Use CBG] (CAMG)
Chloritic Marl [Obsolete Name and Code: Use BRHD, CBG, GLML] (-4494)
Cambridge Bed [Obsolete Name and Code: Use CBG] (-4521)
Phosphate Bed [Obsolete Name and Code: Use CBG] (-3279)
Coprolite Bed [Obsolete Name and Code: Use CBG] (-3904)
Glauconitic Marl [Obsolete Name and Code: Use CBG] (-113)
Nodule Bed [Obsolete Name and Code: Use CBG] (-2056)
Alternative Name(s): none recorded or not applicable
Type Section  Established in brickpits as exposures become available. Currently Arlesey Brickpit (in 1992). Active clay pit to west of mainline railway, west of Arlesey. Disused parts of pit used for landfill. Outcrop varies according to working. 
Reference Section  Arlesey Brickpit [TL 1879 3476] and Borehole TL13SE45 [TL 1887 3463] Part borehole core held in BGS, NGDC, Keyworth. 
Hopson, P M. 1992. Geology of the Letchworth, Northwest Hitchin and Holwell district, Hertfordshire. 1:10 000 Sheets TL 13SE and TL 23 SW. British Geological Survey Technical Report, WA/92/42. 
Edmonds, E A and Dineham, C H. 1965. Geology of the country around Huntingdon and Biggleswade. Memoir of the British Geological Survey. Sheets 187 and 204 (England and Wales). 
Fitton, W H, 1836. Observations on some of the strata between the Chalk and the Oxford Oolite, in the south-east of England. Transactions of the Geological Society of London, Vol.4, 103-378, 379*-388*. 
Hancock, J M (Editor). 1972. Cretace. Ecosse, Angleterre, Pays de Galles. Lexique Stratigraphique International, Vol.1, fascicule 3a XI. 
Hart, M B. 1973. Foraminiferal evidence for the age of the Cambridge Greensand. Proceedings of the Geologists' Association, Vol.84, 65-82. 
Hawkes, L. 1943. The erratics of the Cambridge Greensand - their nature provenance and mode of transport. Quarterly Journal of the Geological Society of London, Vol.99, 93-104. 
Jukes-Browne, A J. 1875. On the relations of the Cambridge Gault and Greensand. Quarterly Journal of the Geological Society of London, Vol.31, 256-316. 
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. 
Seeley, H. 1866. The rock of the Cambridge Greensand. Geological Magazine, Vol.3, 302-307. 
Wilkinson, I P. 1988. Ostracoda cross the Albian/Cenomanian boundary in Cambridgeshire and western Suffolk, Eastern England. Development in Palaeontology and Stratigraphy, Vol.11, 1229-1244. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: