The BGS Lexicon of Named Rock Units — Result Details

Middle Chalk Formation [Remains In Informal Use But Generally Regarded As Obsolete Onshore]

Computer Code: MCK Preferred Map Code: MCk
Status Code: Pending Upgrade
Age range: Cenomanian Age (KE) — Turonian Age (KT)
Lithological Description: White pure chalk with some flint seams and very shelly beds. Comprises from base: hard indurated chalk with flaser marls (Melbourn Rock) to exceptionally shelly chalk with flints into chalk with well defined marl seams.
Definition of Lower Boundary: Rests on Plenus Marls (topmost Lower Chalk). Coincides with the base of the Melbourn Rock.
Definition of Upper Boundary: At the base of the Chalk Rock (lowermost Upper Chalk).
Thickness: 75 - 95m in the Hitchin area.
Geographical Limits: Essentially East Anglia by above definition, but has been applied across the whole of Southern England.
Parent Unit: Chalk Group (CK)
Previous Name(s): Chalk, Middle (Now Middle Chalk Formation) (-2934)
Alternative Name(s): none recorded or not applicable
Reference Section  For lower third of Middle Chalk at Steeple Morden Quarry. Disused quarry at site of 'whiting' works shows 25-30m of strata from Melbourn Rock upwards. (See Hopson, 1991). 
Reference Section  For base of Ashwell Quarry. Disused and partly backfilled quarry in private garden south of Ashwell shows Melbourn Rock overlying Plenus Marls. (See Smith, 1992). 
Smith, A, 1992. Geology of the Henlow, Stotfold and Ashwell districts. British Geological Survey Technical Report, WA/92/22. 
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. 1991. Geology of the Barkway, Reed, Therfield and Kelshall district. British Geological Survey Technical Report, WA/91/06. 
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. 
Penning, W H and Jukes-Browne, A J, 1881. Geology of the neighbourhood of Cambridge. Memoir of the Geological Survey, Old Series Sheets 51SW and part 51NW (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E267 E269 E270 E271 E272 E273 E274 E281 E343 E220 E221 E222 E239 E240 E241 E266 E282 E284 E298 E299 E327 E129 E314 E283 E237 E064 E072 E160 E146 E145 E161 E162 E132 E148 E175 E188 E189 E190 E204 E205 E206 E207 E223 E238 E252 E253 E254 E255 E256 E257 E258 E259 E268