| Computer Code: |
MCK |
Preferred Map Code: |
MCk |
| Status Code: |
Full |
| 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.
Name remains in informal use but generally regarded as obsolete onshore. |
| 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 - 95 m 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) [Obsolete Name and Code: Use MCK]
(-2934)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| 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). |
| Reference Section |
For lower third of Middle Chalk at Steeple Morden Quarry. Disused quarry at site of 'whiting' works shows 25-30 m of strata from Melbourn Rock upwards (See Hopson, 1991). |
| Reference(s): |
| 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). |
| 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. |
| Smith, A, 1992. Geology of the Henlow, Stotfold and Ashwell districts. British Geological Survey Technical Report, WA/92/22. |
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
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
E267
E269
E270
E271
E272
E273
E274
E281
E343
|
