| Computer Code: |
LCK |
Preferred Map Code: |
LCk |
| Status Code: |
Full |
| Age range: |
Cenomanian Age (KE)
— Cenomanian Age (KE) |
| Lithological Description: |
A grey marly chalk with marl content decreasing upwards. No flint. Comprises a thin basal bed of glauconitic marl (Cambridge Greensand) overlain by more typical Lower Chalk sequence that is usually divided into a lower "Chalk Marl" with rhythmic alternations of chalk and marl, and an upper "Grey Chalk" separated by a distinctive hard band. (Totternhoe Stone).
Name remains in informal use but generally regarded as obsolete onshore. |
| Definition of Lower Boundary: |
In Hitchin area, unconformity. Base of Cambridge Greensand resting on Gault Clay. |
| Definition of Upper Boundary: |
Sharp contact with overlying Middle Chalk the base of which is marked by Melbourn Rock, a hard nodular chalk. Top of Lower Chalk marked by a thin but distinctive yellowish marl (Plenus Marl). |
| Thickness: |
45-80 m in Hitchin area. |
| Geographical Limits: |
As defined above it is restricted to East Anglia, but the term can be applied more widely if defined differently. Limits necessarily vague. |
| Parent Unit: |
Chalk Group (CK)
|
| Previous Name(s): |
Chalk, Lower (now Lower Chalk Formation) [Obsolete Name and Code: Use LCK]
(-2893)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
In Hitchin district (221) to show Lower Chalk. Open farmland to the south of Shillington. Aspley End south-south-east for 2.1 km. |
| Reference Section |
In Biggleswade district (204) to show the Upper Junction. Ashwell Quarry. Disused and mainly backfilled quarry - now a private garden on southern side of Ashwell Village 400 m south east of the main church (Smith, 1992). |
| Reference Section |
In Hitchin district (221) to show Lower Junction. Arlesey Brickpit. Active clay pit with changing positions of working faces. To west of mainline railway. |
| Reference(s): |
| Jukes-Browne, A J and HILL, W, 1887. On the lower part of the Upper Cretaceous series in west Suffolk and Norfolk. Quarterly Journal of the Geological Society of London, Vol.43, p.544-598. |
| 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). |
| 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. |
| 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. |
| Smith, A, 1992. Geology of the Henlow, Stotfold and Ashwell districts. British Geological Survey Technical Report, WA/92/22. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E221
E220
E204
E266
E282
E284
E298
E299
E327
E129
E314
E283
E237
E064
E072
E160
E146
E145
E161
E162
E132
E148
E130
E173
E175
E187
E188
E189
E190
E205
E206
E207
E222
E238
E239
E240
E252
E253
E254
E255
E256
E257
E258
E259
E268
E267
E269
E270
E271
E272
E273
E274
E281
E343
|
