| Computer Code: |
JKES |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Santonian Age (KS)
— Campanian Age (KC) |
| Lithological Description: |
The Jukes Formation typically consists of moderately hard, white, occasionally greyish white, variably argillaceous, chalky limestones. Occasional harder limestone bands occur together with comparatively few nodular chert developments. |
| Definition of Lower Boundary: |
The base of the Jukes Formation is defined by a downward change from moderately hard, relatively chert-free chalks, to darker, consistently harder, argillaceous, cherty chalks of the Lamplugh Formation. This lithological change corresponds to a consistent increase in sonic velocity, sometimes accompanied by a slight downward increase in gamma values. |
| Definition of Upper Boundary: |
The upper boundary of the Jukes Formation is characterized by a downward change from relatively soft chert-bearing argillaceous chalks to harder white chalks with fewer cherts. There is a corresponding slight downward decrease in gamma values and a more marked increase in sonic velocity. There is considerable variability in the sonic response over the formation as a whole as a result of the cyclic interbedding of thin argillaceous units, hard chalks and occasional hard chert-rich bands. The top of the unit is often marked by a thin, hard chalk unit (e.g. well 49/5-1). |
| Thickness: |
The Jukes Formation ranges up to 500 m. |
| Geographical Limits: |
The Jukes Formation is widely distributed throughout the Southern North Sea Basin but may vary in thickness due to intra-basinal tectonic controls and post-Cretaceous erosion. |
| Parent Unit: |
Chalk Group (CK)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 49/24- 1: 840-1060 m (2756-3478 ft) (Lott and Knox, 1994). |
| Reference Section |
North Sea well 38/24- 1: 1448-1585.5 m (4751-5202 ft) (Lott and Knox, 1994). |
| Reference Section |
North Sea well 49/05- 1: 1265.5-1679.5 m (4152-5510 ft) (Lott and Knox, 1994). |
| Reference(s): |
| 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. |
| NAM and RGD (Nederlandse Ardolie Maatschappij and Rijks Geologische Dienst) 1980. Stratigraphic nomenclature of the Netherlands. Transactions of the Royal Dutch Geological and Mining Society of Delft. |
| Whitham, F. 1993. The stratigraphy of the Upper Cretaceous Flamborough Chalk Formation north of the Humber, north-east England. Proceedings of the Yorkshire Geological Society, Vol.49, 235-258. |
| Wood, C J and Smith, E G. 1978. Lithostratigraphical classification of the Chalk in North Yorkshire, Humberside and Lincolnshire. Proceedings of the Yorkshire Geological Society, Vol. 42, 263-287. |
| Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
