| Computer Code: |
RODY |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Albian Age (KA)
— Albian Age (KA) |
| Lithological Description: |
Central to Northern North Sea: Mudstones (calcareous and chalky) with sporadic thin beds of argillaceous limestone. Mudstones are soft to hard, blocky to fissile, micaceous, glauconitic and sometimes silty. They are mainly pale to dark grey, but often red-brown, brick red, olive grey and dark brown. The red coloration is more often developed in the lower and upper parts of the formation and used for infromal subdivision. The interbedded limestones are white to pale grey, tan and re-brown to pink; firm; argillaceous and microcrystalline.
Southern North Sea: Calcareous mudstones, chalky mudstones and chalky limestones of pink, pale red, red-brown to brown grey coloration. They are firm to hard and become increasingly calcareous up-section. |
| Definition of Lower Boundary: |
A downward change from grey and red brown chalky mudstones and calcareous mudstones with interbedded limestones to dark grey, non-calcareous, low-velocity mudstones (Carrack Formation). On wireline logs, the boundary is defined by a downward increase in gamma values and a decrease in velocity. Locally, where the basal beds are absent, the boundary is sharp (e.g. Well 16/12b-6 in the southern Viking Graben) and in some areas of the Inner Moray Firth the boundary is a downward change to sandstone (Wick Sandstone Formation). In the Southern North Sea, the boundary is disconformable in some wells on structural highs, where formation rests on Jurassic or older strata. |
| Definition of Upper Boundary: |
In the Central and Northern Noth Sea there is a subtle downward change from interbedded pale to dark grey and pink limestones, argillaceous chalks and calcareous mudstones (Hidra Formation, Chalk Group) to less calcareous mudstones and chalky mudstones with interbedded limestones (Rødby Formation). The boundary corresponds with a downward increase in gamma-ray values and a downward decrease in sonic velocity. In the Southern North Sea the boundary is less subtle and corresponds to the change from grey and white chalk (Hidra Formation) to red-brown chalky mudstones (Rødby Formation). |
| Thickness: |
up to c.180 m. |
| Geographical Limits: |
Central North Sea, South Viking Graben, Moray Firth, Central Graben, Southern North Sea (as far south as approx. 52 degrees 30 minutes N) and off the coast of Yorkshire, Lincolnshire and Norfolk. It is equivalent to the Hunstanton Chalk (formerly Red Chalk) onshore and the Upper Holland Marl Member, Holland Formation of the Dutch Sector of the North Sea Basin. |
| Parent Unit: |
Cromer Knoll Group (CRKN)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
North Sea well 14/04- 1, 1219-1279 m depth (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 14/20- 8 at 2530.5-2670.5 m depth (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 16/12b- 6 at 3977.5-4087.5 m depth (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 29/02a- 2 at 3464-3511 m depth (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 44/24- 1 at 1365-1393 m depth (Rhys, 1974; Lott and Knox, 1994). |
| Reference Section |
North Sea well 48/22- 3 at 397.5-420.5 m depth (Rhys, 1974; Lott and Knox, 1994). |
| Reference Section |
North Sea well 49/24- 1 at 1295.5-1325 m depth (type section for the 'Red Chalk Formation' of Rhys, 1974) (Rhys, 1974; Lott and Knox, 1994). |
| Reference(s): |
| Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1. |
| Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8. |
| Larsen, G. 1966. Rhaetic-Jurassic-Lower Cretaceous sediments in the Danish Embayment (a heavy mineral study). Danmarks Geologiske Undersogelse, series B, No.2, 35pp. |
| Johnson, H and Lott, G K. 1993. 2. Cretaceous of the Central and Northern North Sea. In Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. |
| Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) |
| 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 |
