The BGS Lexicon of Named Rock Units — Result Details
Offa Formation
| Computer Code: | OFFA | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Sinemurian Age (JS) — Pliensbachian Age (JE) | ||
| Lithological Description: | The Offa Formation consists of a rhythmically interbedded sequence of dark grey mudstones with moderately thick beds of argillaceous limestone and, locally, thin ferruginous developments. | ||
| Definition of Lower Boundary: | The lower boundary is characterised by a sharp downward change from dark grey mudstones to paler, harder, argillaceous limestones (Penda Formation), together with a sharp down-section increase in velocity and slight decrease in gamma values. | ||
| Definition of Upper Boundary: | The upper boundary is marked by a downward change from hard, silty and sandy limestones (Ida Formation) to mudstones. This corresponds to a gradual or weak increase of gamma-ray values, but a marked decrease in velocity. | ||
| Thickness: | Up to c. 190 m. | ||
| Geographical Limits: | Southern North Sea Basin (quadrants 41-43, 46-49, 51-53). | ||
| Parent Unit: | Lias Group (LI) | ||
| Previous Name(s): | Lias Group
(LI)
|
||
| Alternative Name(s): | Redcar Mudstone Formation Charmouth Mudstone Formation |
||
| Stratotypes: | |||
| Type Section | North Sea well 47/14a- 9 between 1108 and 1169 m (Lott and Knox, 1994). | ||
| Reference Section | North Sea well 42/24- 1 between 559 and 753 m (Lott and Knox, 1994). | ||
| Reference Section | North Sea well 48/11b- 4 between 1242.5 and 1412.5 m (Lott and Knox, 1994). | ||
| Reference Section | North Sea well 49/12a- 7 between 1837 and 1899 m (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. | |||
| 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 | |||