The BGS Lexicon of Named Rock Units — Result Details
Penda Formation
| Computer Code: | PEND | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Rhaetian Age (TR) — Sinemurian Age (JS) | ||
| Lithological Description: | The Penda Formation comprises thinly interbedded, dark grey, hard, argillaceous limestone and dark grey, calcareous mudstone. Limestones show a spiky, high velocity response on wireline logs. Several minor sedimentary cycles, from carbonate-poor to carbonate-rich beds are reflected in the changing velocity response. Three informal subdivisions can be recognised: P1 (basal Penda Formation) comprises thinly interbedded, hard, argillaceous, dark grey or brown, finely crystalline limestones and thin, dark grey mudstones. The unit is occasionally silty or sandy, with traces of glauconite. P2 comprises thinly interbedded, dark grey to brown mudstones, with sporadic, harder, argillaceous limestones. The unit shows a low velocity signature compared to the units above and below. P3 (middle and upper parts of the Penda formation) forms the bulk of the formation and is composed of argillaceous limestone. It is characterised by low gamma values and consistently high velocity. | ||
| Definition of Lower Boundary: | The lower boundary is characterised by a sharp downward transition from carbonate-dominated lithologies (Penda Formation) to organic-rich mudstones (Penarth Group). There is a marked down-section decrease in velocity and increase in gamma values. | ||
| Definition of Upper Boundary: | The upper boundary is characterised by a downward change from limestone-poor mudstones (Offa Formation) to limestone dominated lithologies (Penda Formation). This coincides with a sharp downward decrease in velocity response. | ||
| Thickness: | Up to 250 m. | ||
| Geographical Limits: | Southern North Sea Basin (quadrants 35, 40-44, 46-49, 51-53). | ||
| Parent Unit: | Lias Group (LI) | ||
| Previous Name(s): | Lias Group
(LI)
|
||
| Alternative Name(s): | Redcar Mudstone Formation Scunthorpe Mudstone Formation |
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| Stratotypes: | |||
| Reference Section | North Sea well 42/29- 1 between 1096 and 1266.5 m (Lott and Knox, 1994). | ||
| Type Section | North Sea well 47/29a- 1 between 667 and 767 m (Lott and Knox, 1994). | ||
| Reference Section | North Sea well 48/11b- 4 between 1412.5 and 1672 m (Lott and Knox, 1994). | ||
| Reference Section | North Sea well 49/12a- 7 between 1899 and 2052 m (Lott and Knox, 1994). | ||
| Reference(s): | |||
| 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. | |||
| 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. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||