The BGS Lexicon of Named Rock Units — Result Details
Plenus Marls Member
| Computer Code: | PLMA | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Cenomanian Age (KE) — Cenomanian Age (KE) | ||
| Lithological Description: | Northern Province: Thinly bedded dark-coloured calcareous mudstone (marl) overlain by rubbly limestone and calcareous silty beds followed by a higher calcareous mudstone siltstone (marl). Southern Province: Interbedded coloured marl and chalk. Upper Cretaceous, Cenomanian (Metoicoceras geslinianum Zone). | ||
| Definition of Lower Boundary: | Northern Province: An uneven erosion surface that may be stained with iron minerals and glauconite, at the top of a succession of marly chalk (the Ferriby Chalk Formation). This member and the newly proposed Black Band Member above, generally form a topographical slack at outcrop, which facilitates the mapping of the base of the Welton Formation, and can also be recognised from its higher gamma-ray geophysical log signature in boreholes. Southern Province: Conformable beneath the lowest marl on the underlying Zig Zag Chalk Formation. Sequence constitutes the lowest member of the Holywell Nodular Chalk Formation and the White Chalk Subgroup. | ||
| Definition of Upper Boundary: | Northern Province: Conformable at the base of the Black Band (the 'Main Black Band' of Wood et al., 1997), the lowest unit of the Black Band Member. Southern Province: Conformable at the bedding plane above the highest marl and below the hard nodular limestone of the Melbourn Rock Member. | ||
| Thickness: | Northern Province: About 1.15 m at the type site but to as little as 0.25 m elsewhere. Southern Province: Usually in the range 1 to 1.5 m but known to be up to 3.0 m at the Holywell Cafe cliff section in Eastbourne. | ||
| Geographical Limits: | Widespread within the Southern, Transitional and Northern provinces and offshore in the North Sea area. Forms the most characteristic downhole geophysical signature in the whole of the Chalk Group. In the Northern Province the distribution is not known in detail but it is suspected that this member forms part of the succession formerly identified as the Black Band in boreholes and seismic sections. | ||
| Parent Unit: | Holywell Nodular Chalk Formation (HCK) | ||
| Previous Name(s): | Expanded Standard Black Band Succession [Obsolete Name and Code: Use PLMA, BKBD]
(-3220)
Plenus Marls Member (Northern Province) [Obsolete Name and Code: Use PLMA] (PLMN) Variegated Beds [Obsolete Name and Code: Use PLMA] (-60) Belemnite Marls [Obsolete Name and Code: Use BM, PLMA] (-4475) Flixton Member [Obsolete Name and Code: Use PLMA] (-700) Plenus Marl [Obsolete Name and Code: Use PLMA] (PLNM) Basal Beds [Obsolete Name and Code: Use PLMA, BKBD, SPN] (-3221) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Merstham Greystone Limeworks in Surrey. Southern Province type section in old quarry. | ||
| Reference Section | Melton Bottom upper quarry. This is the stratotype for the whole Welton Chalk Formation. | ||
| Reference Section | South Ferriby Quarry, Lincolnshire. | ||
| Type Section | Melton Ross Quarry, Lincolnshire. Northern Province type section. | ||
| Reference(s): | |||
| Sumbler, M G. 1999. The stratigraphy of the Chalk Group in Yorkshire and Lincolnshire. British Geological Survey Technical Report WA/99/02. | |||
| Gaunt, G D, Fletcher, T P and Wood, C J. 1992. Geology of the country around Kingston upon Hull and Brigg. Memoir of the British Geological Survey, sheets 80 and 89 (England and Wales). 172pp. | |||
| Jeans, C V. 1980. Early submarine lithification in the Red Chalk and Lower Chalk of Eastern England; a bacterial control model and its implications. Proceedings of the Yorkshire Geological Society, Vol.43, 81-157. | |||
| Witham, F. 1991. The stratigraphy of the Upper Cretaceous Ferriby, Welton and Burnham formations north of the Humber, north-east England. Proceedings of the Yorkshire Geological Society, Vol. 48, 227-254. | |||
| Wood, C J, Batten, D J, Mortimore, R N and Wray, D S. 1997. The stratigraphy and correlation of the Cenomanian-Turonian boundary interval succession in Lincolnshire, northern England. Freiberger Forschungsheft, Reihe C, Vol. 468, 333-346. | |||
| Hopson, P M. 2005. A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, with statements on the Chalk of Northern Ireland and the UK Offshore Sector. British Geological Survey Research Report RR/05/01 102pp. ISBN 0 852725175 | |||
| Wood, C J and Mortimore, R N. 1995. An anomalous Black Band succession (Cenomanian-Turonian boundary interval) at Melton Ross, Lincolnshire, eastern England and its international significance. Berliner Geowissenschaftliche Abhandlungen, Reihe E, Vol.16, 277-287. | |||
| Jefferies, R P S. 1963. The stratigraphy of the Actinocamax plenus Subzone (Turonian) in the Anglo-Paris Basin. Proceedings of the Geologists' Association, Vol.74, 1-33. | |||
| Dodsworth, P. 1996. Stratigraphy, microfossils and depositional environments of the lowermost part of the Welton Chalk Formation (late Cenomanian to early Turonian, Cretaceous) in eastern England. Proceedings of the Yorkshire Geological Society, Vol.51, 45-64. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E237 | |||