The BGS Lexicon of Named Rock Units — Result Details
Thanet Formation
| Computer Code: | TAB | Preferred Map Code: | TS |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Thanetian Age (GT) — Thanetian Age (GT) | ||
| Lithological Description: | Typically composed of homogeneous, bioturbated, glauconitic silty fine-grained sand, with sandy silt, silt or sandy, silty clay especially in the lower part, forming a coarsening-upwards sequence. The deposits are generally pale yellow-brown in colour, typically with a 'peppering' of dark-coloured glauconite grains. Sparse white mica occurs throughout. Rare coarse gravel is present in places in London. Patchy calcareous, siliceous or ferruginous cement occurs locally. A thin gravel and cobble bed (the 'Bullhead Bed') is generally present at the base. It comprises unworn green-coated flints in a matrix of green, glauconite-rich clayey sand. Dispersed and degraded volcanic ash occurs at least locally in the Thanet Formation (Ellison and Lake, 1986; Knox, 1979). The Thanet Formation was deposited on an inner to outer marine shelf, above fair-weather wave base (Ellison et al., 1994). The heavy mineral content of the sands suggests a Scottish provenance, in contrast to that of the overlying Upnor Formation, but similar to that of most of the younger Palaeogene formations (Morton, 1982). Late Paleocene; early to mid-Thanetian (Blake, 1903; Ellison et al., 1994; King, in prep.). | ||
| Definition of Lower Boundary: | The base of the Thanet Formation is the base of the basal sandy, clayey flint gravel bed, which rests on the Chalk Group, often on an irregular, karstic surface modified by dissolution in groundwater. | ||
| Definition of Upper Boundary: | The Thanet Formation is overlain unconformably by the Upnor Formation in most areas but by the Reading Formation in parts of Essex. Generally, an upwards change from yellow-brown, glauconitic silty fine-grained sands of the Thanet Formation to greenish glauconitic medium- to coarse-grained, locally gravelly, variably clayey sand of the Upnor Formation. In the type section and in some other places, the grain-size contrast is less and the boundary correspondingly more difficult to identify. | ||
| Thickness: | In central London, the Thanet Formation is typically 10 to 15 m thick, diminishing westwards to where it is overstepped by the Lambeth Group in west London and Surrey. The formation is generally thicker in the eastern parts of the London Basin, and is greatest in North Kent, where it generally ranges from about 20 m up to 30 m, increasing to as much as 37 m in the Canterbury district (Hester, 1965; Smart et al., 1966). In places significant parts of the Thanet Formation have been removed by erosion prior to deposition of the Lambeth Group (Curry, 1981). At Beacon Hill, west of Faversham, the thickness is about 24 m, whereas at Goodnestone it is little more than 18m (Holmes, 1981). | ||
| Geographical Limits: | The Thanet Formation occurs in the central and eastern London Basin, as far north as southern Suffolk, where it passes laterally into the Ormesby Clay Member. To the west of London, it is overstepped by the Upnor Formation. | ||
| Parent Unit: | Montrose Group (MONT) | ||
| Previous Name(s): | Thanet Sands [Obsolete Name and Code: Use TAB]
(-1856)
Thanet Sand [Obsolete Name and Code: Use TAB] (TS) Thanet Beds [Obsolete Name and Code: Use TAB] (-2473) Thanet Sands Formation [Obsolete Name and Code: Use TAB] (-3708) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | Charlton Pit (or Gilbert's Pit), just south-west of Maryon Park, Charlton, London Borough of Greenwich [TQ 418 786] (Daley, 1999; Ellison et al., 1994; Whitaker, 1889). | ||
| Reference Section | Bradwell Borehole 217 (TM00NW43) [TM 01769 09156], Essex, from 60.2 to about 82.3 m depth (Jolley, 1992, p. 211). | ||
| Reference Section | Stanford-le-Hope Borehole (TQ68SE33) [TQ 6965 8241], Essex, from 29.04 to 57.05 m depth (Lake et al., 1986). | ||
| Reference Section | Jubilee Line Extension Borehole 404T (TQ37NW2118) [TQ 33638 79604], Bermondsey, London, 41.1 to 53.05 m depth, (Ellison et al., 1994). | ||
| Reference Section | Loats Pit, Blackheath, London Borough of Lewisham [TQ 382 766] (Greater London Authority, 2009). | ||
| Reference Section | Cray Valley Golf Course sand pit, London Borough of Bromley [TQ 489 692] (Greater London Authority, 2009). | ||
| Type Section | Cliffs and foreshore east of Herne Bay, Kent [TR 203 687 to 215 693] (Curry, 1981; Daley, 1999; Ward, 1978) expose the upper part of the formation as Beds A to I of Ward (1978), probably with several metres overlap with the more proximal sequence at Pegwell Bay (Knox et al., 1994, p.49). | ||
| Type Section | Cliffs near Little Cliffsend, Pegwell Bay, Kent [TR 3545 6440] (Curry, 1981; Daley, 1999; Ward, 1977) expose the lower part of the formation. | ||
| Reference(s): | |||
| Aldiss, D T. 2014. The stratigraphical framework for the Palaeogene successions of the London Basin, UK. British Geological Survey Open Report OR/14/008. 95 pp. | |||
| Curry, D. 1981. Thanetian. 255-265 in Stratotypes of Palaeogene stages. Pomerol, C (editor). Mémoire Hors Série du Bulletin d'Information des Géologues du Bassin du Paris, No. 2. | |||
| Daley, B. 1999. London Basin: eastern localities. 23-72 in British Tertiary Stratigraphy. Daley, B, and Balson, P (editors). Geological Conservation Review Series 15. | |||
| Ellison, R A, Knox R W O'B, Jolley, D W, and King, C. 1994. A revision of the lithostratigraphical classification of the early Palaeogene strata of the London Basin and East Anglia. Proceedings of the Geologists' Association, Vol. 105, 187-197. | |||
| Ellison, R A, and Lake, R D. 1986. Geology of the country around Braintree. Memoir of the British Geological Survey, Sheet 223 (England and Wales). | |||
| Haynes, J. 1956. Certain smaller British Paleocene foraminifera. Contributions from the Cushman Foundation for foraminiferal research, Vol. 7, 79-101. | |||
| Hester, S W. 1965. Stratigraphy and palaeogeography of the Woolwich and Reading Beds. Bulletin of the Geological Survey of Great Britain No. 23, 117-137. | |||
| King, C. in prep. A revised correlation of Palaeogene and Neogene deposits in the British Isles. Geological Society of London Special Report. | |||
| Knox, R W O, Hine, N M, and Ali, J R. 1994. New information on the age and sequence stratigraphy of the type Thanetian of southeast England. Newsletters on Stratigraphy, Vol. 30, 45-60. | |||
| Knox, R W O. 1979. Igneous grains associated with zeolites in the Thanet Beds of Pegwell Bay, Northeast Kent. Proceedings of the Geologists' Association, Vol. 90, 55-59. | |||
| Lake, R D, Ellison, R A, Henson, M R, and Conway, B W. 1986. Geology of the country around Southend and Foulness. Memoir of the British Geological Survey, Sheet 258 and 259 (England and Wales). | |||
| Morton, A C. 1982. The provenance and diagenesis of Palaeogene sandstones of southeast England as indicated by heavy mineral analysis. Proceedings of the Geologists’ Association, Vol. 93, 263-274. | |||
| Siesser, W G, Ward, D J, and Lord, A R. 1987. Calcareous nannoplankton biozonation of the Thanetian Stage (Palaeocene) in the type area. Journal of Micropalaeontology, Vol. 6, 85-102. | |||
| Smart, J G O, Bisson, G and Worssam, B C. 1966. Geology of the Country around Canterbury and Folkestone. Memoir of the Geological Survey of Great Britain, Sheets 289, 305 and 306 (England and Wales). | |||
| Whitaker, W. 1872. The geology of the London Basin, Part I. The Chalk and the Eocene beds of the southern and western tracts. Memoir of the Geological Survey of England and Wales, Vol. IV. | |||
| Whitaker, W., 1889. The geology of London and part of the Thames Valley (Explanation of Sheets 1, 2 and 7). Memoir of the Geological Survey of the United Kingdom Vol. 1. Descriptive geology. | |||
| Blake, J H. 1903. The geology of the country around Reading. Memoir of the Geological Survey of England and Wales, Sheet 268 (England and Wales). | |||
| Gardner, J S. 1883. On the Lower Eocene section between Reculver and Herne Bay. Quarterly Journal of the Geological Society London, Vol. 39, 197-210. | |||
| Greater London Authority. 2009. London's Foundations - protecting the geodiversity of the capital. (City Hall, London: Greater London Authority.) ISBN 978 1 84781 250 6 | |||
| Holmes, S C A. 1981. Geology of the country around Faversham. Memoir of the Geological Survey, Sheet 273 (England and Wales). | |||
| Jolley, D W, 1992. Palynofloral association sequence stratigraphy of the Palaeocene Thanet Beds and equivalent sediments in eastern England. Review of Palaeobotany and Palynology, Vol.74, p.207-237. | |||
| Ward, D J. 1977. The Thanet Beds exposure at Pegwell Bay, Kent. Tertiary Research, Vol. 1, p. 69-76. | |||
| Ward, D J. 1978. The Lower London Tertiary (Palaeocene) succession of Herne Bay, Kent. Institute of Geological Sciences, Report 78/10. | |||
| Prestwich, J, 1852. On the structure of the strata between the London Clay and the Chalk, etc, part 111. The Thanet Sands. Quarterly Journal of the Geological Society, Vol.8, p.235-268. | |||
| 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. | |||
| Whitaker, W. 1866. On the "Lower London Tertiaries" of Kent. Quarterly Journal of the Geological Society London, Vol.22, 404-435. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E270 E256 E269 E162 E285 E206 E207 E222 E240 E241 E257 E258 E259 E271 E272 E273 E274 | |||