The BGS Lexicon of Named Rock Units — Result Details

Blackheath Member

Stratotypes:
Computer Code:	BLB	Preferred Map Code:	notEntered
Status Code:	Full
Age range:	Ypresian Age (GY) — Ypresian Age (GY)
Lithological Description:	The Blackheath Member is dominated by flint gravel, partly clast-supported, in a matrix of fine- to coarse-grained sand, with lenses of sand and thin clay layers. The gravel is almost exclusively black and well-rounded, and composed of flint, and rare siliceous sandstones and conglomerates (resembling sarsen stones and 'puddingstone' and probably representing silcretes from the Lambeth Group). The clasts are generally less than 20 mm in diameter although cobbles up to 150 mm long are known (Baker and Priest, 1919; Dewey et al., 1924; Ellison et al., 1994). The gravels are interlayered, interlensed or interdigitated with pale-coloured fine-grained non-glauconitic quartz and flint sands, locally with scattered gravel and, at Charlton, a basal bed of clay pellets. Streaks of concentrated heavy minerals occur in the sands (Dewey et al., 1924). Both gravels and sands locally include shell-rich beds (coquinas) and occasional thin beds of grey clay. Cross-bedding occurs in the gravels and ripple-bedding in the sands, with the gravel beds forming series of superimposed channel-fill deposits (Ellison et al., 2004, fig. 24; Tracey, 1986). Calcareous, siliceous or ferruginous cements occur in places, locally forming masses several metres thick (Dewey and Bromehead, 1921; Dewey et al., 1924), particularly in the extensive outcrops in south-east London. In degraded sections, the deposit can appear to consist entirely of sandy gravel. The most common fossils are of shallow marine or brackish-water molluscs, but a coral, various fish, reptiles, a bird, and a considerable terrestrial mammal fauna have also been recorded (Hooker, 1991, 2010). At the type locality, the Blackheath Member consists of marine shoreface deposits (Hooker, 2010), containing shelly fossil faunas indicating both marine and brackish environments. Early Eocene (early Ypresian), after the Paleocene-Eocene Thermal Maximum (PETM) (Hooker, 2010). Hooker (2010) notes that there is no evidence that the Apectodinium (dinoflagellate) acme (that proxies the PETM) extends into the Blackheath Member. He infers that the Blackheath Member was deposited during the later part of calcareous nannoplankton zone NP9, partly by its position relative to the Woolwich Formation and to the Oldhaven Member, and partly by comparison of its mammal fossil faunas with those of the North American Big Horn Basin. He argues that it is probably about 55 Ma old.
Definition of Lower Boundary:	The Blackheath Member lies on an erosional surface, in part deeply channelled, cut into the Upper Shelly Clay or older parts of the Lambeth Group, and locally into the Thanet Formation and the Chalk Group. At the Charlton Pit, in some places the Blackheath Member rests on the Striped Loams of the Woolwich Formation and in others on strata as old as the Upnor Formation (Hooker, 2010; Leach and Young, 1908). At Abbey Woods, the Blackheath Member rests on strata ranging from the lower part of the Upnor Formation to the lower part of the Thanet Formation within about 300 m lateral distance. At the north-east side of Plumstead Common, the Blackheath Member rests on the Shelly Clay of the Woolwich Formation, but only about 350 m to the south it rests on the Upnor Formation (Leach and Polkinghorne, 1906).
Definition of Upper Boundary:	The Blackheath Member is overlain at an erosive surface by the Oldhaven Member (Harwich Formation) (as at Swanscombe, King, 1981, and Cobham, Hooker, 2010, p. 4), which mainly consists of glauconitic fine-grained sand (although a basal gravel bed is present in places) or more extensively by the Walton Member (London Clay Formation), which is mainly composed of silty clay, some sandy, with a thin basal sandy and gravelly bed.
Thickness:	At the type section, the unit has been measured as 4.3 m thick, although an unknown part has been removed from the top by erosion, and past exposures nearby imply that at least 9 m are present (Hooker, 2010). Mapped outcrop patterns imply that the Blackheath Member is locally as much as 24 m thick (Dewey et al., 1924).
Geographical Limits:	The Blackheath Member occurs in south-east London from Croydon to Greenwich and Erith, with outliers in north-west Kent, especially around Swanscombe and Shorne (Chandler, 1923; Dines et al., 1954). Sand-filled channels occur in subcrop to the north-west of the main outcrop, under parts of central and south-west London (King, in prep.).
Parent Unit:	Harwich Formation (HWH)
Previous Name(s):	Blackheath Beds [Obsolete Name and Code: Use CHGR, BLB] (-2081) Abbey Wood Member [Obsolete Name and Code: Use BLB] (965) Blackheath Pebble Member [Obsolete Name and Code: Use BLB] (966)
Alternative Name(s):	none recorded or not applicable
Type Section	Charlton Pit (or Gilbert's Pit), just south-west of Maryon Park, Charlton, London Borough of Greenwich (Daley, 1999). Hooker (2010) designated this as the type locality for his Blackheath Formation.
Reference Section	Elmstead Rock Pit, Chislehurst, Kent (Daley, 1999b; Hooker, 2010). This section contains an unusually rich fossil fauna.
Reference Section	Abbey Wood, London Borough of Bexley (Hooker, 2010).
Reference Section	A2 Well Hall Road cutting, Eltham (Ellison et al., 2004, fig. 24; Tracey, 1986).
Reference(s):
Baker, H A, and Priest, S. 1919. Excursion to East Wickham and Plumstead: Saturday, September 6th, 1919. Proceedings of the Geologists' Association, Vol. 30, 199-204.
Dewey, H, and Bromehead, C E N. 1921. The geology of the South London. Memoir of the British Geological Survey, Sheet 270 (England and Wales).
Dines, H G, Holmes, S C A, and Robbie, J A. 1954. Geology of the country around Chatham. Memoir of the Geological Survey, Sheet 272 (England and Wales).
Hooker, J J. 1991. The sequence of mammals in the Thanetian and Ypresian of the London and Belgian basins. Location of the Palaeocene-Eocene boundary. Newsletters in Stratigraphy, Vol. 25, 75-90.
Leach, A L, and Polkinghorne, B C. 1906. Excursion to East Wickham and Bostal Heath. Proceedings of the Geologists' Association, Vol. 19, 341-347.
Leach, A L, and Young, A C. 1908. Excursion to Charlton and Erith: Saturday, May 2nd, 1908. Proceedings of the Geologists' Association, Vol. 20, 505-508.
Tracey, S. 1986. Lower Tertiary strata exposed in a temporary excavation at Well Hall, Eltham, south-east London. Tertiary Research, Vol. 7, 107-123.
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.
Hooker, J J. 2010. The mammal faunas of the early Eocene Blackheath Formation of Abbey Wood, London. Monograph of the Palaeontographical Society, London, 164, 1-162.
Ellison, R A, Woods, M A, Allen, D J, Forster, A, Pharaoh, T C and King, C. 2004. Geology of London. Memoir of the British Geological Survey, Sheets 256 (North London), 257 (Romford), 270 (South London), 271 (Dartford) (England and Wales).
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.
King, C. in prep. A revised correlation of Palaeogene and Neogene deposits in the British Isles. Geological Society of London Special Report.
Daley, B. 1999. London Basin: eastern localities, In: Daley, B, Balson, P (Eds.), British Tertiary Stratigraphy. Geological Conservation Review Series 15, pp. 23-72.
Whitaker, W. 1866. On the "Lower London Tertiaries" of Kent. Quarterly Journal of the Geological Society London, Vol.22, 404-435.
Chandler, R.H., 1923. The Tertiary section at Shorne Wood, Cobham, Kent. Proceedings of the Geologists' Association 34, 137-141.
Cooper, J, 1976. British Tertiary stratigraphical and rock terms, formal and informal, additional to Curry, 1958. Lexique Stratigraphique International. Tertiary Research Special Paper No.1, Tertiary Research Group.
Dewey, H, Bromehead, C E N, Chatwin, C P and Dines, H G. 1924. The geology of the country around Dartford. Memoir of the Geological Survey, Sheet 271 (England and Wales).
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.
King, C. 1981. The stratigraphy of the London Clay and associated deposits. Tertiary Research Special Paper No.6. (Backhuys: Rotterdam).
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.
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E270 E257 E271 E272

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