| Computer Code: |
HWH |
Preferred Map Code: |
Har |
| Status Code: |
Full |
| Age range: |
Ypresian Age (GY)
— Ypresian Age (GY) |
| Lithological Description: |
The Harwich Formation varies regionally. In the south of the London Basin, it typically comprises glauconitic silty or sandy clays, silts and fine- to coarse-grained glauconitic sands, some gravelly, varying to flint gravel beds. Thin beds of grey clay occur in some parts, as do shell-rich beds and thin beds of argillaceous limestone. Volcanic ash is a significant minor component in some parts of Kent and southern Essex. The Harwich Formation commonly includes a shelly marine fauna but locally a brackish water fauna.
In East Anglia, the Harwich Formation comprises mainly bioturbated silty clays and sandy clayey silts with subordinate sandy silts and silty sands, some of which are glauconitic. There is a notable component of volcanic ash, both disseminated and in discrete beds (Knox and Ellison, 1979; Knox and Harland, 1979).
Fossils include marine invertebrates, especially molluscs, with birds and mammals (Benton and Cook, 2006; Hooker, 1991, 1996, 1998, 2010).
The Harwich Formation is considered to have been deposited in a shallow marine shelf environment, with the 'proximal' sandy facies closer to shore, with relatively slow and interrupted sedimentation which was at times within storm wave-base, and including shoreface deposits. The Blackheath Member is interpreted as the deposits of tidal channels and nearshore sand and gravel bars (Ellison et al., 1994). Inner to mid-shelf environments are represented in the 'distal' muddy facies of East Anglia.
Early Eocene (early Ypresian). |
| Definition of Lower Boundary: |
The base of the Harwich Formation is an eroded unconformity surface on the underlying Reading or Woolwich Formation, or, locally south of London, the Thanet Formation or the Chalk Group. The base is sharply defined, being formed by a planar or slightly undulose discontinuity with a basal lag of very well-rounded flint gravel and fine to coarse quartz grains in a finer glauconitic matrix. Burrows commonly extend down into underlying beds. |
| Definition of Upper Boundary: |
The top of the Harwich Formation is a discontinuity marking the upwards change from sandy sediments to silty clays and clayey silts of the transgressive marine Walton Member (London Clay Formation). In distal areas there is commonly a thin bed of silty sand at the top of the Harwich Formation, overlain by sandy clay (Ellison et al., 1994). |
| Thickness: |
Up to 24 m in East Anglia. Locally up to 24 m in south-east London, more generally up to 10 m but commonly less than 2 m. |
| Geographical Limits: |
The Harwich Formation occurs almost throughout the London Basin, and in parts of East Anglia. It is locally absent, for example in parts of London, where the London Clay lies directly on the Lambeth Group. |
| Parent Unit: |
Thames Group (THAM)
|
| Previous Name(s): |
London Clay Basement Bed [Obsolete Name and Code: Use HWH]
(LCBA)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Partial Type Section |
Cliff and foreshore at Wrabness [TM 1726 3233] (King, 1981). |
| Partial Type Section |
Cliff and foreshore at Walton-on-the-Naze [TM 267 244] (King, 1981). |
| Partial Type Section |
BGS Shotley Gate Borehole (TM23SW 19) [TM 2439 3460] (Knox and Ellison, 1979). |
| Reference(s): |
| King, C. 1981. The stratigraphy of the London Clay and associated deposits. Tertiary Research Special Paper No.6. (Backhuys: Rotterdam). |
| 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. 1958. Part 3a XII Palaeogene. Lexique Stratigraphique International. Whittard, W F, and Simpson, S (editors). Vol. 1 Europe (Paris: Centre Nationale de la Research Scientifique.) |
| Ward, D J. 1978. The Lower London Tertiary (Palaeocene) succession of Herne Bay, Kent. Institute of Geological Sciences, Report 78/10. |
| Knox, R W O, and Harland, R. 1979. Stratigraphical relationships of the early Palaeogene ash-series of NW Europe. Journal of the Geological Society, London, Vol. 136, 463-470. |
| Hooker, J J. 1998. Mammalian faunal change across the Paleocene-Eocene transition in Europe. 91-102 in Late Paleocene-Early Eocene climatic and biotic events in the marine and terrestrial records. Aubry, M-P, Lucas, S G, and Berggren,W A (editors). (New York: Columbia University.) |
| 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. |
| Knox, R.W.O., Ellison, R.A., 1979. A Lower Eocene ash sequence in SE England. Journal of the Geological Society 136, 251-253. |
| Benton, M J, and Cook, E. 2006. British Tertiary fossil bird GCR sites. 125-161 in Mesozoic and Tertiary Fossil Mammals and Birds of Great Britain. Benton, M J, Cook, E, and Hooker, J J (editors). |
| 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. |
| Hooker, J J. 1996. Mammals from the Early (late Ypresian) to Middle (Lutetian) Eocene Bracklesham Group, southern England. Tertiary Research, Vol. 16, 141-174. |
| 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. |
| Whitaker, W. 1866. On the "Lower London Tertiaries" of Kent. Quarterly Journal of the Geological Society London, Vol.22, 404-435. |
| 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. |
| Prestwich, J. 1850. On the structure of the strata between the London Clay and the Chalk in the London and Hampshire Tertiary systems. Part I Quarterly Journal of the Geological Society, London, Vol. 6, 252-281. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E191
E257
E268
E269
|
