London Clay

London Clay Formation
Stratigraphic range: Ypresian

London Clay at Reculver
Type Formation
Unit of Thames Group
Underlies Bagshot Formation (London Basin), Wittering Formation and Poole Formation (Hampshire Basin and English Channel)
Overlies Harwich Formation
Thickness up to 150 m
Location
Region southern England

Geological map of the London Basin; the London Clay is marked in dark brown.
Eroding London Clay cliffs at The Naze in Essex.

The London Clay Formation is a marine geological formation of Ypresian (Lower Eocene Epoch, c. 56–49 Ma) age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from the Lower Eocene indicate a moderately warm climate, the tropical or subtropical flora. Though sea levels changed during the deposition of the Clay, the habitat was generally a lush forest – perhaps like in Indonesia or East Africa today – bordering a warm, shallow ocean.

The London Clay is a stiff bluish clay which becomes brown when weathered. Nodular lumps of pyrite and crystals of selenite (sometimes called "waterstones") frequently exist in the clay, and large septarian concretions are also common. These have been used in the past for making cement. They were once dug for this purpose at Sheppey, near Sittingbourne, and at Harwich, and also dredged, off the Hampshire coast. The clay is still used commercially for making bricks, tiles, and coarse pottery in places such as Michelmersh in Hampshire.[1] It is infertile for gardens and crops.

Distribution and geology

The London Clay is well developed in the London Basin, where it thins westwards from around 150 metres (492 feet) in Essex and north Kent to around 4.6 metres (15 feet) in Wiltshire.[2] though it is not frequently exposed as it is to a great extent covered by more recent Neogene sediments and Pleistocene gravel deposits. One location of particular interest is Oxshott Heath, where the overlying sand and the London Clay layers are exposed as a sand escarpment, rising approximately 25 metres (82 feet). This supported a thriving brick industry in the area until the 1960s. The London Clay is also well developed in the Hampshire Basin, where an exposure 91 metres (299 ft) thick occurs at Whitecliff Bay on the Isle of Wight and around 101 metres (331 ft) is spread along 6 kilometres (4 miles) of foreshore at Bognor Regis, West Sussex.[3]

The clay was deposited in a sea up to 200 metres (660 ft) deep at the eastern end. Up to five cycles of deposition (representing transgression followed by shallowing of the sea) have been found, most markedly at the shallower, western end. Each cycle begins with coarser material (sometimes including rounded flint pebbles), followed by clay which becomes increasingly sandy. The final cycle ends with the Claygate Beds.[2]

Claygate Beds

The youngest part of the London Clay, known as the Claygate Beds or Claygate Member forms a transition between the clay and the sandier Bagshot Beds above. This is shown separately on many geological maps, and often caps hills. It is up to 15 metres (49 ft) thick at Claygate, Surrey.[2] It is now believed to be diachronous, with the formation at Claygate for example being the same age as the end of the fourth cycle of deposition further east.[4]

Fossil flora and fauna

Notable coastal exposures from which fossils can be collected are on the Isle of Sheppey in Kent and Walton-on-the-Naze, Essex in the London Basin, and Bognor Regis in the Hampshire Basin.

Plant fossils, especially seeds and fruits, are found in abundance and have been collected from the London Clay for almost 300 years.[5] Some 350 named species of plant have been found, making the London Clay flora one of the world's most diverse for fossil seeds and fruits.[6] The flora includes plant types found today in tropical forests of Asia and demonstrates the much warmer climate of the Eocene epoch, with plants such as Nypa (Nipah palms) and other palms being frequently encountered. The following plants list is incomplete and is based on the research by Marjorie Chandler.[5] and research works done by the paleobotanist Steven R. Manchester[7] and by professor of plant palaeobiology Margaret Collinson.[8]

Plants

Pteridophytes

Gymnosperms

  • †Araucarites spp.
  • †Doliostrobus stenbergi - fossils in the past named †Araucarites are said to be of this genus, it is now placed in its own family, †Doliostrobaceae.
  • ?Taxaceae indet.
  • Cephalotaxus bowerbanki
  • †Cupressinites spp.
  • Libocedrus adpressa
  • †Quasisequoia sp.
  • Podocarpus argillaelondinensis?

Angiosperms

  • †Caryotispermum cantiense
  • †Palmospermum bracknellense
  • †Palmospermum cooperi
  • †Palmospermum davisi
  • †Palmospermum elegans
  • †Palmospermum jenkinsi
  • †Palmospermum minutum
  • †Palmospermum ornatum
  • †Palmospermum ovale
  • †Palmospermum subglobulare
  • Nypa burtini (syn. Nipa burtini)
  • †Caricoidea obovata
  • †Polycarpella caespitosa
  • Alnus richardsoni (syn. Petrophiloides richardsoni) – an alder
  • †Juglandicarya bognorensis
  • †Juglandicarya cooperi
  • †Juglandicarya depressa - the most common Juglandacarya species in the London Clay
  • †Juglandicarya lubbocki
  • †Juglandicarya minuta
  • †Petrophiloides richardsoni - among the two most abundant Juglandaceae species in the London Clay
  • †Pterocaryopsis bognorensis - related to the genus Pterocarya
  • †Myristicacarpum chandlerae
  • †Anonaspermum anonijorme - related to the genera Anona and Polyalthia, most similar species is Annona muricata
  • †Anonaspermum cerebellatum - Uvaria, Melodorum and Orophea shows closest resemblance to the fossil
  • †Anonaspermum commune
  • †Anonaspermum complanatum - related to Anona and Melodorum
  • †Anonaspermum corrugatum - related to the genera Anona and Melodorum
  • †Anonaspermum minimum - related to Dasymaschalon clusiflorum
  • †Anonaspermum obscurum
  • †Anonaspermum ovale - related to the genera Anona and Melodorum
  • †Anonaspermum pulchrum - related to Dasymaschalon clusiflorum
  • †Anonaspermum punctatum - related to the genera Bocagea, Orophea, Unonopsis, and Guatteria
  • †Anonaspermum rotundatum - distantly related to Polyauhia
  • †Anonaspermum rugosum
  • †Anonaspermum subcompressum
  • †Crowella globosa
  • †Laurocalyx bowerbanki
  • †Laurocalyx dubius
  • †Laurocalyx fibrotorulosus
  • †Laurocalyx globularis
  • †Laurocalyx magnus
  • †Laurocarpum crassum
  • †Laurocarpum cupuliferum
  • †Laurocarpum davisi
  • †Laurocarpum inornatum
  • †Laurocarpum minimum
  • †Laurocarpum minutissimum
  • †Laurocarpum ovoideum
  • †Laurocarpum paradoxum
  • †Laurocarpum proteum
  • †Laurocarpum pyrocarpum
  • †Laurocarpum sheppeyense
  • †Protoaltingia europaea
  • †Protoravensara sheppeyensis
  • †Plataninium decipiens[9]
  • †Protobarclaya eocenica
  • †Bowerbankella tiliacoroidea
  • †Davisicarpum gibbosum
  • †Eohypserpa parsonsi
  • †Frintonia ornata
  • †Menispermoxylon - close to the extant genus Tinomiscium
  • †Microtinomiscium foveolatum
  • †Tinomiscoidea scaphiformis
  • Tinospora excavata
  • †Wardenia davisi
  • Symplocos curvata
  • Symplocos quadrilocularis
  • Symplocos trilocularis
  • Symplocos bognorensis
  • †Sapoticarpum rotundatiim
  • †Sapoticarpum latum
  • †Sapoticarpum duhium
  • †Sapotispermum sheppeyense - allied to Chrysophyllum and Sideroxylon
  • †Hightea elliptica
  • †Hightea turgida
  • †Myrtospermum sp.
  • †Palaeorhodomyrtus suhangulata - allied to Rhodomyrtus
  • Dalbergia sp.
  • †Leguminocarpon nervosum
  • †Mimosites browniana
  • †Palaeobruguiera elongata
  • †Palaeobruguiera lata
  • Oncoba variabilis
  • † Saxifragispermum spinosissimum
  • †Decaplatyspermum bowerbanki
  • †Wetherellia variahilis - related to Hugonia
  • Erythropalum europaeum - Only one extant species of this genus which is a scandent shrubs or liana
  • Erythropalum jenkinsi
  • Erythropalum turbinatum
  • Olax depressa
  • Ehretia clausentia
  • Ehretia ehretioides
  • †Ochrosella ovalis
  • †Ochrosoidea sheppeyensis
  • †Bursericarpum aldwickense
  • †Bursericarpum bognorense
  • †Bursericarpum ovale
  • †Bursericarpum venablesi
  • †Palaeobursera bognorensis
  • †Protocommiphora europaea
  • Choerospondias sheppeyensis
  • †Dracontomelon minimum
  • †Dracontomelon subglobosum
  • Lannea europaea
  • Lannea jenkinsi
  • †Lobaticarpum variabile
  • Odina europaea
  • Odina jenkinsi
  • Odina subreniformis
  • †Pseudosclerocarya subalata
  • †Spondiaecarpon operculatum - according to several botanists, the pyritized specimens, originally described as Spondiaecarpon operculatum, represent locule casts of Torricellia sp.
  • †Cranmeria trilocularis
  • †Minsterocarpum alatum - closely related to the crape myrtle or crepe myrtle genus Lagerstroemia
  • †Pachyspermum quinqueloculare
  • †Tamesicarpum polyspermum
  • †Cantitilia polysperma
  • †Echinocarpus sheppeyensis
  • †Urticicarpum scutellum
  • †Euphorbiospermum bognorense
  • †Euphorbiospermum cooperi
  • †Euphorbiospermum eocenicum
  • †Euphorbiospermum obliquum
  • †Euphorbiospermum subglobulare
  • †Euphorbiospermum subovoideum
  • †Euphorbiospermum venablesi
  • †Euphorbiotheca minima
  • †Euphorbiotheca sheppeyensis
  • †Lagenoidea bilocularis
  • †Lagenoidea trilocularis
  • †Wetherellia variabilis
  • †Cucurbitospermum cooperi
  • †Cucurbitospermum equiaelaterale
  • †Cucurbitospermum sheppeyense
  • †Cucurbitospermum triangulare
  • †Cupanoides grandis
  • †Cupanoides tumidus
  • †Palaeallophylus minimus
  • †Palaeallophylus rotundatus
  • †Palaealectryon spirale
  • †Sapindospermum cooperi
  • †Sapindospermum davisi
  • †Sapindospermum jenkinsi
  • †Sapindospermum revolutum
  • †Canticarya gracilis
  • †Canticarya ovalis
  • †Canticarya sheppeyensis
  • †Canticarya ventricosa
  • †Caxtonia elongata
  • †Caxtonia glandulosa
  • †Caxtonia rutacaeformis
  • †Citrispermum sheppeyense
  • †Clausenispermum dubium
  • †Eozanthoxylon glandulosum
  • †Rutaspermum bognorense
  • †Rutaspermum minimum
  • †Shrubsolea jenkinsi
  • †Zanthoxylon compression
  • †Zanthoxylon bognorense
  • †Celastrinoxylon ramunculiformis
  • †Sphinxia ovalis
  • †Beckettia mastixioides
  • Cornus ettingshausenii
  • †Dunstania ettinghauseni
  • †Dunstania multilocularis
  • †Langtonia bisulcata
  • †Lanfrancia subglobosa
  • Mastixia cantiensis
  • Mastixia grandis
  • Mastixia parva
  • †Portnallia bognorensis
  • †Portnallia sheppeyensis
  • Nyssa bilocularis
  • Nyssa cooperi
  • †Palaeonyssa multilocularis
  • †Icacinicarya echinata
  • †Icacinicarya forbesii
  • †Icacinicarya foveolata
  • †Icacinicarya glabra
  • †Icacinicarya ovalis
  • †Icacinicarya platycarpa
  • †Icacinicarya reticulata
  • †Icacinicarya rotundata
  • †Icacinicarya nodulifera
  • Iodes corniculata
  • Iodes davisii
  • Iodes eocenica
  • Iodes multireticulata
  • Natsiatum eocenicum
  • †Palaeophytocrene ambigua
  • †Palaeophytocrene foveolata
  • †Sphaeriodes ventricosa
  • †Stizocarya communis

Animals

Animal fossils include bivalves, gastropods, nautilus, worm tubes, brittle stars and starfish, crabs, lobsters, fish (including shark and ray teeth), reptiles (particularly turtles), and a large diversity of birds. A few mammal remains have also been recorded. Preservation varies; articulated skeletons are generally rare. Of fish, isolated teeth are very frequent. Bird bones are not infrequently encountered compared to other lagerstätten, but usually occur as single bones and are often broken.

The following fauna species list follows Clouter (2007).[10]

Vertebrates

Mammals
Birds
Reptiles

Crocodylians

Snakes

Turtles and tortoises

Turtle fossils from Sheppey
Bony fish
Cartilaginous fish

Crustaceans

Exuvia of Hoploparia

Molluscs

Cephalopods
Bivalves

Anomiidae

Astartidae

Gastropods
Tusk shells

Echinoderms

Ophiura wetherelli from the London Clay of Bognor Regis

Annelids

Cnidarians

Other invertebrates

Ichnofossils

Engineering

The presence of a thick layer of London Clay underneath London itself, providing a soft yet stable environment for tunnelling, was instrumental in the early development of the London Underground, although this is also the reason why London has no true skyscraper buildings, at least to the same degree as many other cities throughout the world. Erecting tall buildings in London requires very deep, large and costly piled foundations.

London Clay is highly susceptible to volumetric changes depending upon its moisture content.[13] During exceptionally dry periods or where the moisture is extracted by tree root activity, the clay can become desiccated and shrink in volume, and conversely swell again when the moisture content is restored. This can lead to many problems near the ground surface, including structural movement and fracturing of buildings, fractured sewers and service pipes/ducts and uneven and damaged road surfaces and pavings. Such damage is recognised to be covered by the interpretation of subsidence in buildings insurance policies, and the periods of dry weather in 1976/77 and 1988/92, in particular, led to a host of insurance claims. As a result, many insurance companies have now increased the cost of premiums for buildings located in the most susceptible areas where damage occurred, where the clay is close to the surface.

Tunnels in London Clay

The London Clay is an ideal medium for driving tunnels, which is why the London Tube railway network expanded quickly north of the Thames, but south of the Thames the stratum at tube level is water-bearing sand and gravel (not good for tunnelling) with London Clay below, which is why there are few tube tunnels there. London Clay has a stand-up time long enough to enable support to be installed without urgency. It is also almost waterproof, resulting in virtually no seepage of groundwater into the tunnel. It is over-consolidated, which means that it is under pressure, and expands upon excavation, thus gradually loading the support, i.e. it is not necessary to stress the support against the ground.

Agriculture

Due to its impermeability especially when exposed by ploughing, London clay does not make good agricultural soil. In Middlesex, it has historically been called "ploughing up poison."[14]

See also

Notes

  1. ↑ Often called Eohippus
  2. ↑ Includes "Primobucco" olsoni
  3. ↑ Sometimes placed in Aprionodon
  4. ↑ Sometimes placed in Physodon
  5. ↑ Sometimes placed in Rhinoptera
  6. ↑ Sometimes called Hypotodus robustus
  7. ↑ Sometimes called Eugomphodus macrotus
  8. ↑ Sometimes placed in Acanthius
  9. ↑ Sometimes placed in Xendolamia
  10. ↑ Sometimes called Necrozius bowerbanki
  11. ↑ Sometimes placed in Eutrephoceras
  12. ↑ Sometimes called Modiolus depressus
  13. ↑ Sometimes placed in Striarca
  14. ↑ Sometimes placed in Cyprina
  15. ↑ Sometimes called A. rugatus
  16. ↑ Sometimes called Pitaria tenuistriata
  17. ↑ Sometimes placed in Ledina
  18. ↑ Sometimes called Amussium corneum
  19. ↑ Sometimes placed in Protocardium
  20. ↑ Sometimes placed in Pteria
  21. ↑ Sometimes placed in Ostrea
  22. ↑ Sometimes considered a variety of Scala undosa
  23. ↑ Sometimes called A. sowerbyii
  24. ↑ Sometimes placed in Tibia
  25. ↑ Sometimes in Hemipleurotoma
  26. ↑ Sometimes placed in Conospirus
  27. ↑ Sometimes in Hemipleurotoma
  28. ↑ Sometimes in Hemipleurotoma
  29. ↑ Sometimes in Hemipleurotoma
  30. ↑ Sometimes S. bifaci or S. bifacsi
  31. ↑ Sometimes included in T. teretrium
  32. ↑ Sometimes included in T. teretrium
  33. ↑ Sometimes placed in Galeodea
  34. ↑ Sometimes called Newtoniella charlsworthi
  35. ↑ Sometimes called Solarium pulchrum
  36. ↑ Sometimes placed in Natica
  37. ↑ Sometimes called Fusinus unicarinatus
  38. ↑ Sometimes placed in Bartonia
  39. ↑ Sometimes called Euthriofusus complanatus
  40. ↑ Sometimes called Euthriofusus transversarius
  41. ↑ Sometimes placed in Ficus
  42. ↑ Sometimes called Murex argillaceus
  43. ↑ Sometimes called T. tenuiplica
  44. ↑ Sometimes placed in Aurinia
  45. ↑ Sometimes placed in Calyptraea
  46. ↑ Sometimes placed in Adeorbis
  47. ↑ Sometimes called Onutusus extensa
  48. ↑ Sometimes placed in Asteropecten
  49. ↑ Sometimes placed in Rhizochrinus

References

  1. ↑ "Michelmersh Brick and Tile Company". Retrieved 2013-05-19.
  2. 1 2 3 Sumbler, M. G. (1996). London and the Thames Valley. British Regional Geology series (4th ed.). British Geological Survey. ISBN 0-11-884522-5.
  3. ↑ Melville, R. V. & E. C. Freshney (1992). The Hampshire Basin and adjoining areas. British Regional Geology series (4th ed.). British Geological Survey. ISBN 0-11-884203-X.
  4. ↑ Ellison, R. A.; et al. (2004). Geology of London: Special Memoir for 1:50,000 Geological sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales). British Geological Survey. ISBN 0-85272-478-0.
  5. 1 2 Chandler, M.E.J. 1961. The lower Tertiary floras of southern England I. Palaeocene floras, London Clay flora. London: British Museum (Natural History).
  6. ↑ Collinson, M. (1983). Fossil plants of the London Clay. The Palaeontological Association.
  7. ↑ https://www.researchgate.net/profile/Steven_Manchester/publications
  8. ↑ https://pure.royalholloway.ac.uk/portal/en/persons/margaret-collinson(aaab3619-3c87-4750-9bcb-e845e326b952)/publications.html
  9. ↑ Poole, I., K.L. Davies and H.P. Wilkinson 2002. A review of the platanaceous woods from the Eocene paratropical rainforest of south-east England. Botanical Journal of the Linnean Society, 139: 181–191.
  10. ↑ Clouter, Fred (June 29, 2007). "London Clay Species List". Retrieved June 16, 2008.
  11. ↑ Alexandre F. Bannikov & James C. Tyler (1995). "Phylogenetic revision of the fish families Luvaridae and †Kushlukiidae (Acanthuroidei), with a new genus and two new species of Eocene luvarids" (PDF). Smithsonian Contributions to Paleobiology. 81: 1–45. doi:10.5479/si.00810266.81.1.
  12. ↑ W. J Quayle (1987). "English Eocene Crustacea (lobsters and stomatopod)" (PDF). Palaeontology. 30 (3): 581–612.
  13. ↑ Buildings on Clay The effects of geology, climate and vegetation on heave and settlement, Derek Clarke and Joel Smethurst
  14. ↑ View of the Agriculture of Middlesex: With Observations on the Means of Its Improvement, and Several Essays on Agriculture in General. By Board of Agriculture (Great Britain), John Middleton. Published by G. and W. Nicol, second edition, 1807. Page 20.
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