Weald Clay or the Weald Clay Formation is a Lower Cretaceous sedimentary rock unit underlying areas of South East England, between the North and South Downs, in an area called the Weald Basin. It is the uppermost unit of the Wealden Group of rocks within the Weald Basin, and the upper portion of the unit is equivalent in age to the exposed portion of the Wessex Formation on the Isle of Wight. It predominantly consists of thinly bedded mudstone. The un-weathered form is blue/grey, and the yellow/orange is the weathered form, it is used in brickmaking.

The formation was deposited in lagoonal, lacustrine and alluvial conditions that varied from freshwater to brackish. The climate at the time of deposition is thought to have been semi-arid, and prone to fire. The clay alternates with other subordinate lithologies, notably hard red-weathering beds of ironstone, limestone (Sussex Marble) and sandstones, notably including the calcareous sandstone unit referred to as the Horsham Stone. It has a gradual, conformable contact with the underlying Tunbridge Wells Sand Formation, and has a sharp, unconformable contact with the overlying Atherfield Clay Formation, a shallow marine unit deposited after marine transgression during the Aptian.

Physical properties

The weathered and unweathered forms of the Weald Clay have different physical properties. Blue looks superficially like a soft slate, is quite dry and hard and will support the weight of buildings quite easily. Because it is quite impermeable, and so dry, it does not get broken by tree roots. It is typically found at 750mm down below a layer of yellow clay. Yellow, found on the surface, absorbs water quite readily so becomes very soft in the winter. The two different types make quite different bricks.

Paleofauna

Vertebrates Vertebrates reported from the Weald Clay Genus Species Location Stratigraphic position Material Notes ImagesBaryonyxB. walkeriSmokejack Clay PitUpper Weald ClayMultiple partial skulls, one of which had an associated postcranial skeleton."Table 4.1," in Weishampel, et al. (2004). Page 72.A spinosauridHorshamosaurusH. rudgwickensisRudgwick BrickworksUpper Weald Clay"Vertebrae, partial fore and hindlimbs, osteoderms.""Table 17.1," in Weishampel, et al. (2004). Page 367.A dubiousRaven, T. J., P. M. Barrett, S. B. Pond, and S. C. R. Maidment. 2020. Osteology and taxonomy of British Wealden Supergroup (Berriasian–Aptian) ankylosaurs (Ornithischia, Ankylosauria). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2020.1826956 genus of nodosaurid ankylosaur belonging to Polacanthinae. Originally named as a species of Polacanthus.Blows, W.T., 2015, British Polacanthid Dinosaurs – Observations on the History and Palaeontology of the UK Polacanthid Armoured Dinosaurs and their Relatives, Siri Scientific Press, 220 pp.IguanodonI. bernissartensisSmokejack Clay PitUpper Weald ClayIguanodontian, also known from the Wessex Formation.MantellisaurusM. atherfieldensisSmokejack Clay PitUpper Weald ClayIguanodontian, also known from the Wessex FormationValdosaurusV. canaliculatusGalton, P.M., 2009, "Notes on Neocomian (Late Cretaceous) ornithopod dinosaurs from England - Hypsilophodon, Valdosaurus, "Camptosaurus", "Iguanodon" - and referred specimens from Romania and elsewhere", Revue de Paléobiologie 28(1): 211-273HeathfieldLower Weald ClayA dryosaurid, also known from the Wessex FormationLeptocleidus L. superstesNHM R4828 (holotype)PliosauroidWyleyia"10.18 West Sussex, England; 1. Hastings Beds" in Weishampel, et al. (2004). Page 559.W. valdensis West SussexDorsetisaurusIndeterminateKeymer Tile WorksSauropodaIndeterminateSmokejacks, BexhillAnuraIndeterminateKeymer Tile WorksLowerMaxillary fragmentUrodelaIndeterminateKeymer Tile WorksLowerAtlas vertebraHas been suggested to have a close relationship with Balveherpeton from Germany.

Invertebrates Numerous insect species are known from several localities in the Weald Clay, including Rudgwick Brickworks, Auclaye Brickworks, Smokejacks and Clockhouse Brickworks Invertebrates reported from the Weald Clay Genus Species Location Stratigraphic position Material Notes ImagesPrincipialaP. rudgwickensisRudgwick BrickworksUpper Weald ClaySingle partial fore-wingAn Ithonidae lacewing, the second in PrincipialaEnglathaumaE. crabbiRudgwick BrickworksBMB 021962/3 almost complete forewingA englathaumatid scorpionflyE. mellishaeSmokejacksWing and wing fragmentsCretophasmomimaC. traceyae SmokejacksForewingA stick insectValdicossusV. mikewebsteriSmokejacksUpperHindwingA member of PalaeontinidaeV. chesteriCooden BeachLowerHindwingIlerdocossus I. prowsei Clockhouse BrickworksLowerA member of PalaeontinidaeProraphidiaP. hopkinsiJ. E. Jepson and E. A. Jarzembowski. 2008. Two new species of snakefly (Insecta: Raphidioptera) from the Lower Cretaceous of England and Spain with a review of other fossil raphidiopterans from the Jurassic/Cretaceous transition. Alavesia 2:193-201A member of MesoraphidiidaeTuranophlebia T. anglicanaG. Fleck, G. Bechly, X. Martínez-Delclòs, E. A. Jarzembowski, and A. Nel. 2004. A revision of the Upper Jurassic-Lower Cretaceous dragonfly family Tarsophlebiidae, with a discussion on the phylogenetic positions of the Tarsophlebiidae and Sieblosiidae (Insecta, Odonatoptera, Panodonata. Geodiversitas 26(1):33-59Dragonfly, member of TarsophlebiidaeBrochocoleusB. keenani B. tobiniSmokejacksUpperMember of OmmatidaeDiluticupesD. crowsonaeZygadenia Z. tuberculata, Z. angliaeA. G. Ponomarenko. 2006. On the Types of Mesozoic Archostematan Beetles (Insecta, Coleoptera, Archostemata) in the Natural History Museum, London. Paleontological Journal 40(1):90-9CionocoleusC. elizabethae, C. watsoni E. A. Jarzembowski, E. V. Yan, B. Wang and H. Zhang. 2013. Ommatin beetles (Insecta: Coleoptera) from the Lower Cretaceous of northeast China and southern England. Terrestrial Arthropod Reviews 6:135-161 C. minimusOmmaO. elongatumKeymer Tile Works Lower

Flora Plants reported from the Weald Clay Genus Species Location Stratigraphic position Material Notes ImagesWeichseliaW. reticulataA tree fernBrachyphyllumConifer leavesPagiophyllumConifer leavesPseudofrenelopsisP. parceramosaA conifer belonging to the extinct family Cheirolepidiaceae

See also

Wealden District London Clay Oxford Clay List of dinosaur-bearing rock formations

Footnotes

References Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .