Weald Clay

 ( Geology Of England ) 

Weald Clay or the Weald Clay Formation is a Lower Cretaceous sedimentary rock unit underlying areas of South East England, between the North Downs 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 .

The formation was deposited in , lacustrine and Alluvial plain conditions that varied from freshwater to Brackish water. 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.

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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.

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Paleofauna

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Vertebrates

Baryonyx	B. walkeriSmokejack Clay Pit	Upper Weald Clay	Multiple partial skulls, one of which had an associated postcranial skeleton."Table 4.1," in Weishampel, et al. (2004). Page 72.A Spinosauridae
Horshamosaurus	H. rudgwickensisRudgwick Brickworks	Upper 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.
Iguanodon	I. bernissartensis	Smokejack Clay Pit	Upper Weald Clay		Iguanodontian, also known from the Wessex Formation.
Mantellisaurus	M. atherfieldensis	Smokejack Clay Pit	Upper Weald Clay		Iguanodontian, also known from the Wessex Formation
Valdosaurus	V. 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): 211-273Heathfield	Lower Weald Clay		A Dryosauridae, also known from the Wessex Formation
Leptocleidus	L. superstes			NHM R4828 (holotype)	Pliosauroid
Wyleyia"10.18 West Sussex, England; 1. Hastings Beds" in Weishampel, et al. (2004). Page 559.	W. valdensis	West Sussex
Dorsetisaurus	Indeterminate	Keymer Tile Works
Sauropoda	Indeterminate	Smokejacks, Bexhill
Frog	Indeterminate	Keymer Tile Works	Lower	Maxillary fragment Sweetman, S.C; Evans, S. E. (2025). 9781444367119, Palaeontological Association. ISBN 9781444367119
Salamander	Indeterminate	Keymer Tile Works	Lower	Atlas vertebra	Has been suggested to have a close relationship with Balveherpeton from Germany.

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Invertebrates Numerous insect species are known from several localities in the Weald Clay, including Rudgwick Brickworks, Auclaye Brickworks, Smokejacks and Clockhouse Brickworks

Principiala	P. rudgwickensis	Rudgwick Brickworks	Upper Weald Clay	Single partial fore-wing	An Ithonidae lacewing, the second in Principiala !
Englathauma	E. crabbi	Rudgwick Brickworks		BMB 021962/3 almost complete forewing	A englathaumatid scorpionfly
	E. mellishae	Smokejacks		Wing and wing fragments
Cretophasmomima	C. traceyae	Smokejacks		Forewing	A Phasmatodea !
Valdicossus	V. mikewebsteri	Smokejacks	Upper	Hindwing	A member of Palaeontinidae !
	V. chesteri	Cooden Beach	Lower	Hindwing !
Ilerdocossus	I. prowsei	Clockhouse Brickworks	Lower		A member of Palaeontinidae !
Proraphidia	P. 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 2:193-201				A member of Mesoraphidiidae !
Tarsophlebiidae	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):33-59				Dragonfly, member of Tarsophlebiidae !
Brochocoleus	B. keenani B. tobini	Smokejacks	Upper		Member of Ommatidae !
Diluticupes	D. crowsonae
Zygadenia	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):90-9			!
Cionocoleus	C. 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. minimus			!
Omma	O. elongatum	Keymer Tile Works	Lower	!

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Flora

Weichselia	W. reticulata				A tree fern
Brachyphyllum					Conifer leaves
Pagiophyllum					Conifer leaves
Pseudofrenelopsis	P. parceramosa				A conifer belonging to the extinct family Cheirolepidiaceae

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See also

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

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Footnotes

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

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