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Geological formation in England

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 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.

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.

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. A spinosauridHorshamosaurusH. rudgwickensisRudgwick BrickworksUpper Weald Clay"Vertebrae, partial fore and hindlimbs, osteoderms. "A dubious genus of nodosaurid ankylosaur belonging to Polacanthinae. Originally named as a species of Polacanthus. IguanodonI. bernissartensisSmokejack Clay PitUpper Weald ClayIguanodontian, also known from the Wessex Formation. MantellisaurusM. atherfieldensisSmokejack Clay PitUpper Weald ClayIguanodontian, also known from the Wessex FormationValdosaurusV. canaliculatusHeathfieldLower Weald ClayA dryosaurid, also known from the Wessex FormationLeptocleidus L. superstesNHM R4828 (holotype)PliosauroidWyleyiaW. valdensisUrodelaIndeterminateKeymer Tile WorksLowerAtlas vertebraHas been suggested to have a close relationship with Balveherpeton from Germany.