Wadhurst Clay Formation

The Wadhurst Clay Formation is a geological unit which forms part of the Wealden Group and the middle part of the now unofficial Hastings Beds. These geological units make up the core of the geology of the High Weald in the English counties of West Sussex, East Sussex and Kent.

The other component formations of the Hastings Beds are the underlying Ashdown Formation and the overlying Tunbridge Wells Sand Formation. The Hastings Beds in turn form part of the Wealden Group which underlies much of southeast England. The sediments of the Weald, including the Wadhurst Clay Formation, were deposited during the Early Cretaceous Period, which lasted for approximately 40 million years from 140 to 100 million years ago. The Wadhurst Clay is of Early to Late Valanginian age. The Formation takes its name from the market town of Wadhurst in East Sussex.

The Wadhurst Clay comprises predominantly medium to dark bluish grey over-consolidated clays, silts, mudstones, and shales. These lithologies often occur with subordinate amounts of pale grey silty mudstones, laminated siltstones, sandstones, conglomerate, shelly limestones and clay-ironstones. When they become exposed to the elements at the surface, the mudstones often degrade over a short period of time and weather to yellowish brown and greenish grey clays.

The formation thickness ranges from 55m in the Tenterden area, to 30m near Lewes and varies in between. In Kent, the Wadhurst Clay has been proven to over 70m thick near Tunbridge Wells and in West Sussex up to 80m near Horsham.

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