| Atherfield Clay Formation | |
| Period: | Aptian |
| Type: | Geological formation |
| Prilithology: | Mudstone |
| Otherlithology: | Sandstone, Ironstone |
| Unitof: | Lower Greensand Group |
| Subunits: | Chale Clay Member |
| Underlies: | Ferruginous Sands, Hythe Formation |
| Overlies: | Vectis Formation, Weald Clay |
| Thickness: | on the Isle of Wight, up to in the Weald |
| Region: | Europe |
| Extent: | Southern England |
The Atherfield Clay Formation is a geological formation in Southern England. Part of the Lower Greensand Group it dates to the Aptian age of the Early Cretaceous. The deposit is of marine origin largely consisting of massive yellowish brown to pale grey mudstones.[1] The pterosaur Vectidraco is known from the formation.[2] As is the Sandownid turtle Sandownia.