Geology of East Sussex
East Sussex is best known geologically for the identification of the first dinosaur by Gideon Mantell, near Cuckfield,[2] to the famous hoax of the Piltdown Man[3] near Uckfield.
[1] The northern margin of the basin was formed by a series of normal faults, against what was then an area of land, known to geologists as the London-Brabant Massif.
The Weald Basin gently subsided throughout the Jurassic, Cretaceous and Early Palaeogene leading to a thick succession of sedimentary rocks being deposited.
In East Sussex the Purbeck Group is formally subdivided into the Blues and Greys Limestones members, which are typically made up of calcilutite and shelly calcarenites.
[8] The Greys Limestones Member is of particular significance as it marks the boundary between the Purbeck Beds and the overlying Ashdown Formation of the Early Cretaceous.
These strata underlie the county from the boundary with West Sussex at East Grinstead, through the Ashdown Forest to Hastings and Pett Level on the coast.
[10] At this location the formation can be followed from the axis of the Wealden Anticline at Lee Ness Ledge through the well distinguished marker beds and horizons to its juncture with the Wadhurst Clay at Hastings Castle to the west and Cliff End to the east.
[12] The mudstones often degrade in a short period of time when they become exposed at the surface and weather to heavy ochre and greenish grey clays.
The ore was deposited in a tropical environment within which iron brought in from the eroding mountains in the west was altered into small nodules of ilmenite.
A succession of clays and sands was deposited into the subsiding basin, with much of the source material also being delivered from the north and east as well as the west.
The Greensands and the Gault best define the Wealden Anticline, running in a broad horseshoe from Folkestone in the East, to Petersfield in Hampshire in the West and back to Eastbourne.
[4] The Gault is one of the most fossil rich horizons in the UK; yielding plentiful bivalves, cephalopod (including ammonites) and gastropods.
The Chalk Group is the most well known rock in East Sussex, forming the Downs and where it meets the sea the spectacular Seven Sisters and geologically and biologically rich cliffs from Brighton to Newhaven.
Inversion of the basin is closely correlated to compressional events within the Alps and occurred alongside deformation in Hampshire, Dorset and northern France.
The basin was compressed between two 'blocks' of basement rocks, with the northward movement of the block against the London Platform;[1] the areas of land that earlier in the Weald's history supplied the sediments.
