Geology of the Isle of Wight : a brief explanation of the Isle of Wight geological sheet : parts of sheet 330, 331, 344 and 345 Isle of Wight (England and Wales)

This sheet explanation provides a summary of the geology of the Isle of Wight district (Special Sheet) arising from the British Geological Survey’s Isle of Wight Integrated Project. This project, commenced in September 2007 and completed in 2013, sought to improve the understanding of the nearsurface geology, and create representational models of the 3D structure. This will provide essential framework information for use by the geological community operating in this classic area of British geology. This sheet explanation and accompanying 1:50 000 scale geological map special sheet are principally aimed at users in academia, local authorities and statutory bodies, but also at the large number of ‘geotourists’ that are such an important part of the island’s economy. A Special Issue of the Proceedings of the Geologists’ Association (Geologists’ Association, 2011) introduced by Hopson (2011) gives further detailed accounts of the recent work by BGS on the island. The Isle of Wight (Figure 1), the largest island in England at 384 km2, is separated from the mainland by the Solent. This body of water is essentially the drowned lower reaches of an extensive Quaternary river system draining much of southern central England. The island’s protective presence offshore of the south coast within the English Channel strongly influences the tidal regime within the Solent system and led directly to the development of Southampton and Portsmouth as major ports. Large parts of the island form Areas of Outstanding Natural Beauty (ANOBs) and a considerable length of the coastline in the south-west and north-west of the island is designated as Heritage Coast (Figure 2). Topographically the diamond shape of the island is the direct result of the presence of a central, east–west orientated ridge, of complex tectonic origins, founded on the steeply dipping, moderately hardened, Chalk Group (Figure 3). The softer sediments of the Palaeogene forming lower-lying, ground within the northern, mainland-facing, part of the island are protected from extensive tidal erosion by this Chalk ridge. To the south-west of the central ridge, sediments of the Early Cretaceous, forming low cliffs, suffer extensive erosion from Atlantic storms funnelling up the Channel. The south-eastern coast, eastward of St Catherine’s Point, is protected by a capping of more durable, essentially horizontal Upper Greensand and Chalk strata forming the Southern Downs but here an extensive, deeply seated, landslide (the largest in north-west Europe) considerably modifies the coastal geomorphology.