The BGS Lexicon of Named Rock Units — Result Details

Vectis Formation

Computer Code: VTIS Preferred Map Code: V
Status Code: Full
Age range: Barremian Age (KB) — Aptian Age (KP)
Lithological Description: Dark grey siltstones and mudstones with subordinate beds of sandstone, shelly limestone, clay ironstone and ironstone. Commonly described as thinly-bedded mudstone ("shale" or "paper shale") and the whole is generally finely- and evenly-bedded.
Definition of Lower Boundary: The lower boundary is conformable and marked by an abrupt change from the brightly coloured (generally red tinged) friable sandstones and calcareous mudstones of the Wessex Formation up into the dull grey and blue-grey mudstones of the Vectis Formation. In the Isle of Wight Memoir the section at Brixton Bay (p.13), now called Brighstone Bay, places the lower boundary at the base of "red sand with bones" (the "Hypsilophodon Bed") (Osborne White, 1921). This "bone bed" (a red pedogenic siltstone) is now considered as being several metres below the base of the formation as alluded to in the footnote on that Memoir page.
Definition of Upper Boundary: The upper boundary is taken at the change from grey mudstones with an eroded and burrowed upper surface in contact with the overlying dark green to greyish green basal glauconitic very shelly sandstone of the Perna Bed Member (Insole et al., 1998) of the Atherfield Clay Formation. This boundary is generally some 4 to 5m above a distinctive shelly limestone associated with a "Beef-Bed" (fibrous calcite commonly showing cone-in-cone structures).
Thickness: Maximum of c.66m on the Isle of Wight.
Geographical Limits: Isle of Wight and Dorset in the vicinity of Swanage. Westward and northward the formation is removed by erosion.
Parent Unit: Wealden Group (W)
Previous Name(s): Wealden Shales (-1255)
Wealden Shales (Isle Of Wight) [Obsolete Name And Code: Use VTIS] (WSH)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Brightstone Bay, Isle of Wight, from Atherfield Point [SZ 452 791] northwestward towards Barnes Chine [SZ 435 808] from where each of the three members have been defined by Daley and Stewart (1979); Stewart (1981). The section from Atherfield Point to Hanover Point [SZ 379 837] shows the whole of the exposed Wealden Group in the degraded cliffs with the Wessex Formation forming the core of the Brightstone Anticline at cliff base. A repeat of the Vectis Formation is seen from Hanover Point north-westward along the cliff forming Compton Bay [SZ 36 85]. 
Reference Section  Sandown Bay, Isle of Wight from the Yaverland [SZ 611 850] to Red Cliff [SZ 620 853]. 
Reference(s):
Osborne White, H J. 1921 [1994 reprint]. A short account of the geology of the Isle of Wight. Memoirs of the Geological Survey of Great Britain. 235pp. [HMSO.] 
Arkell, W J. 1947. Geology of the country around Weymouth, Swanage, Corfe and Lulworth. Memoir of the British Geological Survey. Sheets 341, 342, 343 and small portions of sheets 327, 328 and 329 (England and Wales). 
Insole, A, Daley, B, and Gale, A. 1998. The Isle of Wight. Geologists’ Association Guide. No. 60. (The Geologists’ Association.)  
Daley, B and Stewart, D J. 1979. Weekend field meeting: The Wealden Group in the Isle of Wight. Proceedings of the Geologists' Association, Vol.90, 51-54. 
Kerth, M and Hailwood, E A. 1988. Magnetostratigraphy of the Lower Cretaceous Vectis Formation (Wealden Group) on the Isle of Wight, southern England. Journal of the Geological Society, Vol.145, 351-360. 
Stewart, D J. 1981. A field guide to the Wealden Group of the Hastings area and the Isle of Wight. 3.1-3.32 in Elliott, T (Editor), Field Guides to Modern and Ancient Fluvial Systems in Britain and Spain, International Fluvial Conference, Keele University, UK. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable