The BGS Lexicon of Named Rock Units — Result Details

Osborne Member

Computer Code: OSB Preferred Map Code: notEntered
Status Code: Full
Age range: Priabonian Age (GI) — Priabonian Age (GI)
Lithological Description: Green, olive and red calcareous clays and lime-rich muds with discontinuous beds of concretionary limestone.
Definition of Lower Boundary: Underlain at a sharp contact by the brown and grey thin-bedded clays with shell beds of the Fishbourne Member of the Headon Hill Formation on the Isle of Wight.
Definition of Upper Boundary: Overlain sharply by Bembridge Limestone across much of the northern Isle of Wight and by the Seagrove Bay Member in the northeast of the Island (but see Supplementary Information in relation to the St Helens Member [King, in press] which comprises fine- to coarse-grained calcareous sand at the base resting on a sharp erosional channeled contact with the Osborne Member).
Thickness: On the Isle of Wight up to 9.5m in the western exposures and 13.5m in the eastern exposures.
Geographical Limits: The Osborne Member is present throughout the northern part of the Isle of Wight and in the area around Beaulieu Heath (mapped as the Osborne Beds) on the mainland in Hampshire, England.
Parent Unit: Headon Hill Formation (HEHI)
Previous Name(s): Osborne Beds (-5237)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Cliff section at Whitecliff Bay, Isle of Wight where up to 10.7m of red and green colour-mottled calcareous clays are seen in infrequent exposures on the foreshore and in the slipped cliffs. Insole and Daley (1985). 
Type Section  Cliff exposures near Osborne House, SE of Cowes (Isle of Wight) [SZ 5296], but these were subsequently obliterated by land-sliding. Insole and Daley (1985) defined a replacement section at Whitecliff Bay. 
Reference(s):
Insole, A and Daley, B. 1985. A revision of the lithostratigraphy of the Late Eocene and Early Oligocene strata of the Hampshire Basin, Southern England. Tertiary Research, Vol.7, 67-100. 
White, H J O. 1921. A short account of the geology of the Isle of Wight. Memoir of the Geological Survey of Great Britain, (1994 reprint). 
Forbes, E. 1856. On the Tertiary fluvio-marine Formation of the Isle of Wight. Memoir of the Geological Survey of Great Britain  
King, C. In press. A correlation of Tertiary rocks in the British Isle and adjacent areas. Special Report of the Geological Society of London, No.12. 
Gale, A S. 2007. Tertiary Research Group Field Meeting on the Isle of Wight, June 9th-10th, 2007. http://www.trg.org/reports/trgiow2007.html  
Melville, R V and Freshney, E C. 1982. British Regional Geology: the Hampshire Basin and adjoining areas (4th Edition).(London ,HMSO for Institute of Geological Sciences). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E330 E331