The BGS Lexicon of Named Rock Units — Result Details

Monk's Bay Sandstone Formation

Computer Code: MBSA Preferred Map Code: MBS
Status Code: Full
Age range: Albian Age (KA) — Albian Age (KA)
Lithological Description: Osborne White (1921) described the formation as "highly ferruginous coarse sand or grit" and Casey (1961) described it as "gritty, reddish-brown sands with pebbles and phosphatic nodules". There is a concentration of nodules at the base. The nodules contain abundant shelly material including ammonites, gastropods and bivalves.
Definition of Lower Boundary: The base of the formation is a sharp eroded surface where there is a marked down-section change from gritty, reddish-brown sandstone to the yellow and white quartz sandstone at the top of the underlying rhythmical succession of the Sandrock Formation. This depositional break is called the 'Mid tardefurcata break' by Casey (1961).
Definition of Upper Boundary: The upper boundary is gradational, where the reddish brown ferruginous coarse-grained sandstones of the Monk's Bay Sandstone Formation pass up into dark grey mudstones of the Gault Formation.
Thickness: Up to 21.9m at Red Cliff. Thickens towards the north-east from as little as 5cm at Punfield on the Dorset coast, and on the Isle of Wight, to 1.8m at Compton Bay, 3.7m at Blackgang, 9.1m at Bonchurch (Osborne White, 1921).
Geographical Limits: The Monk's Bay Sandstone Formation crops out on the Isle of Wight between Red Cliff, in the east, and Compton Bay, in the west, although away from the coast it is rarely seen in section. It is also present between Luccombe Bay and Chale Bay on the southern part of the island, although here landslides obscure the unit in some areas. A few centimetres thickness of this unit was recorded at Punfield Cove [SZ 039 810], on the Dorset coast (Osborne White, 1921), although this is shown as undivided Lower Greensand on 1:50 000-scale Sheet 343.
Parent Unit: Lower Greensand Group (LGS)
Previous Name(s): Carstone (Isle Of Wight) [Obsolete Name And Code: Use MBSA] (CAW)
Carstone Of The Isle Of Wight (-2312)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Near the chalybeate spring (a term denoting iron-rich waters or a mineral spring) about 200m northwest of South View House, southeast of Blackgang Chine [SZ 485 767] (Osborne White, 1921). 
Type Section  The Monk's Bay cliff section [SZ 579 780] is the parastratotype as it does not contain the full succession. The section exposes 10.5m of ferruginous and pebbly sandstones and grit between the Sandrock Formation at the base and Gault Formation at the top (Osborne White, 1921). See also the Reference Section at Red Cliff. 
Reference Section  The coastal section north of Red Cliff [SZ 627 856] where about 22m of brown sandstones and argillaceous gritstones are situated between the Sandrock and Gault formations represents the thickest succession on the island, but access is difficult (Osborne White, 1921, p.30). Although Red Cliff would be the natural name for this unit the principal red units in the cliffs are those of the Ferruginous Sand with only a relatively inaccessible red bed at the top of the cliffs being the "Carstone of the Isle of Wight". 
Reference Section  The unit is seen at the top of the cliff on either side of Luccombe Chine [SZ 583 793] and then to the south and south-westward to Bonchurch where the "Carstone is finely displayed" (Osborne White, 1921). Access is frequently difficult although the beach is strewn with blocks of this unit. 
Reference(s):
Casey, R, 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. 
Reid, C, and Strahan, A. 1889. Geology of the Isle of Wight. Mem. Geol. Surv. G.B., (2nd edition). (Geological Survey of England and Wales.) 
Fitton, W H. 1847. A stratigraphical account of the section from Atherfield to Rocken-end on the south-west coast of the Isle of Wight. Quarterly Journal of the Geological Society of London, Vol.3, 289-327. 
Insole, A, Daley, B, and Gale, A. 1998. The Isle of Wight. Geologists’ Association Guide. No. 60. (The Geologists’ Association.)  
Whitaker, W and Jukes-Browne, A J. 1899. The geology of the borders around The Wash: including Boston and Hunstanton. Memoir of the Geological Survey of England and Wales. 
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.] 
Strahan, A. 1886. Notes on the relations of the Lincolnshire Carstone. Quarterly Journal of the Geological Society, London, 42, 481-493. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable