The BGS Lexicon of Named Rock Units — Result Details

Snettisham Clay Member

Computer Code: SNC Preferred Map Code: SnC
Status Code: Full
Age range: Barremian Age (KB) — Barremian Age (KB)
Lithological Description: At Heacham, Jackson (1911) recorded greyish brown clay with a seam of fossiliferous clay ironstones in the upper part and ironstone concretions scattered throughout. Sand partings are present and, in the Gayton Borehole, bioturbation is represented by tracks, trails and burrows. (Gallois, 1994). A rich shelly fauna has been recovered from the Snettisham Clay Member. Locally (between Heacham and Appletone), a pebble bed is present at the base and at Snettisham Brickworks a hard clay ironstone occurs in the lower part of the member.,
Definition of Lower Boundary: The base is probably an erosion surface. In the Leziate, Ashwicken and East Winch areas the Snettisham Clay appearsto have cut out the lower and middle parts of the Dersingham Formation and rests on the clean sands of the Leziate Sandstone Member, Sandringham Sands Formation. At Heacham and Snettisham, silts and clays of the Snettisham Clay Member rest on pale yellow sands of the Dersingham Formation. At Dersingham Common, silty clay rests on a pebble bed comprising quartz, quartzite, chert, limestone and phosphate, which in turn rests on soft, brown and white, fine- to medium-grained sands.
Definition of Upper Boundary: At Dersingham Common, Snettisham and in the Gayton Borehole the upper boundary is an erosion surface, where the clay and silt of the Snettisham Clay Member is overlain by pebbly, ferrugionous sands of the Carstone Formation. At Dersingham Common a spring line picks out the Carstone/Snettisham Clay boundary. The boundary appears to be conformable in the Hunstanton Borehole, where the red-brown mudstone of the Snettisham Clay is overlain by oolitic, sily and sandy mudstones of the Roach Formation.
Thickness: 1.5 to 6m.
Geographical Limits: The member crops out between Heacham and Ashwicken and is present in boreholes (e.g. the Gayton Borehole).
Parent Unit: Dersingham Formation (DEB)
Previous Name(s): Snettisham Beds (-3039)
Snettisham Clay (-532)
Snettisham Clay Formation (-1833)
Dersingham Beds/Snettisham Clay [Obsolete Code: See DEB And SNC] (DESC)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Gayton Borehole, TF71NW/10 between 30.48 and 32.6m depth. Gallois, 1994. 
Reference Section  Dersingham Common. Gallois, 1994. 
Reference Section  Feathers Hotel, Dersingham. The base of the member was exposed in a shallow valley-side exposure opposite the hotel. Gallois (1994, p.87). 
Type Section  Heacham Brickworks, Mount Pleasant. Jackson (1911) recorded the full thickness of the Snettisham Clay as 9m of greyish brown clay with a line of fossiliferous clay ironstones about 3m from the top and ironstone concretions scattered throughout. Gallois (1994); Whitaker and Jukes-Browne (1899). 
Reference(s):
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. 
Gallois, R W. 1984. The Late Jurassic to Mid Cretaceous rocks of Norfolk. Bulletin of the Geological Society of Norfolk, Vol.34, 3-64. 
Casey, R and Gallois, R W. 1973. The Sandringham Sands of Norfolk. Proceedings of the Yorkshire Geological Society, Vol.41, 1-22. 
Larwood, G P. 1961. The Lower Cretaceous deposits of Norfolk. 280-292 in Larwood, G.P and Funnell, B M (editors), The Geology of Norfolk. Transactions of the Norfolk and Norwich Naturalists' Society. 
Jackson, F. 1911. The rocks of Hunstanton and its neighbourhood (2nd edition). (London: Premier Press.) 
Gallois, R W, 1994. The geology of the country around King's Lynn and The Wash. Memoir of the British Geological Survey, Sheet 145 and part of 129 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable