The BGS Lexicon of Named Rock Units — Result Details

Upper Mottled Beds (Reading Formation)

Computer Code: UMBED Preferred Map Code: notEntered
Status Code: Index Level
Age range: Ypresian Age (GY) — Ypresian Age (GY)
Lithological Description: Like the Upper Mottled Clay, the Upper Mottled Beds typically consists mainly of clay and silt, with some sand and occasional gravel. The clay of the Upper Mottled Beds tends to be less variable in colour than that of the Lower Mottled Beds. It is typically grey mottled with brown but may also be mottled or multicoloured red or yellow. Beds of dark grey or black clay occur locally. This unit can include channel-form bodies of cross-bedded, fine- to medium-grained sand. It does not contain glauconite. It is locally weakly bioturbated or with a low-diversity non-marine (brackish water) mollusc fauna. Parts of the Upper Mottled Beds that are derived from the Woolwich Formation may include more sand, and relicts of little-altered sediment of the Woolwich Formation.
Definition of Lower Boundary: The base of the Upper Mottled Beds, like the Upper Mottled Clay, is a sharply-defined boundary at base of vari-coloured mottled clay or fine- to medium-grained sand overlying fine-grained sands, silts or clays of the Laminated Beds (Woolwich Formation). Where the Woolwich Formation is absent, the nature of the boundary between the Lower Mottled Beds and the Upper Mottled Beds is not well known.
Definition of Upper Boundary: The top of the Upper Mottled Beds is the top of the Reading Formation. It is generally sharply defined, at an upward change from vari-coloured mottled clay to glauconitic sands and sandy clays of the Harwich Formation, or to sandy clays of the Walton Member (London Clay Formation), or to shelly grey clays of the Upper Shelly Clay
Thickness: none recorded or not applicable
Geographical Limits: Like the Upper Mottled Clay, the Upper Mottled Beds is probably present throughout the Reading Formation outcrop and subcrop. It passes eastwards into the Woolwich Formation, or is cut out between the Upper Shelly Clay and the rest of the Woolwich Formation, or is cut out beneath the Harwich Formation.
Parent Unit: Not Entered (?)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The type area of the Upper Mottled Beds is central London. No type section has been designated. Ellison et al., 2004, fig. 20; Page and Skipper, 2000. 
Reference(s):
Ellison, R A, Woods, M A, Allen, D J, Forster, A, Pharaoh, T C and King, C. 2004. Geology of London. Memoir of the British Geological Survey, Sheets 256 (North London), 257 (Romford), 270 (South London), 271 (Dartford) (England and Wales). 
Aldiss, D.T., 2012. The stratigraphical framework for the Palaeogene successions of the London Basin, UK. British Geological Survey Open Report OR/12/004. Available from http://nora.nerc.ac.uk/17121/. 
Ellison, R A, 1983. Facies distribution in the Woolwich and Reading Beds of the London Basin, England. Proceedings of the Geologists' Association, Vol. 94, 311-319. 
Ellison, R A, Knox R W O'B, Jolley, D W and King, C, 1994. A revision of the lithostratigraphical classification of the early Palaeogene strata of the London Basin and East Anglia. Proceedings of the Geologists' Association, Vol.105, 187-197. 
Page, D P, and Skipper, J A E. 2000. Lithological characteristics of the Lambeth Group. Ground Engineering, Vol. 33, 38-43. 
Skipper, J A. 1999. The stratigraphy of the Lambeth Group (Paleocene) of South East England. PhD thesis, Imperial College, London. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable