| Computer Code: |
UMCL |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Ypresian Age (GY)
— Ypresian Age (GY) |
| Lithological Description: |
The Upper Mottled Clay typically consists mainly of clay and silt, with some sand and occasional gravel. The clay of the Upper Mottled Clay tends to be less variable in colour than that of the Lower Mottled Clay. 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. These may be of significance for regional correlation at the interface between the upper and the lower parts of the Reading Formation where the Woolwich Formation is absent.
This unit can include channel-form bodies of cross-bedded, fine to medium-grained sand. It is locally weakly bioturbated or with a low-diversity non-marine (brackish water) mollusc fauna.
The Upper Mottled Clay comprises fluviatile sediments rather similar to those of the Lower Mottled Clay and is likewise thought to have been deposited under non-marine conditions, on a large coastal plain crossed by rivers. The colour-mottling formed shortly after deposition in a tropical or sub-tropical climate with seasonal rainfall: it is not due to modern weathering processes (Ellison, 1983; Hooker, 1991).
Early Eocene (earliest Ypresian). See Reading Formation. |
| Definition of Lower Boundary: |
The base of 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 Clay and the Upper Mottled Clay is not well known. It seems to be marked by a bed of grey clay, or by lignite fragments, or both, at least locally. These presumably form the basal layer of the Upper Mottled Clay. |
| Definition of Upper Boundary: |
The top of the Upper Mottled Clay 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: |
Up to 8 m recorded, possibly more to the west of London. |
| Geographical Limits: |
The Upper Mottled Clay 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: |
Reading Formation (RB)
|
| 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 Clay is central London. No type section has been designated (Ellison et al., 2004, fig. 20). |
| Reference Section |
Jubilee Line Extension Borehole 404T (TQ37NW 2118), Bermondsey, London, 25.05 to 29.63 m depth (Ellison et al., 1994; Ellison et al., 2004, fig. 15, p. 32). This borehole passes through the two parts of the Reading Formation, here separated by the Woolwich Formation. |
| 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). |
| 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. |
| Hooker, J J. 1991. The sequence of mammals in the Thanetian and Ypresian of the London and Belgian basins. Location of the Palaeocene-Eocene boundary. Newsletters in Stratigraphy, Vol. 25, 75-90. |
| Ellison, R.A., 1983. Facies distribution in the Woolwich and Reading Beds of the London Basin, England. Proceedings of the Geologists' Association 94, 311-319. |
| Page, D P, and Skipper, J A E. 2000. Lithological characteristics of the Lambeth Group. Ground Engineering, Vol. 33, 38-43. |
| Aldiss, D T. 2014. The stratigraphical framework for the Palaeogene successions of the London Basin, UK. British Geological Survey Open Report OR/14/008. 95 pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
