The BGS Lexicon of Named Rock Units — Result Details
Ormesby Clay Member
| Computer Code: | OC | Preferred Map Code: | OC |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Selandian Age (GS) — Thanetian Age (GT) | ||
| Lithological Description: | The Ormesby Clay is variably glauconitic, partly calcareous clay, commonly silty at the base, with a basal gravel bed. The gravelly bed is typically between 0.1 and 0.2 m thick, comprising unworn green-coated flints in a matrix of bright green, glauconitic-rich sand or sandy silt. The mudstone is intensively bioturbated, blocky and poorly bedded. It is mostly pale grey to dark greenish grey but also includes a bed of red-grey mudstone and thin bands of grey-green mudstone. Sporadic, thin altered tephra layers occur in the lower part (Ellison et al., 1994). The Ormesby Clay differs from offshore portions of the Lista Formation principally in containing significant glauconite (King, in prep.). Marine; outer neritic to upper bathyal (King, in prep.). Late Paleocene (Ellison et al., 1994) and references therein. Late Selandian to mid-Thanetian (King, in prep.), based on dinoflagellate cysts (Zone DP10 to Subzone DP11b) (Jolley, 1992). | ||
| Definition of Lower Boundary: | The base of the Ormesby Clay is the base of the basal sandy flint gravel bed, which rests unconformably on the Chalk Group. | ||
| Definition of Upper Boundary: | The top of the Ormesby Clay is an erosion surface (King, in prep.). The uppermost few centimetres commonly includes burrows filled from the overlying sediment. In Norfolk and parts of Suffolk, an upwards change from bioturbated glauconitic clay to dark grey-brown, laminated sandy clay or muddy sand of the Upnor Formation (previously the Hales Clay). In southern Suffolk, an upwards change to interbedded medium-grained sand and laminated grey-green mudstone of the Upnor Formation. | ||
| Thickness: | 27.45 m in the type section, reducing to about 10 m at Sizewell, Suffolk. Assumed to thin further southwards towards the Ipswich-Felixstowe High (Boswell, 1915; Jolley, 1992). | ||
| Geographical Limits: | The Ormesby Clay occurs onshore in East Anglia at subcrop only, from the Ipswich-Felixstowe axis northwards. The upper part of the Ormesby Clay passes southwards into the Thanet Formation, a more proximal marine facies, between Ipswich and Sizewell, across the Ipswich-Felixstowe High (Ellison et al., 1994; Jolley, 1992). The lower part of the Ormesby Clay is cut out onto this structural axis and comprises a sequence not represented to the south in the Thanet Formation (Knox, 1996b; Knox et al., 1994). | ||
| Parent Unit: | Lista Formation (LIST) | ||
| Previous Name(s): | Ormesby Clay [Obsolete Name and Code: Use OC]
(-5089)
Ormesby Clay Formation [Obsolete Name and Code: Use OC] (-5090) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Ormesby A Borehole (TG51SW 7A) between 112.4 m and 139.85 m depth (Cox et al., 1985; Knox et al., 1990). | ||
| Reference Section | Hales Borehole (TM39NE 7) Norfolk, from 32.18 TO 57.77 m depth (Jolley, 1996, fig. 9; Knox, 1996; Knox et al., 1990). | ||
| Reference Section | Sizewell C3 Borehole (TM46SE 42), Suffolk (Ellison et al., 1994). | ||
| Reference(s): | |||
| Jolley, D.W., 1996. The earliest Eocene sediments of eastern England: an ultra-high resolution palynological correlation, In: Knox, R.W.O., Corfield, R.M., Dunay, R.E. (Eds.), Correlation of the Early Palaeogene in Northwest Europe. Geological Society of London Special Publication 101, pp. 219-254. | |||
| Knox, R W O. 1996. Tectonic controls on sequence development in the Palaeocene and earliest Eocene of southeast England: implications for North Sea stratigraphy. 209-230 in Sequence Stratigraphy in British Geology. Hesselbro, S P, and Parkinson, D N (editors). Geological Society of London Special Publication, No. 103. | |||
| Knox, R W O, Hine, N M, and Ali, J R. 1994. New information on the age and sequence stratigraphy of the type Thanetian of southeast England. Newsletters on Stratigraphy, Vol. 30, 45-60. | |||
| Cox, F C, Hailwood, E A, Harland, R, Hughes, M J, Johnston, N, and Knox, R W O. 1985. Paleocene sedimentation and stratigraphy in Norfolk, England. Newsletters on Stratigraphy, Vol. 14, 169-185. | |||
| Knox, R W O, Morigi, A N, Ali, J R, Hailwood, E A, and Hallam, J R. 1990. Early Palaeogene stratigraphy of a cored borehole at Hales, Norfolk. Proceedings of the Geologists' Association, Vol. 101, 145-151. | |||
| Jolley, D W, 1992. Palynofloral association sequence stratigraphy of the Palaeocene Thanet Beds and equivalent sediments in eastern England. Review of Palaeobotany and Palynology, Vol.74, p.207-237. | |||
| 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. | |||
| 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. | |||
| Boswell, P G H. 1915. The stratigraphy and petrology of the Lower Eocene deposits of the north-eastern part of the London Basin. Quarterly Journal of the Geological Society, Vol. 71, 536-591. | |||
| King, C. in prep. A revised correlation of Palaeogene and Neogene deposits in the British Isles. Geological Society of London Special Report. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E132 E148 E162 E176 E191 | |||