The BGS Lexicon of Named Rock Units — Result Details

Wrabness Member

Computer Code: WRAB Preferred Map Code: notEntered
Status Code: Full
Age range: Ypresian Age (GY) — Ypresian Age (GY)
Lithological Description: The Wrabness Member comprises tuffaceous clayey silts and silty clays, with both disseminated ash and numerous distinct tephra layers (Unit A), overlain with apparent disconformity by bioturbated fine-grained silty sand with clay interbeds (Unit B). There is a concentration of glauconite in sandy clayey silt at the base of Unit A (Jolley, 1996; King, in prep.). Layers of concretionary argillaceous limestone occur at several levels, including the tabular Harwich Stone Band (HARS), which is about 0.25 m thick and which includes a central ash bed (Elliott, 1971; Jolley, 1996; King, 1981, in prep.; Knox and Ellison, 1979). The occurrence and correlation of the ash in the Wrabness Member is described by Knox (1983, 1996b) and Knox and Morton (1988). Occurrences at Walton-on-the-Naze have yielded an extensive assemblage of fossil birds (George and Vincent, 1977; Harrison, 1983; Harrison and Walker, 1977). Marine: inner to mid shelf. Early Eocene (early Ypresian).
Definition of Lower Boundary: The base of the Wrabness Member, which rests on the silts and sands of the Orwell Member, is marked by a sharply-defined discontinuity surface and a basal concentration of glauconite.
Definition of Upper Boundary: The top of the Wrabness Member is marked by the disconformable base of the Walton Member mudstones, which contain sporadic well-rounded flint gravel (Jolley, 1996). According to King (1981, p.25), the Walton Member has much less glauconite and much less bioturbation.
Thickness: Up to about 24 m (King, in prep.).
Geographical Limits: The Wrabness Member occurs in eastern Essex and southern Suffolk. It passes south with basal onlap into the Oldhaven Member of north Kent, and west into the Swanscombe Member (King, 1981; Jolley, 1996).
Parent Unit: Harwich Formation (HWH)
Previous Name(s): Harwich Member [Obsolete Name And Code] (HWM)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The cliffs north of Wrabness (and about 700 m east of Wrabness Point) [TM 1726 3233], which expose the complete member from the contact with the underlying Orwell Member to that with the overlying Walton Member (London Clay Formation) (Daley, 1999b; Daniels, 1971; Jolley, 1996; King, 1981; Knox and Ellison, 1979). 
Reference Section  The upper part of the Wrabness Member is exposed in the cliffs and foreshore at The Naze, north of Walton-on-the-Naze [TM 267 244] (Jolley, 1996). 
Reference Section  The Harwich Stone Band is exposed on the foreshore on the eastern side of the Harwich promontory, between Beacon Cliff [TM 2629 3166] and Harwich Green [TM 2630 3233] (Daley, 1999b). 
Reference Section  Cliff and foreshore exposures at Ferry Cliff on east bank of River Deben just east of Woodbridge, Suffolk [TM 2774 4854] to [TM 2800 4867] (George and Vincent, 1976; King, 1981) expose the lower part of the Wrabness Member, including the Harwich Stone Band (Daley, 1999b). 
Reference(s):
Aldiss, D T. 2014. The stratigraphical framework for the Palaeogene successions of the London Basin, UK. British Geological Survey Open Report, OR/14/008. 95pp. 
Daley, B. 1999. London Basin: eastern localities, In: Daley, B, Balson, P (Eds.), British Tertiary Stratigraphy. Geological Conservation Review Series 15, pp. 23-72. 
Elliott, G.F., 1971. Eocene volcanics in south-east England. Nature Physical Science 230, 9. 
George, W, and Vincent, S. 1976. Some river exposures of London Clay in Suffolk and Essex. Tertiary Research, Vol. 1, 25-28. 
Harrison, C J O, and Walker, C A. 1977. Birds of the British Lower Eocene. Tertiary Research Special Paper, Vol. 3, 1-52. 
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. 
King, C. in prep. A revised correlation of Palaeogene and Neogene deposits in the British Isles. Geological Society of London Special Report. 
King, C. 1981. The stratigraphy of the London Clay and associated deposits. Tertiary Research Special Paper No.6. (Backhuys: Rotterdam). 
Knox, R W O. 1983. Volcanic ash in the Oldhaven Beds of southeast England, and its stratigraphical significance. Proceedings of the Geologists' Association, Vol. 94, 245-250. 
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., Ellison, R.A., 1979. A Lower Eocene ash sequence in SE England. Journal of the Geological Society 136, 251-253. 
Daniels, M C S. 1971. Report of a field meeting to Wrabness, Stour estuary, Essex. Tertiary Times, Vol. 1, 67-70. 
George, W, and Vincent, S. 1977. Report of a field meeting to Walton-on-the-Naze and Wrabness, Essex 2.X.1976, with notes on the London Clay of Walton. Tertiary Research, Vol. 1, 83-90. 
Harrison, C J O. 1983. Fossil birds from the London Clay of Essex: the W. George and S. Vincent collections. Tertiary Research, Vol. 5, 81-83. 
Knox, R W O, and Morton, A C. 1988. The record of early Tertiary N. Atlantic volcanism in sediments of the North Sea Basin. 407-419 in Early Tertiary volcanism and the opening of the NE Atlantic. Morton, A C, and Parson, L W (editors). Geological Society of London Special Publication, No. 39. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable