The BGS Lexicon of Named Rock Units — Result Details

Hales Clay Member

Computer Code: HAC Preferred Map Code: HaC
Status Code: Pending Upgrade
Age range: Ypresian Age (GY) — Ypresian Age (GY)
Lithological Description: The Hales Clay Member comprises clay and silt with variable amounts of sand, and sporadic bentonitic volcanic ash layers. The lower part (HC1) comprises bioturbated silt, whereas the much thicker upper part (HC2) comprises silty clay, silt and sandy silt with thin beds of fine-grained sand. The base of Unit HC2 is an interburrowed omission surface overlain by a glauconitic interval.
Definition of Lower Boundary: Originally, the base of the Hales Clay Member was placed at the base of Unit HC1 where clay and silt overlying glauconitic mudstone of the Ormesby Clay Member (Knox et al. 1990). As emended by Jolley (1996), it was placed at the base of unit HC2, at an interburrowed omission surface overlain by a glauconitic interval (King, in prep.), overlying bioturbated silt of unit HC1, now assigned to the Upnor Formation.
Definition of Upper Boundary: The top of the Hales Clay Member is taken where silty clays, clayey silts and thin sands, give way to the tuffaceous siltstones of the Wrabness Member at a sharply-defined discontinuity surface and with a concentration of glauconite in the overlying sediments (Jolley, 1996).
Thickness: About 13m
Geographical Limits: none recorded or not applicable
Parent Unit: Harwich Formation (HWH)
Previous Name(s): Hales Clay (-4106)
Alternative Name(s): none recorded or not applicable
Type Section  The Hales Borehole (TM39NE7) Norfolk, from 16.56 to 32.18m depth as originally defined; 16.56 to 29.52m depth as emended by Jolley (1996), Knox (1996b) and King (in prep.). 
Reference Section  Ormesby A Borehole (TG51SW7A) (Cox et al., 1985). 
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 
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. 
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. 
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. 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, 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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E162 E191