The BGS Lexicon of Named Rock Units — Result Details

Top Rock Bed

Computer Code: TRK Preferred Map Code: TRk
Status Code: Full
Age range: Turonian Age (KT) — Coniacian Age (KO)
Lithological Description: Hard cream limestone with scattered brownish phosphatic nodules commonly green-coated at the top. Mineralised hardground or chalkstone bed.
Definition of Lower Boundary: The base is conformable within the Kensworth Nodular Chalk Member at an indistinct boundary marking a significant increase in nodularity between 2 and 3m above the uppermost hardground of the Chalk Rock Member.
Definition of Upper Boundary: The upper boundary is conformable at the hardground surface marked by the change from mineralised hard chalkstone to soft white smooth chalk.
Thickness: 0.8 to 1.0m in Cambridgeshire. 0.3m to 1.0m in to Chilterns, to which areas it is essentially confined.
Geographical Limits: The Chilterns within Hertfordshire and possibly Buckinghamshire.
Parent Unit: Kensworth Nodular Chalk Member (KNCK)
Previous Name(s): Kensworth Nodular Chalk Member (KNCK)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Quarry faces at Hitch Wood Hill End (Hitchin). See Hopson et al. (1996, p.55, Figure 17). 
Reference Section  Quarry faces at Kensworth (Leighton Buzzard). The full succession through the underlying Chalk Rock Member to 5m above the Top Rock Bed is visible. See Shephard Thorn et al. (1994). 
Type Section  Uppermost quarry face in the Reed Pit near Royston in Cambridgeshire. The full succession of the bed is visible. 
Reference(s):
Penning, W H and Jukes-Browne, A J, 1881. Geology of the neighbourhood of Cambridge. Memoir of the Geological Survey, Old Series Sheets 51SW and part 51NW (England and Wales). 
Bromley, R G and Gale, A S. 1982. The lithostratigraphy of the English Chalk Rock. Cretaceous Research, Vol.3, 273-306. 
Hancock, J M. 1989. Sea-level changes in the British Region during the late Cretaceous. Proceedings of the Geologists' Association, Vol.100, 565-594. 
Brighton, A G. 1928. Notes on the Middle and Upper Chalk of the Cambridge District. Geological Magazine, Vol.65, 368-371. 
Worssam, B C and Taylor, J H. 1969. The geology of the country around Cambridge. Memoir of the Geological Survey of Great Britain, Sheet 188 (England and Wales). 
Hopson, P M, Aldiss, D T and Smith, A. 1996. The geology of the country around Hitchin. Memoir of the British Geological Survey, Sheet 221 (England and Wales). 
Shepard-Thorn, E R, Moorlock, B S P, Cox, B M, Allsop, J M and Wood, C J. 1994. Geology of the country around Leighton Buzzard. Memoir of the British Geological Survey, Sheet 220 (England and Wales). 
Hopson, P M. 2005. A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, with statements on the Chalk of Northern Ireland and the UK Offshore Sector. British Geological Survey Research Report RR/05/01 102pp. ISBN 0 852725175 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E206 E220 E221