The BGS Lexicon of Named Rock Units — Result Details

Munday's Hill Phosphatic Sandstone Formation

Computer Code: MHPS Preferred Map Code: notEntered
Status Code: Full
Age range: Albian Age (KA) — Albian Age (KA)
Lithological Description: In the stratotype area, the formation generally comprises poorly cemented pebbly ferruginous sandstone and argillaceous, glauconitic and phosphatic fine- to coarse-grained, locally pebbly, sandstone and sandy mudstone including "carstone" and "boxstone" clasts. Dark or buff-coloured phosphatic concretions and worn and reworked phosphatic pebbles and fossils are common, and generally form several discrete horizons. Locally, in the stratotype area and some nearby localities, a thin (c.0.6m), pale to pinkish-yellow to pale brown micritic limestone (Shenley Limestone Member) occurs in the lower part of the formation, associated with thin ironstone horizons. In the northwestern Weald the coeval strata becomes more argillaceous, but can always be distiguished from the mudstones of the overlying Gault Formation by its sandier and more glauconitic character. These deposits have not been named separately. In East Anglia, coeval strata are represented by the Carstone Formation.
Definition of Lower Boundary: In the stratotype area, the lower boundary is an unconformity, marked by the facies change from clayey siltstone or trough cross-bedded sandstone of the underlying Woburn Sand Formation, to pale micritic limestone of the Shenley Limestone Member. Where the Shenley Limestone is absent, the common phosphatic nodules, ferruginous sandstone and pebbles in dark, greenish-grey, clayey glauconitic sandstone of the Munday's Hill Phosphatic Sandstone serve to distinguish it from the pale or ferruginous facies of the underlying Woburn Sand Formation.
Definition of Upper Boundary: The upper boundary is a non-sequence, usually marked by a phosphatic nodule-pebble bed horizon, and coincident with the facies change from dark, greenish-grey, clayey, glauconitic sandstone with common horizons of phosphatic nodules-pebbles of the underlying Munday's Hill Phosphatic Sandstone, to dark-grey, smooth-textured mudstone of the Gault Formation. In some places the base of the Gault Formation is represented by about 1.2 m of red fissile mudstone which has been termed the "Red Clay" or "Cirripede Bed" (Toombs, 1935).
Thickness: Up to 2.5m in the Munday's Hill area.
Geographical Limits: Bedfordshire, Buckinghamshire.
Parent Unit: Lower Greensand Group (LGS)
Previous Name(s): Junction Beds (parts) of Wonham and Elliott (1996). (-3551)
Transition Series (-1695)
Transition Series (Carstone And Shenley Limestone) Of Johnson And Levell (1995). (-4192)
Junction Beds [Obsolete Name And Code] (JUB)
Alternative Name(s): none recorded or not applicable
Type Area  The northwestern Weald area. 
Type Section  Munday's Hill Pit [SP 9394 2798]. The Formation is also found in numerous sand pits exposing the Lower Greensand in the Leighton Buzzard area, Bedfordshire. 
Lamplugh, G W. 1922. On the junction of the Gault and Lower Greensand near Leighton Buzzard, Bedfordshire. Quarterly Journal of the Geological Society of London, Vol.78, 1-81. 
Owen, H G. 1972. The Gault and its junction with the Woburn Sands in the Leighton Buzzard area, Bedfordshire and Buckinghamshire. Proceedings of the Geologists' Association, Vol.83, 287-312. 
Owen, H G. 1992. The Gault-Lower Greensand Junction Beds in the northern Weald (England) and Wissant (France), and their depositional environment. Proceedings of the Geologists' Association, Vol.103, 83-110. 
Toombs, H A. 1935. Field meeting to Leighton Buzzard, Bedfordshire. Proceedings of the Geologists' Association, Vol.46, 432-435. 
Eyers, J. 1995. Correlation of the Lower Greensand Group (Woburn Sands and Carstone) of the Bedfordshire Province, England. Cretaceous Research, Vol.16, 385-413. 
Johnson, H D and Levell, B K. 1995. Sedimentology of a transgressive, estuarine sand complex: the Lower Cretaceous Woburn Sands (Lower Greensand), southern England. Special Publication of the International Association of Sedimentologists, No.22, 17-46. 
Eyers, J. 1991. The influence of tectonics on early Cretaceous sedimentation in Bedfordshire, England. Journal of the Geological Society of London, Vol. 149, 405-414. 
Owen, H G, Shephard-Thorn, E R and Sumbler, M G. 1996. Lower Cretaceous. 61-75 in Sumbler, M G (Ed), British Regional Geology: London and the Thames Valley (4th edition). (London: HMSO for the British Geological Survey.) 
Casey, R, 1961. The stratigraphical palaeontology of the Lower Greensand. Palaeontology, Vol.3, 487-621. 
Wonham, J P and Elliott, T. 1996. High resolution sequence stratigraphy of a mid-Cretaceous estuarine complex: the Woburn Sands of the Leighton Buzzard area, southern England. 41-62 in Hesselbo, S P and Parkinson, D N (eds), Sequence Stratigraphy in British Geology. Geological Society Special Publication, No.103, 41-62. 
Smart, P J. 1997. The basal Gault and Gault-Woburn Sands junction beds in Chamberlain's Barn Quarry, Leighton Buzzard, Bedfordshire, England. Proceedings of the Geologists' Association, Vol.108, 287-292. 
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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable