The BGS Lexicon of Named Rock Units — Result Details

Grantham Formation

Computer Code: GRF Preferred Map Code: GrF
Status Code: Full
Age range: Aalenian Age (JA) — Aalenian Age (JA)
Lithological Description: Mudstones, sandy mudstones and argillaceous siltstone-sandstone, which is commonly ferruginous, and containing generally abundant plant debris, interpreted as both non-marine and marine facies, comprising several shallowing-upwards,delta-type rhythms with typically a tripartite succession comprising: a generally pale, locally carbonate-cemented and commonly ferruginous more or less argillaceous sand or sandstone at the base, which may have a rootleted seatearth at the top, overlain in the type area at least, by a median unit of marine shaly sandy mudstone designated the Stainby Member, which farther to the south is represented by a dark carbonaceous shaly clay, named the "Coaly Bed", which may be equivalent, overlain by an upper, possibly rhythmic succession of alternating sand or sandstone with mudstone or sandy mudstone that may be rootletted in parts.
Definition of Lower Boundary: Generally a sharp erosional, or in some places apparently transitional boundary, with ferruginous sandstone or ironstone of the Northampton Sand Formation, the top of which may be rootletted, or where the latter is absent, grey mudstone of the Whitby Mudstone Formation, with a localised conglomeratic bed of reworked Northampton Sand pebbles at the base.
Definition of Upper Boundary: A sharp or apparently transitional and somewhat arbitrary interpreted boundary with limestones of the Lincolnshire Limestone Formation. which may be very sandy at the base, distinguished from the Grantham Formation by the presence of shell debris and peloids.
Thickness: From typically about 2m to 5m in the type area, and extremely variable, locally ranging up to 15m in channels, for example, 13.6m measured in the Copper Hill Borehole [SK 9787 4265] near Ancaster.
Geographical Limits: From approximately the line of the River Humber, where the unit may be overstepped by the Lincolnshire Limestone Formation, southwards to the Kettering-Peterborough area, just beyond the southern limit of the Lincolnshire Limestone, where it is assumed to be overstepped by the Rutland Formation (see Bradshaw, 1978). Beds between the Humber and Market Weighton, formerly classified as the "Lower Estuarine Series" of de Boer et al. (1958) are now included in the Lincolnshire Limestone (Gaunt et al., 1980, pp.8, 29; 1992, p.45). The supposed "Lower Estuarine Series" and "White Sands" in the area south of Kettering-Peterborough are now known to represent the much younger, late Bajocian-Bathonian, Stamford Member of the Rutland Formation or, in the Brackley district, the equivalent Horsehay Sand Formation.
Parent Unit: Inferior Oolite Group (INO)
Previous Name(s): Lower Estuarine Beds (-2215)
Lower Estuarine "Series" [Obsolete Name And Code: See CLH, GRF, SWK And EBB] (LET)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  In Colsterworth No.2 Mine, 1 mile WSW of Colsterworth Church. 3.59m of Grantham Formation, between Northampton Sand Ironstone and Lincolnshire Limestone (Kent, 1975). 
Type Area  The Grantham area of south Lincolnshire, north Leicestershire and Rutland, and Market Overton to Leadenham. 
Reference Section  Sproxton Quarry, extant section. Richardson, 1939; Kent, 1975; Cox, B M, and Sumbler, M G. 2002. 
Reference Section  Graded Quarry face adjoining the A43 Weldon Bypass, Northants, possibly equivalent to the Barn Close No 1 borehole. An extant section. See Kent 1975 for additional reference sections in former ironstone workings;most are now obscured. 
Type Section  Colsterworth No. 2 Mine near Stainby, Lincolnshire, which is now obscured. Kent,1975. 
Reference(s):
Bradshaw, M J. 1978. A facies analysis of the Bathonian of eastern England. (University of Oxford: Unpublished PhD thesis.) 
De Boer, G, Neale, J W and Penny, L F. 1958. A guide to the geology of the area between Market Weighton and the Humber. Proceedings of the Yorkshire Geological Society, Vol.31(2), 157-209. 
Gaunt, G D, Ivimey-Cook, H C, Penn, I E and Cox, B M. 1980. Mesozoic rocks proved by the Institute of Geological Sciences boreholes in the Humber and Acklam areas. Report of the Institute of Geological Sciences, No. 79/13. 
Kent, P E, 1975. The Grantham Formation in the East Midlands: Revision of the Middle Jurassic, Lower Estuarine Beds. Mercian Geologist, Vol.5, No.4, p.305-327, 2 text-figs. 
Judd, J W. 1875. The geology of Rutland and parts of Lincoln, Leicester, Northampton, Huntingdon and Cambridge. Memoir of the Geological Survey of Great Britain (Old Series sheet 64). 
Taylor, J H. 1963. Geology of the country around Kettering, Corby and Oundle. Memoir of the Geological Survey of Great Britain. Sheet 171 (England and Wales). 
Gaunt, G D, Fletcher, T P and Wood, C J. 1992. Geology of the country around Kingston upon Hull and Brigg. Memoir of the British Geological Survey, sheets 80 and 89 (England and Wales). 172pp. 
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E089 E127 E080 E158 E102 E103 E128 E144 E142 E171 E114 E143 E157 E170 E185