| Computer Code: |
STAI |
Preferred Map Code: |
GrF |
| Status Code: |
Full |
| Age range: |
Aalenian Age (JA)
— Aalenian Age (JA) |
| Lithological Description: |
A dark grey to brownish, fissile, laminated mudstone and siltstone, and more massive laminated mudstone, locally containing marine bivalves such as Gervillella and Modiolus, and the brachiopod Lingula, succeeded by a rootletted seatearth in the upper part of the unit, where it forms the basal interpreted marine part, of a second shallowing-upward rhythm of the Grantham Formation. |
| Definition of Lower Boundary: |
Generally a sharp boundary resting on sandstone or sandy mudstone, often developed as a seatearth, forming the lower part of the Grantham Formation. |
| Definition of Upper Boundary: |
A transitional, and somewhat arbitrary boundary, with interpreted non-marine mudstones, siltstones and sandstones forming the upper part of the Grantham Formation, which in some places is overlain directly by limestones of the Lincolnshire Limestone Formation. |
| Thickness: |
Up to about 1.5 m thick, typically about 1 m thick in the type area,and 1.42 m thick in the type section. |
| Geographical Limits: |
According to Kent (1975 fig 1), the unit is more or less restricted to the type area, although it is more likely that it is much more widespread, particularly to the north, such as identified by Gaunt et al. (1992), in North Lincolnshire. |
| Parent Unit: |
Grantham Formation (GRF)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
The Grantham area of south Lincolnshire, north Leicestershire and Rutland, from Market Overton to Ancaster. |
| Reference Section |
Sproxton Quarry, extant section. Richardson, 1939; Kent, 1975; Cox, B M, and Sumbler, M G. 2002. See Kent (1975) for additional reference sections in former ironstone workings, although most are now obscured. |
| Type Section |
Glebe Mine, Stainby,Lincolnshire, possibly obscured. Kent,1975. |
| Reference(s): |
| 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. |
| Cox, B M, and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E080
E089
E102
E114
E127
E142
E143
E157
|
