| Computer Code: |
JG |
Preferred Map Code: |
JG |
| Status Code: |
Full |
| Age range: |
Pliensbachian Age (JE)
— Pliensbachian Age (JE) |
| Lithological Description: |
Grey mudstone beds with numerous Gryphaea, sporadic limestone nodules and thin shelly limestone beds. Fauna also includes serpulids, other bivalve species, ammonites and belemnites. Forms a slight feature, and Gryphaea conspicuous in clay soil. |
| Definition of Lower Boundary: |
Change up from mudstone with large argillaceous limestone nodules and small phosphatic nodules at some levels, of undifferentiated Charmouth Mudstone Formation into mudstone with abundant Gryphaea (as described under Lithology). In reference section Copper Hill Borehole (SK94SE/56), base lies at 121.45 m depth. |
| Definition of Upper Boundary: |
Change up from mudstone with limestone nodules and numerous Gryphaea (as described under Lithology) into silty limestone, overlain by mudstone with ironstone nodules (equivalent to the Pecton Ironstone Bed of north Lincolnshire) of undifferentiated Charmouth Mudstone Formation; at 118.60 m depth in reference section Copper Hill Borehole (SK94SE/56). |
| Thickness: |
1 to 3 m; 2.85 m in reference section. |
| Geographical Limits: |
East Midlands: north Leicestershire to Linclonshire. Not recognised in the Charmouth Mudstone Formation of north Lincolnshire, or south Leicestershire, where it passes south into part of the mudstone-dominated Charmouth Mudstone Formation. Berridge et al, (1999) assert that the Jericho Gryphaea Bed, plus the overlying strata equivalent to the Pecton Ironstone Bed correlate with the '85 Marker' (Ibex Zone) (Horton and Poole, 1977) of the Charmouth Mudstone Formation of the south Midlands. |
| Parent Unit: |
Charmouth Mudstone Formation (CHAM)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
BGS Copper Hill Borehole (SK94SE/56). |
| Partial Type Section |
750 m WNW of Gonerby Grange Berridge et al., 1999. |
| Reference(s): |
| Horton, A and Poole, E G, 1977. The lithostratigraohy of three geophysical marker horizons in the Lower Lias of Oxfordshire. Bulletin of the Geological Survey of Great Britain, Vol.62, 13-33. |
| Brandon, A, Sumbler, M G, and Ivimey-Cook, H C. 1990. A revised lithostratigraphy for the Lower and Middle Lias (Lower Jurassic) east of Nottingham, England. Proceedings of the Yorkshire Geological Society, Vol. 48, 121-141. |
| Berridge, N G, Pattison, J, Samuel, M D A, Brandon, A, Howard, A S, Pharaoh, T C, and Riley, N J. 1999. Geology of the Grantham district. Memoir of the British Geological Survey, sheet 127 (England and Wales). |
| Carney, J N, Ambrose, K and Brandon A. 2002. Geology of the Melton Mowbray district - a brief explanation of the geological map. British Geological Survey Sheet Explanation, Sheet 142 (England and Wales). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E127
E142
|
