| Lithological Description: |
| Medium and dark grey fossiliferous mudstone and siltstone, laminated and bituminous in part, with thin siltstone or silty mudstone beds and rare fine-grained calcareous sandstone beds; dense, smooth argillaceous limestone nodules very common at some horizons; phosphatic nodules at some levels. Nodular and fossiliferous limestones occur at the base in some areas. |
| Definition of Lower Boundary: |
| In Cleveland Basin, base of mudstone resting upon ooidal limestone or sideritic mudstone nodules of the Cleveland Ironstone (see Cox, B M, et al, for more details). Elsewhere, at base of mudstone overlying ironstone of the Marlstone Rock Formation. |
| Definition of Upper Boundary: |
| In most areas, sharp, eroded boundary with limestones or sandstones of the Inferior Oolite Group (East Midlands Shelf) or the Ravenscar Group or Dogger Formation (Cleveland Basin). In Ravenscar area, and in much of Worcester Basin arbitrary boundary in transition to sandy sediments of the Blea Wyke Formation or Bridport Sand Formation respectively |
| Thickness: |
| To c.120m |
| Geographical Limits: |
| Cleveland Basin, East Midlands Shelf and Worcester Basin (i.e. Yorkshire coast to Mendip). |
| Stratotypes: |
| Reference Section |
Copper Hill Borehole. Depths 17.31 - 63.70m. |
| Type Section |
Coastal exposures from Hawsker Bottoms to Whitby Harbour. |
| Type Area |
North Yorkshire Coast. |
| Reference Section |
BGS Stowell Park Bore, Gloucs (Reg. No. SP01SE/1) 122.28 - 220m depth (Green, G W and Melville, R V, 1956; Melville, R V, 1956; Spath, L F, 1956; Ivimey-Cook, H C, 1993; Sumbler, M G and Barron, A J M, 1995; Sumbler, M G, Barron, A J M and Morigi, A N, 2000. |
| Reference(s): |
| Ivimey-Cook, H C and Powell, J H, 1991. Late Triassic and early Jurassic biostratigraphy of the Felixkirk Borehole, North Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.48, 367-374. |
| Powell, J H, 1984. Lithostratigraphic nomenclature of the Lias Group in the Yorkshire Basin. Proceedings of the Yorkshire Geological Society, Vol.45, p.51-57. |
| Berridge, N G and others. 1999. Geology of the country around Grantham. Memoir of the British Geological Survey. |
| Green, G W and Melville, R V, 1956. The stratigraphy of the Stowell Park Borehole (1949-1951). Bulletin of the Geological Survey of Great Britain, No.11, p.1-66. |
| Melville, R V, 1956. Stratigraphical palaeontology, ammonites excluded, of the Stowell Park Borehole. Bulletin of the Geological Survey of Great Britain, No.11, 67-139. |
| Cox, B M, Sumbler, M G and Ivimey-Cook, H C, 1999. A Formational framework for the Lower Jurassic of England and Wales (Onshore Area). British Geological Survey Research Report No. RR/99/01. |
| Howarth, M K, 1962. The Jet Rock Series and the Alum Shales Series of the Yorkshire coast. Proceedings of the Yorkshire Geological Society, Vol.33, 381-422. |
| Sumbler, M G, Barron, A J M and Morigi, A N, 2000. Geology of the Cirencester district. Memoir of the British Geological Survey, Sheet 235 (England and Wales). |
| Spath, L F, 1956. The Liassic ammonite faunas of the Stowell Park Borehole. Bulletin of the Geological Survey of Great Britain, No.11, 140-164. |
| Howarth, M K, 1992. The ammonite family Hildoceratidae in the Lower Jurassic of Britain. Part 1. Monograph of the Palaeontographical Society London: 1-106, pls 1-16. (Publ. No.586, part of Vol.145 for 1991). |
| Sumbler, M G and Barron, A J M, 1995. Geological notes and local details for 1: 10 000 Sheet SP01SE (Chedworth). British Geological Survey Technical Report, WA/95/73. |
| Ivimey-Cook, H C, 1993. The biostratigraphy of the Lower Jurassic of the Stowell Park Borehole. British Geological Survey Technical Report WH/93/174R. |
| Howarth, M K, 1973. The stratigraphy and ammonite fauna of the Upper Liassic Grey Shales of the Yorkshire coast. Bulletin of the British Museum (Natural History), Geology Series, Vol.29, 235-288. |
