Inferior Oolite

Inferior Oolite Group
Stratigraphic range: Aalenian–Bathonian PreꞒ Ꞓ O S D C P T J K Pg N (Middle Jurassic)
Inferior Oolite at Leckhampton Hill, Gloucestershire.
Type	Group
Sub-units	East Midlands Lincolnshire limestone Grantham Formation Northampton Sand Formation Cotswolds Salperton Limestone Aston Limestone Birdlip Limestone Dorset -Lower, Upper Inferior Oolite Formations
Underlies	Great Oolite Group
Overlies	Lias Group
Thickness	0 - 120 m
Lithology
Primary	limestones
Other	sandstone, mudstone
Location
Country	England

The Inferior Oolite is a sequence of Jurassic age sedimentary rocks in Europe. It was deposited during the Middle Jurassic. ^[1] The Inferior Oolite Group as more recently defined is a Jurassic lithostratigraphic group (a sequence of rock strata) in southern and eastern England . It has been variously known in the past as the Under Oolite (or Oolyte), the Inferior Oolite, the Inferior Oolite Series and the Redbourne Group. ^[2]

Outcrops

The rocks are exposed from Dorset and Somerset eastwards and northwards through the English Midlands to Yorkshire. ^[3] It is present at depth in the Wessex-Weald Basin, where it reaches its greatest thickness of 120 m.

Lithology and stratigraphy

Inferior Oolite (Doulting Stone) at Doulting Stone Quarry, England.

The group consists of up to 120 m thickness of oolitic limestones and subordinate sandstones and mudstones laid down during the Jurassic Period. In the East Midlands it consists of (in descending order i.e. oldest last) the Lincolnshire Limestone, Grantham and Northampton Sand formations whereas in the Cotswold Hills it consists of the Salperton Limestone, Aston Limestone and Birdlip Limestone formations. ^{[4] [5]} The Salperton Limestone contains the Clypeus Grit, a somewhat shelly grainstone that contains the large-diameter echinoid Clypeus ploti as well as Stiphothyris terebratulid brachiopods, and large mussel-like bivalves. ^[6] The limestones are rich in organic material. The ammonite Parkinsonia parkinsoni , an index fossil for the Bathonian, ^[7] is native to the Inferior Oolite of Burton Bradstock.^{[ citation needed ]}

Within Dorset, the Oolite is not subdivided into separately named formations, but is simply considered the Inferior Oolite Formation, sometimes subdivided into the Lower and Upper Inferior Oolite Formations. Within the vicinity of Yeovil it is divided into members which are in ascending order the Corton Denham Member, which predominantly consists of blue siltstone is about 2.5 m thick with the transitional top consisting of green Marl, the Oborne Ironshot Member, the term "ironshot" refers to ferruginised Oolite. ^[8] The upper portion of which contains intensely bioturbated limestone. Moving Into the Upper Inferior Oolite the Sherborne Limestone Member, which consists of exposed yellow brown fresh grey bioclastic limestone, while the overlying Combe Limestone Member, consists of rubbly limestone and marl, a full stratigraphy of the locality is given below

Stratigraphy of the Inferior Oolite at Frogden Quarry, Dorset [9]
Formation	Member	Bed	Lithology	Thickness	Ammonite Zone
Upper Inferior Oolite Formation	Combe Limestone Member		Broken limestone and marl	Over 5.6 metres	Garantiana Zone-Parkinsoni Zone
	Sherborne Limestone Member	Redhole Lane Beds	Blocky Limestone	2 metres	Garantiana Zone, Dichotoma Subzone
		Sherborne Building Stone Beds	Mottled, blocky limestone	~1.5 metres
		Acanthothyris Beds	"Brown sandy biomicrites interbedded with brown marls"	Up to 1.5 metres
Lower Inferior Oolite Formation	Oborne Ironshot Member	Oborne Road Stone Bed	Bioturbated and intensely burrowed limestone	~0.8 metres	Niortense Zone
		Frogden Ironshot Bed	Ferruginous oolite	~1.2 metres	Sauzei to Humphriesianum Zones
	Corton Denham Member	Green Grained White Marl	Marl	0.01-0.15 metres	Laeviuscula Zone
		Blue Bed	Very hard blue intensely burrowed siltstone	0.85-1 metre	Laeviuscula Zone, Trigonalis Subzone
		Corton Denham Beds	Lenticular hard blue-grey siltstone, in channels. separated by nodular siltstone	Seen to 2 metres	Concavum-Ovale Zones

Vertebrate fauna

Ornithopod tracks geographically located in North Yorkshire, England. ^[1] Ornithopod and theropod tracks present in North Yorkshire, England. ^[10] A supposed dermal spine long thought to be from a stegosaur is actually a caudal vertebra referable to Archosauria indet. ^[11]

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Dinosaurs of the Inferior Oolite
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Cetiosaurus	C. epioolithicus	North Yorkshire, England. [10]				Duriavenator Magnosaurus
	Indeterminate	Wiltshire, England. [12]
Duriavenator	D. hesperis	Dorset, England. [13]		"Skull elements." [14]
Magnosaurus [13]	M. nethercombensis [13]	Dorset, England. [13]		"Dentaries, vertebrae, pubis, femora, [and] tibiae." [14]
Megalosaurus [1]	M. hesperis [1]	Dorset, England. [13]		"Skull elements." [14]	Moved to the new genus Duriavenator in 2008.
	Indeterminate	Northamptonshire, England. [15] Somerset, England. [16]			Indeterminate Megalosaurid material.
Thyreophora	Indeterminate [11]	Dorset, England. [1]

See also

• Earth sciences portal
• Paleontology portal
• Dinosaurs portal

• List of dinosaur-bearing rock formations

Footnotes

1. Weishampel, David B; et al. (2004). "Dinosaur distribution (Middle Jurassic, Europe)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 538–541. ISBN   0-520-24209-2.
2. Waters, C.N. et al. 2007 Stratigraphical Chart of the United Kingdom: Southern Britain British Geological Survey (poster)
3. British Geological Survey 1:50,000 scale geological map (England & Wales) sheets
4. British Geological Survey. "Inferior Oolite Group". BGS Lexicon of Named Rock Units. Retrieved 5 January 2023.
5. Waters, C.N. et al 2007 Stratigraphical Chart of the United Kingdom:Southern Britain British Geological Survey (poster)
6. "Clypeus Grit Member". British Geological Survey. 2025. Retrieved 21 February 2025. Parent Unit: Salperton Limestone Formation
7. Wynn Jones, R: Applied Paleontology. page 146, Cambridge University Press
8. "Upper Inferior Oolite, Middle Jurassic, Bristol and Gloucester region - Earthwise". earthwise.bgs.ac.uk. Retrieved 8 October 2019.
9. Chandler, Robert B.; Whicher, John; Dodge, Martin; Dietze, Volker (1 November 2014). "Revision of the stratigraphy of the Inferior Oolite at Frogden Quarry, Oborne, Dorset, UK". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 274 (2): 133–148. doi:10.1127/0077-7749/2014/0429. ISSN   0077-7749.
10. "Dinosaur distribution (Middle Jurassic; Europe; North Yorkshire, England)." Weishampel, et al. (2004). Page 539.
11. Peter M. Galton (2017). "Purported earliest bones of a plated dinosaur (Ornithischia: Stegosauria): a "dermal tail spine" and a centrum from the Aalenian-Bajocian (Middle Jurassic) of England, with comments on other early thyreophorans". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 285 (1): 1–10. doi:10.1127/njgpa/2017/0667.
12. "Dinosaur distribution (Middle Jurassic; Europe; Wiltshire, England)." Weishampel, et al. (2004). Page 540.
13. "Dinosaur distribution (Middle Jurassic; Europe; Dorset, England)." Weishampel, et al. (2004). Page 539.
14. "Table 4.1," in Weishampel, et al. (2004). Page 73.
15. "Dinosaur distribution (Middle Jurassic; Europe; Northamptonshire, England)." Weishampel, et al. (2004). Pages 539-540.
16. "Dinosaur distribution (Middle Jurassic; Europe; Somerset, England)." Weishampel, et al. (2004). Page 538.

References

• M. J. Benton and P. S. Spencer. 1995. Fossil Reptiles of Great Britain. Chapman & Hall, London 1-386
• J. B. Delair. 1973. The dinosaurs of Wiltshire. The Wiltshire Archaeological and Natural History Magazine 68:1-7
• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp.  ISBN   0-520-24209-2.