Inferior Oolite

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]

Inferior Oolite Group
Stratigraphic range: (Middle Jurassic)
Inferior Oolite at Leckhampton Hill, Gloucestershire.
TypeGroup
Sub-unitsEast Midlands

Cotswolds

  • Salperton Limestone
  • Aston Limestone
  • Birdlip Limestone
Dorset -Lower, Upper Inferior Oolite Formations
UnderliesGreat Oolite Group
OverliesLias Group
Thickness0 - 120 m
Lithology
Primarylimestones
Othersandstone, mudstone
Location
CountryEngland

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 limestones are rich in organic material. The ammonite Parkinsonia parkinsoni, an index fossil for the Bathonian,[6] is native to the Inferior Oolite of Burton Bradstock.

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.[7] 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[8]
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.[9] A supposed dermal spine long thought to be from a stegosaur is actually a caudal vertebra referable to Archosauria indet.[10]

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.[9]
Duriavenator
Magnosaurus

Indeterminate
  • Wiltshire, England.[11]

Duriavenator

D. hesperis
  • Dorset, England.[12]

"Skull elements."[13]

Magnosaurus[12]

M. nethercombensis[12]
  • Dorset, England.[12]

"Dentaries, vertebrae, pubis, femora, [and] tibiae."[13]

Megalosaurus[1]

M. hesperis[1]
  • Dorset, England.[12]

"Skull elements."[13]

Moved to the new genus Duriavenator in 2008.

Indeterminate
  • Northamptonshire, England.[14]
  • Somerset, England.[15]
 Indeterminate Megalosaurid material.

Thyreophora

Indeterminate[10]
  • Dorset, England.[1]

See also

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. Wynn Jones, R: Applied Paleontology. page 146, Cambridge University Press
  7. "Upper Inferior Oolite, Middle Jurassic, Bristol and Gloucester region - Earthwise". earthwise.bgs.ac.uk. Retrieved 8 October 2019.
  8. 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.
  9. "Dinosaur distribution (Middle Jurassic; Europe; North Yorkshire, England)." Weishampel, et al. (2004). Page 539.
  10. 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.
  11. "Dinosaur distribution (Middle Jurassic; Europe; Wiltshire, England)." Weishampel, et al. (2004). Page 540.
  12. "Dinosaur distribution (Middle Jurassic; Europe; Dorset, England)." Weishampel, et al. (2004). Page 539.
  13. "Table 4.1," in Weishampel, et al. (2004). Page 73.
  14. "Dinosaur distribution (Middle Jurassic; Europe; Northamptonshire, England)." Weishampel, et al. (2004). Pages 539-540.
  15. "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.
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