# Inferior Oolite

The Inferior Oolite is a sequence of Jurassic age sedimentary rocks in Europe. It was deposited during the Middle Jurassic. 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.

## Outcrops

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

## Lithology and stratigraphy

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. 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. The limestones are rich in organic material. The ammonite Parkinsonia parkinsoni, an index fossil for the Bathonian, 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. 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 :
| Formation | Member | Bed | Lithology | Thickness | Ammonite Zone |
| Upper Inferior Oolite Formation | Combe Limestone Member | Combe Limestone Member | Broken limestone and marl | Over 5.6 metres | Garantiana Zone-Parkinsoni Zone |
| Upper Inferior Oolite Formation | Sherborne Limestone Member | Redhole Lane Beds | Blocky Limestone | 2 metres | Garantiana Zone, Dichotoma Subzone |
| Upper Inferior Oolite Formation | Sherborne Limestone Member | Sherborne Building Stone Beds | Mottled, blocky limestone | ~1.5 metres | |
| Upper Inferior Oolite Formation | Sherborne Limestone Member | 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 |
| Lower Inferior Oolite Formation | Oborne Ironshot Member | Frogden Ironshot Bed | Ferruginous oolite | ~1.2 metres | Sauzei to Humphriesianum Zones |
| Lower Inferior Oolite Formation | Corton Denham Member | Green Grained White Marl | Marl | 0.01-0.15 metres | Laeviuscula Zone |
| Lower Inferior Oolite Formation | Corton Denham Member | Blue Bed | Very hard blue intensely burrowed siltstone | 0.85-1 metre | Laeviuscula Zone, Trigonalis Subzone |
| Lower Inferior Oolite Formation | Corton Denham Member | 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. Ornithopod and theropod tracks present in North Yorkshire, England. A supposed dermal spine long thought to be from a stegosaur is actually a caudal vertebra referable to Archosauria indet.
| 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 | Material | Notes | Images |
| Cetiosaurus | C. epioolithicus | North Yorkshire, England. | | | Duriavenator Magnosaurus |
| Cetiosaurus | Indeterminate | Wiltshire, England. | | | Duriavenator Magnosaurus |
| Duriavenator | D. hesperis | Dorset, England. | "Skull elements." | | Duriavenator Magnosaurus |
| Magnosaurus | M. nethercombensis | Dorset, England. | "Dentaries, vertebrae, pubis, femora, [and] tibiae." | | Duriavenator Magnosaurus |
| Megalosaurus | M. hesperis | Dorset, England. | "Skull elements." | Moved to the new genus Duriavenator in 2008. | Duriavenator Magnosaurus |
| Megalosaurus | Indeterminate | Northamptonshire, England. Somerset, England. | | Indeterminate Megalosaurid material. | Duriavenator Magnosaurus |
| Thyreophora | Indeterminate | Dorset, England. | | | Duriavenator Magnosaurus |