Inferior Oolite Group | |
---|---|
Stratigraphic range: (Middle Jurassic) | |
Type | Group |
Sub-units | East Midlands Cotswolds 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]
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.
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.[ 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. [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] | |||||
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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 |
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
| Notes Uncertain or tentative taxa are in small text; |
Dinosaurs of the Inferior Oolite | ||||||
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Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
C. epioolithicus |
| |||||
Indeterminate |
| |||||
D. hesperis |
| "Skull elements." [13] | ||||
M. nethercombensis [12] |
| "Dentaries, vertebrae, pubis, femora, [and] tibiae." [13] | ||||
Megalosaurus [1] | M. hesperis [1] |
| "Skull elements." [13] | Moved to the new genus Duriavenator in 2008. | ||
Indeterminate | Indeterminate Megalosaurid material. | |||||
Indeterminate [10] |
| |||||
The Oxford Clay is a Jurassic marine sedimentary rock formation underlying much of southeast England, from as far west as Dorset and as far north as Yorkshire. The Oxford Clay Formation dates to the Jurassic, specifically, the Callovian and Oxfordian ages, and comprises two main facies. The lower facies comprises the Peterborough Member, a fossiliferous organic-rich mudstone. This facies and its rocks are commonly known as lower Oxford Clay. The upper facies comprises the middle Oxford Clay, the Stewartby Member, and the upper Oxford Clay, the Weymouth Member. The upper facies is a fossil poor assemblage of calcareous mudstones.
The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group in south-east England. The name is derived from the district known as the Isle of Purbeck in Dorset where the strata are exposed in the cliffs west of Swanage.
Magnosaurus was a genus of theropod dinosaur from the Middle Jurassic of England. It is based on fragmentary remains and has often been confused with or included in Megalosaurus.
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The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group in the lithostratigraphy of southern England. The Wealden group consists of paralic to continental (freshwater) facies sedimentary rocks of Berriasian to Aptian age and thus forms part of the English Lower Cretaceous. It is composed of alternating sands and clays. The sandy units were deposited in a flood plain of braided rivers, the clays mostly in a lagoonal coastal plain.
Duriavenator is a genus of theropod dinosaur that lived in what is now England during the Middle Jurassic, about 168 million years ago. In 1882, upper and lower jaw bones of a dinosaur were collected near Sherborne in Dorset, and Richard Owen considered the fossils to belong to the species Megalosaurus bucklandii, the first named non-bird dinosaur. By 1964, the specimen was recognised as belonging to a different species, and in 1974 it was described as a new species of Megalosaurus, M. hesperis; the specific name means 'the West' or 'western'. Later researchers questioned whether the species belonged to Megalosaurus, in which many fragmentary theropods from around the world had historically been placed. After examining the taxonomic issues surrounding Megalosaurus, Roger B. J. Benson moved M. hesperis to its own genus in 2008, Duriavenator; this name means "Dorset hunter".
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The Calcaire de Caen or Calcaires de Caen Formation; French for Caen Limestone, is a geological formation in France. It dates back to the mid-Bathonian of the Jurassic. It was often quarried for building work and is referred to as Caen Stone.
The Taynton Limestone is a geological formation in Oxfordshire in the United Kingdom. It dates to the Middle Jurassic, mid-Bathonian stage. It predominantly consists of ooidal grainstone. The term "Stonesfield Slate" refers to slaty limestone horizons within the formation that during the 18th and 19th centuries were extensively quarried for use in roof tiling within the vicinity of Stonesfield, Oxfordshire. Previously these were thought to belong to the Sharp's Hill Formation, but boreholes and shaft sections suggest that at least three horizons within the Taynton Limestone were quarried for the slate. These horizons are well known for producing a diverse set of fossils including those of plants, insects as well as vertebrates, including some of the earliest known mammals, pterosaurs as well as those of first dinosaur ever described, Megalosaurus.
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