The Charmouth Mudstone Formation is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

, dating to the Early

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

(

Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...

– Pliensbachian). It forms part of the lower

Lias Group The Lias Group or Lias is a lithostratigraphic unit (a sequence of rock strata) found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany. It consists of marine limestones, ...

. It is most prominently exposed at its type locality in cliff section between

Lyme Regis Lyme Regis ( ) is a town in west Dorset, England, west of Dorchester, Dorset, Dorchester and east of Exeter. Sometimes dubbed the "Pearl of Dorset", it lies by the English Channel at the Dorset–Devon border. It has noted fossils in cliffs and ...

and

Charmouth Charmouth is a village and civil parish in west Dorset, England. The village is situated on the mouth of the River Char, around north-east of Lyme Regis. Dorset County Council estimated that in 2013 the population of the civil parish was 1,31 ...

(alongside the underlying

Blue Lias The Blue Lias is a formation (stratigraphy), geological formation in southern, eastern and western England and parts of South Wales, part of the Lias Group. The Blue Lias consists of a sequence of limestone and shale layers, laid down in latest ...

) but onshore it extends northwards to

Market Weighton Market Weighton ( ) is a town and civil parishes in England, civil parish in the East Riding of Yorkshire, England. It is one of the main towns in the East Yorkshire Wolds and lies midway between Kingston upon Hull, Hull and York, about from e ...

Yorkshire Yorkshire ( ) is an area of Northern England which was History of Yorkshire, historically a county. Despite no longer being used for administration, Yorkshire retains a strong regional identity. The county was named after its county town, the ...

, and in the subsurface of the East Midlands Shelf and

Wessex Basin The Wessex Basin is a petroleum-bearing geological area located along the southern coast of England and extending into the English Channel. The onshore part of the basin covers approximately 20,000 km2 and the area that encompasses the Englis ...

. The formation is notable for its fossils, including those of ammonites and marine reptiles and rare dinosaur remains. The formation played a prominent role in the history of early paleontology, with its Lyme Regis-Charmouth exposure being frequented by fossil collectors including

Mary Anning Mary Anning (21 May 1799 – 9 March 1847) was an English fossil collector, fossil trade, dealer, and palaeontologist. She became known internationally for her discoveries in Jurassic marine fossil beds in the cliffs along the English Cha ...

Stratigraphy

Shales With Beef Member

The Shales With Beef Member is around 28–30 metres thick in the Lyme Regis-Charmouth region and predominantly consists of thinly bedded medium to dark grey mudstone, blocky calcareous pale-weathering mudstone and brown-grey organic-rich mudstones with frequent

bedding Bedding, also called bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environment ...

parallel

veins Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal c ...

of fibrous

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

("beef"), that are usually less than 10 centimetres thick. Several beds of nodular and tabular limestone are also present. It is the lowest unit of the formation and directly overlies the Blue Lias Formation, with the boundary being marked by a prominent bioturbated horizon. Notable persistent marker beds within the member include the laminated calcareous siltstone "Fish Bed", "Table Ledge", which consists of lens beds of limestones with mud content with nests of rhynchonellid

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s, the Devonshire Head and the Spittles limestones and the Birchi Nodules (which are septarian concretions) The upper boundary with the Black Ven Marl Member is marked by the prominent laterally persistent limestone Birchi Tabular Bed.

Black Ven Marl Member

The Black Ven Marl Member is around 43 metres thick consists of thinly bedded dark mudstones, with several laterally persistent cementstone horizons, notable horizons include the Lower and Upper Cement beds and the Stellare nodules.

Belemnite Marl Member

The Belemnite Marl Member is around 20 to 27 metres thick, and consists of interbedded pale and dark grey calcareous mudstone, with numerous belemnites, hence the name. The top of the member is marked by the Belemnite Stone Bed

Green Ammonite Member

The Green Ammonite Member is up to 31 metres thick predominantly consists of medium grey mudstones, with 3 limestone horizons, Lower Limestone; Red Band, and Upper Limestone, it is conformably overlain by the Dyrham Formation in some areas, but in the Charmouth area there is an erosive

unconformable An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

boundary with the much younger Early Cretaceous (

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

) aged

Gault The Gault Formation is a geological formation of stiff blue clay deposited in a calm, fairly deep-water marine environment during the Lower Cretaceous Period (Upper and Middle Albian). It is well exposed in the coastal cliffs at Copt Point in Fo ...

clays.

Paleobiota

Ammonites

Sauropterygia

Ichthyosauria

Thalattosuchia

Pterosauria

Dinosauria

Fish

Numerous fish species are known from the Charmouth Mudstone and underlying Blue Lias, from such horizons as the "Fish Bed" of the Shales With Beef Member.

Insects

Numerous species of insect are known from concretions, predominately in the Black Ven Marl Member.

Plants

, England * Sorthat Formation, Denmark * Hasle Formation, Denmark * Zagaje Formation, Poland * Drzewica Formation, Poland * Ciechocinek Formation, Poland * Borucice Formation, Poland * Rotzo Formation, Italy * Saltrio Formation, Italy * Moltrasio Formation, Italy * Marne di Monte Serrone, Italy * Calcare di Sogno, Italy * Podpeč Limestone, Slovenia * Coimbra Formation, Portugal * El Pedregal Formation, Spain * Fernie Formation, Canada * Whiteaves Formation, British Columbia * Navajo Sandstone, Utah * Aganane Formation, Morocco * Tafraout Group, Morocco * Azilal Formation, Morocco * Budoš Limestone, Montenegro * Kota Formation, India * Cañadón Asfalto Formation, Argentina *

Los Molles Formation The Los Molles Formation is a geologic formation of Early to Middle Jurassic age, located at northern and central part of Neuquén Basin at Mendoza Shelf in Argentina Argentina, officially the Argentine Republic, is a country in the s ...

, Argentina * Kandreho Formation, Madagascar *

Elliot Formation The Elliot Formation is a geological formation and forms part of the Stormberg Group, the uppermost geological group that comprises the greater Karoo Supergroup. Outcrops of the Elliot Formation have been found in the northern Eastern Cape, so ...

, South Africa * Clarens Formation, South Africa * Evergreen Formation, Australia * Cattamarra Coal Measures, Australia *

Hanson Formation The Hanson Formation (also known as the Shafer Peak Formation) is a geologic formation on Mount Kirkpatrick and north Victoria Land, Ross Dependency, Antarctica. It is one of the two major dinosaur-bearing rock groups found on Antarctica to date; ...

, Antarctica * Mawson Formation, Antarctica

References

{{Reflist Geologic formations of England Jurassic England Jurassic System of Europe Sinemurian Stage Pliensbachian Stage