The Aylesbeare Mudstone Group is an early

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geology, geological science associated with the study of stratum, strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are ...

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

(a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) in southwest

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. The name is derived from the village of

Aylesbeare Aylesbeare is a village and civil parish in the East Devon district of Devon, England, east of Exeter. According to the 2001 census the parish, which includes the hamlet of Nutwalls, had a population of 527. Known for the Site of Special Scienti ...

in east

Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...

. The Group comprises the Littleham Mudstone Formation, the Exmouth Mudstone and Sandstone Formation and the underlying Clyst St Lawrence Formation. The

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

are exposed on the coast between

Exmouth Exmouth is a harbor, port town, civil parishes in England, civil parish and seaside resort, sited on the east bank of the mouth of the River Exe and southeast of Exeter. In 2011 it had a population of 34,432, making Exmouth the List of town ...

and

Budleigh Salterton Budleigh Salterton is a seaside town on the coast in East Devon, England, south-east of Exeter. It lies within the East Devon Area of Outstanding Natural Beauty, and forms much of the electoral ward of Budleigh, whose ward population at t ...

where the

type section A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...

is defined. The rocks of the Aylesbeare Mudstone Group have also previously been known as the Aylesbeare Group and the Aylesbeare Mudstone Formation.

Stratigraphy

Exmouth Mudstone and Sandstone Formation

Around 200 - 255m of silty

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

s between the coast near Exmouth north to Aylesbeare, beyond which it is not separately mapped. It includes numerous

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

lenses which can be up to 30m thick. This sequence has been known by various names in the past including the Exmouth Sandstones, Exmouth Formation and the Exmouth Mudstone and Sandstone Member amongst others. The type section is in the coastal exposures between Exmouth and Straight Point.

Littleham Mudstone Formation

Around 200m of silty mudstone in the Exeter area rising to 275m thickness on the coast between

Littleham Littleham is a village and civil parish in the Torridge district of north Devon in south west England, about south of Bideford. The parish had a population of 446 at the 2011 census. The parish is bounded by the River Torridge in the north-eas ...

Cove and Budleigh Salterton (type section). The formation has been mapped northwards from Littleham to the vicinity of Aylesbeare but is not separately distinguished beyond there. This sequence has previously been referred to variously as the Littleham Beds, the Littleham Formation and the Littleham Mudstones.

Clyst St Lawrence Formation

The formation comprises between 30 and 50m of sand and silt, representing weathered sandstone and siltstone, at outcrop between the east Devon hamlets of Westwood and Mutterton.

References

{{Reflist Triassic System of Europe Lower Triassic Series Geology of Devon Geological groups of the United Kingdom