The Lias Group or Lias is a

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

unit (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 ...

) found in a large area of western Europe, including the

British Isles The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...

, the

North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...

, the

Low Countries The Low Countries (; ), historically also known as the Netherlands (), is a coastal lowland region in Northwestern Europe forming the lower Drainage basin, basin of the Rhine–Meuse–Scheldt delta and consisting today of the three modern "Bene ...

and the north of

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

. It consists of marine

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...

s and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

s. ''Lias'' is a Middle English term for hard limestone, used in this specific sense by geologists since 1833. In the past, geologists used ''Lias'' not only for the sequence of rock layers, but also for the timespan during which they were formed. It was thus an alternative name for the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

of the

geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...

. It is now more specifically known that the Lias is

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

in age (over a period of 20 million years between ) and thus also includes a part of the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

. The use of the name "Lias" for a unit of time is therefore slowly disappearing.

Subdivisions

In southern

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 ...

, the Lias Group is often divided into Lower, Middle and Upper subgroups. In Southern England the Lias is divided into the following formations (from top to base): * Bridport Sand *

Beacon Limestone The Beacon Limestone Formation, historically known as the Junction Bed, is a formation (geology), formation of the early Jurassic age (Pliensbachian–Toarcian). It lies above the Dyrham Formation and below the Bridport Sand Formation. It forms p ...

Dyrham Formation The Dyrham Formation is a geologic formation in England. It preserves fossils dating back to the early part of the Jurassic period (Pliensbachian). See also * List of fossiliferous stratigraphic units in England See also * Lists of fossil ...

Charmouth Mudstone The Charmouth Mudstone Formation is a Formation (geology), geological formation in England, dating to the Early Jurassic (Sinemurian–Pliensbachian). It forms part of the lower Lias Group. It is most prominently exposed at its type locality in cl ...

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 ...

In the East Midlands Shelf the Lias is divided into the following formations (from top to base): *

Whitby Mudstone The Whitby Mudstone is a Toarcian (Early Jurassic; ''Falciferum''-''Bifrons'' in regional chronostratigraphy) geological formation in Yorkshire and Worcestershire, England.Marlstone Rock * Charmouth Mudstone *

Scunthorpe Mudstone The Scunthorpe Mudstone is a geologic formation in England. It preserves plesiosaur fossils dating back to the Late Triassic (Rhaetian) to Early Jurassic (Hettangian) period. It predominantly consists of grey mudstone with thin beds of argillaceo ...

In the

Cleveland Basin The Cleveland Basin is a sedimentary basin in Yorkshire, England. Formed initially by rifting during the Mississippian period of the Early Carboniferous. It is West–East trending and lies between the intrabasinal highs of the Askrigg Block a ...

in Yorkshire the Lias is divided into the following formations (from top to base): * Whitby Mudstone * Cleveland Ironstone * Staithes Sandstone * Redcar Mudstone In

South Wales South Wales ( ) is a Regions of Wales, loosely defined region of Wales bordered by England to the east and mid Wales to the north. Generally considered to include the Historic counties of Wales, historic counties of Glamorgan and Monmouthshire ( ...

only the Blue Lias is present. The Lias is underlain by the Late Triassic

Penarth Group The Penarth Group is a Rhaetian age (Triassic) lithostratigraphic group (a sequence of rock strata) which is widespread in Britain. It is named from the seaside town of Penarth near Cardiff in south Wales where strata of this age are exposed in ...

, and overlain by the

Inferior Oolite The Inferior Oolite is a sequence of Jurassic age sedimentary rocks in Europe. It was deposited during the Middle Jurassic.Weishampel, David B; et al. (2004). "Dinosaur distribution (Middle Jurassic, Europe)." In: Weishampel, David B.; Dodson, Pet ...

in most of England and the

Dogger Formation Dogger may refer to: Places * Dogger Bank, a large shallow area in the North Sea between Britain and Denmark ** Dogger, a sea area in the North Sea, noted in shipping forecasts within the Dogger Bank People Individuals * Paul Dogger (1971), a ...

Ravenscar Group The Ravenscar Group is a Jurassic lithostratigraphic group (a sequence of rock strata) found within the Cleveland Basin of North Yorkshire, extending into both the Hambleton and Howardian Hills. The name is derived from Ravenscar on the North Y ...

in the Cleveland Basin. In some areas there is a stratigraphic hiatus, and the rocks are overlain by Cretaceous marine sediments. There are restricted outcrops of Lias rocks on the west coast of

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

where, in the Sea of the Hebrides depositional basin on

Skye The Isle of Skye, or simply Skye, is the largest and northernmost of the major islands in the Inner Hebrides of Scotland. The island's peninsulas radiate from a mountainous hub dominated by the Cuillin, the rocky slopes of which provide some o ...

Raasay Raasay (; ), sometimes the Isle of Raasay, is an island between the Isle of Skye and the mainland of Scotland. It is separated from Skye by the Sound of Raasay and from Applecross by the Inner Sound, Scotland, Inner Sound. It is famous fo ...

and

Mull Mull may refer to: Places *Isle of Mull, a Scottish island in the Inner Hebrides ** Sound of Mull, between the Isle of Mull and the rest of Scotland * Mount Mull, Antarctica * Mull Hill, Isle of Man * Mull, Arkansas, a place along Arkansas Highwa ...

, the Broadford Beds Formation, Pabay Shale Formation and overlying Scalpay Sandstone Formation are assigned to the Lias Group. In

Dutch Dutch or Nederlands commonly refers to: * Something of, from, or related to the Netherlands ** Dutch people as an ethnic group () ** Dutch nationality law, history and regulations of Dutch citizenship () ** Dutch language () * In specific terms, i ...

lithostratigraphy, the name Lias has no official status, however, it is often used for the lower part of the Altena Group in the subsurface of the Netherlands and the southern North Sea. In northern Germany, the Lias Group consists of nine formations (from top to base):Deutsche Stratigraphische Kommission (eds.)
''Stratigraphische Tabelle von Deutschland 2002''
(stratigraphic tables of the German commission on stratigraphy), Potsdam 2002, (PDF: 6.57 MB) * Opalinuston * Dörnten-Formation *

Posidonia Shale The Posidonia Shale (, also called Schistes Bitumineux in Luxembourg) geologically known as the Sachrang Formation, is an Early Jurassic (Early to Late Toarcian) geological formation in Germany, northern Switzerland, northwestern Austria, souther ...

* Amaltheenton * Capricorn Formation * Raricostaten-Formation * Arieten Sandstone * Liassicus Sandstone * Psilonoten Sandstone

References

Notes

Literature

* (2007): ''Jurassic'', in: {{aut, Wong, Th.E.; Batjes, D.A.J. & Jager, J. de (''eds.''): ''Geology of the Netherlands'',

Royal Netherlands Academy of Arts and Sciences The Royal Netherlands Academy of Arts and Sciences (, KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands. The academy is housed in the Trippenhuis in Amsterdam. In addition to various advisory a ...

, pp. 107–125. Early Jurassic Europe Jurassic geology Jurassic England Jurassic Germany Lithostratigraphy of England Lithostratigraphy of Germany Jurassic System of Europe