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 igneou ...
unit (a sequence of rock strata) found in a large area of western Europe, including the
British Isles
The British Isles are a group of islands in the 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 and Outer Hebrides, the Northern Isles, ...
, the
North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...
, the
Low Countries
The term Low Countries, also known as the Low Lands ( nl, de Lage Landen, french: les Pays-Bas, lb, déi Niddereg Lännereien) and historically called the Netherlands ( nl, de Nederlanden), Flanders, or Belgica, is a coastal lowland region in N ...
and the north of
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
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-J ...
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 by ...
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 geochr ...
. It is now more specifically known that the Lias is Rhaetian to
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.
The Toarcian ...
in age (over a period of 20 million years between ) and thus also includes a part of the
Triassic
The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
. The use of the name "Lias" for a unit of time is therefore slowly disappearing.
Subdivisions
In southern
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 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
*
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 geological formation in England. It preserves fossils dating back to the early part of the Jurassic period (Sinemurian–Pliensbachian). It forms part of the lower Lias Group. It is most prominently exposed at ...
*
Blue Lias
The Blue Lias is a 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 Triassic and early Jurassi ...
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 and t ...
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 or Ravenscar Group 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. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...
where, in the Sea of the Hebrides depositional basin on Skye,
Raasay
Raasay (; gd, Ratharsair) or 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. It is famous for being the birt ...
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 Highway ...
Dutch
Dutch commonly refers to:
* Something of, from, or related to the Netherlands
* Dutch people ()
* Dutch language ()
Dutch may also refer to:
Places
* Dutch, West Virginia, a community in the United States
* Pennsylvania Dutch Country
People E ...
lithostratigraphy, the name Lias has no official status, however, it is often used for the lower part of the
Altena Group
Altena (; Westphalian language, Westphalian: ''Altenoa'') is a town in the district of Märkischer Kreis, North Rhine-Westphalia, Germany. The town's castle is the origin for the later Dukes of Berg. Altena is situated on the Lenne river valley, i ...
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 (german: Posidonienschiefer, also called Schistes Bitumineux in Luxembourg) geologically known as the Sachrang Formation, is an Early Jurassic (Toarcian) geological formation of southwestern and northeast Germany, northern Swit ...
Blue Lias
The Blue Lias is a 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 Triassic and early Jurassi ...