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The '''Lias Group''' or '''Lias''' is a [[lithostratigraphy|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 [[Sediment#Shores_and_shallow_seas|marine]] [[limestone]]s, [[shale]]s, [[marl]]s and [[clay]]s.
{{short description|Sequence of rock strata found in a large area of western Europe}}
{{Other uses|Lias (disambiguation){{!}}Lias}}
{{Triassic lithostratigraphy Europe}}
The '''Lias Group''' or '''Lias''' is a [[lithostratigraphy|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 [[Sediment#Shores and shallow seas|marine]] [[limestone]]s, [[shale]]s, [[marl]]s and [[clay]]s.


In the past, the name Lias was often not only used 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]] [[Series (stratigraphy)|epoch]] of the [[geologic timescale]]. We now know that the Lias is [[Rhaetian]] to [[Toarcian]] in age (over a period of ca. 20 million years between [http://toolserver.org/~verisimilus/Timeline/Timeline.php?Ma=200-180 200 and 180 million years ago]) and thus also includes a part of the [[Triassic]]. The use of the name "Lias" for a unit of time is therefore slowly disappearing.
''Lias'' is a Middle English term for hard limestone, used in this specific sense by geologists since 1833.<ref>''Oxford English Dictionary'', ''s.v.'' "lias".</ref> 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]] [[Series (stratigraphy)|epoch]] of the [[geologic timescale]]. It is now more specifically known that the Lias is [[Rhaetian]] to [[Toarcian]] in age (over a period of {{circa}} 20 million years between {{Ma|200|180}}) and thus also includes a part of the [[Triassic]]. The use of the name "Lias" for a unit of time is therefore slowly disappearing.


==Subdivisions==
==Subdivisions==
In southern [[England]], the Lias Group is often divided into Lower, Middle and Upper subgroups. In [[Somerset]] the Lias is divided into the following [[formation (stratigraphy)|formations]] (from top to base):
In southern [[England]], the Lias Group is often divided into Lower, Middle and Upper subgroups. In Southern England the Lias is divided into the following [[formation (stratigraphy)|formations]] (from top to base):

*[[Helwell Marl]]
* [[Bridport Sand Formation|Bridport Sand]]
*[[Doniford Shale]]
* [[Beacon Limestone Formation|Beacon Limestone]]
*[[Quantock Beds]]
*[[Kilve Shale]]
* [[Dyrham Formation]]
*[[Blue Lias]]
* [[Charmouth Mudstone]]
*[[St. Audries Shale]]
* [[Blue Lias]]

*[[Aldergrove Beds]]
In the East Midlands Shelf the Lias is divided into the following [[formation (stratigraphy)|formations]] (from top to base):
⚫
It is underlain by the Late Triassic [[Penarth Group]],<ref>[http://www.fossilsgalore.com/somerset_geological_timeline.htm Somerset Geological TimeLine], fossilgalore.com</ref> and overlain, after a [[Lithostratigraphy#Stratigraphic relationship|stratigraphic hiatus]], by the [[Early Cretaceous]] [[Upper Greensand]] Formation.

* [[Whitby Mudstone]]
* [[Marlstone Rock Formation|Marlstone Rock]]
* Charmouth Mudstone
* [[Scunthorpe Mudstone]]

In the [[Cleveland Basin]] in Yorkshire the Lias is divided into the following [[formation (stratigraphy)|formations]] (from top to base):

* Whitby Mudstone
* [[Cleveland Ironstone Formation|Cleveland Ironstone]]
* [[Staithes Sandstone Formation|Staithes Sandstone]]
* [[Redcar Mudstone Formation|Redcar Mudstone]]

In [[South Wales]] only the Blue Lias is present.

⚫
The Lias is underlain by the Late Triassic [[Penarth Group]],<ref>[https://web.archive.org/web/20110711021202/http://www.fossilsgalore.com/somerset_geological_timeline.htm Somerset Geological TimeLine], fossilgalore.com</ref> and overlain by the [[Inferior Oolite]] in most of England and the [[Dogger Formation]] or [[Ravenscar Group]] in the Cleveland Basin. In some areas there is a [[Lithostratigraphy#Stratigraphic relationship|stratigraphic hiatus]], and the rocks are overlain by Cretaceous marine sediments.

There are restricted outcrops of Lias rocks on the west coast of [[Scotland]] where, in the Sea of the Hebrides depositional basin on [[Skye]], [[Raasay]] and [[Isle of Mull|Mull]], the [[Broadford Beds Formation]], [[Pabay Shale Formation]] and overlying [[Scalpay Sandstone Formation]] are assigned to the Lias Group.<ref>{{cite web|url=http://mapapps.bgs.ac.uk/geologyofbritain/home.html?|title=Geology of Britain viewer|author=British Geological Survey (BGS)|website=mapapps.bgs.ac.uk}}</ref><ref>{{cite web|url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=SCS|title=BGS Lexicon of Named Rock Units|website=www.bgs.ac.uk}}</ref><ref>{{cite web|url=http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=PABS|title=BGS Lexicon of Named Rock Units|website=www.bgs.ac.uk}}</ref><ref>{{cite web|url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BFB|title=BGS Lexicon of Named Rock Units|website=www.bgs.ac.uk}}</ref>


In [[Netherlands|Dutch]] 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.<ref>See for example Wong (2007)</ref>
In [[Netherlands|Dutch]] 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.<ref>See for example Wong (2007)</ref>


In northern Germany, the Lias Group consists of nine formations (from top to base):<ref>Deutsche Stratigraphische Kommission (eds.): [http://www.gfz-potsdam.de/portal/-?$part=binary-content&id=1809196&status=300&language=en ''Stratigraphische Tabelle von Deutschland 2002''] (stratigraphic tables of the German commission on stratigraphy), Potsdam 2002, ISBN 3-00-010197-7 (PDF: 6,57 MB)</ref>
In northern Germany, the Lias Group consists of nine formations (from top to base):<ref>Deutsche Stratigraphische Kommission (eds.): [http://www.gfz-potsdam.de/portal/-?$part=binary-content&id=1809196&status=300&language=en ''Stratigraphische Tabelle von Deutschland 2002''] {{Webarchive|url=https://web.archive.org/web/20081025174855/http://www.gfz-potsdam.de/portal/-?$part=binary-content&id=1809196&status=300&language=en |date=2008-10-25 }} (stratigraphic tables of the German commission on stratigraphy), Potsdam 2002, {{ISBN|3-00-010197-7}} (PDF: 6.57 MB)</ref>


*[[Opalinuston]]
* [[Opalinuston]]
*[[Dörnten-Formation]]
* [[Dörnten-Formation]]
*[[Posidonia Shale]]
* [[Posidonia Shale]]
*[[Amaltheenton]]
* [[Amaltheenton Formation|Amaltheenton]]
*[[Capricornu-Formation]]
* [[Capricorn Formation]]
*[[Raricostaten-Formation]]
* [[Raricostaten-Formation]]
*[[Arieten Sandstone]]
* [[Arietenkalk Formation|Arieten Sandstone]]
*[[Liassicus Sandstone]]
* [[Liassicus Sandstone]]
*[[Psilonoten Sandstone]]
* [[Psilonoten Sandstone]]


==See also==
==See also==
*[[White lias]]
*[[Blue Lias]]
* [[White lias]]


==References==
===Notes===
===Notes===
{{reflist}}
{{reflist}}


===Literature===
===Literature===
*{{aut|Wong, Th.E.}}, 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]], pp. 107–125.
* {{aut|Wong, Th.E.}} (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]], pp.&nbsp;107–125.


[[Category:Early Jurassic Europe]]
[[Category:Jurassic geology]]
[[Category:Jurassic England]]
[[Category:Jurassic Germany]]
[[Category:Lithostratigraphy of England]]
[[Category:Lithostratigraphy of England]]
[[Category:Jurassic]]
[[Category:Lithostratigraphy of Germany]]
[[Category:Jurassic System of Europe]]

[[de:Lias]]
[[nl:Lias (tijdvak)]]

Latest revision as of 19:06, 3 September 2022

For other uses, see Lias.
System Series Stage Age (Ma) European lithostratigraphy
Jurassic Lower Hettangian younger Lias
Triassic Upper Rhaetian 201.4–208.5
Keuper
Norian 208.5–227.0
Carnian 227.0–237.0
Middle Ladinian 237.0–242.0
Muschelkalk
Anisian 242.0–247.2
Bunter or Buntsandstein
Lower Olenekian 247.2–251.2
Induan 251.2–251.9
Permian Lopingian Changhsingian older
Zechstein
Major lithostratigraphic units of northwest Europe with the ICS's geologic timescale of the Triassic.[1]

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, shales, marls and clays.

Lias is a Middle English term for hard limestone, used in this specific sense by geologists since 1833.[2] 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 epoch of the geologic timescale. It is now more specifically known that the Lias is Rhaetian to Toarcian in age (over a period of c. 20 million years between 200 to 180 million years ago) and thus also includes a part of the Triassic. The use of the name "Lias" for a unit of time is therefore slowly disappearing.

Subdivisions

[edit]

In southern England, 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):

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

In the Cleveland Basin in Yorkshire the Lias is divided into the following formations (from top to base):

In South Wales only the Blue Lias is present.

The Lias is underlain by the Late Triassic Penarth Group,[3] and overlain by the Inferior Oolite 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 where, in the Sea of the Hebrides depositional basin on Skye, Raasay and Mull, the Broadford Beds Formation, Pabay Shale Formation and overlying Scalpay Sandstone Formation are assigned to the Lias Group.[4][5][6][7]

In Dutch 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.[8]

In northern Germany, the Lias Group consists of nine formations (from top to base):[9]

See also

[edit]

References

[edit]

Notes

[edit]
  1. ^ Ogg, James G.; Ogg, Gabi M.; Gradstein, Felix M. (2016). "Triassic". A Concise Geologic Time Scale: 2016. Elsevier. pp. 133–149. ISBN 978-0-444-63771-0.
  2. ^ Oxford English Dictionary, s.v. "lias".
  3. ^ Somerset Geological TimeLine, fossilgalore.com
  4. ^ British Geological Survey (BGS). "Geology of Britain viewer". mapapps.bgs.ac.uk.
  5. ^ "BGS Lexicon of Named Rock Units". www.bgs.ac.uk.
  6. ^ "BGS Lexicon of Named Rock Units". www.bgs.ac.uk.
  7. ^ "BGS Lexicon of Named Rock Units". www.bgs.ac.uk.
  8. ^ See for example Wong (2007)
  9. ^ Deutsche Stratigraphische Kommission (eds.): Stratigraphische Tabelle von Deutschland 2002 Archived 2008-10-25 at the Wayback Machine (stratigraphic tables of the German commission on stratigraphy), Potsdam 2002, ISBN 3-00-010197-7 (PDF: 6.57 MB)

Literature

[edit]
  • Wong, Th.E. (2007): Jurassic, in: Wong, Th.E.; Batjes, D.A.J. & Jager, J. de (eds.): Geology of the Netherlands, Royal Netherlands Academy of Arts and Sciences, pp. 107–125.
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