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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
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
Jurassic
epoch of the geologic timescale. It is now more specifically known that the Lias is Rhaetian
Rhaetian
to Toarcian
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.

Contents

1 Subdivisions 2 See also 3 References

3.1 Notes 3.2 Literature

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

Helwell Marl Doniford Shale Quantock Beds Kilve Shale Blue Lias St. Audries Shale Aldergrove Beds

It is underlain by the Late Triassic
Triassic
Penarth Group,[3] and overlain, after a stratigraphic hiatus, by the Early Cretaceous Upper Greensand Formation. There are restricted outcrops of Lias rocks on the west coast of Scotland
Scotland
where, in the Sea of the Hebrides depositional basin on Skye, Raasay
Raasay
and Mull, the Broadford Beds Formation, Pabay Shale
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
Netherlands
and the southern North Sea.[8] In northern Germany, the Lias Group consists of nine formations (from top to base):[9]

Opalinuston Dörnten-Formation Posidonia Shale Amaltheenton Capricornu-Formation Raricostaten-Formation Arieten Sandstone Liassicus Sandstone Psilonoten Sandstone

See also[edit]

Blue Lias White lias

References[edit] Notes[edit]

^ Gradstein, F.M.; Ogg, J.G.; Smith, A.G. (2005), A Geologic Time Scale 2004, Cambridge University Press, ISBN 9780521786737  ^ Oxford English Dictionary, s.v. "lias". ^ Somerset
Somerset
Geological TimeLine[permanent dead link], fossilgalore.com ^ http://mapapps.bgs.ac.uk/geologyofbritain/home.html? ^ http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=SCS ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=PABS ^ http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BFB ^ See for example Wong (2007) ^ Deutsche Stratigraphische Kommission (eds.): Stratigraphische Tabelle von Deutschland 2002 (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, p

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