|System||Series||Stage||Age (Ma)||European lithostratigraphy|
|Bunter or Buntsandstein|
|Major lithostratigraphic units of northwest Europe with the ICS's geologic timescale of the Triassic.|
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. 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 ) and thus also includes a part of the Triassic. The use of the name "Lias" for a unit of time is therefore slowly disappearing.
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.
In northern Germany, the Lias Group consists of nine formations (from top to base):
- Posidonia Shale
- Arieten Sandstone
- Liassicus Sandstone
- Psilonoten Sandstone
- 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 Geological TimeLine, fossilgalore.com
- 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)
- 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.