Old Red Sandstone

The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also extends northwards into Greenland and Svalbard.[3] These areas were a part of the ancient continent of Euramerica/Laurussia. In Britain it is a lithostratigraphic unit (a sequence of rock strata) to which stratigraphers accord supergroup status[4] and which is of considerable importance to early paleontology. For convenience the short version of the term, ORS is often used in literature on the subject. The term was coined to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain.

Old Red Sandstone
Stratigraphic range: Late Silurian-earliest Carboniferous 419–358 Ma
Folded Old Red Sandstone rock formation at St Annes Head in Pembrokeshire, Wales
Sub-unitsSee text
ThicknessMore than 4 km (13,000 ft) (Shetlands)
OtherConglomerate, shale, mudstone, siltstone, limestone
RegionNorth Atlantic
CountryCanada, Greenland, Ireland, Norway, United Kingdom
Extent700 km (430 mi)[1]
Hutton's angular unconformity at Siccar Point where 370-million-year-old Devonian Old Red Sandstone overlies 435-million-year-old Silurian greywacke.[2]