Old Red Sandstone

Old Red Sandstone
Name	Old Red Sandstone
Period	Devonian
Type	Sedimentary rock sequence
Lithology	Sandstone, conglomerate, siltstone, shale, mudstone
Namedfor	Caledonian orogeny region
Namedby	Hugh Miller
Region	Northwestern Europe, North America

Old Red Sandstone The Old Red Sandstone is a Devonian-age terrestrial sedimentary sequence notable for its fluvial, lacustrine, and alluvial deposits and for preserving early vertebrate and plant assemblages. It underpins key geological interpretations linked to the Caledonian orogeny, Variscan orogeny, Emsian and Frasnian stages and has been studied in contexts including the Silurian–Devonian transition, the Rhenish Massif, and the Appalachian Mountains. Research on the sequence has involved fieldwork at sites such as Shetland Islands, Scotland, Wales, Norway, and parts of Greenland and Newfoundland and Labrador.

Geology and Stratigraphy

The stratigraphic architecture of the Old Red Sandstone is framed by basin development during the Caledonian orogeny with subsequent modification during the Variscan orogeny and is correlated with units in the Munchener Bucht, Armorican Massif, and the Appalachian Basin. Regional schemes use stage names like Lochkovian, Pragian, Emsian, Eifelian, Givetian, Frasnian, and Famennian to subdivide successions tied to formations mapped in Caithness, Sutherland, Pembrokeshire, and Cornwall. Sequence stratigraphy integrates data from the Old Red Sandstone Supergroup with unconformities related to the Scandian phase and with synorogenic conglomerates adjacent to terranes such as Avalonia and Laurentia.

Lithology and Sedimentary Environments

Lithological assemblages include arkosic sandstones, multicolored siltstones, fining-upward fluvial cycles, braided-channel conglomerates, playa-lake mudstones, and episodic tufas associated with hydrothermal springs in rift settings. Sediment provenance studies point to sources in uplifted blocks tied to the Grampian Highlands, Iapetus Ocean closure terranes, and crystalline basement exposures like the Lewisian complex and Moine Supergroup. Paleocurrent indicators correlate with depositional systems reconstructed in the Orkney Islands and along strike to basins adjacent to Baltica and Laurentia.

Age and Correlation

Biostratigraphic and radiometric constraints tie the sequence to the Devonian Period, ranging roughly from the Lochkovian through the Famennian. Correlations have been made with the Old Red Sandstone of North America equivalents in the Mackenzie Mountains and the Newfoundland Appalachians, and with coeval sequences in the Rhenohercynian Zone and Bohemian Massif. Zircon U–Pb dating from interbedded tuffs and detrital populations has been used alongside palynology from basins such as Lothian and Galloway to refine age models.

Paleontology and Fossil Assemblages

The rock record contains diverse vertebrate fauna including early sarcopterygians, osteichthyans, placoderms, and early tetrapodomorphs documented from localities like Gilmore, Scotland, East Kirkton and Rhynie Chert analogues, with plant assemblages of lycophytes and progymnosperms comparable to those in the Devonian plant radiation. Trace fossils, coprolites, and preserved freshwater bivalves and arthropods provide paleoecological context similar to assemblages studied in the Eifel and Old Red Sandstone of Norway. Important fossil producers include lagerstätten and bonebeds that have been tied to macroevolutionary events such as the Devonian nekton revolution and vertebrate terrestrialization episodes.

Distribution and Regional Occurrences

Exposures occur across the British Isles (notably Caithness, Shetland Islands, Pembrokeshire, and Anglesey), in Scandinavia (including Norway and Sweden), in the Faroe Islands, in Greenland, and in parts of eastern North America (notably Newfoundland and Labrador and the Maritimes Basin). Correlative basins include the Munster Basin, the Rhineland Basin, the Mackenzie Basin, and rifted margins adjacent to the closure of the Iapetus Ocean and the assembly of Euramerica.

Economic Uses and Quarrying

Sandstones within the sequence have been quarried historically for building stone in towns such as Edinburgh, Dundee, Aberdeen, St Davids and St Ives and used in infrastructure projects in London and Bristol. Conglomerates and flagstones have supplied dimension stone and paving material exported via ports like Leith and Bristol Harbour. Resource assessments have evaluated reservoir potential for shallow groundwater and for conventional hydrocarbons in basins such as the North Sea periphery and exploration drilling has targeted porosity/permeability trends recognized in the Permian Basin analogue studies.

History of Research and Nomenclature

Early study of the sequence involved pioneers such as Hugh Miller, Roderick Murchison, Adam Sedgwick, and Charles Lapworth who worked across localities in Scotland, Wales, and England while debates over the Devonian system intersected with rivalries between proponents of the Silurian and Old Red Sandstone concepts. Stratigraphic nomenclature evolved through contributions from the British Geological Survey, regional geological surveys of Norway and Greenland, and international committees like the International Commission on Stratigraphy which standardized correlations using global stage names. Modern syntheses draw on work by researchers affiliated with institutions such as the Natural History Museum, London, the University of Edinburgh, the University of Oxford, and the University of Cambridge.

Category:Geologic formations