Editing Old Red Sandstone (section)

== Sedimentology ==
[[File:OldRedSandstoneBeddingPlane.jpg|thumb|[[Bed (geology)|Bedding]] plane of Old Red Sandstone with [[quartz]] and [[chert]] pebbles, central England; scale bar is 10 mm]]

The Old Red Sandstone describes a group of [[sedimentary rock]]s deposited in a variety of environments in the late [[Silurian]], through  the [[Devonian]] and into the earliest part of the [[Carboniferous]]. The body of [[Rock (geology)|rock]], or [[facies]], is dominated by [[Terrigenous deposit|terrigenous deposits]] and [[conglomerate (geology)|conglomerates]] at its base, and progresses to a combination of [[dune]]s, and sediments that may have been laid down in [[lake]]s, [[river]], estuaries, and possibly other coastal environments. The Old Red Sandstone was long thought to have been deposited mostly in freshwater, but more recent studies have discovered marine fossils (such as [[Brachiopod|brachiopods]])<ref name="Goujet & Emig 1985">{{cite journal |last1=Goujet |first1=D |last2=Emig |first2=C. C. |title=Des Lingula fossiles, indicateurs de modifications de l'environnement dans un gisement du Dévonien inférieur du Spitsberg |journal=Des Lingula fossiles, indicateurs de modifications de l'environnement dans un gisement du Dévonien inférieur du Spitsberg |date=1985 |volume=301 |issue=13 |pages=945–948 |url=http://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=8419776 |issn=0764-4450}}</ref> in some locations. Its vertebrate fauna also occurs in typically marine environments,<ref name="Janvier 2007">{{cite journal |last1=Janvier |first1=Philippe |title=Living Primitive Fishes and Fishes From Deep Time |journal=Fish Physiology |date=1 January 2007 |volume=26 |pages=1–51 |doi=10.1016/s1546-5098(07)26001-7 |url=https://doi.org/10.1016/S1546-5098(07)26001-7 |publisher=Academic Press|isbn=978-0-12-373671-0 |url-access=subscription }}</ref> and an [[Isotope geochemistry|isotopic]] study also found significant marine influence indicating a [[Brackish water|brackish]] environment in mineralised tissues of its vertebrates,<ref name="Goedert et al. 2018">{{cite journal |last1=Goedert |first1=Jean |last2=Lécuyer |first2=Christophe |last3=Amiot |first3=Romain |last4=Arnaud-Godet |first4=Florent |last5=Wang |first5=Xu |last6=Cui |first6=Linlin |last7=Cuny |first7=Gilles |last8=Douay |first8=Guillaume |last9=Fourel |first9=François |last10=Panczer |first10=Gérard |last11=Simon |first11=Laurent |last12=Steyer |first12=J.-Sébastien |last13=Zhu |first13=Min |title=Euryhaline ecology of early tetrapods revealed by stable isotopes |journal=Nature |date=June 2018 |volume=558 |issue=7708 |pages=68–72 |doi=10.1038/s41586-018-0159-2 |pmid=29849142 |bibcode=2018Natur.558...68G |url=https://doi.org/10.1038/s41586-018-0159-2 |language=en |issn=1476-4687|url-access=subscription }}</ref> even in taxa that had long been thought to have been freshwater inhabitants.<ref name="George & Blieck 2011">{{cite journal |last1=George |first1=David |last2=Blieck |first2=Alain |title=Rise of the Earliest Tetrapods: An Early Devonian Origin from Marine Environment |journal=PLOS ONE |date=14 July 2011 |volume=6 |issue=7 |pages=e22136 |doi=10.1371/journal.pone.0022136|doi-access=free |pmid=21779385 |bibcode=2011PLoSO...622136G }}</ref><ref name="Laurin 2024">{{cite journal |last1=Laurin |first1=Michel |title=Habitat of early stegocephalians (Chordata, Vertebrata, Sarcopterygii): a little saltier than most paleontologists like? |journal=Fossil Record |date=30 December 2024 |volume=27 |issue=3 |pages=299–332 |doi=10.3897/fr.27.123291 |doi-access=free |language=en |issn=2193-0074}}</ref> Thus, at least some strata appear to have been deposited on the coast, probably in marginal marine environments.

The familiar red colour of these rocks arises from the presence of [[iron oxide]], but not all the Old Red Sandstone is red or sandstone{{snd}}the sequence also includes conglomerates, [[mudstones]], [[siltstones]] and thin [[limestones]] and colours can range from grey and green through to red and purple.  These deposits are closely associated with the erosion of the Caledonian Mountain chain which was thrown up by the collision of the former continents of [[Avalonia]], [[Baltica]] and [[Laurentia]] to form the [[Old Red Sandstone Continent]]- an event known as the [[Caledonian Orogeny]].

Many fossils are found within the rocks, including early fishes, arthropods and plants. As is typical with terrestrial [[red beds]], the vast majority of the rock is not fossil-bearing; however there are isolated, localized beds within the rock that do contain fossils. Rocks of this age were also laid down in [[South West England]] (hence the name 'Devonian'; from [[Devon]]) though these are of true marine origin and are not included within the Old Red Sandstone.<ref name=Barclay>{{cite book | last = Barclay | first = W.J. | title = The Old Red Sandstone of Great Britain | publisher = Joint Nature Conservation Committee (JNCC) | location = City | year = 2005 | isbn = 978-1-86107-543-7 |url=http://www.jncc.gov.uk/page-2936}}</ref>