New Red Sandstone

New Red Sandstone
Stratigraphic range: Permian to Triassic
Thickness up to 2000 metres
Lithology
Primary sandstone
Other arkose, conglomerate, breccio-conglomerate
Location
Region Global
Country United Kingdom
Extent Originally in Scotland, range extended to all red-bed sequences of Permian and Triassic age in southwest England, and parts of northwest and northeast England.
Exeter, Devon, ancient city walls of Isca Dumnoniorum with medieval and Roman elements

The New Red Sandstone, chiefly in British geology, is composed of beds of red sandstone and associated rocks laid down throughout the Permian (280 million years ago) to the end of the Triassic (about 200 million years ago), that underlie the Jurassic-Triassic age Penarth Group.[1] The name distinguishes it from the Old Red Sandstone which is largely Devonian in age, and with which it was originally confused due to their similar composition.

Its upper layers consist of mudstones, but most of the formation consists of reddish to yellowish sandstones, interbedded with rare evaporite minerals such as halite and gypsum. These indicate deposition within a hot and arid palaeo-environment, e.g. a desert or sabkha.[2]

Geographical distribution

The New Red Sandstone was originally identified in Scotland, at quarries in Elgin. It covers large parts of the Moray Firth Basin. In this area it overlies the Old Red Sandstone unconformably (missing the intervening rocks), and both sandstones were used extensively in architecture in the Highlands and Islands of Scotland. It also covers much of central England, where it generally forms a low-lying plain except for the Mid Severn Sandstone Plateau. Thick layers (up to 1100 m thick) are present in the faulted Cheshire Basin which also extends beneath north Shropshire. There are numerous escarpments forming small prominent hills within this area. The sandstone also underlies parts of Lancashire and Cumbria, and east of the Pennines it extends through Nottinghamshire and central Yorkshire. Smaller outcrops occur in other parts of Britain such as the Red Cliffs of Dawlish and East Devon.

Lithology

In terms of its lithology, the New Red Sandstone comprises true sandstones, mudrocks and evaporite strata[1]. The sandstone units are monomineralic, consisting only of quartz grains (negligible amounts of other minerals may be present), and they are cemented together with the ferric iron oxide haematite (Fe2O3). The presence of this particular iron oxide is evidence for a terrestrial environment of deposition such as a desert, and gives the rocks the red colour which they are named after. The common effect of rusting produces exactly the same deposit, but as a result of a different process. The sandstone units generally lack fossils (as do most terrestrial rocks). The grains in the member have a high degree of sphericity, are very well sorted and typically have a small size range (0.5 mm to 2 mm).

The NRS is a texturally mature rock. Certain units of the New Red Sandstone (e.g. Hopeman Sandstone Formation and Helsby Sandstone Formation) feature commonly as building stone in due to their abundance and mechanical strength.

Fossils

The New Red Sandstone has yielded many fossils, including the world famous Elgin Reptiles. These are late Permian to earliest Triassic in age, and include mammal-like reptiles and some of the earliest predecessors of dinosaurs.[2]

Building uses

Exeter Castle, Devon, c1068 Anglo-Saxon and Norman elements of New Red Sandstone with reused earlier Roman elements

Many ancient buildings of Devon Red Sandstone can be found in Exeter the ancient capital of Devon,[3] notably the castle, Roman / medieval city walls, several churches and many buildings of the Cathedral Close. The local quarry was at Heavitree by which name the local sandstone - actually a type of breccia - is generally known.[4]

See also

References

  1. 1 2 http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=NRS
  2. 1 2 Benton MJ and Walker AD. 1985. Palaeoecology, taphonomy and dating of Permo-Triassic reptiles from Elgin, North-East Scotland. Palaeontology 28:207-234.
  3. ↑ http://www.devon.gov.uk/geo-devonrocksgeologyguide.pdf
  4. ↑ http://www.devon.gov.uk/geo-heavitree-quarry.pdf
  • Palmer, Douglas. Earth Time: Exploring the Deep Past from Victorian England to the Grand Canyon. Chichester: John Wiley & Sons, Ltd, 2005. ISBN 0-470-02221-3 pp. 137–8, 159.
  • Durrance, E & Laming, D.J.C. The Geology of Devon University of Exeter Press 1982 ISBN 0-85989-247-6.
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