New Red Sandstone
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The New Red Sandstone is a chiefly-British geological term for the Triassic red beds that underlie the Jurassic Lias; the term distinguishes it from the Devonian Old Red Sandstone. Its upper layers consist of mudstones, but most of the formation consists of reddish sandstones, interbedded with evaporite minerals like salt and gypsum; these indicate deposition in a hot, arid environment.
The New Red Sandstone covers much of central England, where it generally forms a low-lying plain. Thick layers are present in the faulted Cheshire and north Shropshire basin, which features escarpments forming small prominent hills. 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.
Lithologically, the New Red Sandstone (often shortened in literature to the acronym NRS) comprises true sandstones, mudrocks and evaporite strata. The sandstone member is 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 sandstone member lacks macrofossils (as do many terrestrial rocks). The grains in the member have a high degree of sphericity, are very well sorted and have a small size range (0.5mm to 2mm). It is a mature rock and is a common building stone in the Cheshire area.
[edit] References
- 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.
