Old Red Sandstone
Old Red Sandstone | |
---|---|
Ma | |
North Atlantic | |
Country | Canada, Greenland, Ireland, Norway, United Kingdom |
Extent | 700 km (430 mi)[1] |
Old Red Sandstone, abbreviated ORS, is an assemblage of rocks in the North Atlantic region largely of
Sedimentology
The Old Red Sandstone describes a group of
The familiar red colour of these rocks arises from the presence of
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.[1]
Stratigraphy
Since the Old Red Sandstone consists predominantly of rocks of terrestrial origin, it does not generally contain marine fossils which would otherwise prove useful in correlating one occurrence of the rock with another, both between and within individual sedimentary basins. Accordingly, local stage names were devised and these remain in use to some extent today though there is an increasing use of international stage names. Thus in the Anglo-Welsh Basin, there are frequent references to the Downtonian, Dittonian, Breconian and Farlovian stages in the literature. The existence of a number of distinct sedimentary basins throughout Britain has been established.[1]
Orcadian Basin
The Orcadian Basin extends over a wide area of North East Scotland and the neighbouring seas. It encompasses the Moray Firth and adjoining land areas, Caithness, Orkney and parts of Shetland. South of the Moray Firth, two distinct sub-basins are recognized at Turriff and at Rhynie. The sequence is more than 4 kilometres (13,000 ft) thick in parts of Shetland. The main basin is considered to be an intramontane basin resulting from crustal rifting associated with post-Caledonian extension, possibly accompanied by strike-slip faulting along the Great Glen Fault system.[8]
Argyll
There are a scatter of exposures of the Old Red Sandstone around
Midland Valley of Scotland
The
Scottish borders
A series of outcrops occur from East Lothian southwards through Berwickshire. Hutton's famous unconformity at Siccar Point occurs within this basin - see History of study below.
Anglo-Welsh Basin
This relatively large basin extends across much of South Wales from southern Pembrokeshire in the west through Carmarthenshire into Powys and Monmouthshire and through the southern Welsh Marches, notably into Herefordshire, Worcestershire and Gloucestershire. Outliers in Somerset and north Devon complete the extent of this basin.
With the exception of south Pembrokeshire, all parts of the basin are represented by a range of lithologies assigned to the Lower Devonian and to the Upper Devonian, the contact between the two being unconformable and representing the complete omission of any Middle Devonian sequence. The lowermost formations are of upper Silurian age, these being the Downton Castle Sandstone Formation and the overlying Raglan Mudstone Formation except in Pembrokeshire where a more complex series of formations is recognized. In the east of the basin, the top of the Raglan Mudstone is marked by a well-developed
Pembrokeshire
The sequence in Pembrokeshire differs from that of the main part of the basin and falls into two parts.[15]
In North Pembrokeshire to the north of the Ritec Fault, both the middle and upper ORS are missing with only the lower ORS present; this is divided into an earlier Milford Haven Group comprising in ascending order, the Red Cliff, Sandy Haven and Gelliswick Bay formations and a later Cosheston Group with, again in ascending order, its constituent Llanstadwell, Burton Cliff, Mill Bay, Lawrenny Cliff and New Shipping formations. These respectively equate with the Temeside, Raglan Mudstone and St Maughans formations of the central and eastern part of the basin.
- [middle and upper ORS missing]
- Cosheston Group
- Milford Haven Group
- Gelliswick Bay Formation
- Sandy Haven Formation (including Townsend Tuff Beds)
- Albion Sands Formation / Lindsway Bay Formation
- Red Cliff Formation
In south Pembrokeshire to the south of the Ritec Fault, the lower ORS is represented by, in ascending order, the Freshwater East, Moors Cliff and Freshwater West formations. These are unconformably overlain by the Ridgeway Conglomerate Formation. The middle ORS is missing whilst the Upper ORS is represented by the Gupton and West Angle formations.
- Skrinkle Sandstone Group
- [Part of middle ORS missing]
- Ridgeway Conglomerate Formation
- [Part of middle ORS missing]
- Milford Haven Group
- Freshwater West Formation (including Rat Island Mudstone Member and Conigar Pit Sandstone Member)
- Moor Cliffs Formation (including Chapel point calcretes member and Townsend Tuff Bed)
- Freshwater East Formation
The Freshwater East Formation, and corresponding Red Cliff Formation of north Pembrokeshire, are both late Silurian in age.[16]
Anglesey
A small and separate basin exists here where both
History of study
In 1787 James Hutton noted what is now known as Hutton's Unconformity at Inchbonny, Jedburgh, and in early 1788 he set off with John Playfair to the Berwickshire coast and found more examples of this sequence in the valleys of the Tower and Pease Burns near Cockburnspath.[18] They then took a boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of Dunglass and at Siccar Point found what Hutton called "a beautiful picture of this junction washed bare by the sea",[19] where 345-million-year-old Old Red Sandstone overlies 425-million-year-old Silurian greywacke.[2][20]
In the early 19th century, the paleontology of the formation was studied intensively by
's early debates were about the Old Red Sandstone.In older
Use as a building stone
The Old Red Sandstone has been widely used as a building stone across those regions where it outcrops. Notable examples of its use can be found in the area surrounding
Notable buildings
Canada
- New York Life Insurance Building, Montreal
England
- Goodrich Castle, Herefordshire[21]
- Ross-on-Wye market hall, Herefordshire
- Shrewsbury Castle, Shropshire
- Hereford Cathedral, Herefordshire
Scotland
- Arbroath Abbey, Angus
- Muchalls Castle, Aberdeenshire
- St Magnus Cathedral, Orkney[22]
- Stonehaven Tolbooth, Aberdeenshire
Wales
- Raglan Castle, Monmouthshire[21]
- Tintern Abbey, Monmouthshire[21]
- Brecon Cathedral, Powys
See also
References
- ^ ISBN 978-1-86107-543-7.
- ^ a b Cliff Ford (2 September 2003). "Siccar Point". Field Excursion Preview. University of Edinburgh School of GeoSciences. Retrieved 2008-10-20.
- ^ Friend, P.F. and Williams, B.P.J. (eds) 2000 New Perspectives on the Old Red Sandstone. Geological Society, London, Special publications 180 p1,35
- ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=ORS entry in BGS on-line rock lexicon
- ISSN 0764-4450.
- .
- ISSN 1476-4687.
- S2CID 128640763. Retrieved 2010-02-25.
- ^ "Kerrera Sandstone Formation". BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved 31 October 2018.
- ^ British Geological Survey 1:50,000 scale geological map sheet 45W (Scotland) Connel 1991
- ^ British Geological Survey 1:50,000 scale geological map sheet 37W (Scotland) Furnace 2008
- ^ British Geological Survey 1:50,000 scale geological map sheet 44E (Scotland) Lismore 1992
- S2CID 140575299.
- ^ "BGS Lexicon of Named Rock Units - Result Details". webapps.bgs.ac.uk.
- ^ Barclay, W. J. (2005) in The Old Red Sandstone of Great Britain (W. J. Barclay, M. A. E. Browne, A. A. McMillan, E. A. Pickett, P. Stone and P. R. Wilby) Geological Conservation Review series, No 31 JNCC, Peterborough pp. 212–213
- ^ Howells, M. F. 2007 British Regional Geology: Wales (Keyworth, Nottingham. British Geological Survey) pp. 100–101
- ^ British Geological Survey 1:50K special map sheet Anglesey
- ^ Keith Montgomery (2003). "Siccar Point and Teaching the History of Geology" (PDF). University of Wisconsin. Retrieved 2008-03-26.
- ^ "Hutton's Journeys to Prove his Theory". Archived from the original on 2011-07-26. Retrieved 2018-12-14.
- ^ Rance, Hugh (1999). "Hutton's unconformities" (PDF). Historical Geology: The Present is the Key to the Past. QCC Press. Archived from the original (PDF) on 2008-12-03. Retrieved 2008-10-20.
- ^ a b c http://www.museumwales.ac.uk/media/4/9/5/2/Newsletter_5.pdf[permanent dead link]
- ^ BBC. "The Cathedrals of Britain". Retrieved 4 March 2010.