Coralline Crag Formation

Geological formation in England

Coralline Crag Formation
Stratigraphic range: Pliocene PreꞒ Ꞓ O S D C P T J K Pg N ↓
Coralline Crag Formation exposed in Suffolk, England.
Type	Formation
Unit of	Crag Group
Underlies	Norwich Crag Formation
Overlies	Thames Group (unconformity)
Thickness	Up to 25 metres
Lithology
Primary	Sand
Location
Region	England
Country	United Kingdom
Extent	Suffolk

The Coralline Crag Formation is a geological formation in England. It is a series of marine deposits found near the North Sea coast of Suffolk and characterised by bryozoan and mollusc debris. The deposit, whose onshore occurrence is mainly restricted to the area around Aldeburgh and Orford,^[1]^[2] is a series of bioclastic calcarenites and silty sands with shell debris, deposited during a short-lived warm period at the start of the Pliocene Epoch of the Neogene Period.^[3] Small areas of the rock formation are found in locations such as Boyton and Tattingstone to the south of Orford as well as offshore at Sizewell.^[4]

Crag is a local word for a shelly sand. Coralline Crag has sometimes been used historically in the Suffolk coast area for building and a number of quarries exist.^[2] The tower of St Peter's Church in Chillesford is one of only two built using the rock.^[2]

A map, published in 1898, showing the extent of Coralline Crag rocks in Suffolk
Quarried block of Coralline Crag, containing bryozoan fossils, in the wall of St Peter's church in Chillesford in Suffolk
Fossils from the Coralline Crag. From Chatwin (1954).^[5]

References

^ British Geological Survey 1:625,000 scale geological map Bedrock Geology UK South 5th Edn 2007 NERC
^ ^a ^b ^c Suffolk, Natural England. Retrieved 8 August 2016.
^ Brenchley, Patrick J.; Rawson, Peter F., eds. (2006). The Geology of England and Wales (2nd ed.). The Geological Society. pp. 425, 432. ISBN 1-86239-200-5.
^ Richmond Farm SSSI, GeoSuffolk. Retrieved 8 August 2016.
^ Chatwin, C.P. (1954). East Anglia and adjoining areas. British Regional Geology. London: Her Majesty's Stationery Office. pp. 46–47.