OR/14/063 Site assessment - ELC 4: Dunbar Shore, Dunbar
|Whitbread, K, Ellen, R, Callaghan, E, Gordon, J E, and Arkley, S. 2014. East Lothian geodiversity audit. British Geological Survey Internal Report, OR/14/063.|
|ELC_4: Dunbar Shore, Dunbar|
|Location and Summary Description:|
3 to 4 km section of coastline, located to the west, north and east of the town of Dunbar. The site displays a variety of upper Devonian and lower Carboniferous geological strata, structures and intrusions, and coastal geomorphological features. There are also geological links to the social and economic history of the town and the built heritage.
|National Grid Reference:
|Site ownership: Crown||Current use: Open Country|
|Field surveyors: Sarah Arkley, Katie Whitbread, Eileen Callaghan and Rachael Ellen||Current geological designations: 2 GCR sites (GCR ID: 182 and 2301), part of the Firth of Forth SSSI|
|Date visited: 26/03/2014||Other designations: Firth of Forth SPA and Ramsar, Dunbar Conservation Area and John Muir Country Park, North Berwick — Dunbar AGLV|
The town of Dunbar is located on a headland jutting out into the North Sea, in an elevated position with high sea-cliffs and a rocky foreshore. The coastal landscape reflects the underlying geology; the hard igneous rocks which lie beneath the town were more resistant to erosion during the last ice age than the softer sedimentary rocks to the north and south. The siting of this strategically important east coast town must in part be due to the defensive qualities offered by the form of the coastline; the castle and battery were built on rocky promontories, almost surrounded by the sea, and defended the town and its occupants over centuries of invasions; the large solid harbours are cut into bedrock and protected fleets of boats which brought trade, industry and prosperity to the town. Local industries exploited the natural geological resources; including clay to make bricks and tiles at Seafield, near Belhaven; igneous rocks were extracted from a quarry at Knockenhair, western Dunbar; red sandstone removed during the construction of the harbours may have been used as building stone in the harbour walls; and golf is thought to have been played on the raised beaches for almost 400 years.
The extent of the site is from Belhaven Bay to the Dunbar Golf Course, chosen as it includes extensive exposures of Devonian and Carboniferous sedimentary rocks, a selection of Carboniferous volcanic intrusions, a variety of structural features and a wide range of coastal and glacial Quaternary landforms.
Thick bedded sandstone belonging to the Kinnesswood Formation is exposed in cliffs near the coastal path north of Dunbar (west of the leisure centre). The sandstone is strongly cross-bedded and there are accumulations of mudstone rip-up clasts at the base of some beds; these were deposited by large rivers. In the upper part of the sequence seen are developed nodular concretions, some of which clearly developed around plant roots (referred to as rhizocretions). These cornstone beds are interpreted as fossil calcrete soils which developed in an arid or semi-arid climate (Photo ELC_4 P2).
The Lower Carboniferous sedimentary rocks, exposed in the western part of the site (Belhaven Bay), belong to the upper part of the Ballagan Formation and are composed of thin cementstones (dolomitic limestones) and mudstones, interbedded with sandstone and siltstone (Photo ELC_4 P3 & 4). The sediments are thought to have been deposited in fluvial and shallow lagoonal environments and display sedimentary structures such as ripples and trace fossils (Photo ELC_4 P5). The presence of surfaces with fossil mudcracks indicates a terrestrial environment. The strata appear gently folded and faulted where exposed on the intertidal shore platform near Belhaven Point, and has been intruded by a number of dykes of various compositions.
The strata are latterly traversed by a group of ENE–WSW trending quartz-dolerite dykes, best seen at Belhaven Bay (Photo ELC_4 P6) and also form the offshore skerries north of Dunbar. Basaltic intrusions are additionally present within the site; the best example forms the foundations of The Battery and displays superb columnar jointing (Photo ELC_4 P7).
Quaternary Deposits and Landforms
Access and Additional Information
Along the sea front, and particularly around the Victoria and Cromwell harbours, there are a significant number of information boards describing and illustrating the local history and wildlife of the area.
However, there is little mention of the local geology or landscape, despite it being an important factor in the siting and building of Dunbar Castle, the Battery and the two harbours; and in how the local area has been shaped during the Ice Age. The information described in these few pages should show that there is great scope for introducing geology to those that visit the Dunbar area, particularly with the town’s association to John Muir, who campaigned for the preservation of natural environments through his work as an environmentalist, geologist and botanist.
|Stratigraphy and Rock Types|
|Age: Devono-Carboniferous||Formation: Upper Old Red Sandstone and Kinnesswood Formation|
|Rock type: Sandstones, siltstones and mudstones|
|Age: Lower Carboniferous||Formation: Ballagan Formation|
|Rock type: Sandstone, siltstone and dolomitic limestone (cementstone)|
|Age: Lower Carboniferous||Formation: Southern Scotland Dinantian Plugs and Vents Suite|
|Rock type: Tuff and breccia|
|Age: Upper Carboniferous||Formation: Central Scotland Late Carboniferous Tholeiitic Dyke Swarm|
|Rock type: Quartz-microgabbro (quartz-dolerite)|
|Age: Carboniferous to Early Permian||Formation: Midland Valley Carboniferous to Early Permian Alkaline Basic Dyke Suite|
|Rock type: Microgabbro (dolerite)|
|Age: Quaternary||Formation: Raised marine deposits of Flandrian Age|
|Rock type: Sand and gravel with shells|
|Assessment of Site: Access and Safety|
|Road access and parking||Good access from Belhaven Bay car park and there are various places to park with access to the coast from Dunbar town centre. The John Muir Way footpath follows the coastline around Dunbar and allows excellent access to and/or views of most of the site.|
|Safety of access||Well-trodden footpaths generally provide good, safe access for visitors to look at outcrops and landforms along most of the site, but care should be taken if leaving the main paths. Access to the shore platform is restricted north of Dunbar where there are high vertical cliffs. All visitors should be aware of the tide times when planning a visit, as many of the exposures are only visible at low tide, and due to the high cliffs an unwary visitor could be cut off from their planned exit route.|
|Safety of exposure||Although the majority of the cliffs appear stable, care should always be taken when beneath cliffs of any height and visitors should not stand beneath any overhanging areas. The rocky intertidal areas have an uneven surface, and are in places boulder-strewn and often slippery with algal growth. Stout footwear is recommended. The site may feel very exposed under certain weather conditions, and the weather forecast should be checked before visits.|
|Access||Access is along the foreshore/beach and there are numerous footpaths leading down to the site from the town and car park.|
|Current condition||Rock exposures are generally clean and free of vegetation or litter, due to washing from tides, but the intertidal zones can be covered in seaweed or barnacles obscuring small-scale geological features.|
|Current conflicting activities||Two golf courses are located adjacent to the site and may restrict access to parts of the site, but paths are generally present along their shore edge or access can be gained by walking along the foreshore.|
|Restricting conditions||Tide: many of the geological exposures are located in the intertidal range and therefore covered at high tide.|
|Nature of exposure||Vertical cliff sections, intertidal & beach exposures and coastal landforms.|
|Assessment of Site: Culture, Heritage & Economic Value|
|Historic, archaeological & literary associations||Dunbar Castle (dating from around the 13th century), The Battery (built in 1781), Dunbar’s Harbours (Cromwell and Victoria) and McArthur’s Store may all have used local stone in their construction. Dunbar is the birthplace of John Muir (naturalist and early advocate of the preservation of the natural environment) and the Town House Museum in Dunbar (displays a variety of local history).|
|Aesthetic landscape||Coastal landscape.|
|History of Earth Sciences||John Muir’s birthplace.|
|Economic geology||Information from the John Muir Birthplace Fact Sheet, Number 3.12-Dunbar Geology: “A lot of the stone was exploited in Muir’s time. The Castle Rock was quarried for walls and buildings as a new harbour was created. Marls and mudstones to the west were burnt for cement and deposits of clay at Belhaven were worked for brick and tile manufacture. To the east many tons of fossiliferous limestones and shales were burnt every year for lime (used as mortar and field dressing).”|
|Assessment of Site: GeoScientific Merit|
|Geomorphology||Regional||Excellent||May and Hansom, 2003; Gordon and Sutherland, 1993||X|
|Site Geoscientific Value|
The shore section at Dunbar has excellent exposures of both volcanic (particularly phreatomagmatic deposits) and sedimentological (particularly paleosols) features, indicative of Carboniferous volcanic and terrestrial (including fluvial) environments. There are also excellent exposures of raised beaches and their relationship with the underlying rocks.
|Assessment of Site: Current site usage|
|Community||The attractive town, local history, scenic coastline and easy access means both locals and visitors from further afield are regularly passing through the site. The two golf courses located on raised beaches adjacent to the site additionally draws people to the area.|
|Education||The site displays a wide variety of features suitable for educational visits. Most of the site has good safe accessibility and would be suitable for larger groups. The site has potential for geosciences research, and teaching potential for Higher/Further and School level education. Use of the site for teaching purposes may be enhanced by leaflets or online information. Members of the general public would benefit from on-site interpretation such as sign boards or a Geo-trail.|
|Assessment of Site: Fragility and potential use of the site|
|Fragility||Weathering/erosion; development of coastal defences may affect the geodiversity.|
|Potential use||Research, Higher/Further Education, School Education, On-site interpretation, On-site geotrail, Multidisciplinary.|
|An outstanding site containing a wide variety of good quality geological and geomorphological features. This site exposes a long, semi-continuous section through typical upper Devonian to lower Carboniferous sedimentary strata. The strata display a variety of characteristic sedimentary structures which allow an interpretation of the environment at the time of deposition, with an excellent assortment of early Carboniferous volcanic intrusions (particularly vents and dykes) and of pyroclastic rocks, and a selection of structural geological features (particularly faults and fractures) which have cut though the strata. The site additionally displays classic examples of landforms typically found along rocky coastlines, some of which have been nationally recognised. It is an attractive coastal site with easy access and has numerous links to the built heritage and social/economic history of the local area, with ample opportunity to enhance existing visitor information with some geology.|
- MCADAM, A D, and CLARKSON, E N K. 1986. Lothian geology: An excursion guide. (Edinburgh: Edinburgh Geological Society, Scottish Academic Press).
- MAY, V J, and HANSOM, J D. 2003. Coastal Geomorphology of Great Britain, Geological Conservation Review Series, No. 28, Joint Nature Conservation Committee, Peterborough, 754 pp.
- GORDON, J E, and SUTHERLAND, D G. 1993. Quaternary of Scotland. Geological Conservation Review Series, No. 6, Chapman and Hall, London, 695 pp.