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Carnlough Coastal Peat and Raised Beach RidgesAntrim
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Summary Full report
Site Type: Coastal section
Site Status: PASSI
District: Larne Borough Council
Grid Reference: D287171
Rocks
Rock Age: Quaternary (Holocene, Pleistocene)
Interest
Fossil Groups: Plant
Other interest: No data, Late-glacial deposit, Marine deposit, beach ridge, buried peat, gravel beach, pollen analysis, radiocarbon dating, raised beach gravel

Summary of site:

There are very few sites that relate the series of climatic and botanical events at the close of the last ice age and the period immediately following. This is the key time when the colonization of Ireland by plants began. The Carnlough beach site provides an important window on this world.

Coring through beach deposits has yielded a long succession at Carnlough. The lowest deposit (bed 1) is a glacial till (boulder clay) with basalt and chalk fragments, topped by about 8m of finely laminated silts and clays (bed 2). Above them is a bed of beach gravel (bed 3), 20-30cm thick, consisting of chalk and basalt shingle with a sand matrix. Then follows a thin blue sticky clay (bed 4), topped by up to 45cm of sand with clay partings (bed 5). Above this there is a sandy silt, up to 10cm in thickness (bed 6). The lower of the two peats (bed 7) follows - black, compact and 15-25cm thick. On top is a blue-grey sandy silt (bed 8), up to 20cm thick, which is surmounted by the upper peat (bed 9), woody, dark brown and compacted. Carbon dates were obtained from the peats. Two from the lower peat were around 11,600-11,700 years before present and one from the top peat and another from a fragment of embedded wood suggest an age of 8,100 years. The lower peat had a low ratio of tree pollen and also showed plentiful juniper. The upper peat has much more tree pollen, starting with willow, birch and pine, followed by a dramatic increase in hazel simultaneous with the decline of juniper, grasses and crowberry. The sequence of events appears to start with the final stage of the Midlandian glaciation (represented by bed 1), followed by the glacial retreat with rainfall and meltwater sweeping the glacial muds, sands and gravels on to low ground and into temporary lakes and lagoons (bed 2). The sea then began to encroach, laying down shingle (bed 3) but what the sandy silts of beds 4, 5 and 6 represent is not clear. The lower peat indicates a cold tundra-like landscape (probably an interval called the Woodgrange Interstadial), while bed 2 suggests the onset of a period of intense cold with frequent frosts, almost certainly the Nahanagan Stadial (a stadial is a short period of cold) between 11,000 and 10,000 years ago. The upper peat shows strong and sustained climatic improvement, the establishment of woodland and the decline of cold climate plants of open ground. There are two shingle ridges behind the shore, running parallel with it, that could be the product of raised sea level around 6,000 years ago but it is not certain whether the peats run beneath them - so there is need for further research. The site is of Irish importance because it provides rare information about changes in the coastal environment from the final stages of the last glaciation to around 6,000 years ago. The only threat to the site would be beach works. In normal circumstances the succession is covered by beach sand and consequently protected from modern erosion.


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