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Earth Science Conservation Review
| Culnafay | Antrim |
| Site number: | 1251 | ||
| Locality Type: | Field, Subcrop | Status: | ASSI |
| Grid Reference: | H99209828 | ||
| Google maps: | 54.82224,-6.45664 | ||
| County: | Antrim | Council area: | Mid & East Antrim Borough Council |
| Period: | Quaternary | ||
| Stages: | Holocene | ||
| Site Description | |
|---|---|
| Highlights: | |
Culnafay is a small remnant of the once extensive diatomite deposits of the Lough Neagh and Lower Bann. Recording the environmental history of the area through part of the Holocene, the deposits are of importance to a number of research specialisms. | |
| Introduction: | |
The area is of special scientific interest because of its deposits of diatomite and associated materials. Diatomite consists of accumulated diatom frustules with differing amounts of clay, silt, sand and peat. Diatoms are microscopic aquatic plants, surrounded by a silica box, or frustule, of various shapes, depending on the species. The diatomite (also known as Kieselguhr or Bann clay) deposits in Northern Ireland were one of the most extensive freshwater diatomite sequences of post-glacial age in the world. | |
| Description: | |
At Culnafay, as in much of the Bann valley, the diatomite was probably deposited in an elongated lake, as indicated by its essentially linear form. The dominance of benthic (bottom dwelling) species of diatom in the lowest records marks the former presence of a shallow water body, but this was probably isolated from the main lough. The change to deeper water conditions is reflected by the increased presence of planktonic (free floating) species at higher levels. Basal deposits are of early Atlantic age (post 7500 years BP), but the upper sequence has been truncated by erosion. The diatomite record also contains Mesolithic occupation sites and it is one of the key locations for the Irish Mesolithic - Middle Stone Age - chronology. It also shows the lateral transition from diatomite to glacial till, marking the former shoreline. This is the last large deposit of good quality diatomite remaining in this area. Its natural topography indicates how the landscape might have appeared during the time of formation. | |
| Importance: | |
The diatomite is of international importance for biological, geological, hydrological and climatological reasons. Its archaeological significance is also considerable, given its contemporaneous links with sites of early human settlement. This assemblage gives a record of past environmental conditions in the Lough Neagh basin, and of climatic change since the last period of Irish ice. These remaining sites are amongst the most important deposits of freshwater diatomite in the world, and are unique when considered with the associated materials. | |
| Interpretation: | |
The deposits were mainly formed between 7500 and 5000 before present (BP), and are found on low lying land around the northern shore of Lough Neagh and in the Lower Bann valley. Although diatomite was formed in water and represents the extent of a former, larger Lough Neagh, the presence in the deposits of archaeological remains shows that these marginal areas were only seasonally inundated. | |
| Conclusions: | |
The diatomite deposits of the Lough Neagh and Lower Bann areas have mainly been lost through commercial extraction. The remaining locations are of considerable significance to a range of research specialisms as well as their association with a lost industry. | |
| Notes: | |
Diatomite, also known locally as Bann Clay, occurs in a deposit up to 0.9m thick in the valley of the River Bann between Toome [H 990 907] and Portglenone [C 980 039]. It was deposited in freshwater lakes during early post-glacial times and consists of the microscopic siliceous skeletons of diatoms. When dry, it is a friable, white, chemically inert powder that can be used as a filler in paint, plastic and rubber manufacture, but also as an absorbent in animal litter, an abrasive for metal polish, an insulant, and as a filtration agent in the food and pharmaceutical industries. Diatomite was extracted manually on a small scale until the late 1960s but is no longer worked. (GSNI source) See also site reports for Ballymacombs More (Record no. 1250) and Toome (Record no. 1252) and Introduction to the diatomite deposits of Northern Ireland (Record no. 1253) | |
| Keywords | |
|---|---|
| Minerals: | Diatomite |
| Rocks: | Diatomite |
| Fossil Groups: | Diatoms |
| Access | |
|---|---|
| Approach: | No public access. Adjoining small parking area related to slipway and pontoon |
| Restrictions: | Private land |
| Management: | |
Agricultural land used for grazing and silage production | |
| Threats: | Activities that change the host environment or physically disturb the deposits. Land drainage, deep ploughing, afforestation , development |
| Record type: | ESCR report | ||
| Entered by: | I J Enlander | ||
| Last updated: | 27 Mar 2019 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Culnafay, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1251. Accessed on 2026-11-06. |
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