Toome

Also within

Londonderry County

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Habitats

Fast flowing river and stream

Geology & landscape

Geological Period: Quaternary

Landscape processes: Glacial, Peatland / Mire

Description

Toome Holocene peat and related stratigraphy The area is of special scientific interest because of its diatomite deposits. 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, ofvarious shapes, depending on the species. The diatomite also known as Kieselguhr or Barm clay deposits in Northern Ireland were one of the most extensive freshwater diatomite sequences of post-glacial age in the British Isles. Past commercial exploitation in the Lough Neagh basin has reduced the area of intact material to a small number of localities. The deposits were mainly formed between 7500 and 5000 years before present BP, and are found in low lying land around the northern shore of Lough Neagh and in the Lower Barm 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. At Toome the diatomite forms part of the lowest lake terrace of Lough Neagh and is up to 2m above the present lough level. The stratigraphic record shows a change in dominance from benthic bottom dwelling species of diatom to planktonic free floating species, indicating a transition to a deeper water environment. The former is of late Boreal age pre-7500 years BP. Deposition continued here beyond 5000 years BP sub-Boreal as indicated by the pollen record in the upper layers. This site contains the longest total sequence of diatomite and associated deposits 3-4m thick in places encountered in a recent survey of the remaining diatomite deposits of the Bann valley. In addition, the site shows associations with organic material early reedswamp peats and geomorphological features sandbanks together with former river channels or lagoons. This location is also of importance as any geomorphological changes here would have had considerable influence on water levels in the lough, given its position as the sole outlet for the entire Lough Neagh basin since post glacial times. 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 ofearly human settlement in Ireland. This assemblage gives a record of past water levels in the Lough Neagh basin, and of climatic change. These remaining sites are amongst the most important deposits of freshwater diatomite in the British Isles, and are unique when considered with the associated materials. https://www.daera-ni.gov.uk/publications/toome-assi

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