The use of a cultural overlay in defining Landscape Character Areas (LCAs) means that they frequently subdivide natural physiographic units. It is common therefore for significant geomorphological features to run across more than one LCA. It is also possible in turn, to group physiographic units into a smaller number of natural regions. These regions invariably reflect underlying geological, topographic and, often, visual continuities between their component physiographic units, and have generally formed the basis for defining landscape areas such as AONBs. It is essential therefore, that in considering the 'Geodiversity' of an individual LCA, regard should be given to adjacent LCAs and to the larger regions within which they sit. In the original Land Utilisation Survey of Northern Ireland, Symons (1962) identified twelve such natural regions.
This LCA lies within the region described as the Central Lowlands. This region owes its large-scale morphology to the early Tertiary subsidence of the Lough Neagh basin into the magma chamber from which the basalts that underlie much of the landscape originated. This has produced a largely centripetal drainage system from the rim of the basin into Lough Neagh that ultimately drains northwards via the Lower Bann. To the south of the Lough Neagh basin, the lowlands extend southwestwards along a Caledonian structural trend into the Monaghan-Clones depression. In the east of the region the lowlands extend northeastwards along the fault-guided Lagan Valley. There are no strong topographical barriers in the region and boundaries between LCAs tend to be subtle. The low gradients of the rivers, especially on the clay lowlands immediately around Lough Neagh, create inherent drainage problems and frequently it is only the slopes of the many drumlins that provide permanently dry sites. The Lough Neagh Basin was a major ice accumulation centre during the Late Midlandian and much of the lowland areas to the north and south of the Lough are dominated by extensive drumlin swarms.
The Lough Neagh Peatlands is a low-lying marshy landscape with small, protruding drumlins, found on the southern shores of Lough Neagh. Much of the area has been previously worked for peat and has been extensively modified through extraction; there are distinct sharp changes of level marking areas where peat extraction has taken place. There are areas of regenerating birch and willow scrub and farmland, wherever drainage permits.
Pre-Quaternary (Solid) GeologyThe stratigraphy of this area is made up of the mapped formations in the table, the youngest of which usually overlie the oldest.
Stratigraphic Table (youngest rocks at the top of the table)| Tertiary - Lough Neagh Group, about 20 million years old |
| Tertiary - Lower Basalt Formation basalts - about 55 million years old |
| Cretaceous - Ulster White Limestone - about 100 million years old |
| Triassic - Mercia Mudstone and Sherwood Sandstone groups - spanning 240 to 210 milion years old |
| Carboniferous - Millstone Grit and Coal Measures - about 300 million years old |
75% of LCA64 is underlain by Tertiary Lough Neagh Group. The eastern area comprises Tertiary basalts, the western area is underlain by Triassic and Cretaceous.
Carboniferous
The Coal Measures are exposed in the far eastern extension of LCA64 (Coalisland Brick Pit - ESCR Site 247).
Quaternary (Drift) GeologyNorthern Ireland has experienced repeated glaciations during the Pleistocene period that produced vast amounts of debris to form the glacigenic deposits that cover >90% of the landscape. Their present morphology was shaped principally during the last glacial cycle (the Midlandian), with subsequent modification throughout the post-glacial Holocene period. The Late Midlandian, the last main phases of ice sheet flow, occurred between 23 and 13ka B.P. from dispersion centres in the Lough Neagh Basin, the Omagh Basin and Lower Lough Erne/Donegal. The clearest imprint of these ice flows are flow transverse rogen moraines and flow parallel drumlin swarms which developed across thick covers of till, mostly below 150m O.D. during a period that referred to as the Drumlin Readvance. At the very end of the Midlandian, Scottish ice moved southwards and overrode parts of the north coast. Evidence for deglaciation of the landscape is found in features formed between the glacial maximum to the onset of the present warm stage from 17 and 13ka B.P. - a period of gradual climatic improvement. Most commonly these are of glaciofluvial and glaciolacustrine origin and include: eskers, outwash mounds and spreads, proglacial lacustrine deposits, kame terraces, kettle holes and meltwater channels (McCarron et al. 2002). During the Holocene, marine, fluvial, aeolian and mass movement processes, combined with human activities and climate and sea-level fluctuations, have modified the appearance of the landscape. The landforms and associated deposits derived from all of these processes are essentially fossil. Once damaged or destroyed they cannot be replaced since the processes or process combinations that created them no longer exist. They therefore represent a finite scientific and economic resource and are a notable determinant of landscape character.
The drift geology map for this LCA shows it to be predominantly underlain by Late Midlandian till associated with the large ice mass that was centred on the Lough Neagh Basin. Superimposed on the till are post-glacial spreads of alluvium associated with the floodplains of the Blackwater and Bann. Around the Lough shore there is a narrow band of lacustrine alluvium that has most probably been exposed by the lowering of Lough Neagh in historical times to improve drainage conditions within the Basin. Of possibly greater geomorphological significance is an area of glaciofluvial deposits in the west of the LCA between Washing Bay and Coalisland. This appears to be an extension of the sands and gravels of the Moneymore Complex that occurs mainly in LCAs 42,45 and 49 to the west and north. The Moneymore complex consists of discontinuous sand and gravel mounds and spreads in a north/south oriented belt in the Lough Neagh lowlands to the east of the Sperrin highlands between Moneymore, Coalisland and Dungannon. The landforms are dissected and consist predominately of ice-marginal and extra-marginal glaciolacustrine sequences superimposed upon the western Lough Neagh drumlin field. The stratified deposits formed in association with localised and variable palaeolake levels during the final deglacial stages of the region. Sediment supply was largely from a small, lowland residual ice-mass within the Lough Neagh basin and meltwater draining the eastern margin of the Sperrin highlands. As indicated in the geomorphological description above, much of the LCA is now blanketed by peat. The narrow band of lacustrine alluvium around the Lough shore has most probably been exposed by arterial drainage works, such as those completed in 1942, designed to lower Lough Neagh and to improve drainage conditions within the surrounding Basin.
Key Elements ASSI030 lough neagh
Largest lake in the British Isles, supporting beds of submerged aquatic vegetation with marginal swampy woodland and wet grassland.
Sites/units identified in the Earth Science Conservation Review247 Coalisland Brick Pit
Best exposure of Coal Measures strata of Westphalian age. Unfossiliferous mudstones with thin beds of sandstones. Fossiliferous bands with brachiopods and goniatites.