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 Western River Basins. This region consists essentially of the connected river systems that drain the Carboniferous and Old Red Sandstone plateau of County Tyrone, as well as the foothills of the Sperrin Mountains to the east and Donegal to the west. The region extends from the Omagh Basin in the south, northwards along the lower Foyle valley. The Omagh Basin has particular significance as an ice centre during the Late Midlandian and is now largely covered by a complex mixture of glaciofluvial sands and gravels and drumlins overlying Rogen moraines. When the headwaters of these river systems rise together they have in the past been responsible for serious flooding at the bottleneck of Strabane. Although this has been mitigated by extensive drainage control works in and around the town.
The broad valley of the Camowen River and its tributaries lies to the south of Mullaghcarn and to the west of the granite outcrop of Cregganconroe. Sandstones, minor outcrops of granite and Quartz Porphyry and rounded deposits of glacial moraine form minor ridges and underlie much of the valley. The valley is enclosed, to the north and east, by higher land that provides an overall sense of containment. The 'crinkly' silhouette of the granite outcrops of Cregganmore are a local landmark. The landscape is a complex, patchy mosaic of conifer plantations, marsh and pastures. There are numerous branching streams and peaty marsh extends across the low-lying parts of the valley floor. There are extensive conifer plantations on the shallow slopes just above the marsh and pastures on the ridges of glacial moraine. The landscape pattern varies in scale, according to landform. Parts of the valley with a more undulating character, such as the Drumnakilly area, have a higher proportion of pasture, while conifer plantations and marsh predominate in the flatter, low-lying areas to the south. The landscape resembles a complex maze, and has a disorientating, enclosed character. The landscape can therefore be summarised as one of glacial moraine, deposited within the valley, which has produced an undulating, complex landscape between the Sperrins and the Fintona Hills with broad, shallow valley with winding rivers and numerous branching streams.
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. The older formations can be upside down (tectonically inverted).
Stratigraphic Table (youngest rocks at the top of the table)Carboniferous - youngest strata, about 350 million years old |
Omagh |
Devonian - about 400 million years old |
Shanmullagh |
Raveagh |
Gortinfinbar |
Shanmaghery (Barrack Hill Andesite at top) |
Ordovician - about 500 million years old |
Tyrone Volcanic Group (including Copney Pillow Lavas & rhyolites) |
Beragh, Tremoge Glen and Carrickmore Granite |
Tyrone Plutonic Complex gabbro |
Un-named Caledonian quartz porphyry and tonalite |
Dalradian (Neoproterozoic) - Mullaghcairn - about 600 million years old |
Moinian - Corvanaghan Psammite - about 1000 million years old |
This LCA is dominated by Caledonian and Devonian rocks (both roughly 400 milion years old) of the Fintona Block succession (Fermanagh). Overall, the area can be split into four main areas: a central deformed (broadly east-west) Tyrone Volcanic Group succession; the southwestern and southeastern Carrickmore and Beragh granites; the southeastern (Devonian) Shanmullagh Formation and a northwestern (NE-SW trending) faulted succession of Dalradian and Carboniferous along the Omagh Thrust.
Two tectonic phases have affected the area: the Caledonian (Ordovician - Silurian) and Variscan (end Carboniferous). Consequently NE-SW faults, folds, intrusions and minor fabrics posses this orientation. The Omagh Thrust crosses the northwest corner of LCA23.
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 more than 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 LCA is largely underlain by Late Midlandian till, deposited by ice that moved northeastward across the valley towards the Sperrins uplands. However, the complexity of the present-day terrain derives primarily from the deglacial deposits that were laid down towards the end of the Midlandian as the ice retreated southwestwards. The LCA contains elements of two deglacial complexes that are important scientifically and for their sand and gravel resources. They are summarised below.
The Ballygawley Deltas Complex in the west of the LCA is contained within the northeast-southwest upland axis of the Fintona Hills and extends from Ballygawley in the south to Carrickmore and Sixmilecross in the north. The delta complex is characterised by a well-defined assemblage of sand and gravel delta and outwash surfaces, extending from the Fintona Hills axis northwards, and sand and gravel ridges oriented generally NE-SWaround Gortfin. It terminates at the 130 m contour that demarcates the northern sand and gravel limit. Small areas of this complex overlap into LCAs 16, 17, 22 and 45. Most of the complex is in LCA 44.
The Murrins Complex is principally represented by a series of eskers running northeast to southwest through the centre of the LCA covering some 1.5km2. The Murrins complex as a whole is located in the lowland area between Carrickmore to the southeast and the upland massif of Mullaghcarn and adjacent hills to the northwest. The northern part of the complex terminates at the foothills of the Sperrin Mountains near Greencastle. Associated esker ridges up to 8 km long occur to the south at Beragh, Coolesker, Seefin and Cloghfin. Sediments are mainly superimposed upon bedrock to the west and north, and glacial till to the east and south. The complex is characterised by proglacial outwash, frontal moraines, small retreat moraines, local high level deltas and discontinuous feeder eskers and local kettling and meltwater erosion. Most of the complex lies to the north and east in LCAs 43, 22, 24, 25 and 26.
Key Elements Deglacial ComplexesBALLYGAWLEY DELTA COMPLEX
This landform assemblage is of high importance because of it shows that glaciolacustrine sedimentation took place within the uplands as ice margins withdrew north and south from the Fintona Hills axis. Sediment exposures generally show well-sorted and interbedded sand and gravel facies typical of a glaciolacustrine depositional environment. Correlatable delta and outwash surfaces identify a relative chronology of lake drainage, regulated by ice marginal retreat and the uncovering of points of lake outflow. Sand and gravel ridges around Tiroony indicate that retreat of the northern ice margin was characterised by both active and inactive phases.
Sixmilecross - Tiroony ice marginal complex
This area is a part of the Ballygawley Delta Complex and runs along the boundary between LCAs 44, 22 and 23. It is of importance in understanding the recent glacial history of Northern Ireland. Landforms consist of ice-marginal sand and gravel ridges that are increasingly hummocky towards the west. Sand and gravel landforms in the Glashagh Burn valley are generally pristine and this intactness is an important landscape attribute. Topographic diversity is the result of the juxtaposition of outwash surfaces, aligned ridges, meltwater channels and bedrock uplands. The morainic system around Sixmilecross is a major landscape feature, and is crossed by the Marshall Country Trail.
SEEFIN ESKER (Murrins Complex)
A well-marked, steep-sided sinuous ridge extends northwestwards from the Cloghfin River towards a flat sand and gravel surface at Mullaghslin in the south centre of the LCA. The ridge is an esker which probably relates to continuing ice activity along the flanks of the Fintona Hills, at a time when Lough Neagh Basin ice still occupied the Pomeroy valley and the Irish ice mass was separating into local, topographically constrained, ice bodies.
Other sites/units identified in the Earth Science Conservation Review AONBA small area of Sperrin AONB (1968) occurs in the north of the LCA.