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, but grades westwards in to the Plateau and Valley Lands of Fermanagh. 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.
Surrounding the small towns of Ballinamallard and Irvinestown, is a broad area of lowland farmland. The shores of Lower Lough Erne lie to the west and to the east the lowland stretches as far as the foothills to the south of the Sperrins. The lowlands are underlain by beds of Old Red Sandstone. To the north of Irvinestown, ice movement has exposed harder limestone crags and eroded small lough basins, for example at Parkhill and Maghera. The land form is broadly aligned along a NW-SE axis, with elongated drumlin ridges divided by narrow stream valleys. The main channel and numerous tributaries of the Ballinamallard River link the linear hollows in a complex drainage pattern and the river valley is a local landscape feature. The landscape can therefore be summarised as rolling drumlin lowlands with deep hollows and linear valleys and broken rocky topography to north of Irvinestown. In the northwest of the LCA at Kiltierney Deer Park, next to Parkhill Lough is an isolated karst drainage system that contains the only accessible cave in the Ballyshannon limestone in Northern Ireland (see key elements below).
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)Tertiary - dolerite dykes, about 60 million years old |
Carboniferous - about 350 million years old |
Slievebane (Group) |
Greenan Sandstone |
Mullaghmore Sandstone (east only) |
Bundoran Shale |
Ballyshannon Limestone (including Waulsortian Limestone) |
Claragh Sandstone |
Devonian - Shanmullagh - about 400 million years old |
Neoproterozoic (Dalradian) metamorphic rocks, about 650 million years old |
This LCA is dominated by Carboniferous rocks of the Kesh - Omagh succession in faulted contact with Devonian and Neoproterozoic.Tertiary dolerite dykes extend through the area.
The Devonian Tedd Formation comprises conglomerates that occur in a fault slice of the Castle Archdale Fault in the north of LCA15, exposed at Tedd Cross Pit (ESCR Site 53). The Shanmullagh red sandstones, mudstones and siltstones with subordinate andesitic lavas are typical of the Old Red Sandstone facies: this formation underlies over one third of the central area of LCA15, south of the Omagh Thrust. Exposed at Drumharvey Quarry (ESCR Site 54); Lisdoo Pit ( ESCR Site 56); Dromore Cutting (ESCR Site 55) and Knockaraven Pit (ESCR Site 57). Ballyshannon Limestone includes the Crockanaver Limestone Member exposed at the type section (ESCR Site 57). Ballinimallard Mudstone Formation is exposed in the Makenny stream section (ESCR Site 227). Slievebane Group (Westphalian, Upper Carboniferous). Interbedded volcaniclastic conglomerates, sandstones, thin mudstones. Restricted to a 1km-wide, NE-SW faulted slice in the Omagh Thrust - Castle Archdale Fault through the north of LCA15. The Tullanglare Mudstone Formation (youngest Carboniferous rocks exposed in Ireland) are seen at Tullanaguiggy ASSI (118).
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 iceflows 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. 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.
This LCA is essentially a drumlin dominated landscape underlain by extensive deposits of Late Midlandian till deposited by ice that moved southwestwards across the area from a centre in the Omagh Basin. Within Northern Ireland drumlins take a variety of forms; some are rounded in plan, although the majority are elongated in the direction of ice flow. Some have sharp crests, whereas others are more whaleback in profile. Although most drumlins are composed of glacial till or tills, a small number are 'drumlinoid features' are rock-cored and some are composed of sand and gravel. Where drumlins are rock cored there may have been significant frost shattering prior to their shaping by ice flow. It is possible therefore to see tails of shattered debris within till leading away from the feature in the direction of flow (Davies and Stephens 1978). It is generally accepted that the drumlins of Northern Ireland were formed by deposition beneath fast flowing ice. In the majority of cases this has resulted in a thick layer of Upper (younger) Till overlying a core of Lower (older) Till. This pattern has been observed across Northern Ireland, apart from a limited area in the north of County Down. The precise temporal relationship between the two tills has not been definitively resolved, but Davies and Stephens (1978) refer to an organic layer between the tills in County Fermanagh that has been dated at 30 500 ± 1170/1030 years B.P. and shelly material between the tills on the Ards Peninsula dated at 24 050 ± 650 years B.P.. However, these deposits only indicate that the Lower Till is older than the dates obtained.
It can be argued that an equally important component of any 'drumlin landscape' are the similarly numerous inter-drumlin hollows. The majority of these hollows would have held open water from local runoff at the end of the Pleistocene. Whilst some continue to exist as isolated small loughs, many have now been infilled by sediment washing off the surrounding drumlins. This has created typically flat-bottomed, marshy areas between the drumlins that are subject to seasonal inundation. Much of the infilling probably occurred early in the Holocene, as the landscape adjusted to increasingly temperate conditions. However, erosion may also have been accelerated in historical times, when rural population densities were considerably higher and much of the lowland landscape of Northern Ireland was more intensively cultivated. Whatever the stimulus for erosion and deposition, the sediments within these hollows typically contain an important record of local environmental change.
In recent years, researchers have also identified in the central and southern Omagh Basin, a great many subglacial diamict (till) ridges that lie transverse to the southwestwards Late Midlandian ice flow (e.g. Knight and McCabe 1997). These ridges can be anything from 0.5 - 2.5km in length and 100 - 450m wide and have been interpreted as rogen moraines. Some of ridges were streamlined and overprinted by subsequent drumlin development, while others remained unaffected. In some cases eskers were draped across the ridges during final deglaciation. This combination of subglacial bedforms is used to suggest that during the last deglacial phase ice masses were highly mobile and that flow was episodic due to variations in the subglacial thermal regime. One consequence of this was a high sediment flux to the ice margins that in turn generated significant glaciofluvial complexes. Within this LCA the most significant deglacial component in the landscape is the Ballinamallard esker that forms part of a 3.1km2 area of the Fintona Hills Glaciofluvial Complex in the central east part of the LCA. This is characterised by east-west aligned sand and gravel ridges, interpreted as subglacial eskers and ice-marginal moraines, kame terraces, and small outwash spreads developed in local, topographically-controlled depocentres. Most of this complex is in LCA 16, where a fuller description can be found.
Key Elements ASSI118 TULLANAGUIGGY
The Tullanaglare Mudstone Formation , for which this site is the stratotype , includes a group of fine-grained sediments that are the youngest , accurately dated , Carboniferous rocks exposed in Ireland
Karst FeaturesKILTIERNEY DEER PARK
This area of karst has been greatly affected by the modifications to the area for agricultural purposes however many of the karst features remain intact and represent an isolated lowland karst drainage unit in the Ballyshannon Limestone. The Deer Park is an important archaeological site and there are a number of scheduled sites within the area.
Deglacial Complexes/Sand and Gravel ResourcesBallinamallard esker
Esker ridge fragments form an almost continuous belt from Sidaire (Fermanagh LGD) to Trillick. Ridges are aligned northeast to southwest and are associated with outwash spreads in the vicinity of Trillick. They are characterised by discontinuous, generally straight sand and gravel ridges aligned northeast-southwest and are interpreted as subglacial eskers deposited from southwest to northeast during deglaciation under relatively high hydraulic pressure. Ridges are often contained within a broad (100-150 m wide, 10-30 m deep) meltwater channel which is cut between diamict-dominated bedforms aligned northwest-southeast (interpreted as Rogen moraines), and into bedrock. The Ballinamallard esker chain is well-preserved with little or no sand and gravel despoliation and is considered to be of high importance. Aggregate extraction occurs in outwash and esker deposits to the east of the esker and the proximity of active extraction suggests that this area is under threat.
Other sites/units identified in the Earth Science Conservation Review53 Tedd Cross
Upper palaeozoic - Devonian. Red-bed sedimentary rocks of the Tedd Formation. Although deposited here in a late Devonian basin, the source of the sediments was elsewhere.
54 Drumharvey
Upper palaeozoic - Devonian. Exposures of Shanmullagh Formation. Some sandstones display ripple marks.
56 Lisdoo
Upper palaeozoic - Devonian. Shanmullagh Formation. Exposures of fossiliferous green mudstones containing miopores, with thin beds of sandstone.
55 Dromore
Upper palaeozoic. Exposure of Devonian red-beds of Shanmullagh Formation. Mostly sandstones interbedded with thin mudstones and siltstones. Some unusual channelised sandstones present.
57 Knockaraven
Upper Palaeozoic - Devonian. Shanmullagh Formation. Exposures of interbedded purple-red and brown sandstones and siltstones.
216 Crockanaver Quarry
Carboniferous. Exposure of stratotype for Crockanaver Limestone Member of Ballyshannon Limestone Formation.
227 Makenny
Carboniferous. Exposure of lithologies of Ballinamallard Mudstone Formation. Some fossils, including plant fragments, near top of section.