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,, although it grades westwards into the valley floor of the River Foyle and eastwards into the Northe Derry Uplands and Sperrin Mountains. The Western River Basins 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 Burngibbagh and Drumahoe landscape character area includes the long, linear valley system of the Burngibbagh and the lower Faughan River and its enclosing ridges. The valley lies to the east of Londonderry and is parallel to the River Foyle. The valley has a strong linear form and is aligned along a NE-SW fault-guided axis of Caledonian trend. The valley floor is relatively flat and well defined and the enclosing ridges have a broad, rounded landform with open summits. The higher summits, such as Gortree Hill and Clondermot, are capped with moorland, which stands out clearly against the surrounding green pastures. The Faughan River enters the Burngibbagh and Drumahoe valley system at its central point and then turns abruptly north to follow the natural fault-line. The valley is more open at this point and there is industrial development on the outskirts of the settlement of Drumahoe, as well as development spreading westwards from Londonderry along the A6. The southern part of the valley, which contains the Burngibbagh, has a more secluded character. The Faughan Valley is of high scientific interest due to the presence of extensive glaciolacustrine and glaciofluvial deposits consisting of deltas, moraines, eskers and outwash plains occurring in close field associations. There is scope to restore some of the disused sand and gravel quarries in the Gorticross area.
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 - about 350 million years old |
Barony Glen |
Dalradian (Neoproterozoic) - about 600 million years old |
Un-named metabasites |
Londonderry |
Ballykelly |
This LCA is dominated by Dalradian (Neoproterozoic) strata of the Londonderry succession. Structural strike is dominantly east-west to northeast - southwest (NE-SW) with overall northerly dip in the north. These rocks were originally sediments with igneous intrusions: they have been metamorphosed and deformed, such as those seen at ESCR Site 336, Kittybane Quarry.
Two tectonic phases have affected the area: the Caledonian (Ordovician - Silurian) and Variscan (end Carboniferous). Caledonian deformation is very apparent throughout the Dalradian succession.
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 drift geology map for this LCA shows a landscape dominated by a mosaic of drift-free summits and lowlands masked by a cover of Late Midlandian till. The latter was laid down by ice that flowed northeastwards along the Foyle Valley, and the direction of flow is recorded by a mix of streamlined drumlins and rock ridges. However, the Quaternary features that are of possibly greatest geomorphological and geological significance are located within areas of deglacial sand and gravel. Of particular interest are those found in the valley of the lower Faughan, that form part of the Faughan/Dungiven Basins Complex. Although extensive sand and gravel deposits also occur in the valley of the Burngibbagh and in the west of the LCA, where there is a small area of the Foyle Valley Complex.
The Faughan/Dungiven Basins Complex in this LCA consists of 2.1km2 of outwash deposits along the lower Faughan Valley. The complex itself consists of glaciofluvial deposits that are primarily deltaic in origin and are situated along structural lows in the upper Faughan and upper Roe drainage basins. The area is of high scientific interest due to the presence of extensive glaciolacustrine and glaciofluvial deposits consisting of deltas, moraines, eskers and outwash plains occurring in close field associations. The high relief range allows pleasant views both from the basin bottoms and from the Sperrin valleys. There is a general lack of commercial sand and gravel production in the area except immediately east of Dunnamanagh and another, larger pit at Moyagh. Most of the complex occurs in LCA 30, smaller areas occur in LCAs 27, 29, 33, 34 and 37.
The Foyle Valley Complex in this LCA consists of a small area (0.9km2) on the western border with LCA 27. The complex itself is a widespread assemblage of landforms which are genetically linked by formation during ice-margin retreat westward from the Sperrin valleys during the last deglacial cycle. Strong control on ice-margin configuration and meltwater drainage patterns was exercised by bedrock topography, serving to focus meltwater along the valley axes. This resulted in the formation of thick, flat-topped glaciofluvial terraces. Increases in sediment supply or temporary reductions in ice-margin retreat rates resulted in the accumulation of thick belts of hummocky moraine. Most of the complex can be found in LCA 27, smaller areas in LCAs 20, 21, 26 and 29.
Key Elements Deglacial Complexesthe Faughan/Dungiven Basins Complex
Deltaic deposits are preserved at seven principal locations and are of special scientific interest, as their widespread extent and relationship to proglacial water levels implies that substantial, deep lakes were impounded along the Faughan and upper Roe valleys as Irish ice masses retreated southwards and Scottish ice advanced southwestwards into the lower Roe valley. The upper Roe (Dungiven) and middle to upper Faughan valley basins have been used for mineral aggregate production in the northwest of the province for approximately twenty years.
the Foyle Valley Complex
The complex has a high scientific value, for understanding the complexity of deglacial processes and records ice retreat westward from the western Sperrin valleys into the topographic low of the Foyle valley, indicating ice pressure from the direction of the Omagh basin to the south during the last deglacial cycle.
Other sites/units identified in the Earth Science Conservation Review336 Kittybane Quarry
Precambrian. Quality outcrop of Ballykelly Formation on south of Lough Foyle Syncline. Preserved sedimentary structures.