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 Upper Ballinderry Plateau itself, is a rolling, relatively prosperous farmland landscape on the southern and western fringes of Derrykillultagh which extends to the edge of Lurgan. There is a steep escarpment along the southern margins of the landscape, overlooking the broad Lagan valley. This escarpment is subdued in comparison to the main plateau edge that overlooks Belfast, but nonetheless is dissected by a number of incised streams creating steep-sided glens. The original landscape character assessment identifies Friars Glen, between the village of Aghalee and Soldierstown as having a fairly steep, wooded character. The north of the LCA corresponds approximately to the lower dip slope of the South Antrim basalt escarpment. As such, the structural control of the basalt flows has produced a gently undulating landscape with limited fluvial incision. The south of the LCA is of interest because at the end of the Midlandian it was an axis of drainage westwards into the Lough Neagh basin. This has left behind limited, but important deposits of glaciofluvial sands and gravels.
Pre-Quaternary (Solid) GeologyThe stratigraphy of this area is made up of these mapped formations, the youngest (top) of which usually overlie the oldest (at the base). The older formations can be upside down (tectonically inverted).
Stratigraphic Table (youngest rocks at the top of the table)| Tertiary - intrusives, especially dolerite, about 55 million years old |
| Tertiary - Lower & Upper Basalt Formation, between 50 and 60 million years old |
| Cretaceous - Hibernian Greensand and Ulster White Limestone, about 100 million years old |
| Triassic - Mercia Mudstone Group, about 210 million years old |
| Triassic - Sherwood Sandstone Group, about 230 million years old |
LCA109 comprises 80% Lower Basalt Formation.
Triassic Sherwood Sandstone Formation sandstones comprise red, purple and brown cross-stratified sandstones, siltstones with minor clay beds and partings. Outcrop restricted to small incursions of LCA109 into the western parts of the Lagan Valley. The Triassic Mercia Mudstone Group comprises red silstones and mudstones, predominantly red-brown and unfossiliferous in the lower parts of the exposed succession, becoming grey-green, sometimes fossiliferous and sometimes carbonate-cemented toward the top.
The Cretaceous limestone and greensand succession is found in linear, fault-bounded exposures below the Tertiary basalt escarpment of LCA109. Clarehill Quarry (ESCR Site 284) exposes examples of silicified paramoudra - a giant fossil burrow.
NW-SE trending dolerite dykes are mapped in the Triassic succession in the east of the area. The basalt formations comprise a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles) that dominate LCA109. The basalts rest unconformably on the older formations. They are extensively quarried for construction materials in this area, especially roadstone.
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 underlain for the most part by Late Midlandian till laid down by ice that moved rapidly across the area from a centre in the Lough Neagh Basin. As long ago as 1939, Charlesworth in his seminal paper on the glaciation of northeast Ireland identified a number of drumlins in the south this area and their orientation can be used to confirm the eastwards/southeastwards flow of this ice. 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. 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. 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.
Of considerable interest, though only of limited areal extent, are a series of glaciofluvial deposits that occur in the centre and south of the LCA. These are part of the Lagan Valley Deglacial Complex. This is a discontinuous belt of glaciofluvial and glaciolacustrine deposits that occurs for 40km along the axis of the Lagan valley from Belfast WSW to Aghalee, Co. Antrim. The complex consists of four main elements; (1) poorly exposed deltaic sands which underlie most of south Belfast; (2) steep-sided esker remnants at Lisburn; (3) flat-topped cross-valley ridges with associated feeder channels at Drumbeg, Sandymount and Hillhall; (4) a flat glaciofluvial outwash spread at the Maze. Kettle-hole depressions and meltwater channels also occur occasionally, including a drainage channel that runs northwestwards through Broad water to Aghalee on the border with LCA 62. Glaciofluvial deposits in this LCA consist of a small area of deltaic sediments in the west, overlapping with LCA 62, The Ballindery Esker and part of the Causeway End Esker that continues eastwards into LCAs 108 and 97. Most of the Complex can be found in LCAs 97, 106 and 107, with minor areas in LCAs, 62 and 108.
There are a number of other, isolated areas of glaciofluvial deposition that may be related to ice marginal conditions at the end of the Midlandian. Davies and Stephens (1978) consider that the final stages of ice-wasting in the east of Northern Ireland probably involved wide scale stagnation, downwasting and withdrawal inland towards the Lough Neagh lowlands (p.176). This would have left upland areas such as the Antrim Plateau ice free and surrounded by encircling ice.
Key Elements Deglacial ComplexesLAGAN VALLEY DEGLACIAL COMPLEX,
The Lagan Valley Deglacial Complex is highly important in understanding the complexity of deglacial processes. Streamlined landforms along the margins of the valley and glacially moulded bedforms indicate ice advance and episodes of fast ice flow from the west. Glaciolacustrine deposits indicate that during initial deglaciation the lower valley contained an ice-dammed lake, probably impounded by Scottish ice in outer Belfast Lough. A lobe of Irish ice located in the valley, related to ice pressure from the Lough Neagh Lowlands contained subglacial conduits now recorded by eskers that probably supplied sediment to the Malone deltaic sands that now underlie most of south Belfast. The phased retreat of the ice lobe further westward is recorded by cross-valley ice-contact ridges. During the final deglaciation, drainage was to the west, indicating a reversal in the drainage gradient probably due to isostatic depression of the Lough Neagh Lowlands during the last glacial cycle.
Sites/units identified in the Earth Science Conservation Review284 Clarehill Quarry
Mesozoic. Well exposed paramoudras of Ballymagarry Chalk Member. Representative sequences of attentuated Ulster White Limestone Formation in Lagan Valley.
452 Broad Water
Preserved largest glacial drainage channel in Lagan Valley, formerly linking Glacial Lough Lagan and Glacial Lough Neagh.