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 can be viewed naturally as an extension of the region described as the Central Lowlands, although it extends southwards into the adjacent region of the Uplands and Drift Covered lowlands of Down and Armagh. 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. 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 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 Donaghcloney Valley is at the head of the broad River Lagan valley. It is a broad, flat-bottomed valley which lies between the Upper Ballinderry Plateau to the north and the Kilwarlin Plateau to the south. The River Lagan meanders tightly at the entrance to the broader valley to the northeast and is a prominent focus in views. It occupies a small channel but its visual presence is emphasised by streamside willows and the historic remnants of water mills near the head of the valley.
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 - various intrusives, about 55 million years old |
| Tertiary - Lower Basalt Formation, about 55 million years old |
| Cretaceous - Hibernian Greensand & Ulster White Limestone Groups, about 100 million years old |
| Triassic - Mercia Mudstone & Sherwood Sandstone Group, between 240 and 210 million years old |
| Silurian - Hawick Group, about 430 million years old |
| Ordovician (predominant) - Moffat Shale and Gala Sandstone, about 450 milion years old |
The northwestern edge of the LCA comprises the Cretaceous - Tertiary low escarpment. 50% Sherwood Sandstone, 20% Mercia Mudstone, 10% Cretaceous, 10% Lower Palaeozoic, 10% Lower Basalt Formation and various intrusives.
Lower Palaeozoic greywacke sandstones and shales vary from a few centimetres to a few metres in thickness with a large proportion of rock fragments and a fine-grained matrix. The greywackes are commonly quarried as a source of aggregate; they are interbedded with thinner beds of siltstone or mudstone, commonly arranged as fining-up cycles. Minor conglomerates and volcanic ash-beds (or bentonites) occur.
Triassic - Sherwood Sandstone Formation sandstones comprise red, purple and brown cross-stratified sandstones, siltstones with minor clay beds and partings.
Below the Cretaceous - Tertiary escarpment and above the Sherwood Sandstones to the north and northeast of LCA80, low ground is underlain by soft sedimentary rocks of the Triassic Mercia Mudstone Group. The Mercia Mudstone Group is 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. These sediments were formed in an arid, enclosed shallow seaway or saline lake between 230 and 215 million years ago.
The Cretaceous succession forms a discontinuous northeast-southwest oriented strip below the low basalt escarpment that occurs to the north of this LCA. At the base, fossiliferous, phosphatic, conglomeratic greensands (0-1m thick) rest unconformably on the strata listed above. Above the greensand occur the limestones of the Ulster White Limestone Group. These sediments were laid down in a tropical sea some 90 million years ago. The limestones contain palaeokarst, or fossil caves of possible late Cretaceous, or probable early Tertiary age.
The Tertiary-aged basalt formation comprises a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles).
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 a river valley underlain by Late Midlandian till deposited by ice that moved southwards out of the Lough Neagh Basin. Superimposed upon this are extensive alluvial deposits associated with the floodplain of the upper Lagan.