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 Uplands and Drift Covered Lowlands of Down and Armagh. The generally subdued relief associated with the underlying basement complex of highly folded Palaeozoic strata provides the unity of this region. Relative relief is provided in the north by the Silurian hills that overlook the lower Lagan Valley, The Newtownhamilton Plateau in south Armagh, the Caledonian igneous complex of Slieve Croob and the structural depression that underlies and defines Strangford Lough. Below ca 350m, there is an almost complete mantle of drumlins forming an internationally acknowledged type example of a 'drumlin swarm'.
The Craigavon Plateau is the southwestern tip of the Upper Ballinderry Plateau area. It is found to the south of the Lough Neagh Peatlands landscape and the M1 Motorway and includes the extensive urban areas of Lurgan, Craigavon, and east Portadown. The plateau has a gently rolling or undulating land form, with steeper slopes on the margins of the Donaghcloney Valley, to the northeast and to the valley of the Upper Bann to the south. Small, winding, steep-sided valleys are attractive features on the southern edges of the plateau.
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 Lough Neagh Group, about 20 million years old |
| Tertiary - Lower Basalt Formation & Shane's Hill Rhyodacite, about 55 million years old |
| Cretaceous - Hibernian Greensand & Ulster White Limestone Groups, about 100 million years old |
| Ordovician (predominant) - Moffat Shale and Gala Sandstone, about 450 million years old |
80% of the LCA comprises Tertiary Lower Basalt Formation. Fault-bounded Tertiary Lough Neagh Clays to the west and Cretaceous and Lower Palaeozoic to the south-east.
Lower Palaeozoic greywackes are of sandstone grade and 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.
The Cretaceous greensand and white limestone (chalk) succession forms a discontinuous strip below the low basalt escarpment that occurs to the northwest of this LCA, except in the southwest.
The Tertiary Lower Basalt Formation comprises a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles). The top of the Lower Basalt Formation is marked by an eruptive volcanic phase and extensive weathering in many areas: in LCA79 the eruptions area recorded by the Shane's Hill Rhyodacites.
The western area of LCA79 is underlain by clays and lignites of the Lough Neagh Group in faulted contact with the Lower Basalt Formation. These supra-basalt non-marine deposits have been extracted for brick clays and lignite.
NW - SE oriented faults occur throughout the area: the most important of which is in the west of LCA79 as it brings Lough Neagh Group into contact with Lower Basalt Formation.
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 almost entirely by Late Midlandian till related to the southwards flow across the area of ice from a centre in the Lough Neagh Basin. This flow is indicated by a limited number of drumlins that are to be found in the south of the LCA. Although most drumlins within Northern Ireland 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.
The terrain in the west of the LCA has been influenced by the presence to the south of the Poyntz Pass glacial drainage channel. This channel formed during the deglaciation of the Lough Neagh lowlands, when there was a period when downwasting ice occupied the Lower Bann valley and prevented the northwards drainage of the proto-Lough Neagh. Lake levels then rose until an alternative outlet was found to the south via Poyntz Pass and Newry to Carlingford Lough (Davies and Stephens 1978).