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 considered as an extension of the region described as the Central Lowlands, although it derives much of its character from proximity to and the visual impact of the escarpment of the Antrim Plateau. The central Lowlands owe much of their 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 Carrickfergus Shoreline itself, forms a fringe of flat land, 1km to 3km wide, between the high basalt ridge of the Carrickfergus Farmed Escarpment to the north and Belfast Lough to the south. The accommodating relief has been utilised by extensive development that runs more or less continuously along the length of the shore and extends westwards to the outskirts of Newtownabbey. Orford (in Whalley et al. 1985) has described Belfast Lough as the fault-guided boundary between the Palaeozoic basement to the south and the Tertiary lava plateau to the north. There has been considerable man made modification of the shoreline over the last one hundred years. And most of the coastal road system and the northern edge of Belfast is on 'made ground'. Some minor sea level falls have accompanied this landfill. Sediment supply to the Lough is now very limited and in some cases, as at Carrickfergus, shoreline extensions have overstepped existing sediments and have required the construction of coastal defences. Tertiary dyke swarms orthogonal to the lough shore have acted as natural groynes and have lead to the limited development of crenellate bays.
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.
Stratigraphic Table (youngest rocks at the top of the table)| Tertiary Intrusive dykes and sills - about 55 million years old |
| Tertiary Lower Basalt Formation, around 55 million years old |
| Cretaceous Hibernian Greensand & Ulster White Limestone, about 100 million years old |
| Jurassic Waterloo Mudstone Formation. About 205 million years old |
| Triassic Sherwood Sandstone Group, Mercia Mudstone Group, Penarth Group, between 250 and 200 million years old |
This LCA extends along the north side of Belfast Lough to the parallel escarpment. LCA129 contains igneous and sedimentary rocks of Triassic to Tertiary age.
In general, Cretaceous greensands and limestones or Tertiary basalts rest unconformably on a range of older Mesozoic rock units.
Sherwood Sandstone Group strata occur at Greenisland - a small, folded outcrop (ESCR Site 451).
Below the Cretaceous - Tertiary escarpment to the northwest of LCA129, 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. Exposed at ESCR Site 450 - Carrickfergus Castle. The group is an aquiclude, soft and contains anhydrite, making it part of the landslip sequence, acting as a horizon of failure. Within LCA129 the Mercia Mudstone Group contains two c.150 metre-thick successions of halite or rock salt. Above the Mercia Mudstone Group, the Triassic Penarth Group comprises a succession (from the base) of carbonate-cemented siltstones, limestones, mudstone and black shales. The succession is interpreted as representing the latest Triassic transgression of the sea; this continued into the earliest Jurassic.
The Cretaceous succession forms a faulted outcrop strip to the northeast of LCA129. Above the basal greensands occur the limestones of the Ulster White Limestone Group. The limestones are quarried extensively for lime and aggregate outside of the LCA.
Tertiary-aged basalts comprise a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles) of the Antrim Lava Group. Only the Lower Basalt Formation crops out in this area, where its hard, durable nature makes it resistant to erosion. The main dolerite dyke intrusion of the area occurs beneath Carrickfergus Castle, where it intrudes Mercia Mudstone Group (causing local thermal metamorphism and hardening) and providing the erosion-resistant headland that forms the castle headland (ESCR 451). A less obvious dolerite intrusion occurs within the Lower Basalt Formation at the northeastern tip of LCA129. One major fault (or fault zone) is mapped in the northeast of LCA129. This NNW-SSE oriented normal fault juxtaposes Lower Basalt Formation and underlying Cretaceous and Jurassic with Mercia Mudstone Group sediments to the northeast, demonstrating a post-early Tertiary age for movement.
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 predominantly underlain by Late Midlandian till associated with the large ice mass that was centred on the Lough Neagh Basin. The composition of this till largely reflects that of the underlying solid geology and the carry over from one outcrop to another in this area is very limited - although some far-travelled erratic pebbles can be found. Thus, tills from the basalt are characteristically dark brown, those from Palaeozoic rocks bluish grey and those from Triassic rocks reddish brown.
In addition to the till cover, there is a very important extent of raised beach deposits along most of the coastline as far north as Kilroot. These deposits are the result of post-glacial flooding by a rising sea level, of a landscape that was still isostatically depressed following the disappearance of Midlandian ice. Griffith and Wilson (1982) describe these deposits as extending inland from the present-day storm beach to an abandoned cliff line cut in the till. Sections exposed west of Thompson's Point have revealed a basal bed of large rounded basalt cobbles with occasional chalk boulders below 1.5m of calcareous sand containing bands of cobbles. The beach deposits mostly rest directly on a wave-cut Trias platform and occasionally on a till platform. At Carrickfergus, sand and gravel of raised beach age have been found that contain Mesolithic stone tools.
Finally, ribbons of alluvial deposits mark the floodplains of the present-day rivers.
Key Elements ASSI104 OUTER BELFAST LOUGH
Outer Belfast Lough is a structurally defined feature, possibly marking the continuation of the major Southern Uplands Fault from Scotland to Ireland. The site is important for the Ordovician seris of spilitic lavas, black shales and greywackes. The Carboniferous series of the Holywood group are also of significance and the Permian rocks are the best exposed series of rocks of this age in Ireland. The habitat range includes open mud flats, boulder and rock shore, extensive mussel beds and a narrow shoreline strip of semi-natural vegetation including small, isolated pockets of beach-head saltmarsh.
Sites/units identified in the Earth Science Conservation Review450 Carrickfergus Castle
Exposures of Mercia Mudstone Group, with massive dolerite intrusion on which Carrickfergus Castle is built. Below the castle examples of contact metamorphosed country rock.
451 Greenisland
Exposures through folds of Sherwood Sandstone and Mercia Mudstone Groups. Also exposure of Estuarine Clays (Holocene).