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 Antrim Plateau and Glens. This upland area is dominated by a series of structural plateaux that dip gently in towards the Lough Neagh Basin. Detailed topography is largely controlled by a succession of Tertiary basalt lava flows that define successive, large-scale steps within the landscape. The plateaux are separated from each other and their frequently dramatic margins are fretted by often fault-guided, steep-sided glens. Recession of the plateaux margins has exposed underlying Mesozoic strata and, in some areas, the Palaeozoic basement. The plateaux margins are typically characterised slope failures that range from large rotational landslides to individual blockfalls.
The Larne Glens are the deeply incised valleys of the Glencloy and Glenarm Rivers, which extend inland from the coast. The settlements of Carnlough and Glenarm are situated on the coast at the mouths of the glens. There are dramatic contrasts in colour and landscape character between the lush, diverse glen landscapes and the exposed uplands of the Larne Basalt Moorland. To the north east of the glens, a narrow coastal strip is backed by the dramatic moorland slopes of the Garron Plateau. Old quarry workings produce dramatic features along the steep glen slopes, especially on the slopes above Carnlough where the old quarry scars are distinctive landmarks. They are of earth science interest and have been designated as an ASI. The scenic character of the glens is reinforced by well managed landscape elements which contribute to a high quality landscape worthy of conservation. It is part of the designated Antrim Coast and Glens Area of Outstanding Natural Beauty (AONB). The landscape can therefore be summarised as one of incised glens with smooth ridges rising to stepped moorland summits and opening out towards the Larne coast. Of particular geomorphological interest are the coastal slopes below the Garron Plateau. These comprise large rotational landslides that form a major feature of the Antrim coast, with many of the larger blocks more than 100m across. These rotational features are thought to have been most active in the immediate post-glacial period when the supporting ice had disappeared from the plateau edge and when there was abundant moisture to aid slippage. The large-scale rotational failures may effectively be viewed as relict features under present-day conditions, but surface modification of the slopes continues through smaller-scale rockfalls, debris slides and dissection of the larger blocks. However, present-day modification is not restricted to slope failure but also includes weathering of the basalt and chalk. An excellent example of modification through weathering can be seen on the seaward side of the coast road at Garron Point. In this area chalk is directly exposed to marine action with the result that several weathering zones can be identified related to their proximity to the sea and weathering forms that are typical of so-called marine karst. The intertidal and splash zones are most directly affected by marine activity and are characterised by extensive pitting of the chalk surface attributed to salt weathering and limited biological weathering by lichen and algae.
The coastline of east Antrim has been described by Orford (in Whalley et al. 1985) as comprising high, stepped coastal slopes formed on the ice-trimmed eastern margin of the Antrim Plateau. Post-ice cambering and Pleistocene neotectonic movement along Tertiary faults has produced a highly unstable cliff line with numerous rotational landslides often masked on their seaward side by slumped drift deposits. Shoreline sediments are predominantly basalt and chalk boulders with a matrix of sand and clay from debris flows that are moved longshore and offshore. The SW-NE trending Antrim Glens define offset re-entrant bays in which sand and gravel have been deposited as prograding beach ridges. The coast road runs along a series of raised beach platforms that are mainly of late- and post-glacial age and are most prominent at Larne. The coast road is protected along much of its length by a reflective sea wall that denies much fresh sediment to the beach and has resulted in the scouring away of beach sediment down to a boulder lag. North of Cushendall the basalt is replaced by Triassic sediments and the Palaeozoic basement. Good examples of abrasion platforms with associated stacks, arches and caves occur, testify to the scale of post-glacial isostatic uplift in the area. The coastline is described in further detail by Carter (1991), including human impact on the coast related in particular to sand and gravel removal.
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, sills and volcanic plugs, around 55 million years old |
| Tertiary | Upper Basalt Formation, about 55 million years old |
| Tertiary | Interbasaltic Formation, about 55 million years old |
| Tertiary | Lower Basalt Formation, about 55 million years old |
| Cretaceous | Hibernian Greensand & Ulster White Limestone, around 100 million years old |
| Jurassic | Waterloo Mudstone Formation, about 200 million years old |
| Triassic | Mercia Mudstone Group, Penarth Group, between 220 and 200 million years old |
LCA123 contains igneous and sedimentary rocks of Triassic to Tertiary age.
In general, Cretaceous greensands and limestones or Tertiary basalts rest unconformably and in faulted contact with and on a range of older Mesozoic rock units.
Below the Cretaceous - Tertiary escarpment in the east of LCA123, low coastal ground is underlain by soft sedimentary rocks of the Triassic Mercia Mudstone Group. The group is an aquiclude, soft and contains anhydrite, making it part of the landslip sequence, acting as a horizon of failure.
The Jurassic Waterloo Mudstone Formation comprises dark grey mudstones and shales, alternating with grey limestones: it occurs as a strip between Mercia Mudstone and Cretaceous greensands (see below).
The Cretaceous succession of greensands with white limestone (or chalk) forms a faulted outcrop strip to the east of LCA123. The limestones are quarried extensively for lime and aggregate. Galboly and Garron chalks seen at Garron Point (ESCR Site 279). Glenarm Chalk Member seen in Glenarm Quarry ESCR Site 280. Creggan Chalk Member seen in Creggan Quarry (ESCR Site 281)
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. Dolerite dykes intrude all older rocks of the area. They are extensively quarried for construction materials, especially roadstone.
Normal faults of differing orientations cross the area, juxtaposing all the above formations. The most linear and laterally traceable faults are those that parallel the coast, being NNW - SSE. Many of these structures have been activated in the last 10,000 years during landslip activity.
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 that much of the top of the coastal escarpment is drift free. However, Late Midlandian till underlies the south of the LCA associated with the large ice mass that was centred on the Lough Neagh Basin. This ice moved approximately northeastwards from an ice divide running along the crestline of the Belfast Hills. In the North of the LCA, the coastal lowland behind Carnlough is also underlain by till, but Prior (1970) has suggested that similar deposits in the glens to the north were laid down by ice that moved northwards along the line of the present-day coastline. The drift map also highlights the extensive coastal landslips discussed in the geomorphological description of the LCA and an area of raised beach deposits at Carnlough (see Key Elements below).
Key Elements ASSI/ASI143 BLACK BURN ASSI (Mostly in LCA 122, a small element overlaps this LCA)
Black Burn Cave is the only known extensive, active cave system developed in the Cretaceous age Ulster White Limestones in Northern Ireland and is probably the most extensive karst drainage system that includes an open passage developed within Cretaceous limestone in the British Isles.
CARNLOUGH ASI
Beds of peat, infrequently exposed on the beach at Carnlough, are known from radiocarbon dating and pollen analysis to be of late-glacial and Holocene age. The peats overly beach gravels below which is a thick sequence of finely laminated silts and clays, and glacial till. Inland of the beach, are two shore-parallel, raised gravel ridges that are probably younger than the peats. The sedimentary sequence preserved at Carnlough records evidence for coastal and landscape change from ca 15 000 to 6 000 years ago.
Karst FeaturesNappan Turlough (split between this LCA and LCA 122)
This small lake, which fills and empties in response to ground water levels, is underlain by the Ulster White Limestone Formation. It has no visible inlet or outletand is commonly dry in summer.
Other sites/units identified in the Earth Science Conservation Review279 Garron Point - Cloghastucan
Mesozoic. Excellent exposures of Galboly Chalk and Garron Chalk Members of Ulster White Limestone Formation. Effects of Dalradian ridge on chalk sedimentation can be seen.
280 Glenarm Quarry
Mesozoic. Type section for Glenarm Chalk Member of Ulster White Limestone Formation. Illustrative of chalk sedimentation in Larne-Lough Neagh Basin.
281 Creggan Quarry
Mesozoic. Thick sequence of type section of Creggan Chalk Member of Ulster White Limestone Formation. Illustrative of chalk sedimentation in Larne-Lough Neagh Basin.
82 Craigcluggan/Skeagh
Tertiary.
AONBAll of this LCA lies within the Antrim Coast and Glens AONB (1988). This designation is indicative of the scenic quality of the landscape.