Carey Valley ASSI

The area is of special scientific interest because of its earth science features, and its fen communities and rare plants. The Carey Valley area is of importance in understanding the recent glacial history of Northern Ireland. The landscape of this area has been defined by events that occurred towards the end of the last Ice Age, between 17,000 and 13,000 years ago, a period of gradual climatic warming. The area contains meltwater channels, glaciofluvial terraces and a flat topped Gilbert type delta in pristine condition. The area is of national importance as an example of a deglacial landform association. It also contains nationally important exposures of the Dalradian age Runabay Head Formation of the Southern Highland Group.

A relatively small frontal moraine is found to the north of Loughareema, marking the frontal position of the ice at the time. The upper valley (to the south-east) acted as a subglacial conduit for meltwater, transporting water and sediments down valley to form the delta surfaces and other landforms. The Altdorragha section of the main (A2) Cushendall to Ballycastle Road passes through the centre of this channel.

At Loughareema the main water flow was enhanced by other subglacial drainage channels which created a plunge pool on the site of the present lake. Today the lake periodically ‘vanishes’ due to the underlying geology. The Ulster White Limestone strata that lies below the site contains a system of pores and fractures that would be expected to allow rapid drainage. However, the peat laden water blocks this system until the hydrostatic pressure of the accumulating water is sufficient to ‘flush’ the peat through, enabling the water to drain.

The available evidence suggests the upper sediments found in the Carey Valley were deposited in a proglacial water body, i.e. in front of an ice mass, as the ice was retreating to the south. Glacial melt water transported sand, gravel and mud from beneath the ice and deposited it in this water body, forming flat topped (Gilbert type) deltas. The flat tops of the deltaic sediments reach a height of approximately 100m above sea level, which therefore corresponds to the position of the surface of the water body. The best developed of the delta surfaces is found southeast of Ballyvoy, between the Drumadoon and Ballynagard townlands.

There are two possible explanations for the particular depth of water recorded; either the relative sea level at this time was 100m higher than at present or the water was dammed in the valley by another ice mass to the north. A higher relative sea level would require greater ice loading on the land surface at this time than has been recorded for other parts of Northern Ireland, but there is also no evidence to suggest a re advance of Scottish ice to the north, which would be required to produce an impounded freshwater lake.

As the level of the proglacial water body dropped, the continuing flow of meltwater began to erode the deposited sediments, leading to the deeply incised landforms observed today. In the upper part of the valley, the Carey River flows through a steep sided meltwater eroded gorge and moving north, terraces at lower levels indicate modification by glaciofluvial processes.

The rocks exposed along the Altdorragha channel are from the Leckpatrick Green Bed Member and are of Upper Dalradian age, some 750 million years old. They constitute the uppermost stratigraphic levels of the Runabay Formation of the Southern Highland Group and are a mixture of contrasting siliciclastic and volcanogenic sediments typical of the Southern Highland Group throughout northern Britain. The sediments were originally laid down as turbidites in marine sedimentary basins on the edge of the Laurentian continent. These basins gradually filled and subsided due to the weight of sediment deposited from the continental landmass. Erosion and deposition of mafic extrusive and intrusive igneous rocks led to the formation of two distinct ‘green beds’ interbedded with the sands and muds of the Formation. The rocks were subsequently deformed and metamorphosed during the Caledonian Orogenesis, or mountain building event, into schists that contain diagnostic metamorphic minerals.
Biological interest within this large geological site is restricted to a mosaic of semi-natural upland habitats overlying the glacial landforms and the plants which they support. Of particular importance is the presence of a small population of yellow saxifrage and the fen communities associated with Loughareema.

Yellow saxifrage is known only from a small number of sites in the north-east of Northern Ireland and from Fermanagh. At Carey Valley, it is found on a steep, semi-eroded face of loose, glacial deposits that continually seeps base-rich water. It is adjacent to the stream at Ess Bridge, in the townland of Coolnagoppogue. The population consists of several distinct colonies, with individual plants scattered in the immediate vicinity. Typical associated species include glaucous sedge, red fescue, jointed rush, lesser clubmoss, grass-of-Parnassus, occasional coltsfoot and a range of bryophytes including calk comb-moss, curled hook-moss and marsh bryum.

The fen communities around Loughareema are concentrated to the west of the road which remains permanently flooded unlike most of Loughareema which is subject to periodic drainage. Water horsetail and bottle sedge swamp has developed in the shallow waters around the periphery of the lough with transitions to fen communities with common sedge, bogbean, marsh horsetail, marsh pennywort and marsh violet. The fen communities are more extensive and diverse to the south, where a series of flushes and soaks are concentrated into a narrow gully feeding into the Lough. The vegetation associated with the central soak is dominated by cow-horn bog-moss and perfoliate pondweed with dioecious sedge a widespread but localised upland species of alkaline flushes, also occurring.
Where the stream enters the lake from the south, an extensive area of bottle sedge fen has developed over a moss carpet of flat-topped bog-moss. Notably, stonewort is also present where the stream enters the lake, further reflecting the base-rich nature of the seepage waters.
The upper region of the flush is dominated by more acidic species such as star sedge and common cottongrass which is more characteristic of the blanket peat communities within which Loughaveema is set. More transitional fen communities dominated by spiky bog-moss also occur where these acidic, upland flushes converge with the more base-rich waters.

Carey Valley also provides a mosaic of upland habitat that is valuable for associated invertebrates, birds and animals, including common lizard.

Site Related Documents

Site map (.PDF 1,861 Kb), Citation and combined Views about Management document (.PDF 340 Kb).