Sheepland Coast ASSI

The area is of special scientific interest because of its coastal flora and fauna and earth science features. Sheepland Coast is a rocky coastline in County Down, with cliff vegetation and other grassland communities. It includes pockets of saltmarsh and strandline along sheltered inlets.

The rock exposures along the Sheepland Coast are exceptional, providing much detail of the important geology of the area. The exposures are composed of Lower Palaeozoic sedimentary rocks of deep marine facies, strongly folded, faulted and weakly metamorphosed. The main rock types are thinly bedded, fine–grained sandstones and siltstones of the Hawick Group. These are Silurian sedimentary rocks of approximately 395 million years old and are part of the Scottish Southern Uplands/Irish Down-Longford Terrane, which records the closure of the Iapetus Ocean during the Caledonian Orogeny. A terrane is a geological unit, discrete in terms of structure and age, and distinct from adjoining areas.

Since 1977, the terrane has attracted international interest because of its interpretation as an accretionary prism. There is ongoing debate concerning the geographical position of the sediments which now form the rocks of this region, namely whether they were fore-arc or back-arc sediments. Irrespective of this, sediments were accreted on the north-western, Laurentian, shore of the Iapetus Ocean during plate collision and ocean closure. The unresolved argument between proponents of these rival hypotheses is critical to understanding of the British and Irish Caledonides.