Benburb-Milltown ASSI

The Benburb – Milltown area is a special place because of its earth science interest. The area provides access to a sequence of sedimentary rocks exposed within the River Blackwater valley.

The River Blackwater gorge between Benburb and Milltown hosts a series of disused quarries, together with natural cliff and river bank exposures. Together these exposures provide access to over 230 metres of Carboniferous rocks while exposures within the River Blackwater provide outcrop of the younger Triassic rocks. The Benburb – Milltown area hosts the reference location for a series of sub-divisions of these rocks.

The oldest rocks date from the Carboniferous period, when this area was part of a seabed experiencing warm, sub-tropical conditions. The area supported a diverse ecosystem, represented by the fossil remains which can be seen in the rocks today. Limestones are especially rich with many types of both solitary and colonial corals including a giant solitary coral named for the area Siphonophyllia benburbensis. Other groups represented include lamp shells (brachiopods), bivalve molluscs, moss animals (bryozoa), sea urchins (echinoids) and stone lilies or crinoids (animals related to star fish). Some of the shale sequences also contain fish remains in the form of teeth and scales.

The younger Triassic rocks, best seen in the Milltown area, represent a change of environment to one of desert conditions. The series of conglomerates and sandstones do not contain any obvious fossils, presumably because the environment in which they formed was not an easy one for life to flourish in and because the conditions at that time would not have preserved any evidence of plants or animals that might have existed. In total some 160 metres of Triassic rock can be accessed here.