Capecastle ASSI

The Capecastle area is a special place because of its earth science interest. The area provides access to an interesting sequence of chalk exposed in the disused quarry.

In the late Cretaceous period, around 85 million years ago, Chalk seas began to encroach into the lowlands of what is now the north east of Ireland. This warm, sub-tropical sea was home to billions of microscopic plants called coccoliths; these fell in an incessant rain on to the sea bed. This white ooze solidified and today forms the Chalk or, in Ireland, the Ulster White Limestone.

At that time the landscape consisted of two lowland areas separated by a prominent north-east/south-west ridge of older Dalradian rock. The sea invaded the lowlands on both sides of the ridge and, over a period of roughly 3 million years, great thicknesses of the chalky ooze accumulated on the sea beds in the separate basins and against the flanks of the ridge.

Around 80 million years ago, the sea finally overwhelmed the ridge and from then on chalk accumulated on the united sea bed for the next 10 million years. Capecastle Quarry sits on the ridge and shows how influential it was on the thickness of chalk found here. Thinner units are found in the quarry compared to the once deeper water areas to the north and south. Once the ridge was overwhelmed by rising sea-levels, chalk units were roughly the same thickness throughout the wider area. The quarry also shows the overlying basalts which were erupted through much of Antrim 60 million years ago.