Summary of site:
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 rich in nutrients and countless billions of microscopic plants called coccoliths clouded its water and fell in an incessant rain on to the sea bed. This creamy white ooze is what today we call 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 trending ridge of ancient Dalradian rock, the Highland Border Ridge. It was around 15km wide and crossed the modern coastline at Fair Head. 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 subsiding 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 ooze accumulated on the united sea bed for the next 10 million years.
Capecastle Quarry sits on the northern flank of the Highland Border Ridge and shows just how influential it was as the Ulster White Limestone was accumulating. The quarry floor is composed of a chalk called the Creggan Chalk Member which in turn is followed by the Boheeshane Chalk Member and then the boldly bedded Larry Bane Chalk Member. It was during the deposition of this last member that the ridge was overwhelmed and the two basins united. Two further chalk members, the Ballintoy Chalk and the Glenarm Chalk form the upper 20m of the quarry face.
The influence of the ridge on sedimentation can be seen in the thickness of the Boheeshane Chalk which is 3m thick in the quarry but over 24m where it is best developed in the more freely subsiding north-westerly Rathlin Basin. Following the inundation, the 8 succeeding chalk members are of much the same thickness from Larne to the north coast.
Fossils are difficult to collect in the Ulster White Limestone, which is significantly harder than the British Chalk, but a small fauna of sponges, sea urchins, brachiopods, bivalve molluscs and belemnites has been found in the quarry.
This abandoned quarry is the best example of the influence of the Highland Border Ridge on late Cretaceous chalk sedimentation in the north of Ireland. It is therefore a key site nationally and should be designated and protected. The usual threats of dereliction, dumping and overgrowth apply in this case with further potential hazards of landfill and forestation in the future.