Kilcoan ASSI

Kilcoan is a special place because of its earth science interest. The disused quarry provides access to a series of Cretaceous sedimentary rocks for which Kilcoan is the type or reference locality.

This site is important because it is the geological reference locality for two named rocks units – the Island Magee Siltstone Member and the Kilcoan Sands Member. These rocks are of Cretaceous age, the geological period that lasted from 145 to 65 million years ago. Towards the end of this period, Northern Ireland was covered by a shallow and warm sea.

The older rocks, that include the rocks found at Kilcoan, belong to a group known as the Hibernian Greensands – because of their colour. The greenish colour is due to the presence of a mineral called Glauconite. It makes up the bulk of some of the rock units at Kilcoan giving them a characteristic dark green colour. The rocks formed at the end of the Cretaceous are the white chalk which can be seen around much of the Antrim coast. The chalk is present at Kilcoan and was the main reason for the quarry to open here.

The rocks found at Kilcoan are mainly sandstones and were deposited about 90 million years ago in an ancient sea. A range of fossils in the rocks tell us something of the life present in this ancient sea and include ammonites, sea urchins, shells (including oysters) and lampshells (Brachiopods).