Cushendall Formation

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Cushendall Formation

The Cushendall Formation is a rock unit in Northern Ireland that dates to the Early Devonian period. It outcrops near Cushendall in County Antrim, including areas around Cushendun Bay and Cushendun Caves.

Geology and age
- It is part of the Cross Sieve Group and is believed to be the youngest formation within the Cross Slieve Group.
- The formation lies above intrusive igneous porphyry and below the Ballyagan Formation.
- It can be up to about 600 metres thick.
- The rocks were formed from rhyolite and basalt fragments, which are overlain by conglomerate. The main lithologies are conglomerate and sandstone, with rhyolite and basalt also present.
- Because fossils are scarce or absent, the age is not dated more precisely than Early Devonian.

History and naming
- The Cushendall rocks were first surveyed in 1886 and thought to be metamorphic.
- Earlier geological maps (1934, 1953) helped define the area as part of the Old Red Sandstone.
- In 1984, Simon defined the Cushendall Formation as its own formation, named after Cushendall.

Paleogeography
- The formation is interpreted to represent an alluvial (river) environment that sometime experienced volcanic activity.

Location
- The Cushendall Formation is found in the Cushendall area of County Antrim, Northern Ireland.