Torr Head
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Geology & landscape
Geological Feature: Rock Outcrop · Rock Type: Limestone, Sandstone
Landscape processes: Volcanic / Igneous
Description
Torr Head Dalradian The outcrop at Torr Head includes the best exposures of metamorphosed limestones in Northern Ireland of Dalradian age. Torr Head is also the type locality for the Torr Head Limestone Formation. The site is of international importance because it is crucial to understanding the correlation with sequences elsewhere in Northern Ireland and in Scotland. Some 600 million years ago, sediment accumulating within an ancient ocean basin formed rocks which were incorporated into an enormous mountain chain. The residual Mountains. The burial and deformation of these rocks altered, or metamorphosed, them. The core of this range forms the uplands of north-east Antrim, as well as the Sperrin through the action of temperature and pressure. In the case of the sequence at Torr Head, both limestone, sandstone and volcanic rocks, the latter formed from cooling magma injected from depth, were metamorphosed and literally turned upside down. Given an absence of fossils in these ancient and deformed rocks, the existence of distinctive units, such as the Torr Head Limestones, permits relationships between associated rocks found here to be compared with those elsewhere. The rock succession is best seen on the southern side of Torr Head. A series of altered sandstones, the Altrnore Formation, contain important evidence that the succession has been overturned. The base of this sequence is marked by a lm thick coarse grit bed. This series is overlain by a 2m thick transitional zone of altered sedimentary rocks with thin limestone beds also present. These pass upwards into 6m of grey to black parallel-bedded limestones of the Torr Head Formation. Where the limestone lies close to the capping igneous mass of epidiorite, it has been further altered to a highly distinctive, coarse-grained, black graphitic limestone. At the top of section the limestone is overlain bt a massive metabasite which extends at least 50m to the top of Torr Head. This succession records the development of comparatively shallow nearshore marine sedimentary environments Torr Head Formation along the margin of Laurentia around 600 million years ago. Volcanic activity around that time resulted in the association of limestone and basaltic rocks recorded at Torr Head. Rifting along the continental margin continued into Upper Dalradian times, when basins developed and were infilled with sediments derived from the nearby continental landmass. This process is recorded in the sudden occurrence of coarse-grained rocks seen at the base of the Altmore Formation. The Dalradian rocks in north-east Antrim were subsequently deformed, folded and subjected to low grade regional metamorphism during the Caledonian Oregeny, a period of mountain building. Structurally, Torr Head and the Torr Head Formation lie on the downwards facing limb of the Altmore Anticline. This north-east to south-west trending recumbent anticline is interpreted as the south-westerly continuation into Northern Ireland of the Scottish Cowal Anticline. https://www.daera-ni.gov.uk/publications/torr-head-assi