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Rock Road Quarry, ArmaghArmagh
South-east end of Rock Road Quarry, near Armagh City, Co. Armagh, showing pale, coral conglomerate bed near base of face, succeeded by typically bedded Asbian limestones.
Summary Full report
Site Type: Quarry (disused)
Site Status: PASSI
District: Armagh District Council
Grid Reference: H871435
Rock Age: Carboniferous (Asbian, Visean)
Rock Name: Armagh Group
Rock Type: Conglomerate, Crinoidal limestone, Limestone
Fossil Groups: Brachiopod, Coral
Other interest: No data, Marine sediments

Summary of site:

This quarry contains what is arguably the highest concentration of fossils found anywhere in Northern Ireland, strikingly presented in a single bed consisting entirely of corals in a mud matrix.

Around 338 million years ago, the area that is now Armagh was an extensive tropical sea, its bed teeming with invertebrate life including groves of crinoids, rich blooms of colonial corals (mostly massive species but with some branching forms), plentiful brachiopods and some molluscs (mostly bivalves but also including sea snails). Sharks with teeth ideally evolved to crush shellfish, their main diet, cruised the clear water in a constant search for food. For a brief period the sea shallowed and produced near perfect conditions for the growth of colonial corals, more than 90% of them cerioid (unbranched) species which grew to enormous sizes (up to 70cm across). These colonies were secured to the sea floor by the shell sands which gave them their stability (there being no solid surfaces for the corals to cement to). The conditions were also ideal for a range of solitary corals, which were similarly embedded in the lime sands in large numbers beneath the canopies of the colonial forms. Catastrophe overtook this entire community in the form of an exceptionally violent storm (perhaps even a tsunami - an earthquake-induced ‘tidal’ wave) which ripped the corals from the sediment and threw them into a confused mass, covering everything in a layer of colonies two metres deep. Solitary corals were also rolled over into the spaces between the colonies and finally a layer of purplish-red shaley clay settled over this entire coral graveyard. The overturned corals never recovered but, in time, the normal sedimentation of clean granular limestones with more widely spaced coral colonies was re-established. This is the interpretation of the limestones in the quarry. At the base, 1.3m of coarse crinoidal limestone is abruptly overlain by 2m of mostly overturned coral colonies (once uprooted the wide tops of the colonies are most stable in the upside down position) coated in purplish-brown mud. Such layered accumulations are called biostromes and are rare events in the fossil record. Following the biostrome there are a further 22m of fairly coarse grained, calcite cemented, lime sands. The beds tend to be thick, with undulating bedding planes coated by a thin purplish shale. There are many indications of burrow feeders working and reworking the sediments in search of food. The solitary corals confirm an Asbian age for these limestones. The many threats to this quarry include seasonal flooding due to the shallow water table, illegal dumping and some instability on the higher faces. But the overwhelming threat is from suburban development, particularly for housing. In anticipation of this, the south-east face (incorporating the biostrome at its base) has recently been raked down and the main interest has been completely buried beneath loose rock. This site is of unique scientific importance and so immediately approachable for educational projects and pure interest and enjoyment that it is imperative that the coral beds are restored to view and comprehensively protected. The destruction of this site would be an important loss to Northern Ireland’s natural heritage.

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