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Killygarry RiverFermanagh
Killgarry River, Co. Fermanagh; stratotype of Drumchorick Siltstone Formation; massive calcareous sandstone overlies sequence of siltstones and thin, often lenticular crinoidal sandstones and bioclastic limestone turbidites.
Summary Full report
Site Type: Stream section
Site Status: PASSI
District: Fermanagh District Council
Grid Reference: H2066
Rocks
Rock Age: Carboniferous (Arundian, Holkerian, Visean)
Rock Name: Benbulben Shale Formation, Drumchorick Siltstone Formation, Tyrone Group
Rock Type: Limestone, Mudstone
Interest
Fossil Groups: Coral, Crinoid
Other interest: No data, Marine sediments

Summary of site:

The stratotype (see glossary) of the Drumchorick Siltstone Formation and its contact with the overlying Benbulben Shale are the principal interest in this riverbed and banks. Both formations are part of the Tyrone Group, a major division, early in the Carboniferous period, that lasted for about 20 million years from around 360 to 340 million years ago.

The rocks in the river are tilted to the south and south west between 15 and 30 degrees which means that the oldest rocks are seen at the north end of the section. The Drumchorick Siltstone appears here at the prominent waterfall which crosses a 70 cm thick bed of limestone which is sandy at its base. The succession then continues as a series of thin and lens-shaped limestone beds enclosed within softer siltstones and mudstones that weather away to leave the limestones projecting. The limestones are full of crinoid ossicles and appear to erode into the underlying shales. In some of the thicker beds there a prominent fossil corals and it is above these beds that the grey mudstones of the Benbulben Shale appear. The total thickness of the Drumchorick Siltstone is estimated at around 100 m. Soon after this junction a north east/south west trending basaltic dyke crosses the section and to its south about 5 m of typical Benbulben Shale lithologies, dark, grey-brown mudstones, can be seen with limestones from 1 to 10 cm thick. The limestones tend to be richly fossiliferous in sharp contrast to the shales which are almost barren. The fossils in the Drumchorick Siltstone confirm a time stage called the Arundian (about 343 million years ago) and the first few metres of the Benbulben Shale may also be of this age. As a stratotype, the locality is of key importance and should be conserved for future study and research


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