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Bannagh RiverFermanagh
PHOTO TO BE ADDED Bannagh River section, Co. Fermanagh.
Summary Full report
Site Type: River bank
Site Status: PASSI
District: Fermanagh District Council
Grid Reference: H16756706, H16906750
Rocks
Rock Age: Carboniferous (Arundian, Visean)
Rock Name: Drumchorick Siltstone Formation, Mullaghmore Sandstone, Tyrone Group
Rock Type: Mudstone, Sand, Sandstone
Interest
Fossil Groups: Brachiopod, Crinoid, Echinoderm, Foraminifera, Polyzoan, Trace fossil
Other interest: cross-bedding, ripple marks, No Data, delta

Summary of site:

The Mullaghmore Sandstone is patchily exposed over 125 sq km north east of Lower Lough Erne, but continuous outcrop is hard to find. This stretch of the Bannagh River provides four good sections in its bed and banks.

The rock is a well-bedded sandstone with few indications of channelling during deposition. Interbedded with the sandstones are frequent thin fossiliferous limestones and ripple-marked horizons of fossil-rich sandstone. One limestone achieves a thickness of 0.3m and has yielded useful fossils. Amongst the lowest beds in the section is a mudstone, almost 1m thick, with a single horizon containing the abundant remains of starfishes and brittle stars (a unique occurrence in the Carboniferous of Northern Ireland). Immediately above the waterfalls at the top of the section, the base of the Drumchorick Siltstone can be seen in a bed a little over 1m thick. It is a much-burrowed, grey, lime-rich sandstone with some sandy mudstones. Further upstream, dredged blocks from the beds immediately above the sandy mudstones show similar sediments, with many indication of intense disturbance by burrow-feeding invertebrates. These blocks have also yielded shelly fossils. From a little higher in the section, microscopic foraminifera have proved useful for relative dating purposes. The environment in this area during Mullaghmore Sandstone times was marginal to a delta dominated by fresh and brackish water conditions. The frequent thin limestones and fossil-rich beds with ripple-marks show many brief periods when shallow, marine intertidal bays or lagoons encroached on to the delta and were colonised by invertebrates. The bed of mudstone with starfishes and brittle stars indicates a phase of relatively still sea bottom conditions, with a plentiful supply of fine food particles. The Drumchorick Siltstone appears to be entirely marine in origin and the plentiful crinoid and brachiopod remains suggest relatively shallow, warm water conditions. There is much evidence, in the form of trace fossils, to indicate a thriving sediment feeding fauna. Foraminifera in the Mullaghmore Sandstone give an age late in the Arundian stage and date the Drumchorick Siltstone to the final years of the same stage, i.e. 343 million years ago, when the Irish area was riding on a plate progressing northwards across the equator. This important and dramatic section extends from the Bannagh Falls into the incised river bed below and clearly demonstrates the diversity of rock types within the Mullaghmore Sandstone Formation as well as the unique starfish bed.


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