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BallyraineyDown
Exposure of the Newforte Breccia Formation in stream marking Ballyrainey Townland boundary.
Summary Full report
Site Type: Stream section
Site Status: PASSI
District: Ards Borough Council
Grid Reference: J455722
Rocks
Rock Age: Permian (Upper Permian)
Rock Name: Belfast Group, Newforte Breccia Formation
Rock Type: Breccia, Greywacke, Sand, Sandstone
Interest
Other interest: No data, No Data

Summary of site:

Outcrops of Permian rocks are restricted to the north-east of Ireland and are rare. It follows that outcrops of formations within the Permian are even rarer, so the poor exposures in the Ballyrainey stream section are therefore both precious and important.

Although Permian rocks are well proved in boreholes in Northern Ireland, the poor surface exposure is a major problem. The Newforte Breccia Formation can only be seen (and then intermittently) over a length of 500m in the small stream section south of Newforte. The rocks consist of angular fragments of Ordovician and Silurian greywacke, sandstone and mudstone from 10mm to 20cm in size set in reddish mudstone and sometimes lime rich marl, with occasional green spots and patches. There are thin beds of sandstone, up to 15cm thick, within the breccias. Following the end of the Carboniferous period, Variscan mountain building elevated the whole of Ireland and created a terrestrial desert landscape. The Newforte Breccia was formed in an upland of this desert, as scree banked against hills carved into the Lower Palaeozoic rocks that provided the angular fragments. The type section of the Newforte Breccia Formation is defined in the Ballyalton borehole, drilled less than 2km to the north-east. In the borehole core, the formation is over 50m thick, with the Lower Permian Coolbeg Breccia beneath and the Triassic Sherwood Sandstone above showing no signs of any break in deposition. The Newforte Breccia Formation is therefore considered to be Upper Permian in age on the grounds of its relative position. The site is of fundamental importance, as the sole outcrop of the formation.


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