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Drapersfield QuarryLondonderry
Ballyloughan Formation (Sherwood Sandstone Group), Drapersfield Quarry, near Cookstown, Co.Londonderry.
Summary Full report
Site Type: Quarry (disused)
Site Status: PASSI
District: Cookstown District Council
Grid Reference: H841768
Rocks
Rock Age: Triassic (Scythian)
Rock Name: Ballyloughan Formation, Sherwood Sandstone Group
Rock Type: Sand, Sandstone
Interest
Other interest: cross-bedding, ripple marks, Aeolian sediment, Fluvial sediments, desert

Summary of site:

A common problem in Northern Ireland is the thick layer of glacial material lying over the solid rock foundations of the landscape. This makes it very difficult to see the geology beneath and in such circumstances any outcrops are valuable, particularly when the rock exposed has a restricted occurrence anyway.

This is the case in Drapersfield Quarry, where the rocks exposed are the red-brown sandstones and mudstones of the Ballyloughan Formation (part of the Sherwood Sandstone Group). Exposure of this formation is so poor that its appearance and limits have had to be defined using a borehole core drilled at Ballyloughan Bridge. The exposure at Drapersfield is the best available and shows around 9m of thinly bedded, red sandstones and mudstones separated by thin partings of darker silty mudstone rich in mica. The sandstones show interesting structures, such as cross bedding, and there are examples where beds have been completely washed out by later events. These rocks were formed during the Triassic period, around 245 million years ago on the margins of a wide river valley. It drained the brief rains on the eastern fringes of a hot desert on the supercontinent called Pangea. The area was then within the tropics. The sediments were not formed in the main river channel but within its flood plain. In this setting the sands settled quickly but the muds and silts took longer, creating the dark red partings that divide up the sequence into regular units. As the best outcrop of this formation, the Drapersfield Quarry section is of regional importance and should be preserved. The formation is also important for its potential to store water, oil and gas, giving added significance and research potential. Landfill could be a slight future risk but there are no other threats to the site.


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