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Drumbally Hill quarry, DesertmartinLondonderry
Summary Full report
Site Type: Quarry (disused)
Site Status: PASSI
District: Magherafelt District Council
Grid Reference: H844935
Rock Age: Carboniferous (Asbian, Visean)
Rock Name: Armagh Group, Desertmartin Limestone Formation
Rock Type: Limestone
Fossil Groups: Brachiopod, Crinoid
Other interest: No data, Marine sediments

Summary of site:

In order to know what is meant by the name allocated to a group of rocks, there must be a typical example somewhere, available for examination. Normally a single site is selected for this purpose, called a stratotype.

When the Desertmartin Limestone Formation was originally named, in 1993, it could be seen in many quarries in the Desertmartin area and no stratotype was selected. Since then, many quarries have been closed and filled, so there is an urgent need to select a stratotype from the rapidly dwindling examples of remaining exposures. This disused quarry, despite its partial flooding, is the best of the survivors and is selected as the stratotype. The main accessible face exposes about 3m of medium to coarse grained limestone, mostly of a pale brown colour with a red to purple stain on weathered surfaces. There are thin layers of sandy limestone and a scattering of quartz pebbles. Fossils are sparse and fragmented, mostly crinoid ossicles and large productid brachiopods, and there are no corals present, despite their dominance to the south. These rocks were formed on a shallow, inshore platform during the Asbian stage of the early Carboniferous period, around 337 million years ago. At this time the area was on the southern fringe of the supercontinent of Laurentia which was slowly drifting and rotating as it crossed the equator. Conditions were tropical. The obvious threats to the stratotype are overgrowth, land fill and dumping.

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