 | | Drummahon Lane, Co. Tyrone; shallow pits excavated at crest of low ridge exposing strata of Skea Sandstone Member, the basal unit of the Bundoran Shale Formation. |
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| Site Type: | Inland exposure | | Site Status: | ASSI | | Council area: | Derry City & Strabane District Council | | Grid Reference: | H228761 | | Bing maps: | 54.63302,-7.64692 | | Google maps: | 54.63302,-7.64692 | | Rocks |
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| Rock Age: | Carboniferous (Arundian, Visean) | | Rock Name: | Bundoran Shale Formation, Skea Sandstone Member, Tyrone Group | | Rock Type: | Conglomerate, Limestone, Sand, Sandstone | | Interest |
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| Minerals: | Dolomite | | Fossil Groups: | Coral, Nautiloid |
| Summary of site: |
| To appreciate this interesting and unusual section it is important to understand the sequence of rocks in the area. At this site we are dealing with two of the major formations of the early Carboniferous period. The lower is the Ballyshannon Limestone Formation and immediately above is the Bundoran Shale Formation. The topmost subdivision of the Ballyshannon Limestone in the area is the Ederny Limestone Member and the lowest of the Bundoran Shale is the Skea Sandstone Member. All these rocks belong to the same time series called the Arundian, defined by its fossils. It started about 345 million years ago and lasted around 2 million years. | | The section in Drummahon Lane reveals some tantalizing rocks. The most common is a conglomerate, an accumulation of rounded pebbles and cobbles, up to 10cm across, in a coarse, gritty matrix. These particles show a remarkable variety, from milky white vein quartz and pale green quartzites, to schists, grey shales and fawn fine-grained sandstones. Most striking are the orange, dolomitized chunks containing fossils. These include nautiloid cephalopods and a range of colonial corals, both rugose and tabulate, and a few solitary forms. All of them give a middle to late Arundian age. The gritty matrix of the conglomerate leaves no doubt that it is the basal level of the Skea Sandstone Member, identical to the stratotype section 3km to the south south west. | | The nature and size of the pebbles and cobbles in the conglomerate make it obvious that they have not travelled far, so their source was close by. The limestone blocks are obviously derived from the Ballyshannon Limestone, almost certainly the fossil rich Ederny Limestone Member which must have been exposed above sea level and actively eroding at the time. Although conglomerates in the Skea Sandstone are found at other sites, this is the only locality where they are so coarse and informative. | | The most obvious threat to the exposures, which are in a recently excavated farm lane, is overgrowth, although there are sufficient loose blocks to provide material if need be. |
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