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Earth Science Conservation Review
| Beaghbeg | Tyrone |
| Site number: | 585 | ||
| ESCC: | EO | ||
| Locality Type: | Crags | Status: | ESCR |
| Grid Reference: | H674828 Centroid | ||
| Google maps: | 54.68921,-6.95483 | ||
| County: | Tyrone | Council area: | Mid Ulster District Council |
| Period: | Ordovician | ||
| Lithostrat: | Tyrone Volcanic Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The Beaghbeg site consists of a number of high quality outcrops of tuffaceous volcanic rocks. These lithologies are typical of many of the tuffaceous volcanic rocks forming the background sedimentation in the Tyrone Volcanic Group This site offers access to abundant outcrop and an opportunity to study field relationships and lithological variations. | |
| Introduction: | |
Beaghbeg is located in unfenced, rough pasture in the Townland of Beaghbeg about 1.7km north-northwest of Dunnamore. The site is approached via farm lanes which run southwards from Beaghmore Road or northwards from Beaghbeg Road. On one of the earliest geological maps of the area, (Portlock, 1843) the combined extent of the Tyrone Volcanic and the Tyrone Plutonic Groups were accurately mapped and clearly distinguished from the mica schists of the nearby Sperrin Mountains and Tyrone Central Inlier. The rocks at Beaghbeg and throughout the surrounding area were described collectively as "metamorphic rocks of hornblendic type" and Portlock noted a variety of hornblendic schistose rocks present at Beaghbeg. On the first edition of the one-inch to the mile geological map (Sheet 26, Draperstown, Geological Survey of Ireland, 1882) the rocks at Beaghbeg were represented as "pyroxenic rocks" loosely classified as "probably of Pre-Cambrian or Upper Laurentian age". The coarse lapillae tuff at Beaghbeg appears to be an along strike equivalent of rocks noted as "remarkable breccias" at Meenascallagh, Cole (1897). Hartley (1933) produced the first detailed lithological map and descriptions of the rocks of the central Tyrone Ordovician volcanic plutonic terrane and incorporated the rocks at Beaghbeg within the division referred to as the Tyrone Igneous Series. On the 1:50,000 scale second edition of Sheet 26 (Draperstown, Geological Survey of Northern Ireland, 1995) Hartley's Tyrone Igneous Series was subdivided into two distinct stratigraphic components, the Tyrone Plutonic Group and the Tyrone Volcanic Group and included the rocks at Beaghbeg within the Tyrone Volcanic Group. In a regional tectono-stratigraphic context, the Tyrone Volcanic Group forms part of an arc-volcanic type geological sequence in the Tyrone-Girvan Sub-Terrane of the Midland Valley Terrane as defined by Bluck et al. (1992). The Tyrone Volcanic Group formed along the Laurentian foreland at the northern margin of the Iapetus Ocean during closure of the Iapetus Ocean during Ordovician times. | |
| Description: | |
The site consists of numerous closely spaced crags and flat scoured outcrops of weathered rock. The rocks are of variable lithologies ranging from fine-grained pale green and greyish chloritic sometimes epidotised tuffs to coarse-grained, conspicuously fragmental, volcanic breccias (lapillae tuffs). Overall, the outcrop has a crude stratification with northeast southwest striking bedding and a broadly coplanar schistosity that is particularly well developed in the fine-grained tuffs. A 75m long by 5m high crag marks the southeastern limit of the delineated site. This crag contains the best exposures of the coarse-grained lapillae tuff. The most conspicuous fragments are pale pink and buff grey coloured felsitic material. Fragments are generally angular and are up to 4 to 5cm in diameter. Other clasts present include banded chert and occasional fragments of red jasper. The rock matrix is composed of fine-grained greenish chloritic material which is often schistose. There is locally evidence of syn- to post-depositional compaction with matrix flow and augening around some clasts. In thin section (JTP 163), the rock contains darker fragments of altered chlorite-rich basic volcanic rocks and pale brown grains of sericitized feldspar. This thin section also contains a contact between coarse-grained tuff and volcaniclastic sandstone consisting of pale-grey and white feldspar and quartz grains in a green chloritic matrix. | |
| Importance: | |
Beaghbeg is a site of national importance offering access, within a compact area, to high quality exposure of the Tyrone Volcanic Group. The site contains exposures of a variety of tuffaceous lithologies and offers a good opportunity to study lithological and sedimentological variation. | |
| Interpretation: | |
The rocks at Beaghbeg form part of an extensive and lithologically variable volcanic sequence (Tyrone Volcanic Group). These rocks formed as the result of explosive volcanic activity in an island arc or back-arc environment. The presence of volcaniclastic sandstone at this site and throughout the Tyrone Volcanic Group indicates that volcanic debris was periodically reworked and redeposited, most probably in shallow water marine environments. The volcanic breccia contains a variable clast content and samples the main lava types (ranging from basic to intermediate and acid in composition) characteristic of a maturing island arc. The presence of chert and jasper albeit in small amounts, together with coarser-grained volcaniclastic rocks indicates the presence or close proximity to a variety of marine environments. Volcanic arc formation was widespread along the northern margin of the Iapetus Ocean during Ordovician times. The Tyrone Volcanic Group is broadly equivalent to the ophiolitic-volcanic associations at Girvan-Ballintrae (Scotland) and Clew Bay (County Mayo) (Hutton et al., 1985). Formation of the island arc and associated back arc environment was driven by the progressive closure of Iapetus which had separated the north American continental plate (Laurentia) from southern Britain (Avalonia). Magmatism was generated by the north-westerly directed subduction of Iapetus oceanic crust and sediment along the Laurentian continental margin. The rocks at Beaghbeg are deformed and many, particularly the finer-grained tuffs, have a well-developed schistosity. Deformation and metamorphism of the Tyrone Volcanic Group took place under lower Greenschist Facies conditions in response to the processes of subduction/obduction of oceanic crust and subsequent transpressional terrain accretion. | |
| Conclusions: | |
Beaghbeg is a site of national importance. It is a valuable educational and research resource providing access to high quality outcrops of volcanic tuff, breccia and volcaniclastic rocks within the Tyrone Volcanic Group. | |
| Notes: | |
For information and references on sites within the Tyrone Basic Plutonic Complex see the following sites: Key Site 580 - Black Rock Key Site 581 - Scalp Hill For information and references on other sites within the Tyrone Volcanic Group see the following sites: Key Site 582 - Mveela More Key Site 583 - Creggan Key Site 584 - Copney Hill Key Site 586 - Bonnety Bush, Altihaskey Key Site 587 - Tullybrick Key Site 588 - Stuhanleanantawey Burn For information and references on Granitoid sites within the Caledonian Complexes of N. Ireland see the following sites: Key Site 589 - Cashel Rock Key Site 590 - Craigballyharky and Craigbardahessiagh Key Site 591 - Craiganawork, Pomeroy Key Site 592 - Tintagh, Slieve Gallion Key Site 593 - Loughmacrory Key Site 594 - Cushendun For general information and references on the Caledonian Igneous Complexes of N. Ireland, and for directions to other regional sites, see the following site: Key Site 595 - Introduction to the Caledonian Igneous Complexes of N. Ireland | |
| Keywords | |
|---|---|
| Rocks: | Breccia, Volcanic, Chert, Lapilli Tuff, Volcaniclastic sediment |
| Structures: | Caledonian |
| Relations: | Extrusion |
| Access | |
|---|---|
| Approach: | The site is approached via farm lanes which run southwards from Beaghmore Road or northwards from Beaghbeg Road. |
| Management: | |
This site encompasses a number of rocky knolls and outcrops in an area of partially fenced rough pasture. At present, the land is only partially used to graze stock. The uneven and rocky nature of the topography probably means that much of the site is unlikely to come under direct threat from building development. The state of vegetation and overgrowth is currently at an acceptable level. However any attempt to cover the outcrop by dumping or vegetation, could degrade the site. Some of the best outcrops at Beaghbeg occur along the crags which bound the south of the site. These rocks have developed a weathered patina and this is where the fragmental nature of the rock is most clearly displayed. Hammering and sampling of such surfaces should be restricted as far as possible. The area of interest at this site is only partially fenced from the surrounding pasture and site visits will almost invariably involve entering areas where there is livestock. Careful management of issues such as safety and continuing access to the site are seen as priorities. The rocks of the Tyrone Volcanic Group are considered to be prospective for a number of minerals including base metals and gold. Licensed mineral exploration has previously been carried out throughout central Tyrone and the area which includes this site is likely to attract further exploration attention in the future. | |
| Threats: | Hammering and sampling of such surfaces should be restricted. |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1882. 1:63,360 Geological Sheet 26 (Draperstown). (Dublin, Ordnance Survey for the Geological Survey of Ireland). GEOLOGICAL SURVEY OF NORTHERN IRELAND, 1995. Draperstown. Northern Ireland Sheet 26. Solid and Drift Geology. 1:50,000. (Keyworth, Nottingham: British Geological Survey). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 04 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Beaghbeg, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=585. Accessed on 2026-11-05. |
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