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Earth Science Conservation Review
| Oughtboy Burn | Tyrone |
| Site number: | 134 | ||
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H592952 Centroid | ||
| Google maps: | 54.80161,-7.07944 | ||
| County: | Tyrone | Council area: | Derry City & Strabane District Council |
| Period: | Precambrian | ||
| Stages: | Dalradian | ||
| Lithostrat: | Glenelly Formation, Oughtboy Burn Member, Southern Highlands Group | ||
| Site Description | |
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| Highlights: | |
Oughtboy Burn contains the stratotype (type section) for the Oughtboy Burn Member, a distinctive chloritic green bed unit within the Glenelly Formation. The site also contains siliciclastic turbidite facies rocks typical of the Glenelly Formation. | |
| Introduction: | |
From its source on the col between Dart Mountain [H602 964] and Carnakilly [H579 966], the Oughtboy Burn flows southwards into the Glenelly River. The site can be accessed 2.5km north of Cranagh from the minor road which runs between Cranagh and the village of Park. The strata in Oughtboy Burn are regionally metamorphosed metavolcanic and metasedimentary rocks which form part of the Glenelly Formation of the Southern Highland Group (Upper Dalradian), see table below. These rocks lie on the southern, inverted limb of a large north-east-south-west trending, south-east-facing F2 fold structure (the Sperrin Overfold). All rocks at this site and in the surrounding area have a well developed composite (S1-S3?) foliation which is axial planar to the Sperrin Overfold. Bedding and foliation dip consistently at about 45 degrees NW and the succession youngs towards the south-east. On the first edition of the one inch to one mile geological map (Sheet 26, Draperstown) (Geological Survey of Ireland, 1882, Nolan, 1884), the green beds in Oughtboy Burn were not distinguished from the surrounding schists and were included within the general category "Chloritic, talcose & micaceous schists" which was, with a few exceptions, applied to all metamorphic rocks in the Sperrin Mountains. When Hartley (1938) produced the first detailed litho- stratigraphic map of the Sperrin Mountains, all rocks in Glenelly and on the southern slopes of the main Sperrin Mountain Range, including Oughtboy Burn, were grouped within the divisions he referred to as "Tourmaline Schists of Glenelly" (North & South). Hartley described the green beds at Oughtboy Burn (and Garvagh Burn) but did not accord them any formal stratigraphic status. He did however suggest that the green beds at Oughtboy may correlate with comparable beds at Henry's Bridge. The main formations in the Sperrins were redefined by Arthurs (1976), who incorporated all the rocks in Glenelly within a revised Glenelly Formation. These revised boundaries, with minor modifications, form the basis of the Upper Dalradian stratigraphy on the second edition of the geological map Sheet 26 (Draperstown) (Geological Survey of Northern Ireland, 1995). This second edition also includes formal recognition of the stratigraphic status of the Oughtboy Burn Member as part of the Glenelly Formation. Recently, the stratigraphic and structural model of the southern Sperrin Mountains favoured by Arthurs (1976) and the Geological Survey of Northern Ireland (1995) has been challenged by Alsop et al. (1993). Alsop has proposed that all formations in the South Sperrins, including the Glenelly Formation, form part of a single Sperrin Formation which belongs to the Argyll Group (Middle Dalradian) not the Southern Highland Group (Upper Dalradian). Recent and ongoing resurvey work by the Geological Survey of Northern Ireland has however found no evidence to support such a radical reinterpretation (Arthurs and Johnston & Smith in Arthurs et al., 1994). TABLE TO BE ADDED Dalradian stratigraphy and ESCR sites in the southern Sperrin Mountains. | |
| Description: | |
Approximately 70 m of chloritic green beds (Oughtboy Burn Member) are exposed intermittently in the bed and banks of Oughtboy Burn [H592 952]. These rocks are mainly dark green and buff coloured speckled schist containing albite and chlorite porphyroblasts in a chlorite and biotite rich matrix.
 At both the stratigraphic base and top of the Oughtboy Burn Member, the green beds appear to be in conformable contact with siliciclastic lithologies typical of the Glenelly Formation These turbiditic lithologies typically include grey quartzo-feldspathic semipelite and psammite interbedded with thin mica schist horizons containing tourmaline. All of the strata in Oughtboy Burn have a well developed composite (S1-S3?) foliation which dips consistently at about 45 degrees towards the north and north-west. The succession is known to be inverted although there is no clear primary way-up evidence visible at this particular site. | |
| Importance: | |
Oughtboy Burn is the stratotype (type section) for the Oughtboy Burn Member. This is an important lithological variant in the otherwise homogenous turbidite facies rocks of the Glenelly Formation. Such horizons have proven to be of some value in establishing local stratigraphy and correlation. It is hoped that research, currently being planned, into the sedimentological and geochemical characterisation of Dalradian green beds in Northern Ireland and Scotland will result in the more widespread use of green beds to establish correlation and understand the provenance of Dalradian volcanism on a regional scale. | |
| Interpretation: | |
The Oughtboy Burn Member is a distinctive chloritic green bed horizon within the Glenelly Formation. These green beds formed from sediments derived predominantly from basic volcanic sources, either directly from air-fall tuffs or from volcaniclastic sediments eroded from basic volcanic rocks within the basin catchment. During Upper Dalradian times, the continental crust along the margin of Laurentia became unstable. The crust thinned and fractured under the influence of a tensional tectonic regime, and a series of marine sedimentary basins developed along the continental margin. These basins filled rapidly during Upper Dalradian times and subsided to accommodate large thicknesses of mainly siliciclastic turbidite facies sediments (Southern Highlands Group, Dart Formation etc.). This tectonism was accompanied by intrusive and extrusive volcanic activity. Although this activity peaked sometime towards the end of the Middle Dalradian (Argyll Group, Dungiven Formation) the presence of "green beds", including the Oughtboy Burn Member, within the Southern Highlands Group is evidence that there was a continuing, albeit periodic, input of volcanically derived sediments well into Upper Dalradian times. | |
| Conclusions: | |
Oughtboy Burn contains the listed stratotype (type section) for the Oughtboy Burn Member and is therefore a site of national importance. Such green bed units act as important marker horizon within the Glenelly Formation and may have an important role to play in understanding the nature and provenance of Dalradian volcanism. | |
| Notes: | |
For site specific information and references on other Dalradian sites in the Sperrin Mountains, Londonderry and Tyrone see the following sites: For Central and Southern Sperrin Mountains: Key Site 130 - Butterlope Glen Key Site 131 - Craig Key Site 132 - Mullaghcarbatagh Key Site 133 - Henry's Bridge, Glensass Burn Key Site 135 - Garvagh Burn Key Site 136 - Barnes Gap Key Site 137 - Barnes Burn Key Site 138 - Golan Burn Key Site 139 - Glendarragh Burn, Glenlark Key Site 140 - Mountfield Old Quarry Key Site 141 - McNally's Burn, Broughderg For North Sperrin Mountains and Londonderry: Key Site 142 - Letterbrat Quarry Key Site 143 - Banagher Glen Quarry Key Site 144 - Strabane Quarry Key Site 145 - Glenmornan River, Artigarvan Key Site 146 - Balix Hill Key Site 147 - Drain Quarry Key Site 148 - Kildoag Quarry Key Site 149 - Loughermore Mountain Key Site 150 - Burntollet and Tamnymore Wood Key Site 151 - Dog Leap, Limavady Key Site 152 - Kittybane Quarry Key Site 153 - Prehen Quarry Key Site 154 - Creevagh Hill Old Quarry For site specific information and references on other Dalradian sites in North-east Antrim see the following sites: Key Site 155 - Benvan Key Site 156 - Escort Port Key Site 157 - Torr Head Key Site 158 - Altmore Burn Key Site 159 - Leckpatrick Point Key Site 160 - Carnaneigh Key Site 161 - Loughan Bay Key Site 162 - Loughareema Channel Key Site 163 - Knocknacarry Bridge Key Site 164 - Cushendun Bay and Rock Port For general information on the Dalradian rocks of Northern Ireland see the following site: Key Site 124 - The Dalradian Rocks of Northern Ireland For general and site specific information on the Pre-Dalradian rocks of Northern Ireland see the following site: Key Site 123 - The Pre-Dalradian Rocks of Northern Ireland For general information and an extensive reference list on the Precambrian of Northern Ireland see the following site: Key Site 122 - An Introduction to the Precambrian of Northern Ireland | |
| Keywords | |
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| Rocks: | Green beds |
| Access | |
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| Management: | |
The Oughtboy Burn site is situated in a remote mountainous area where the sole land-use is hill sheep farming. The Burn is fenced off from the surrounding open moorland. There are no buildings within the vicinity of the stream, and it is unlikely that the site will be threatened by development. Outcrops in the stream are relatively abundant and accessible. The site should be capable of withstanding all reasonable sampling pressures therefore there is no need to impose special restrictions on sampling at this site. | |
| Uses | |
| Uses: | Hill sheep farming |
| References (5) | |||
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| Alsop, G.I. & Hutton, D.H.W., 1993. Major southeast-directed Caledonian thrusting and folding in the Dalradian rocks of mid-Ulster: implications for Caledonian tectonics and mid-crustal shear zones Geological Magazine, vol. 130 pt. 2, pp.233-244. | |||
| Arthurs, J.W., 1976a. The geology and metalliferous mineral potential of the Sperrin Mountains area Geological Survey of Northern Ireland Special Report. | |||
| Arthurs, J.W., Johnston, T.P., Smith, R.A., Alsop, G.I. & Hutton, D.H.W., 1994. Discussion on major southeast-directed Caledonian thrusting and folding in the Dalradian rocks of mid-Ulster: Implications for Caledonian tectonics and mid-crustal shear zones Geological Magazine, vol. 131 pt. 3, pp.417-421. | |||
| Hartley, J.J., 1938. The Dalradian rocks of the Sperrin Mountains and adjacent areas in Northern Ireland Proceedings of the Royal Irish Academy, vol. 44 pt. B. | |||
| Nolan, J., 1884. Explanatory memoir to accompany Sheet 26 of the maps of the Geological Survey of Ireland Memoirs of the Geological Survey of Ireland. | |||
| Map(s): | GSI (1882). 1:63,360 Geological Sheet 26 (Draperstown), Dublin, OS for GSI GSNI (1995). 1:50,000 Draperstown, Northern Ireland Sheet 26, Solid, BGS, Keyworth, Nottingham | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Oughtboy Burn, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=134. Accessed on 2026-11-08. |
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