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Earth Science Conservation Review
| McNally's Burn - Structural | Tyrone |
| Site number: | 647 | ||
| Locality Type: | Stream section | Status: | ESCR |
| Grid Reference: | H671878 Centroid | ||
| Google maps: | 54.73415,-6.95833 | ||
| County: | Tyrone | Council area: | Mid Ulster District Council |
| Period: | Ordovician, Precambrian | ||
| Stages: | Dalradian | ||
| Lithostrat: | Mullaghcarn Formation, Southern Highlands Group, Tyrone Volcanic Group | ||
| Site Description | |
|---|---|
| Introduction: | |
The site is located 1.5km NE of the chapel at Broughderg, County Tyrone. McNally’s Burn is one of several streams, which drain the southern slope of Keraghbrien. Access is via the south bank of the stream (Fig. 13) which passes beneath the Broughderg Road at McNally’s Bridge. The first outcrop is encountered in the burn bed and in the overgrown banks about 200m upstream from McNally’s Bridge. The Sperrin Fault is the regionally important thrust structure that separates the Grampian (Central Highland) Terrane and the Tyrone-Girvan Sub-Terrane in central Ulster. McNally’s Burn offers unique access to both hangingwall and footwall of the Sperrin Fault and contains a range of associated brittle and ductile structures and microstructures. | |
| Description: | |
Accessible exposure of the Omagh Fault is present in McNally’s Burn, approximately 200m upstream from McNally’s Bridge. In the hanging wall, above a waterfall there are exposures of psammitic and semipelitic rocks of the Mullaghcarn Formation (Southern Highlands Group, Upper Dalradian), while, in the footwall of the thrust are highly deformed chlorite, sericite ± epidote and graphitic phyllites (Tyrone Volcanic Group, Ordovician). This site facilitates detailed study of Caledonian deformation as it affected two distinct geological terranes. Ordovician rocks in the footwall have a single penetrative cleavage and an associated mineral lineation. These structures are concordant with the composite S2-S3 and L2-L3 structures in the Dalradian of the hanging wall. In the footwall close to the fault, there are several small-scale imbricate thrust and drag folds closely associated with black slickensided graphitic pelite. | |
| Notes: | |
For general information on the Structural Geology of Northern Ireland, directions to other Structural Geology sites and an extensive reference list see Key Site 641 - Introduction to the Structural Geology of N. Ireland. See also Key Site 141 - McNally’s Burn, Broughderg [Precambrian Stratigraphic block]. | |
| Keywords | |
|---|---|
| Minerals: | Chlorite, Epidote, Graphite |
| Rocks: | Phyllite, Psammite, Semi-pelitic rock |
| Structures: | fault, slickensides, thrust, cleavage |
| Access | |
|---|---|
| Approach: | Access is via the south bank of the stream (Fig. 13) which passes beneath the Broughderg Road at McNally’s Bridge. |
| Record type: | ESCR report | Recorded by: | T.P. Johnston |
| Entered by: | E M Porter | ||
| Last updated: | 23/09/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. McNally's Burn - Structural, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=647. Accessed on 2026-11-06. |
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