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Earth Science Conservation Review
| Glas-na-Bradan - site of local interest | Antrim |
| Site number: | 729 | ||
| Locality Type: | Stream section | Status: | local interest |
| Grid Reference: | J340811,J350806 End(s) of linear site | ||
| Google maps: | 54.66064,-5.92344 | ||
| County: | Antrim | Council area: | Antrim & Newtownabbey Borough Council |
| Period: | Tertiary, Triassic | ||
| Stages: | Lower Triassic, Middle Triassic, Palaeogene, Upper Triassic | ||
| Lithostrat: | Mercia Mudstone Group, Sherwood Sandstone Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The stream section at Glas-na-Bradan exposes the transition between the Sherwood Sandstone Group (Lower Triassic) and the Mercia Mudstone Group (Middle - Upper Triassic). It is one of the few places in this region where the transition is seen. The Triassic marls and mudstones are intruded into by up to six basaltic dykes and there is evidence of contact metamorphism in the country rock. | |
| Description: | |
The Sherwood Sandstone Group (Lower Triassic) typically consists of dull red medium- to coarse-grained sandstones which are micaceous in the thinner bedded horizons and with partings, or more rarely thick bands, of reddish or chocolate-brown marl, particularly in the upper part. By contrast the Mercia Mudstone Group (Middle - Upper Triassic) consists predominantly of mudstones and silty mudstones, usually reddish brown but often grey, chocolate, red or occasionally mottled green. The upwards transition from the Sherwood Sandstone Group to the Mercia Mudstone Group is gradual and the boundary, where seen, is taken at the horizon where mudstone becomes dominant over sandstone. Glas-na-Bradan is one of the few sites where this transition can be seen. The boundary between the two groups is placed at the top of a locally massive white sandstone as follows: TOP MERCIA MUDSTONE GROUP 1. Red and Green marls: 1.21m+ 2. Grey green and red marls with thin siltstones and sandstones: 0.10m SHERWOOD SANDSTONE GROUP 3. White, buff and greenish grey massive sandstone with irregular top, possibly an erosion surface: 1.82m 4. Sandstones and marls in equal proportions grading down into hard green and red marls with sandstone beds up to 15cm: 1.82m 5. Red, buff, yellow cross-bedded sandstones: 3.04m+ The Mercia Mudstone Group mudstones and marls are often baked white, grey and green in the Glas-na-Bradan section by minor basaltic (Palaeogene) intrusions. In total, six dykes are exposed in the stream here, each trending northwest to southeast. Two of the larger dykes [J3352 8122 - J3400 8108] are 12m and 9m wide respectively and have baked the surrounding mudstones for distances of up to one metre from their contacts. Finally a distinctive glacial red boulder clay, typically developed on the Triassic marls and mudstones has been cut through by the Glas-na-Bradan stream and over 6m of the boulder clay are exposed in the stream banks. | |
| Importance: | |
The site has some scientific value as it exposes one of the few sections showing the transition from the Sherwood Sandstone Group (Lower Triassic) to the Mercia Mudstone Group (Middle - Upper Triassic). The site is of educational value as it exposes the transition between the Sherwood Sandstone Group (Lower Triassic) and the Mercia Mudstone Group (Middle - Upper Triassic) and allows demonstration of the changing environments in this area at that time in the Triassic. Further, the sequence is intruded by up to six dykes and contact metamorphic aureoles up to 1m wide can be seen. | |
| Notes: | |
The section lies along the waymarked Newtownabbey Way and the Ulster Way, and is featured in a walk from the 'Walk South Antrim' set published by GSI / GSNI. | |
| Keywords | |
|---|---|
| Rocks: | Basalt, Marl, Mudstone, Sandstone |
| Structures: | dyke |
| Geomorph: | diamicton |
| Access | |
|---|---|
| Approach: | This site is located along a waymarked walking route at Whitehouse. |
| Uses | |
| Educ. Level: | The site is of educational value. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Glas-na-Bradan - site of local interest, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=729. Accessed on 2026-11-06. |
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