Earth Science Conservation Review
| Glas-na-Bradan - site of local interest | Antrim |
| Site Type: | Stream section |
| Site Status: | local interest |
| Council area: | Newtownabbey District Council |
| Grid Reference: | J340811,J350806 |
| Google maps: | 54.66064,-5.92344 |
| Rocks | |
|---|---|
| Rock Age: | Tertiary, Triassic (Lower Triassic, Middle Triassic, Palaeogene, Upper Triassic) |
| Rock Name: | Mercia Mudstone Group, Sherwood Sandstone Group |
| Rock Type: | Basalt, Marl, Mudstone, Sandstone |
| Interest | |
| Other interest: | dyke, diamicton |
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.
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.
| Enlander, I., Dempster, M. & Doughty, P., 2024. Glas-na-Bradan - site of local interest, County Antrim, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=729. Accessed on 2024-12-26 |
| Previous Site | Next Site |