Ellen, R. and Callaghan, E. 2015. Geodiversity Audit of Spireslack and Mainshill Wood Surface Coal Mines. British Geological Survey Commerical Report CR/15/126. 70pp.
Spireslack Locality 9: Johnstone Shell Bed
NGR: [274950 630648]
Key categories of interest Rarity Quality
| Key category of interest | Rarity | Quality |
|---|---|---|
| 1. Palaeontology | 5 | 4 |
| 2. Stratigraphy | 4 | 3 |
| 3. Mineralisation | 4 | 4 |
Access: Good access from lower void.
Current safety: Uneven underfoot and steep but firm in places.
Measures to enhance site: Create a dedicated path to site, clean up loose scree around site.
Key categories in order of interest (1 = primary interest); Rarity, 5 = only example in Spireslack, 1 = many examples in Spireslack; Quality 5 = exceptional preservation in Spireslack, easy access/viewing potential 1 = average preservation in Spireslack, difficult access/viewing potential
Photograph overview with polygon boundary
© Getmapping: Licence Number UKP2006/01
Site description
Geology
The Johnstone Shell Bed, a marine band and important regional stratigraphic marker across the Midland Valley, is exposed at this locality in a small water-washed gully. Marine bands such as these represent a time when Carboniferous Scotland was under the sea, a change from the dominant estuarine and deltaic conditions that typically form the Limestone Coal Formation. As such, these flooding events, where marine life flourished across wide geographical areas, can be recorded and correlated across Scotland. The Johnstone Shell Bed is therefore an important regional stratigraphic horizon across the Midland Valley, containing fossil evidence for the fauna which flourished during marine incursions in Scotland. At the locality, a 50 cm wide exposure of the fossiliferous shell bed is revealed by surface water cutting shaley scree. In the neighbouring seatearth, adjacent to the shell bed, are remnants of the McDonald Coal. Fractures within the coal have been mineralised by ankerite, an orangey brown earthy mineral not found preserved in situ elsewhere in Spireslack. Ankerite is a mineral often associated with coals.
Access and enhancement suggestions
The shell bed is very fragile and friable, although the current cover of shaley scree is protecting it. Measures to prevent erosion of the bed, and cover by scree, should be put in place as this is an important regional stratigraphic marker.