The Cletts, Exnaboe
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Condition (NatureScot)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| F1 | Non-marine Devonian | Favourable | — | 2009-08-18 |
| F2 | Silurian - Devonian Chordata | Favourable | — | 2009-10-14 |
Climate exposure
This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.
Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.
Geology & landscape
Geological Period: Devonian, Silurian
Landscape processes: Coastal
Description
The Cletts, Exnaboe The section of coast from Milburn Geo to Lambhoga Head, 1km east of Exnaboe in South Mainland Shetland is notified for both the non-marine Devonian stratigraphy, in the form of exposures of late Middle Devonian Brindister Flags, and for Silurian- Devonian chordata, represented by fossil fish beds of the Mid-Devonian period. These rocks formed in a wide range of environments and the deposits include aeolian strata, the deep-lake ‘fish-bed’ of Exnaboe, and a sequence of shallow-lake and lake-margin sediments with diverse wave and wave-modified current ripples. The site is of importance in that it facilitates a comparison of the palaeogeography of this the most northerly part of the Orcadian Basin, with that of the main part of the basin. The wind-direction deduced from the aeolian strata, and the chemistry of the deep-water lake sediments of the fish bed are two important elements in this comparison. The rippled sediments overlying the Exnaboe fish bed are exposed in a key section which shows the results of the interaction of rivers and lake waves at the margins of shallow lakes, features not clearly seen elsewhere in the basin. The fish bed is the thickest and most consistent development of fish bearing sediments of freshwater origin occurring in Shetland. Usually these Middle Devonian ‘laminates’ of North Scotland occur roughly at the same horizon and yield an almost identical fauna (the Achanarras-band fauna). This fish bed is unique because it represents sediment deposited in a well established lake, of late Givetian age, about 390 million years ago. Fish of this age are generally rare, but are relatively common and well preserved here. The Cletts, Exnaboe is also the type locality for two species of fossil fish (i.e. the location where the species were first found) - Stegotrachelus finlayi, an early member of the ray-finned fish family that includes most modern fish, and a species of Coccosteus, a primitive armour plated fish.