Bun-an-uillt, Islay
Geological Conservation Review site | GCR #2649 | Structural and Metamorphic Geology | Dalradian
Scotland's geosites are chosen because of their local, national or international importance. Take only photos, leave only footprints: avoid causing any damage to this site. You can walk almost anywhere in Scotland without the need to ask permission or keep to paths, but you have a responsibility to care for your own safety, to respect people's privacy and peace of mind and to cause no damage.
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Summary
This is the only exposed section across the so-called Loch Skerrols Thrust. In fact at this site it appears to be a complex shear zone with later brittle faulting separating white Maol an Fhithich Quartzite of the Lochaber Subgroup Dalradian from pink quartzites of the Bowmore Group. The affinities of the Bowmore Group are not known for certain. It has been variously correlated with the Moine succession and the Torridonian. However, it is now considered probable that the Loch Skerrols Thrust originated as a syn-depositional extension fault which was reactivated during an early compressive phase of the Caledonian orogeny. If this is correct it is unlikely that the Bowmore Group is older than the Dalradian. The most likely suggestion is that it is a lateral correlative of the Crinan Grit of the upper Argyll Group. Thus the Bowmore Group would be a continuation of the Dalradian succession in the north-western limb of the Islay Anticline. This site is the only exposure of one of the more controversial of the major structures affecting the Dalradian of south-west Argyll. Although it is poorly exposed it has considerable importance in terms of the local geology of Islay and the wider relationships of the Lewisian, Colonsay Group, Bowmore Group and the Dalradian, and the Caledonian orogenic front.
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