Argyll Group
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| Argyll Group | |
|---|---|
| Stratigraphic range: Neoproterozoic | |
 Folded and metamorphosed limestone of the Boyne Bay Formation of the Tayvallich Subgroup (the upper part of the Argyll Group) in Boyne Bay, Aberdeenshire | |
| Type | Group |
| Unit of | Dalradian Supergroup |
| Sub-units | Islay, Easdale, Crinan and Tayvallich subgroups |
| Underlies | Southern Highland Group |
| Overlies | Appin Group |
| Thickness | up to 9km |
| Lithology | |
| Primary | psammite |
| Other | semipelite, pelite, quartzite, dolomite, conglomerate |
| Location | |
| Region | Scottish Highlands |
| Type section | |
| Named for | Argyll |
The Argyll Group is a thick sequence of metamorphosed Neoproterozoic sedimentary rocks that outcrop across the Central Highlands of Scotland, east of the Great Glen, as well as appearing in the north of Ireland. It is a subdivision of the Dalradian Supergroup and is itself divided into four units; from oldest to youngest these are the Islay, Easdale, Crinan and Tayvallich subgroups.[1]
The lower boundary of the Islay Subgroup and hence the Argyll Group as a whole is defined at the base of the Port Askaig Tillite Formation, a diamictite which displays limestone clasts overlain by quartzite and granite clasts. The tillite is thickest in its type area and on the Garvellachs. The Schiehallion Boulder Bed of the eastern Grampians correlates with this tillite. The tillite is overlain by the Bonahaven Dolomite and then the Jura Quartzite which can reach up to 5 km thick but which is more typically between 500 and 1000m thick. Psammites and pelites occur within the sequence in the Ladder Hills area.[2]
Easdale Subgroup
The Easdale Subgroup consists of a basal Scarba Conglomerate overlain by the Craignish Phyllite. It also includes pelites, semipelites, psammites and some volcaniclastic rocks. Extending between Jura, Knapdale and the Moray Firth coast, the unit can reach to 3 km thick.[3]