Lochindorb: Neoproterozoic cover - basement relationships and the geology of the Grampian Shear Zone. Led by Dr. Martin Smith

10 October 2026

Following on from previous excursions to Kincraig, the River Findhorn and A’Chailleach in 2024 and 2025 this single day excursion will investigate the final piece in unravelling the geology of the Grampian Shear Zone and cover-basement relationships at the base of the Neoproterozoic Dalradian Supergroup. 

Around Loch an t-Sidhein, south of Lochindorb the evidence for an unconformity near the base of the Neoproterozoic Dalradian Supergroup is complicated by structural repetition caused by Caledonian folding and thrusting. 

The geology was first described by Piasecki and Temperley in the 1988 Moine Excursion Guide. But it was only in the mid-2000’s that the area was remapped by BGS geologists and the complexity of the Grampian Shear Zone and the apparent interleaving of basement and 'cover' rocks was reassessed. 

The aim will be to make an west to east traverse across the area starting in gneissose and migmatitic metasediments of the Badenoch Group (basement). Separating these rocks from the Grampian Group (cover) is a 1 km wide zone of folded and highly sheared rocks. The sheared and folded zone includes a range of rock types including, psammites, quartzites, metagabbros, garnet amphibolites, granite pegmatites, banded non-gneissose rocks and mylonites. Contacts are difficult to find and often obscured by the intrusion of numerous thin late granite sheets associated with the Grantown Granite. 

The traverse ends in relatively weakly deformed banded psammites and semipelites of the Grampian Group.

Contact Dave Longstaff at HighlandGeologicalSociety@gmail.com for further information