Creag Chorcurach

Also within

Ross and Cromarty County

Condition (NatureScot)

Geology & landscape

Rock Type: Mudstone, Quartzite, Sandstone

Description

CREAG CHORCURACH Creag Chorcurach Site of Special Scientific Interest (SSSI) lies in Wester Ross. It is part of an escarpment on the eastern side of Strath Beag at the head of Little Loch Broom. This site contains a section through the Moine Thrust Zone, including a feature known as the Dundonnell Structure. Creag Chorcurach SSSI is a key locality which helps geologists to understand the Moine Thrust Zone, the mechanisms involved in continental plate movements and the sequence of events that led to the development of the Thrust Zone. The Moine Thrust is a large, low angled fault (or fracture) in the earth’s crust, which is exposed along a line from Loch Eriboll to the Isle of Skye. When England and Scotland collided around 430 million years ago, the rocks of the Moine Supergroup were pushed westward along the Moine Thrust by up to 100km. Beneath the Moine Thrust are a number of other thrusts in the Moine Thrust Zone. The geology of the Dundonnell Structure gave geologists convincing evidence that the Moine Thrust is the oldest thrust in the Moine Thrust Zone and that subsequent thrusts developed beneath it, carrying older thrusts on top of them. In the Dundonnell Structure, the Moine Thrust has clearly been folded and domed by the accumulation of younger thrust slices beneath it. The lowest and youngest thrust slice exposed in the Dundonnell Structure is made up of ~530 million year-old Fucoid Beds (fossil-bearing mudstone). Above this is an older thrust slice of Pipe Rock (quartzite with distinctive worm burrows, and slightly older than the Fucoid Beds); and above this a thrust slice of ~1000 million year-old Torridonian sandstone. Above the Torridonian sandstone thrust slice is the Moine Thrust and its overlying Moine rocks. Also of importance and exposed in the SSSI are the Sole Thrust (the lowest, youngest thrust in the Moine Thrust Zone), and the rocks to the west, known as the ‘Foreland’, which have not been affected by the Moine Thrust Zone. The evidence displayed at this site contributes to geologists’ understanding of thrust belts across the world and Creag Chorcurach SSSI is therefore of international importance for geological education and research.