Gwna Mélange on the Lleyn Peninsula, NW Wales

Originally posted for the Guesswhere UK group.

This distinctive piece of coastline is at Trwyn Maen Melyn, near Aberdaron at the western end the Lleyn Peninsula, NW Wales.

In geological circles, these blobby rocks are famous here. They are part of the Gwna Mélange, a chaotic mass of diverse rock fragments, boulders and rafts, some of them 100s of metres across, all set in a fine-grained schist matrix. The age is now thought to be Cambrian and the mélange is an example of an olistostrome, a rock assemblage thought to represent a huge submarine debris flow (or several debris flows) into a deep ocean trench which existed here at that time.

The Gwna Mélange crops out on much of NW Lleyn, Bardsey Island and over considerable parts of N and W Anglesey.