The Great Geoadvent: Door 16

Between the nappes of the ophiolite is a chaotic area of highly deformed metamorphic rocks that came from the oceanic crust and from the continent below it. This area, called a mélange, includes conglomerate – cobbles of differing rock types ‘cemented’ together in a fine grained matrix. Conglomerate forms when mountains erode and cobbles are carried down by rivers to accumulate in large ‘fans’ at their base. Over time the cobble fans are buried under finer sediments which solidify to form conglomerate.

The conglomerate at Funzie is unusual. It built up after the first nappe of oceanic crust was emplaced on the continent. When the second nappe was thrust over it the cobbles were squashed and stretched into rod shapes by the immense pressure generated. The second nappe has now eroded exposing the deformed cobbles beneath.

Text: Geopark Shetland