The geology of the Moray Coast

When most people think of Scotland, the images that come to mind are those of high, heather covered mountains like Ben Nevis, islands like Skye, Arran or Rum, or the endless rugged coastline of the northwest coast. However, there is another half to the country, along the east coast, which few people have explored. For example, the county of Moray offers Burghead Bay, where pill boxes sit half submerged in sand, or there are the frequently climbed sea cliffs below Cummingston and Covesea, and Findhorn Bay, the only natural harbour on the south side of the Moray Firth, where shipwrecks litter the beaches at low tide alongside remnants of an old settlement destroyed by shifting channels.

baryteFig. 1. Baryte mineralisation in Permian sandstone at Hopeman.

In terms of geology, the Moray shore provides evidence of the ancient landscape 250mya, easily found by following the coastal path, a walkable distance east from the village of Hopeman. A short detour onto the beach, behind the brightly coloured huts, reaches small outcrops of Permian sandstone, the Hopeman Sandstone Formation, which occurs continuously along the coast for several kilometres. At this particular spot, the sandstone is heavily mineralised with barytes, primarily as cement holding the medium-sized grains in place, but also as concentrations a few centimetres across that give the outcrop an overall speckled appearance and nearly obliterate the original bedding (Fig. 1). Such an outcrop can also be found near Covesea Lighthouse, as can fluorite in characteristic (but difficult to find) cubic crystals. The mineralisation most likely occurred during the Jurassic, when the Central North Sea area underwent doming, which resulted in mineral-rich fluid-flow through the Permian sandstones.

Continuing eastward, the increasingly narrow and uneven path passes Braemou Well, one of several on the Moray Coast, and Daisy rock, which is a prominent block at the waterline. Several hundred metres further on are strange, wave-beaten sandstone stacks, standing a few metres high and showing colour banding and variable resistance to erosion, This is caused by differing iron content of each bed within. Around the headland, the sandstone forms broad, sweeping bedding surfaces, dipping at an angle of no more than ten degrees towards the sea. These show cross-beds, which are smaller parallel, but inclined layers, which are all that remain of moderately-sized barchans sand dunes. That is, grains of sand were blown up a shallow ‘stoss slope’ to the top of the dune and, on becoming unstable, tumbled down the steeper ‘lee slope’. This process of erosion from the back, transport to and deposition at the front effectively moved the dune forward and, importantly, only the stoss slope is preserved. The presence of sand dunes firstly indicates that Moray in the Permian was a hot, arid desert environment, only 20°N of the Equator and, secondly, from the dip of the cross-beds approximately to the southwest, that the wind blew predominantly from the north.

clashach-coveFig. 2. Cross bedding, a fault surface and caves in Permian sandstone at Clashach Cove.


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