Golspie, Holm, Northern Highlands – an excursion
From: Fannin, Nigel G.T. Edinburgh Geological Society field excursion Orkney May 1991 (unpublished)[
Introduction
These are the first three locations of the May 1991 Edinburgh Geological Society excursion to Orkney.
Locality 1 Berridale (ND 120 225)
The spectacular Berridale gorge provides both a beautiful setting and an opportunity to examine the red bed facies of the Old Red Sandstone (ORS). The sequence is of Middle or possibility Lower ORS age.
Locality 2 Achanarras (ND 150 544)
The Achanarras quarry was worked for flagstones for many years. The best flagstones were obtained from the fine grained, flat layered deposits which were laid down in the deepest and quietest waters of the Oradian lake. The Achanarras lake was the largest and longest surving lake of the Middle ORS period. The Sandwick Fish Beds of Orkney represent a more northerly facies and the Melby Fish Bed of Shetland may represent the most northerly extension of the lake at its highest level. Southwards the remains of the lake are found in marginal facies at Edderton, Cromarty, Nairnside, Clova, Tynet Burn, and Gamrie. Well preserved fish fossils are common. Many of the fish lived in shallower, near-shore waters and when they died the carcasses drifted and sank in deep waters where they were quickly buried in the stagnant bottom waters of the thermally stratified lake. The very fine lamination of the sediments represents seasonal, probably annual, layers and each lamina can be sub-divided into two or three seasonal variations.
Locality 3 Sandside Bay (NC 958 660)
This well exposed section demonstrates a more marginal facies of the Orcadian basin lakes approaching the basement highlands to the west. Several complete cycles of lake transgression and regression are well exposed including lake shore and fluviatile facies. A thick sequence of probable aeolian sands may represent a lake shore sand dune field similar to those found on the fringes of arid zone, transient lakes today.