The Sleat Group
The group consists of up to 3500 m of coarse, grey fluviatile sandstones, with subordinate grey shales, resting unconformably on the Lewisian basement complex. Although the beds have been thrust tens of kilometres from the east as part of the Caledonian Kishorn nappe (Ramsay 1969) their stratigraphic position is secured by a conformable relationship with the overlying Torridon Group, presumed to be only slightly younger (Fig. 19). The Stoer Group does not form part of the Kishorn nappe and its relationship to the Sleat Group is unknown. Lithostratigraphic correlation of the two groups is thought unlikely, however, for reasons given later. Slight Caledonian deformation and very low grade metamorphism have had little effect on sedimentary structures in the Sleat Group between Loch na Dal and Kylerhea, in Skye. The metamorphism has, however, dissuaded attempts at isotopic dating.
The lithology, framework mineralogy of the sandstones, palaeocurrents and stratigraphic nomenclature of the Sleat Group are summarized in Figure 20. No formal facies nomenclature is proposed. The present outcrop is shown in Plate 1.
Figures & Tables
The Torridonian sandstones form one of the principal elements of British stratigraphy. They form the majestic mountains of NW Scotland and also extend westwards under the Minch basin. The sediments were deposited in a Proterozoic rift nearly contemporaneous with the Keweenawan Supergroup of North America.
This book contains the first complete field description of the rocks and the sedimentary environments in which they formed, together with a comprehensive examination of their tectonic and palaeoclimatic significance, geochemistry, palaeomagnetism and diagenesis. It includes the result of over forty years’ work by the author, most of it previously unpublished.