Some studies on the stratigraphy and sedimentation of the Trias of the Western Highlands and Hebrides, Scotland

Abstract

Sediments referred to the Trias outcrop at intervals over a distance of 105 miles (157 km) along the northwestern seaboard of Scotland. A detailed description is given of the field occurrences and successions, and the stratigraphy revised. Important rod sediments in Westor Ross, previously mapped as Trias, are shown to be Torridonian and their significance is discussed. The Trias is very variable in thickness ranging from negligible to over 300 m (1000 ft). Lithological units show rapid lateral variation, and it is impossible to draw detailed comparisons between successions in different areas. The sediments mainly consist of conglomerates and sandstones which are compared of materials derived from formations, known in the area at the present time. The study of textures and sedimentary structures shows that the sediments are fluviatile. Piedmont deposits and sediments which accumulated in an environment intermediate between piedmont and valley-flat are common true valley-flat deposits also occur, represented by thin fine-grained said-stones and siltstones, Concretionary limestones occur throughout the area, except in one locality, find are interpreted as pedocals. The sediments probably, accumulated in a series of partially isolated basins. Sedimentation was influenced early on by a chain of upland area consisting of n sequence, of Torridonian and Cambro-Ordovician sediments which extended from Loch Broom to Iona, west of the present outcrop of the Hoine Thrust. Source areas to the east became dominant later. The climate was probably hot and semi-arid, with seasonal rainfall.