Overview

General aspects of the Torridonian briefly reviewed in the following paragraphs include the significance of the similarity in depositional style shown by the three component groups, their burial history, palaeocontinental setting and regional correlation. The Stoer, Sleat and Torridon Groups are thick fluvial successions, each of which tends to become finer upwards. The last two groups both show an upward progression from locally derived basal breccias into lake deposits, followed by a thick fluvial sequence, as if they were deposited in a regime of decelerating subsidence. In addition, both were derived from progressively more acid source rocks, as the source terrain expanded to embrace not just local basic gneisses, but a wider range of rock types, including sediments. These features are consistent with deposition in an extensional basin subjected to two distinct stretching events. The Stoer Group must represent a much earlier stretching event, for it was lithified and deeply eroded before the Torridon Group was deposited upon it. The upward facies progression in the Stoer Group is like that in the other groups, except that the lacustrine phase (facies Ct3, see Fig. 5 & p. 9) is underdeveloped. The orientation of the basin is suggested by the palaeocurrent directions. Stoer Group directions are bimodal; 77% of the currents flowed westwards (θ = 270°, n = 282) and the remainder eastwards (θ = 069°, n = 84). In the Sleat Group 65% flowed eastwards. In the Torridon Group virtually all the currents flowed ESE (θ=123°), almost exactly perpendicular to the