Palaeomagnetism of Precambrian Sedimentary Rocks from NW Scotland and the Apparent Polar Wandering Path of Laurentia

Abstract

Red sedimentary rocks of the Stoer Group (991 My BP) were resampled through their stratigraphic range (600 m at Stoer Bay). The mean direction of magnetization after thermal cleaning at 500° C is 313,+29 (θ95= 8°) with a corresponding palaeomagnetic pole at 35° N, 234° E. This result is not significantly different from that obtained previously from studies of natural remanent magnetization. A small collection from the base of the overlying Torridon Group (796 My BP) confirms the general reliability of the earlier work on these rocks also, and shows that the large change between the Stoer and Torridon Groups coincides with the unconformity between them. The magnetization of these sediments originated at the time they were laid down. Since NW Scotland used to be part of Laurentia, the Stoer and Torridon Group poles can be compared with those from the late Precambrian of the Canadian Shield. In order to quantify these comparisons, a system of grading poles on a seven‐point scale is introduced, and a generalized polar path for the Canadian Shield drawn. The poles from NW Scotland do not fit onto this path, indicating either that there has been slight rotation of NW Scotland as a marginal block of Laurentia, or that a hitherto unsuspected polar excursion occurred immediately following the Grenvillian orogeny. Copyright © 1974, Wiley Blackwell. All rights reserved