Palaeomagnetic Studies of the Caerfai Series and the

The Caerfai Series carries stable NRM which is probably of Lower Cambrian (otherwise pre-mid-Devonian) age, indicating a palaeomagnetic field direction with declination 185", inclination +23 " (ag5 = 9.1'). This NRM probably originates in the detrital hematite grains rather than in the red cement of these sediments. The corresponding palaeomagnetic pole is at 11 " W, 26 " S. The age of stable NRM in lavas of the Skomer Volcanic Group is less certain. If it is original, results indicate a Lower Silurian (or possibly late Ordovician) geomagnetic field direction with declination 202", inclination-09 " (ag5 = 1%") which corresponds to a palaeomagnetic pole at 3w W, 39 " S. However it is argued that this NRM is more likely to be of Permo-Carboniferous age, in a direction uncorrected for Hercynian warping D = 196 " 1 = + 09 " (a95 = 17"). All rocks studied here have the same polarity with the possible exception of one site in the Skomer volcanics. A tentative interpretation of Lower Palaeozoic data from Britain places the palaeomagnetic pole in the vicinity of 15 " N, 165"E throughout the era and the Devonian, with the exception of a Siluro-Devonian excursion to the south-west. However, other explana-tions involving widespread remagnetization, persistent geomagnetic anomalies or large lateral displacements within Europe, cannot be excluded. 1