Paleomagnetism of the Lower Cambrian Bradore sandstones, and the rotation of Newfoundland

Abstract

Wegener proposed that Newfoundland has rotated 30 degrees anticlockwise relative to Labrador. We report here new paleomagnetic evidence bearing on this hypothesis, obtained from sandstones of the Lower Cambrian Bradore Formation on Canada Bay, Newfoundland. Isothermal remanence tests indicate that the entire natural remanence (NRM) of the samples resides in hematite. The mean NRM direction for 9 sites is D = 153°, I = +52°, α 95 = 15° , confirming R.F. Black's 1964 result from other Bradore exposures in northern Newfoundland, which he compared with rocks in New Brunswick. Although Black's data appeared to support Wegener's hypothesis, his samples had not been thermally treated, whereas thermal demagnetization of our samples led to isolation at 665°C of a very stable component misaligned with the NRM direction. The 665°C component probably was acquired through a C(hemical)RM and/or D(epositional)RM process by the time the rocks became consolidated. After structural correction, this component corresponds to a reverse paleomagnetic pole at 29°N,167°E ( dp = 3°, dm = 5°, 9 sites). Bradore sandstone from two sites located 50 km west of Canada Bay gave comparable (virtual) poles. These results are useful for a potential test of a post-Lower Cambrian rotation of western Newfoundland.