Palaeomagnetism of Lower Cambrian sediments from the Olenek River section (northern Siberia): palaeopoles and the problem of magnetic polarity in the Early Cambrian

Abstract

SUMMARY New palaeomagnetic data from the Lower and Middle Cambrian sedimentary rocks of northern Siberia are presented. During stepwise thermal demagnetization the stable characteristic remanence (ChRM) directions have been isolated for three Cambrian formations. Both polarities have been observed, and mean ChRM directions (for normal polarity) are: Kessyusa Formation (Lower Cambrian) D = 145, I = -4O, N = 12, ug5 = 12.8; pole position: CD = 38S, A = 165E; Erkeket Formation (Lower Cambrian, stratigraphically highly) D = 152, I = -47, N = 23, ug5 = 6.8; pole position: CD =45S, A = 159E; Yunkyulyabit-Yuryakh Formation (Middle Cambrian) D = 166, I= - 33, N = 38, ctg5 = 4.6; pole position: 0 = 36S, L = 140E. These poles are in good agreement with the apparent polar wander path based on the bulk of existing Cambrian palaeomagnetic data from the Siberian platform. In Cambrian times, the Siberian platform probably occupied southerly latitudes stretching from about 35 to O, and was oriented 'reversely' with respect to its present position. Siberia moved northwards during the Cambrian by about 10 of latitude. This movement was accompanied by anticlockwise rotation of about 30. The magnetostratigraphic results show the predominance of reversed polarity in the Early Cambrian and an approximately equal occurrence of both polarities in the part of the Middle Cambrian studied. These results are in good agreement with the palaeomagnetic polarity timescale for the Cambrian of the Siberian platform constructed previously by Khramov et al. ( 1987).