Paleomagnetic investigation of the Beacon Group in the McMurdo Sound region, Antarctica

Abstract

A total of 216 paleomagnetic samples of the Beacon Group (sandstone) were collected from Mt. Circe, Mt. Knobhead, Allan Hills and Mt. Fleming. The respective sedimentary sequences are Pre- or Early-Devonian, Devonian, Permo-Triassic and Triassic. The representative samples were tested for NRM stability against AF and thermal demagnetization, ARM and TRM acquisition, and AF demagnetization of ARM. The following results were obtained. The samples from Mt. Circe and Mt. Knobhead have stable NRM of parallel direction to that of the Ferrar dolerite. From this we conclude that these samples were remagnetized in the Jurassic Age and the primary magnetization disappeared. The samples from Mt. Fleming were also remagnetized by the dyke of the Ferrar dolerite or do not have stable NRM. However, parts of the samples from the Allan Hills have stable depositional remanent magnetization (DRM) of the Permo-Triassic Age. The direction of NRM for these samples is parallel to that of the Ferrar dolerite in the Jurassic Age. This suggests that East Antarctica had no shift of VGP. This conclusion is consistent with the results on the Mesozoic Age in Australia. Thus Australia must have been linked to Antarctica at least up to the Jurassic Age.