Low palaeolatitude of deposition for late Precambrian periglacial varvites in South Australia: implications for palaeoclimatology

The natural remanent magnetisation (NRM) has been determined for periglacial clastic varvites (Elatina Formation) deposited in the Adelaide Geosyncline in South Australia during the Marinoan Glaciation 680 my. ago. The varvites contain abundant silt-sized detrital specular titaniferous haematite and martite that experienced a high-temperature (∼ 600°C) oxidation event prior to deposition, as well as ultrafine haematite and minor goethite pigment. The NRM intensities exhibited little change prior to thermal treatment above 600°C. The mean palaeomagnetic pole lies at latitude = 50.9°S, longitude = 337.1°E and A₉₅ = 2.2° the inferred palaeolatitude of the sampling locality is 5°. This pole position is similar to other late Precambrian poles for Australia. In view of the nature of the NRM and the lack of metamorphism of the rocks the magnetic remanence is regarded as primary (early diagenetic) and dating closely from the time of deposition. The contradiction of very cold climate near sea level in low palaeolatitudes during the late Precambrian brings into question basic tenets in palaeomagnetism and celestial mechanics.