The Palaeomagnetism of Some Cambrian and Ordovician Sediments from the Northern Territory, Australia

Samples for palaeomagnetic investigation were collected from nine horizons in the Jinduckin Formation, of Early Ordovician age, and from four exposures of a red mudstone band within the Middle Cambrian Montejinni Limestone. The mudstone samples responded unsatisfactorily to both alternating field and thermal demagnetization procedures and their magnetization appears to originate from chemical action during weathering in recent times. In contrast, only one site from the Jinduckin Formation failed to respond to thermal cleaning, and a chemical demagnetization technique here was also unsuccessful. Thermally cleaned directions from seven of the other eight sites are assumed to yield the original direction of magnetization of the Jinduckin Formation (D = 252°, I = −14°, α95 = 20°), and are used to derive the mean pole position for the period of its deposition (Long. = 29° E, Lat. = 16° S, A95 = 17°). This is the first result from a current palaeomagnetic study of the lower Palaeozoic red beds of northern Australia.