The Precambrian–Cambrian boundary problem: magnetostratigraphy of the Amadeus Basin, Central Australia

Abstract

A magnetostratigraphic study of Upper Proterozoic to early Cambrian sediments at 4 localities in Central Australia reveals the presence of a magnetic polarity pattern composed of 2 long quiet intervals, first of reversed then of normal polarity, which is then succeeded by a long mixed interval. Lithologic comparisons suggest that this pattern is a reflection of the behaviour of the geomagnetic field at that time, and probably is not a result of varying sedimentation rates. Two sampled sections in the Arumbera Sandstone separated by 80 km both contain the long normal interval followed by the interval of mixed polarity, the detailed comparison of which demonstrates that the Arumbera-Box Hole boundary is unconformable. Elements from the late Precambrian Mt Skinner fauna in the Arumbera Sandstone indicate that the long normal interval is entirely pre-Cambrian, and that the base of the Cambrian occurs within the interval of mixed polarity.A comparison with an additional site sampled across a fossil occurrence in the Central Mount Stuart Formation at Central Mount Stuart indicates that at least 1 of the Upper Proterozoic fossils, Hallidaya brueri, has a considerable vertical distribution in time.If used properly, the magnetic polarity pattern discussed herein offers the possibility of precise intercontinental correlations of stratigraphic sequences near the base of the Cambrian. It is suggested that a stratotype sequence for the base of the Cambrian be chosen in such a manner that the boundary position corresponds to a geomagnetic reversal.

The Lower Cambrian Fossil Record of the Soviet Union

“…The Cambrian thermal regime (Chumakov, 1984), confirmed by data on glauconite minerals, was similar to that of the Jurassic (Nikolaeva, 1981). According to these data, the temperature of seawater in Baltia was about 28 D C, and on the Siberian Platform and its Anabar-Sinsk Facies Region, about 30-38 D C. All the principal epicontinental basins were in low latitudes, as confirmed by paleomagnetic data obtained on fossiliferous sections in Australia, China, Mexico, and Mongolia, and on the East European and Siberian Platforms (Kirschvink, 1978;Khramov and Rodionov, 1980;Barr and Kirschvink, 1983;Zhang and Zhang, 1984;Kirschvink et 01., 1987). Therefore, the chief reason for increasing provincialism is, in our opinion, the fragmentation of the Paleopangea supercontinent (Kirschvink et 01., 1984).…”

Magnetostratigraphy of lower Cambrian strata from the Siberian Platform: a palaeomagnetic pole and a preliminary polarity time-scale

“…Despite the limits of the present data, it seems worthwhile to attempt a comparison of these results with those reported for lower Cambrian sediments in the Amadeus and Georgina basins of Australia (Kirschvink, 1978;Burek, Walter & Wells, 1979). These authors found an interval of mixed polarity in Late Precambrian strata immediately beneath a widespread regional disconformity.…”

Paleomagnetic polarity reversals in Marinoan (ca. 600 Ma) glacial deposits of Australia: Implications for the duration of low-latitude glaciation in Neoproterozoic time

“…10). We make tentative interpretations of polarity here based upon previous paleomagnetic work that covers the post-Marinoan through Cambrian interval in the Amadeus basin (Kirschvink, 1978b), as well as previously published apparent polar wander (APW) paths for east Gondwana (e.g., Powell et al, 1993). According to these interpretations, the Earth's magnetic field in late Neoproterozoic time corre-sponds to reversed polarity for southwest and up directions and normal polarity for north-northeast and down directions; Australia thus is right-sideup near the equator, but mostly in the Northern Hemisphere (see Table 1 and Fig.…”