Evolution of late proterozoic to early paleozoic Adelaide foldbelt, Australia: Comparisons with postpermian rifts and passive margins

A tectonic and sedimentary facies model is proposed to explain progressive evolution of the late Proterozoic to early Paleozoic Adelaide Rift (Geosyncline) of southern Australia. Tectonic and stratigraphic similarities are noted between the Adelaide Rift and many post Permian rifts and passive continental margins. Also the time span of the pre oceaniccrust accretion stage of the rifting process may be of the same order of magnitude, both in the Adelaide Rift and in post-Permian passive margins. These observations suggest that the underlying cause of the rifting process and the resultant crustal response have not changed significantly since late Precambrian times. More specifically the so-called “breakup unconformity”, observed in stratigraphic sequences beneath many present day passive continental margins, has been shown by various authors to correlate in time with earliest oceanic crust accretion, and it often separates underlying non-marine or paralic from fully marine shelf strata. In the Adelaide Rift, the unconformable Precambrian—Cambrian boundary is proposed as the analogue of this breakup unconformity, thereby explaining the apparently sudden influx of largely marine metazoans in Cambrian strata immediately above this unconformity.