Abstract
Abstract The applicability and the uncertainty range of RbSr age determinations on carbonate rocks are discussed briefly. A study of clay minerals isolated from carbonate rocks of the McMinn Formation provides an isochron age of 1429 ± 31 Ma and thus the age for cessation of the Proterozoic McArthur basin sedimentation. The eukaryots recently described in this area are therefore the oldest occurrences found in Earth history. A second sequence of measurements on a homogeneous dolomite siltstone ca. 23 km southeast of the McArthur River (H.Y.C.) PbZn deposits yields an RbSr age of 1537 ± 52 Ma for the Upper Barney Creek Formation in broad agreement with recent age determinations on feldspar beds of this horizon. These data are compared with previous isotopic results. From data presently available it can be concluded that the sediments in the McArthur basin (the type locality of the Carpentarian) were deposited between 1800-1400 Ma.
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