Correlation of Neoproterozoic glacial diamictites in southern Namibia

This talk presents a multi-method approach to construct a conclusive new correlation model for Neoproterozoic glacial units of southern Namibia. Therefore, ten different sections and a variety of samples were studied and analysed with respect to field relationships, whole-rock geochemistry, zircon U-Pb dating and Th-U ratios, Hf isotope measurements and zircon grain size analyses, combined with LA-ICP-MS U-Pb dating of cap carbonates.

Our analyses show that (1) sediments deposited during four Neoproterozoic glacial events in southern Namibia all have very similar detrital zircon characteristics, allowing the interpretation of continuous recycling of the same material over the most part of the Neoproterozoic, which is also supported by the whole-rock geochemical analyses, (2) cap carbonates can be analysed for their U-Pb isotope ratios and provide valuable age determinations, if reset and overprinted areas are recognised and avoided for laser ablation, (3) proving the Sturtian and the Marinoan age for the Numees Fm and the Namaskluft Mbr by U-Pb dating their overlying carbonate sequences was finally possible, (4) the Witvlei Grp sedimentation ends at 579 ± 52 Ma, which is the age of the stromatolites of the Okambara Mbr, representing the uppermost deposits of the Witvlei Grp, and this leads to (5) the onset of the Nama Grp sedimentation for southern Namibia is no earlier than 579 ± 52 Ma.