Late Vendian Closure of the Adamastor Ocean: Timing of Tectonic Inversion and Syn-orogenic Sedimentation in the Gariep Basin

New Pb-Pb age data obtained on stromatolitic dolomite from the oceanic Marmora Terrane in the Pan-African Gariep Belt support previous Ar-Ar age data on early amphibole, that has been related to sea floor metamorphism, and indicate formation of oceanic crust in the Neoproterozoic Adamastor Ocean (Gariep Basin) around 600 Ma. A maximum age for oceanic crust in the Gariep Basin is given by 741±6 Ma, which is the best available minimum constraint on continental rifting in the Gariep Belt. Tectonic inversion to basin closure overlaps in time with the end of a younger glacial period that is recorded both in the oceanic and continental realms and is correlated with the global c. 580 Ma Marinoan glaciation. The rock record up to that time in the Marmora Terrane is completely different to that in the para-autochthonous, continental Port Nolloth Zone in the east of the belt, but the post-glacial sediment successions bear many lithological and geochemical similarities. These younger successions are therefore interpreted as reflecting syn-orogenic deposits in a foredeep, the age of which is constrained between c. 580 and 550 Ma. Comparison of three chemostratigraphic profiles through the post-glacial carbonate succession shows that enrichment in carbonate 13C is, in the first instance, a function of proximity to the basin margin and thus of the extent of ocean water stratification.