Neoproterozoic tectonic and climatic evolution recorded in the Gariep Belt, Namibia and South Africa

The Pan-African Gariep Belt in south-western Namibia and westernmost South Africa provides an excellent window into the interplay between tectonic and climatic changes during the Neoproterozoic era. Recently acquired chemostratigraphic data from cap carbonate sequences above glaciogenic diamictite horizons, together with U-Pb zircon and Pb-Pb carbonate ages, indicate sedimentation in the Gariep Basin from continental break-up around 770 Ma to basin closure and continent collision around 545 Ma. The basin is subdivided into an eastern failed rift graben and a western half graben that evolved into an oceanic basin between the Kalahari and the Rio de la Plata cratons. Three megasequences are distinguished in the external, para-autochthonous part of the belt (Port Nolloth Zone): an early continental, predominantly siliciclastic, sag rift megasequence (M1), a passive continental margin, carbonate-rich megasequence (M2), and a syn-orogenic carbonate and flysch megasequence (M3). Two glaciogenic diamictite horizons at the end of M1 and M2 are recognized and they are correlated with the global similar to750 Ma Sturtian and similar to580 Ma Marinoan glaciations, respectively. While the former is restricted to proximal continental rift shoulders, the latter extends into the oceanic realm which marks the internal part of the belt (Marmora Terrane). Only the younger diamictite is associated with iron formation. The sequence of regressive and transgressive stages recorded by the sediment fill does not reflect simply the tectonic evolution from rifting to drifting and eventual basin closure, but is strongly controlled by severe climatically induced sea-level changes that were either competing with or reinforcing tectonically induced sea-level changes.