A major perturbation of the carbon cycle before the Ghaub glaciation (Neoproterozoic) in Namibia: prelude to snowball Earth? Geochem. Geophys. Geosystems

[1] A large (11–15%) negative shift in d13C is observed in shallow water carbonates directly beneath Neoproterozoic glacial deposits (or correlative disconformity) in northwest Namibia ascribed to a snowball Earth. Reproducibility and stratigraphic concordance of this anomaly in 16 sections across the ancient continental shelf support a primary origin, and field relations show it predates the fall in sea level associated with the Ghaub glaciation. We crudely estimate the duration of the isotopic shift as 0.6 106 years from a simple thermal subsidence model. Similar or larger d13C anomalies are found directly beneat