Reassessment of the sub-basinal correlation of the Ediacaran Kuibis Subgroup (Nama Basin, Namibia) and implications for shallow marine chemostratigraphy

The Kuibis Subgroup (lower Nama Group) in Namibia was deposited during the late Ediacaran in mainly shallow marine environments of a foreland basin that was separated into a northern (Zaris) and southern (Witputs) sub-basin by the Osis Ridge. The succession was correlated between the two sub-basins based on lithostratigraphy, and, more recently, carbonate carbon isotope (δ 13 C carb ) chemostratigraphy. Here, we use satellite imagery integrated with field data to establish a refined stratigraphic framework and correlation of the Kuibis Subgroup across the two sub-basins, independent of δ 13 C chemostratigraphy. The succession consists of alternations between resistant and recessive intervals, reflecting second- and third-order sequences, many of which are traceable throughout the sub-basins and even across the Osis Ridge over distances of ∼300 km. The proposed correlation differs from previous δ 13 C-based correlations, but is similar to older lithostratigraphic correlations, and identifies three second-order sequences in the Kuibis Subgroup in both sub-basins. This correlation scheme is supported by the continuity of distinctive flat-topped surfaces between the sub-basins, which are interpreted to reflect transgressive–regressive sequence boundaries. The integration of published δ 13 C data shows that during deposition of the first two sequences, little sediment accumulated on the ridge crest and the sub-basins each record different δ 13 C values. The third second-order sequence, however, was deposited across the ridge and δ 13 C values are comparable in both sub-basins. Therefore, we suggest that the Zaris and Witputs sub-basins were separated and geochemically distinct during the early stages of the Nama foreland basin. Continued subsidence eventually buried the ridge and connected the two sub-basins.