A Refined Sequence Stratigraphic Framework for the Kuibis Subgroup (lower Nama Group), Southern Namibia

The Nama Foreland Basin of southern Namibia developed along the western margin of the Kalahari Craton during the late Ediacaran (ca. 550–520 Ma). Its formation was driven by collisions with the Congo Craton and the Río de la Plata Craton during the assembly of western Gondwana. The basin is classically subdivided into three structural components: a foredeep (Zaris sub-basin), a forebulge (Osis Ridge), and a back-bulge (Witputs sub-basin). Its sedimentary infill, preserved by the Nama Group, forms a ~3000 m thick mixed siliciclastic–carbonate succession that represents one of the most complete and best-preserved geological records of the Ediacaran–Cambrian transition. The Nama Group comprises three major stratigraphic units—the Kuibis, Schwarzrand, and Fish River subgroups—of which this study focuses on the oldest, the Kuibis Subgroup. Although the Kuibis Subgroup has been the subject of numerous chemo- and lithostratigraphic studies, temporal correlations of strata between the Zaris and Witputs sub-basins remain debated. Recent cyclostratigraphic analyses of the Kuibis Subgroup identified multiple laterally traceable flat-topped surfaces, four of which mark second-order sequence boundaries. Of these four, only three are regionally correlatable across the basin. These results contrast with earlier models which proposed four sequences in the Zaris sub-basin and only two in the Witputs. To complement and ground-truth this cyclostratigraphic correlation scheme, we integrated detailed sedimentary logging and facies analysis from key sections across both sub-basins to construct a revised sequence stratigraphic framework. Our findings suggest that these traceable flat-topped surfaces correspond to key sequence-stratigraphic horizons that can be correlated basin-wide, refining systems tract architecture and sub-basinal connectivity. While observations from the Zaris broadly support existing interpretations, our re-evaluation of stacking patterns and abrupt facies transitions in the Witputs reveals three, rather than two, second-order sequences. The Kuibis succession is therefore characterized basin-wide by three regionally correlative second-order sequences. Accommodation within these sequences reflects steady flexural subsidence of the Osis Ridge, while higher-frequency cyclic stacking patterns, expressed as parasequence sets, record climatically driven sea-level oscillations. Together, these results highlight how tectonics and astronomical climate cycles shaped late Ediacaran carbonate platforms and provide the environmental context needed to better assess where, when, and why early complex animals diversified.