A Basin in Transition: Ecological, Environmental, and Tectonic Shifts Across the Ediacaran–Cambrian Boundary in the Nama Group, Kalahari Craton

The Nama Group (Kalahari Craton) is an archetypal stratigraphic record of the Ediacaran–Cambrian transition. The upper Schwarzrand Subgroup preserves key biostratigraphic markers of this interval, including erniettomorphs, cloudinomorphs, and trace fossils, yet has a complex stratigraphic architecture due to deposition in a foreland basin. Here, we describe the stratigraphy of the upper Schwarzrand Subgroup of the Nama Basin, and collate sedimentologic, geochronologic, carbon isotope chemostratigraphic, and biostratigraphic data. We argue that strata previously identified as the Nomtsas Formation in the Witputs Subbasin are lithostratigraphically and tectonostratigraphically distinct from those in the type area (Farm Nomtsas) in the Zaris Subbasin. Therefore, we introduce the Swartkloofberg Formation as a new name for the terminal Schwarzrand Subgroup in the Witputs Subbasin. While carbonates of the underlying Urusis Formation were deposited within shallow marine environments, the Swartkloofberg Formation records a transition to dominantly siliciclastic deposition, mostly below fair-weather wave base, and with extensive evidence of slope instability. High-relief stromatolite reefs formed diachronously at different localities within both the Urusis and Swartkloofberg formations due to laterally variable accommodation space within the foreland basin. Strata of the Swartkloofberg Formation are interpreted as flysch deposits within an underfilled basin. We propose that the distinct deltaic peritidal and shoreface strata that—in some localities—were previously assigned to the upper Nomtsas Formation, are placed within the unconformably overlying molasse deposits of the Fish River Subgroup. These strata contain the stratigraphically lowest identified occurrences of Treptichnus pedum within the Nama Group, and thus the base of the Cambrian Period. This stratigraphic revision solves several longstanding issues with regional correlation and revises the position of the Ediacaran–Cambrian boundary in the Witputs Subbasin. Accordingly, the Swartkloofberg Formation in the Witputs Subbasin (538.5–