STRATIGRAPHY AND SEDIMENTOLOGY OF THE ZEBRA NAPPE, NAUKLUFT NAPPE COMPLEX, NAMIBIA

The Naukluft Nappe Complex is an outlier of the 650-540 Ma Damara orogen consisting of carbonate and clastic strata organized into several tectonic packages and thrust southwestward atop the Nama group, a carbonate foreland basin sequence that captures the Precambrian-Cambrian boundary. Several of the upper nappes are similar to Marinoan cap carbonates exposed elsewhere in Namibia, but the Zebra Nappe, the lowest of the allocthonous units, has an uncertain age and affinity. We use regional structural mapping, detailed stratigraphic columns, and chemostratigraphy to understand the formation environment of the Zebra Nappe, its internal divisons, tectonic context, and potential correlations with known intervals such as the basal Nama.

The Zebra Nappe contains ~500 m of carbonate and clastic sediments with sedimentary structures consistent with terrestrial, intertidal, and shallow-marine environments. The nappe can be divided into several formations along the lines proposed by Hartnady (1978). We evaluate and refine these divisions through detailed mapping and stratigraphic studies. The lower strata of the nappe shows evidence of subaerial deposition, while the upper sequence contains hummocky cross-bedded grainy limestones, thick shales, and platform-facies dolomites. Stromatolites are found at various levels of the section, but no Ediacaran or calcified fossils are observed. At its base the nappe has slightly negative δ¹³C, ascending to values of +4 in the middle of the section, and a consistent plateau at δ¹³C of -2 expressed at the top of the section. Scatter in δ¹⁸O near the top of the nappe is indicative of meteoric alteration beneath the pre-Karoo peneplain that caps the Naukluft Mountains. Values consistent with the Ediacaran Shuram excursion in δ¹³C are absent. This chemostratigraphic profile of the Zebra Nappe is unlikely to correlate with the basal Nama or an outboard extension of the foreland basin, but it may link with the older Witvlei group, or a missing pre-Damara passive margin of the Kalahari craton.