STRUCTURAL MAP OF THE SOUTHERN NAUKLUFT MOUNTAINS, NAMIBIA

The Zebra Nappe is the youngest allocthonous tectonic unit of the Naukluft Nappe Complex (NNC), an outlier of the 650-540 Ma Damara orogeny that consists of carbonate and clastic strata thrust south- and southwestward over the Nama foreland basin. The tectonic units of the NNC are Neoproterozoic in depositional age, while Damara orogenesis and foreland-basin deposition span the Precambrian-Cambrian boundary.

We present a new structural map of the southern Naukluft Mountains, addressing the pattern of deformation within the Zebra Nappe and its structural relationship with the Nama group and adjacent Naukluft nappes. This is paired with detailed stratigraphic characterization to assess the timing and depositional environment of the Zebra Nappe.

The upper nappes of the Naukluft complex closely resemble cap carbonate sequences exposed elsewhere in Namibia. The Zebra Nappe was originally interpreted as a foreland basin sequence closely related to the Nama Group (Hartnady, 1978), but results reported here indicate a likely passive margin origin. Since the Precambrian-Cambrian boundary is embedded in the younger strata of the Nama foreland basin, these rocks must be relatively older.

The Zebra Nappe contains ~600 m of carbonate and clastic sediments, which broadly shift from peritidal and upper shoreface deposition (often including stromatolites) towards deeper-water outer shoreface facies, including hummocky cross-bedded grainy limestones and shales, and finally to thick carbonate platform strata dominated by interclast dolomite mudstones.

Significant internal shortening is accommodated with a deformational style dependent on rheology. Dolomites at the base of the nappe are imbricated at ~30 m scale, while the middle strata contain variably tight to recumbent folds. The upper carbonate sequence folds openly over a ~5 km baseline.

The Zebra Nappe overlies the Dassie Nappe on a roof thrust, with repeated Dassie imbricates sitting below an apparent passive backthrust. This relationship, along with the more easterly tectonic vergence of the Zebra Nappe, suggests emplacement of the NNC in two phases, with southward blind thrusting of the Dassie and Kudu nappes beneath the Zebra Nappe followed by southwest thrusting of the entire NNC over the Nama Group foreland basin deposits on a major basal detachment.