STRATIGRAPHIC ARCHITECTURE AND FACIES DISTRIBUTION OF THE DEEP-WATER NEOPROTEROZOIC ZERRISSENE GROUP, DAMARA OROGEN, NAMIBIA

Understanding the spatial variability of deep-water facies is of paramount importance to deep-water research because of its revealing information about turbidity current processes and their potential as reservoirs. The Upper Proterozoic Zerrissene Group, exposed in west-central Namibia, provides a unique opportunity to investigate a Precambrian depositional system that showcases the intricacies of lateral facies relationships in an unconfined deep-water setting. The study of over 2000 sq. km of Upper Proterozoic strata is facilitated by the lack of vegetation in the Namib Desert and regular east-west repetition of folded stratigraphy, providing quasi-three-dimensional exposure of the turbidite system. The Zerrissene Group underwent low-grade metamorphism and three significant stages of deformation, which resulted in complex stratigraphy and metamorphic overprint. Still, primary sedimentary structures are preserved locally and serve in interpreting sedimentary processes of the depositing flows.

The depositional architecture of this large, unconfined turbidite system is studied in the Brak River Formation of the Zerrissene Group, where nearly 600 m of strata is exposed in a continuous outcrop over 10 km in length. Three ~150 m thick sand-prone packages are separated by two shale-prone intervals, each on the order of 40 m thick, that can be correlated regionally throughout the study area. Lateral and vertical changes in sandstone bed thickness and organization are documented over thousands of meters and record the spatial and temporal evolution of the basin-floor system. Both thin-to-thick bedded turbidites and slurry beds are observed across continuous exposures and provide a unique opportunity to examine the lateral evolution of their depositional flows within unconfined lobes. These relationships can be quantified to provide a better understanding of predicted lithofacies distributions in less exposed or subsurface analogous systems.