Stratigraphic Transition into and out of a Snowball Glacial: Evidence from the Otavi Platform and Fransfontein Slope, Namibia

Detailed lithostratigraphic studies on the transition from non diamictite to diamictite intervals within the Neoproterozoic are vital in evaluating the nature of presumed glacial events in the Snowball Earth hypothesis. To this goal we examined the fine-scale stratigraphic relationships of units above and below the Ghaub carbonate diamictite in the region of the Fransfontein paleoslope, north central Namibia. Stratigraphic transitions here are marked by sediment gravity flow and ice rafted horizons that pass in a systematic way both into the Ghaub diamictite and out of the Ghaub diamictite. While distinct ice rafted horizons are indeed present within these transitional intervals the nature of inter-bedded sediment gravity flows (composite fining and coarsening) indicate a single ice advance and retreat cycle that bounds the massive to nearly structureless diamictite characteristic of the Ghaub glacial unit. Small-scale structures within the diamictite are indicative of localized shearing, localized production of silt sized matrix, and suppression of turbulent flow. These observations are consistent with a subglacial origin for portions of the Ghaub diamictite interval. Taken together the stratigraphic and sedimentologic observations on the slope setting are consistent with the Snowball Earth hypothesis of a single glacial episode preceded and succeeded by carbonate deposition.