Building a depositional model and life that inhabited it

Neoproterozoic Nama Group sediments in SW Namibia provide an example of the interplay between the deposition of clastics and carbonates that do not obviously follow the “rules” of sequence stratigraphy. The unconformity surface beneath the sediments is planar and extensive. Basal interbedded carbonates and coarse clastics are overlain by a massive influx of fluvial clastics (Kliphoek Member). These fine upwards and are overlain by fine grained clastics with interbedded carbonates and minor turbidite sands (Aar Member) that contain most of the fossils found in this part of the Nama Group. Carbonate beds become more common towards the top of this member, which is overlain by a thick carbonate unit of region extent (Mooifontein Member).

Southwards the basal clastics (Kanies Member) become thicker, while carbonate beds in the overlying Mara Member are more dominant. The Kliphoek Member becomes finer grained but includes some coarse grained clastics, and the Aar Member contains more and thicker carbonate beds. Paleocurrents show a dominant sediment transport towards the west and southwest.

Questions posed by the stratigraphy include whether the basin subsided at a constant rate, where was the shoreline at any given time, where were the input points of the clastic sediments and how and why did the influx rate vary? Did changes in sea level, and therefore shoreline position, influence the deposition of carbonates, or was this mostly influenced by a lack of clastic influx? We do not have accurate ages for the sediments or the rate at which they were deposited.