Lacustrine stromatolites of the Etosha Pan, South West Africa (Namibia)

Abstract

Abstract by author:

In the nearshore oolite shoal represented by the Oosparite Member oncolite fragments acted as nucleii for in situ oncolite development. The low turbulence was sufficient to prevent cryptalgal laminite growth between the oncolites. Initially oncolites grew with a smooth mat morphology but subsequently colloform overgrowths developed as seasonal rains raised the lake level. Silica concretions and stromatolites present in the Oomicrite Member *indicate that the environment alternated between subaerial and sub-aqueous regimes as the shoreline changed in response to seasonal rainfall. This seasonal emergence resulted in potential oncolite nucleii becoming cemented to the substrate and the formation of columnar stromatolites instead of oncolites

Evidence for lake level fluctuations found in the carbonates and halite layering in the Green Clay Member indicate that these sediments formed in a saline playa lake. The upward transition in the succession from offshore clay to calcrete shows that the lake was shrinking as the climate became drier. The presence of low turbulence ooids throughout the succession indicate that lake turbulence was low

Cyanophytes thrived in the shallow well-lit alkaline water and formed stromatolites which were classified according to mat type and geometry. LLH - C, SH - V, and SS - C forms with smooth mat morphology and cauliflower-like colloform mats were identified. Colloform mat structure is interpreted as the deeper water form although development occurred at a depth of less than 2 metres