Abstract

Concentrically rolled-up silty mudrock laminae, 1–2 mm thick, are found in the uppermost of four, 40–110 cm thick interdune beds within a thick aeolian succession of the c. 1.8 Ga Makgabeng Formation, Waterberg Group, South Africa. These curved laminae are analogous to previously described “roll-ups,” biogenic structures generally ascribed to soft-sediment deformation or desiccation of microbial mats overlying either carbonate or siliciclastic sediments, within shallow- to deep-marine paleoenvironments. The Makgabeng roll-ups are thought to reflect desiccation of a microbial mat, followed by resedimentation of cohesive, discrete, curled mat fragments. Their alignment is considered to be the result of an extreme precipitation event. The significance of the South African example of roll-ups is that they appear to have formed within a fully terrestrial paleoenvironment, in one of the oldest known Precambrian deserts. Thus, they represent the oldest evidence for microbial colonisation of a terrestrial setting.

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