Environmental control on diverse stromatolite morphologies in the 3000 Myr Pongola Supergroup, South Africa

A unique outcrop of partly silicified dolomite in the White Umfolozi section of the Pongola Supergroup, South Africa indicates that stromatolites were diverse and adapted to a range of shallow, tidal depositional settings 3000 Myr ago. Composite columnar stromatolitic bioherms 0.7-1.6m high and 0.4-1.0m in diameter formed along the margins of a tidal channel. They were flanked, away from the channel, by flat stratiform and small domical stromatolites growing in low energy tidal flat environments. Conical stromatolites, 0.05-0.30m high and 0.03-0.10m in diameter, accreted in high-energy coarse-grained carbonate sand along the bottom of the tidal channel. The stromatolites probably formed through the activities of filamentous, oxygen-producing, photoautotrophic cyanobacteria.