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.