Rivers might not need plants to meander

Here’s a new study that, if true, this would have some big implications for the nature of the sedimentary record for a lot of Earth History. Research from 1.2 billion year-old sediments in Scotland adds the oldest evidence yet against the idea that we had no large, single-channeled meandering rivers prior to rise of sediment-stabilising terrestrial plants in the Silurian, only braided ones with multiple active channels. Apparently cohesive clay minerals can stabilise a channel enough on their own.

Plants invading the continents does still have an effect, however: it turns rapidly migrating meandering rivers into less rapidly migrating meandering rivers, which leads to a big change in how these systems are preserved in the geologic record. The greening of the subaerial world would also still have had large impacts on geochemical fluxes from the continents due to increased weathering, and possibly also on timescales of sediment routing from source to sink.

Given that weathering patterns and rates were different, I do wonder about the rates and geographical distribution of clay production prior to the Silurian – it could be that whilst meandering rivers were possible, they were still rarer than they became post-greening.