River functioning prior to the rise of land plants: Auniformitarian outlook

The study of geomorphic processes in barren landscapes, Precambrian and modern, has wide implications for planetary science. A long-held status quo has been that, prior to the Palaeozoic evolution of vegetation, fluvial channels would have been invariably shallow, wide, braided in planform and flashier in discharge than vegetated ones. These assumptions are challenged through a threefold analysis of channel morphometry, discharge regimes and planform style. Measurements of modern and Proterozoic channel sections reveal overlapping morphometric ranges irrespective of climate and vegetation, pointing to shared scalar properties. Discharge regimes and planform styles inferred from Proterozoic records are akin to the spectrum observed in modern systems. Current criteria employed to identify meandering planforms are biased towards mud-prone systems, and fail to address the sand-rich nature of prevegetation alluvium. Vegetation forcing on river functioning cannot be entirely downplayed, although available data are construed towards an uniformitarian appraisal of pre-Silurian fluvial dynamics.