Abstract

A long-standing hypothesis links the increased prominence of meandering rivers in the middle Paleozoic to the colonization of terrestrial environments by vegetation. This hypothesis is tested using a data set of Cambrian to Devonian fluvial literature and field examination of key stratigraphic units. According to some researchers, Cambrian to mid-Silurian river systems were braided in planform, with a sharp increase in the abundance of meandering rivers during the Silurian–Devonian. Although meandering systems were largely identified on the basis of thick mudstones and organized channel deposits, the data set record of lateral accretion sets appears to be a robust proxy for the abundance of meandering river point bars. Lateral accretion is first recorded from Pridolian–Lochkovian strata, but is noted in nearly 40% of fluvial case studies by the Famennian. This trend matches the known record of rooted vegetation, suggesting that vegetation progressively stabilized river banks and promoted single-thread channels. However, the presence of Precambrian and extraterrestrial meandering systems indicates that vegetation is not essential for meandering, and the lack of evidence for Cambrian to Silurian (Ludlow) point bars is surprising. If originally present, they may largely have been destroyed by extreme floods, chute cut-offs in coarse-grained meandering systems, and eolian activity.

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