The late Quaternary evolution of the Negro River, Amazon, Brazil: Implications for island and floodplain formation in large anabranching tropical systems

The progradational behavior of the Rio Negro, filling tectonic basins as successive sediment traps with sand in the upper basins and fines in the downstream ones, illustrates how a large river system responses to profound changes in Late Quaternary base level and sediment supply. The most stable equilibrium conditions have been achieved in the Holocene in reaches IIb and IIIa, where an anabranching channel and erosional-relictual island system relatively efficiently convey water and sediment downstream. Reaches IIIb and V never achieved equilibrium conditions during the Holocene, characterised as they are today with incomplete floodplains and open water.