(A) Map of the south of North Island of New Zealand showing location of the Rangitikei River (RR; blue line; DEM generated using topographic data from Land Information New Zealand (https://www.linz.govt.nz/; based on LINZ’s data which are licensed by Land Information New Zealand (LINZ) for re-use under the Creative Commons Attribution 4.0 International licence) and ArcGIS 10.4 software (www.ArcGIS.com)). Blue solid circles indicate the upstream and downstream ends of the studied reach where the terraces have been surveyed. Samples for luminescence analysis come from the area demarcated by a thin black line (see Supplementary Fig. 3). Black dotted line shows the approximate boundary of the Plio-Pleistocene marine deposits of the Wanganui Basin, which constitute the bedrock eroded by the RR in our study area. (B) Graph of relative elevation of terraces T1, T2 and T3 above the RR vs. terrace ages (ages from ref.29). Red triangle shows our single-grain BS MAM dating of T1. (C) Photograph showing T2 and T1 treads and post-T1 incision of the RR into the bedrock (Plio-Pleistocene shallow marine deposits, in light grey colors). (D) Panoramic view of the RR showing the wide area of T1 and less-preserved remnants of T2 and T3. (E) Photograph showing thickness of alluvial deposits overlying T1 strath surface. (F) Photograph showing post-T1 terraces. Open circle shows a barn for scale. (G) Photograph showing alluvial deposits overlying a post-T1 strath surface.