Illuminating past river incision, sediment source and pathways using luminescence signals of individual feldspar grains (Rangitikei River, New Zealand)

Single‐grain post‐infrared infrared stimulated luminescence (SG‐pIRIR) of feldspar has recently been introduced as a method to date Quaternary deposits. The method is particularly appropriate for fluvial deposits that cannot be dated by more conventional quartz optically stimulated luminescence dating and that are heterogeneously bleached (i.e. where only part of the grains is exposed to sufficient light to remove the full luminescence signal). Besides age estimation, single grain equivalent dose (De) distributions also reflect the variable bleaching degree and origins of grains. Thereby, the SG‐pIRIR signal offers a valuable tool to reconstruct sediment pathways. This study builds upon these ideas and develops a dual aspect that combined river terrace dating and SG‐pIRIR sediment pathway reconstruction for fluvial deposits in terraces and modern river floodplain along the Rangitikei River (RR), New Zealand. We found that the RR last aggrading phase (17.4 ± 1.9 ka to 11.6 ± 1.5 ka) was followed by a first phase of fast incision related to knickpoint retreat followed by a steady incision and widening of the RR canyon. The De distribution of fluvial deposits varies accordingly, due in particular to variable input of bedrock particles with saturated pIRIR signal from landsliding of valley flanks. Our study illustrates that the SG‐pIRIR approach is well suited to date terraces and shows how SG‐pIRIR De distributions provide proxies to reconstruct sediment sources and pathways. Along‐stream analysis of luminescence signal reveals the fluvial incision and widening of the Rangitikei River in New Zealand. The single‐grain equivalent dose distributions can be used as a proxy to capture geomorphic process in the fluvial system.