Luminescence signals of quartz and feldspar minerals are widely used to determine the burial age of Quaternary sediments. Although luminescence signals bleach rapidly with sunlight exposure, incomplete bleaching may affect luminescence ages, in particular in fluvial settings where an unbleached remnant signal is commonly encountered in modern alluvium. Here, we use feldspar single-grain post-infrared IR stimulation (pIRIR) dating to show that recent (<11 ka) fluvial terraces of the Rangitikei River (New Zealand) were formed in a context of non-linear incision rate. We relate this pattern to the rapid reinstatement of steady-state incision following the formation of a major, climate-driven, aggradation terrace, causing a phase of accelerated incision. In addition, we show systematic variations in the proportion of unbleached grains in the fluvial sediments over time, mirroring incision rate at the time of deposition. Deposits formed during rapid incision contain fewer bleached grains, which we attribute to large input of unbleached material and limited bleaching opportunities during fluvial transport. This finding demonstrates that the luminescence signals recorded in fluvial terraces not only yield age information, but also inform us on past fluvial transport and ultimately, landscape dynamics.
The critical Coulomb wedge theory has been widely applied to the structural evolution of accretionary wedges and fold and thrust belts, but it also predicts the spreading of a wedge under gravity. This solution may be applied to the formation of gravitational spreading and gliding along passive margins, where elevated pore fluid pressure is common. Following the initial hypotheses of the theory, we provide an alternative expression of the exact solution for a noncohesive wedge, better suited to slope instabilities. Our formulation allows a direct calculation of the fluid pressure required for the system to deform and predicts two kinds of gravitational deformation: shallow slumping and/or deep gravitational spreading rooting on the basal detachment. To verify the predictions of the model, we performed scaled experiments with pore pressure under conditions close to the critical taper hypotheses. The good agreement between our experimental results and the theory confirms the applicability of the critical taper model to the formation of gravitational structures in sedimentary wedges subjected to pore fluid pressure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.