Short time and local spatial scale estimation of sedimentary volumes during the Little Ice Age from sparse data: Case of a Rhône delta palaeochannel (France)

Estimating sediment volumes from fossil fluvial overbank deposits remains challenging, particularly at fine spatial and temporal scales in complex morphologies. This study focuses on a ~7 km 2 concave bank of the Grande Ponche palaeomeander (Rhône Delta, France), where rapid overbank deposition occurred over ~20 years during the Little Ice Age (LIA). Two modelling approaches are evaluated for reconstructing deposit thickness with sinuous geometry from sparse datasets: Discrete Smooth Interpolation (DSI), and kriging applied on a complex grid allowing curvilinear anisotropy to be reproduced. Both approaches yielded similar volume estimates (~0.009–0.01 km 3 ), showing overbank deposits (~0.004 km 3 , ~3.15 mm/yr) and floodplain aggradation (~0.006 km 3 , ~1.43 mm/yr). Compared to conventional techniques, DSI and kriging provided more realistic 3D models capturing spatial anisotropy and proximo-distal thickness gradients, hence prefiguring better sediment volume estimation. Bootstrapping results show volume estimates less sensitive to spatial distribution of sparse data. DSI enabled the reconstruction of levee and crevasse splay within overbank deposits from a minimal dataset. Kriging requires denser data to obtain suitable variograms and then did not achieve these detailed models. However, when applicable, it allows for volume estimate uncertainty that DSI does not provide. The fine-scale sediment volumes at the Grande Ponche reveal the disproportionate geomorphological impact of short-term LIA flood, with aggradation rates far exceeding Holocene and modern Rhône delta averages. These results show that brief intense climatic phases can generate important but spatially localised sediment storage. Improved quantification of such short-term sedimentary pulses strengthens source-to-sink analyses and refines our understanding of sedimentary responses to climatic variability in fluvial-deltaic systems. • Fine-scale sediment volumes estimated for Little Ice Age overbank deposits • Discrete Smooth Interpolation and kriging used to model sediment thickness from sparse data • Curvilinear grid improves kriging performance in sinuous palaeochannels • Overbank deposition during the LIA reached up to 3.15 cm/yr locally • LIA sedimentation rates greatly exceed both Holocene and modern Rhône Delta records