Progradation rates measured at modern river outlets: A first-order constraint on the pace of deltaic deposition

Abstract

We present a compilation of modern shoreline progradation rates measured close to river outlets entering deltaic coastlines, and we discuss how these observations relate to the overall evolution of both modern and ancient deltaic coastlines. We analyzed Landsat‐derived satellite images to identify plan view changes in the subaerial morphology of 331 modern deltaic coastlines. Our rate compilation (km2/year) had a lognormal distribution with parameters <i>μ</i> = −1.85 and <i>σ</i>² = 1.01. We found that the rate data could be predicted to within an order of magnitude by an empirically derived power law using only fluvial water discharge and suspended sediment load as input parameters (^<i>r</i>_pro=10^-2.3<i>Q</i>⁰_w⁵⁹<i>Q</i>⁰_s³⁴). We justified this river‐centric model of our progradation rates by assuming that delta progradation rates measured close to river outlets were more reflective of fluvial processes than of basinal processes, and preliminary tests supported this assumption. Our rate compilation and empirical model could provide useful constraints to guide stratigraphic analysis of ancient source‐to‐sink systems and to build analog and numerical models.