Use of remote-sensing to quantify the distribution of progradation/erosion along a forced-regressive modern coastline: driving factors and impact on the stratigraphic record

Abstract

The long-term development of ancient and modern coastal distributary fluvial systems (DFSs) during periods of relative sea-level highstand or fall usually drive net-progradation of shorelines, though such deposits usually also record annual to millennial-scale deviations in coastal trajectories. A new continental dataset (Digital Earth Australia Coastlines: DEA Coastlines) provides an opportunity to examine such variations in coastal behaviour over annual to decadal scales (1988-2019) and over vast spatial scales. This dataset is herein applied to the 654 km coastline fronting Australia’s largest amalgamated coastal distributary fluvial systems, which is situated in the epicontinental seaway of the Gulf of Carpentaria. Despite the overall forced regressive conditions, only 54% of this coastlines length net-prograded, whereas 47% was eroded. Though temporal cyclicity in progradation and erosion is evident along segments of this coast, these patterns could not be correlated with either the Southern Oscillation Index (R2 = -0.20) or rainfall (R2 = 0.24). Instead, short-term coastline dynamics appear to be the result of complex interactions between fluvial, wave, longshore current, and tidal processes. The high-resolution DEA Coastlines dataset highlights the diachronous, heterochronous, composite, and amalgamated nature of net-progradational stratigraphic strata that can develop in shallow-marine environments where hinge-points between progradating and retrograding coastal segments are dynamic features that migrate with time. Understanding more granular temporal and spatial deviations in coastal trajectory will help to improve models of such complex net-progradational coastal systems.