Internal architecture of coarse-grained barriers in hypertidal environments (France and Argentina): A GPR study

PANCRAZZI, LÉO; TESSIER, BERNADETTE; WEILL, PIERRE; MOUAZÉ, DOMINIQUE; CUITIÑO, JOSÉ; DUPERRON, MARÍA; SCASSO, ROBERTO ADRIÁN

Praga

Congreso; 35º IAS Meeting of Sedimentology; 2022

International Association of Sedimentologists

Barrier spits and beach ridges are different types of coastal barriers controlled predominantly by wave dy-namics. They represent the two end members of a continuum of wave-built features reflecting varying ori-entations of net sediment transport (longshore vs. cross-shore). In hypertidal environments, high amplitudetide-induced sea-level changes as well as strong tidal currents necessarily combine with wave action in theconstruction of spits and beach ridges. In this study, we image the internal architecture of two coarse-grainedcoastal barriers, both located in hypertidal environments: the mixed sand-and-gravel spit at the mouth of thehypertidal Somme estuary in the English Channel (Northern France), and the sand-and-gravel barrier systemsat the inlet of the hypertidal Santa Cruz estuary in Southern Patagonia (Southern Argentina). Maximum tidalranges are 9 and 11 m in the French and Argentinian sites respectively. A great variety of morphologiescompose the two systems, from simple spits and barrier spits to beach ridges. Both sites were investigatedusing ground-penetrating radar (400 MHz GSSI antenna), along with the analysis of aerial photographs anddigital elevation models. Cross-shore and long-shore profiles, with a penetration depth between 2 and 4 me-ters, show a large range of radar facies attributed to erosional surfaces, beachface progradation, along-driftelongation, hooks and spit terminus development, and washover deposits. The in-depth analysis of radararchitecture allows reconstructing the development of individual morphology in the two systems, and helpsto differentiate the influence of wave- and tide-related processes. The most open-sea barrier-spit systems(Somme estuary and Santa Cruz external mouth) show a classic development controlled by the wave-relatedlittoral drift, probably enhanced due to shore parallel flood currents. In contrast, the most internal systems,located along the northern edge of the Santa Cruz inner inlet, feature contrasting morphologies, structuresand directions of elongation, either landward or seaward, reflecting a complex balance between wave- andtide-dominated dynamics on their construction