Architectures and dynamics of a late Quaternary coarse-grained barrier complex at the inlet of a hypertidal estuary (South Patagonia, Argentina)

Abstract

The southern coast of Argentina is known for its high tidal ranges and large coarse-grained coastal barriers that have emerged over time as a result of the regional uplift. Well-preserved barriers can provide critical information about the morphological evolution of the coastal areas, and the relative evolution of the mean sea level, as long as their morphodynamics are well understood. In order to better understand the influence of tides in wave-built sedimentary bodies, an in-depth analysis of the architecture of a barrier system has been realized at the mouth of the Santa Cruz - Chico river estuary (50°S). Maximum tidal range in this estuary is 12 m. A great variety of morphologies compose both sides of the estuary inlet, from simple ridges and barrier spits to beach ridge plains. Barrier spits and beach ridge plains characterize the southern side, whereas elongated simple ridges and barrier spits isolating large tidal flats are more developed on the northern side. The site was investigated using ground-penetrating radar combined with digital elevation model analysis, and some sedimentological observations. Cross-shore profiles, with a penetration depth up to 5 m, show a large range of radar facies attributed to erosional surfaces, beach face progradation, and washover deposits. The slope of the beach face appears to be an effective parameter for differentiating between beach ridges plains and barrier spits, as the latter are characterized by steeper values. The combined analysis of the radar architecture and barrier morphology allows to identify five barrier sets, which have been associated with five different development stages along the late Quaternary: 1) Last Interglacial Maximum (MIS 5e), 2) Last Interglacial (MIS 5e/5c/5a), 3) Mid Holocene transgressive maximum, 4) Mid Holocene highstand reworking, and 5) Holocene regressive stage. Although the morphological model is in line with the observations made by other authors, it would be appropriate to consolidate the model by establishing an absolute chronology.