Spatio-temporal evolution of the coastal shell accumulation in Villarino Peninsula, San Antonio Este, Argentina

Abstract

Accumulations of mollusc shells occur frequently in modern coastal environments, including the large Holocene beach deposits at Villarino Peninsula, Argentina. The evolutive study of modern shell accumulations can be applied to predict and interpret ancient rocks formed by hardparts of mollusc shells. To study the spatio-temporal evolution of these accumulations, a mapping of the spatial boundaries using images acquired from Landsat 5™, 7E™, and 8OLI sensors in 1986, 1992, 1998, 2003, 2013, and 2020. This permitted the delimitation of the boundary between the shelly beach and the surrounding environments for each year. Eight cross-sections of the coastline were placed at geomorphologically representative locations to measure the respective displacements, and to reveal the deposition/progradation, erosion/retrogradation and stability zones. Through this study, it was possible to register the variability of the evolutionary behavior of the shells accumulation along the beach system through a period of 34 years. During this time, the sites with progradation (with a maximum value of +165.49 m) exhibit well-developed shore ridges, whereas the sites with retrogradation (with a maximum value of 53.8 m) and stability, show erosive features of escarpment and beaches with gentle ridges. The mapping of these geoindicators highlighted the coastal drift which occurs along the Villarino Peninsula in a clockwise circular pattern. The beach extensions show a more prominent progradation pattern than the retrogradational one.