The Gravels of the Rio De La Plata: The Holocene Beaches of Bella Vista, Uruguay

Abstract

The R´ıo de la Plata has a r´ıa-type estuary, with a coastal plain dominated by fine to very-fine sands to the south and a tectonic coast to the north dominated by fine to coarse sand. Although the headlands of the river were dominated by fluvial processes related to the deltaic lobes of the Parana River, the Parana´ Guazu, and Parana ´ ´ de las Palmas, the outer estuary is subject to wave action that increased significantly during storms from the SE. Wave statistics confirmed a littoral drift responsible for the spits at the outlets of affluent rivers deflected to the west (Sol´ıs Grande, Sol´ıs Chico). At the northern Uruguayan coast the interval between Bella Vista and Las Flores is composed of gravel that is described here. Bella Vista beach has two berms; the upper berm is partially covered by eolian sands. Las Flores beach consists of a single berm where gravels segregate upward and sand moves toward the river coastline. The storm berm of Bella Vista includes finer gravels (3–6 cm) whereas the gravels from the tidal berms (both beaches) are coarser, from 6 to 15 cm. According to the Zingg diagram, oblate and tabular gravels abraded by the wave action dominate. Considering old photographs, these gravel berms are stable and relicts from the highstand of the Middle Holocene. They were, therefore, derived by waves from submerged deposits originally derived from the Complex Sierra de las Animas.