Chronology of recent sedimentary infill of the Inner Río de la Plata Estuary, Argentina

Abstract

The Inner Río de la Plata Estuary is a sedimentary depositional system that resulted from fuvial-deltaic activity. Gentle Pliocene-Pleistocene slopes make-up the northern side of the estuary whereas small clifs of the same age constitute the southern side. A long coastal estuarine barrier developed at about 6000 years BP when the maximum fooding surface occurred. Attached to this barrier, and at a lower elevation, is a large strandplain (covering an area of about 2400 km2 ) which displays more than 220 beach ridges. In diferent areas, the dating indicates a periodicity of 13.4-13.7 years for the development of each beach ridge. These data are like the periodicity of the ENSO efects, which could be associated with the variability of Sunspots. These ridges were formed shortly after the maximum fooding surface, which was followed by a gradual fall in sea-level that contributed signifcantly to the Inner Río de la Plata Estuary sedimentary infll. In addition, ENSO activities were probably instrumental in the distribution of the main geoforms in the Inner Rio de la Plata Estuary. Small deltas, which were generated by other rivers and creeks such as the Nogoyá Arroyo and the Gualeguay River, developed coevally with the coastal estuarine barrier. The Ibicuy Delta grew in the middle of the inner Río de la Plata Estuary when the former Paraná River fowed northwards during the sea-level fall. The upper part of the delta front was reworked, giving rise to a large dunefeld. Thereafter, a chenier plain developed along with tidal fats. The current Paraná Delta continues to prograde at a rate of about 56-64 m/year (m year−1). The sedimentary infll of the Inner Río de la Plata Estuary occurred along the Holocene.