Modeling the Suspended Sediment Transport in a Very Wide, Shallow, and Microtidal Estuary, the Río de la Plata, Argentina

The impact of the diverse processes responsible for the distribution of suspended sediments in the wide, shallow, and microtidal Río de la Plata estuary and the adjacent shelf is studied by means of a set of process-oriented numerical simulations. Model results show that the large width and the geometry of the estuary play a major role in the sedimentation processes. The widening and deepening of the estuary drives a significant reduction in current speeds at (i) the confluence of the tributaries and (ii) downstream Barra del Indio Shoal. Thus, sediment deposition enhances downstream those areas. Even though tides are of small amplitude in the study area, they have a significant impact on lateral mixing and resuspension of the bottom sediments. Resuspension augments the concentration of fine sediments in the layers close to the bottom, but tidal energy is not enough to lift them to the surface. Winds (which can be quite strong over this area) enhance horizontal mixing, smoothing the pattern produced by tides. Wind waves increase the concentration of sediment by vertical mixing, and their effect is most evident along the southern coast where wind waves lift the sediments resuspended by tides to the surface. The estuarine circulations associated to the bottom salinity front acts retaining sediments upstream the Barra del Indio Shoal, where estuarine currents and flocculation play an important role in sediment deposition.Fil: Moreira, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Simionato, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentin

The Marine Isotopic Stage 3 (MIS 3) in Valleys of the Undulated Pampa, Buenos Aires Province, Argentina

A depositional unit called DU2 identified for the period MIS 3 (ca- 30,000-60,000 yr. B.P.) formed by only one sedimentary facies (F3) was found in the Luján and Salto-Arrecifes rivers basins. F3 is a fluvio?lacustrine unit that overlies in erosive unconformity over eolian sediments with ages of 56,400 ± 6,500 and 50,400 ± 10,200 years B.A. and is unconformably covered by another eolian vitroclastic sandy loess deposit, dated as 32,000 ±4,000 years (Infrared Stimulated Luminescence, IRSL) (Blasi, et al. 2010). It represents the recurrence of ephemeral fluvial streamlets and the development of temporary pools by subsequent damming of channels. It corresponds lithologically to sandy muddy gravel, gravelly muddy sand, gravelly mud, olive to pale olive feldspar and quartz sands, bearing extinct mollusks such as Heleobia ameghini and Diplodon lujanensis. Radiocarbon chronologies obtained on monospecific samples of Cyprideis salebrosa hartmanni and Heleobia ameghini yielded ages of 37,710 ± 840 years 14C B.P. and >40,000 years 14C B.P., respectively. Furthermore, the age obtained through the IRSL technique was of 44,000 ± 6,500 years. Based upon the analyzed bioproxies (malacological, phytoliths and diatomological content) F3 accumulated under variable climatic conditions, ranging from temperate to colder and from subhumid to drier. According to the exhaustive stratigraphic identification, it is proposed that in NE Buenos Aires Province, the so-called Undulated Pampa region, the sediments that were accumulated during MIS3 occur only in the central portion of the studied fluvial basins. This prompted two hypotheses related to the existence of a particular drainage pattern for the Late Pleistocene, different from the present one, and subsequent tectonic controls that allowed the identification of DU2 sediments only in some of the analyzed sections.Fil: Blasi, Adriana María. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Mineralogía y Petrología; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Castiñeira Latorre, Carola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Mineralogía y Petrología; ArgentinaFil: Cusminsky, Gabriela Catalina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Carignano, Ana Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; Argentin