The high-supply, current-dominated continental margin of southeastern South America during the late Quaternary

Abstract

The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-14C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.

Thermal evolution of the western South Atlantic and the adjacent continent during Termination 1

“…3) (Chiessi et al, 2008;Lantzsch et al, 2014). The stepwise rise in sea level following the LGM caused abrupt displacements of the coastline towards the continent trapping a large amount of the La Plata River sediment supply on the shelf and controlling the stepwise decrease in sedimentation rate at our site (Chiessi et al, 2008;Lantzsch et al, 2014). Because of the high sedimentation rates (i.e., ca.…”

“…With the resulting narrow continental shelf, the large sediment supply of the La Plata River was directed to the Rio Grande Cone via the La Plata paleo-valley, which was responsible for the high sedimentation rates typical for the lowermost section of core GeoB6211-2 (Fig. 3) (Chiessi et al, 2008;Lantzsch et al, 2014). The stepwise rise in sea level following the LGM caused abrupt displacements of the coastline towards the continent trapping a large amount of the La Plata River sediment supply on the shelf and controlling the stepwise decrease in sedimentation rate at our site (Chiessi et al, 2008;Lantzsch et al, 2014).…”

“…Temperature estimates are thought to reflect mean annual air temperature (Peterse et al, 2012). During Termination 1, our core site received terrigenous material discharged from the La Plata River drainage basin (LPRDB) as attested by Nd isotopes (Lantzsch et al, 2014). Within the LPRDB, most of the suspended load (Depetris et al, 2003) and particulate organic matter (Depetris and Kempe, 1993) originates from the Bermejo River sub-basin, located in the northwest domain.…”

Variabilidade milenar da Corrente do Brasil e do clima da América do Sul durante o último período glacial

“…Adicionalmente, a região de coleta do testemunho sedimentar, i.e., Cone do Rio Grande, apresenta relativa alta taxa de sedimentação com material terrígeno proveniente predominantemente da Bacia do Rio da Prata (LANTZSCH et al, 2014;RAZIK et al, 2015), i.e., região SEAS (Figura 14).…”

“…Rio da Prata (CHIESSI et al, 2009), incrementando o aporte de sedimentos terrígenos inorgânicos e orgânicos para o Cone do Rio Grande (LANTZSCH et al, 2014;RAZIK et al, 2015), sítio de coleta do testemunho sedimentar GeoB6212-1. Esta Dissertação de Mestrado mostra de forma inédita um aumento da taxa de sedimentação bem como das razões ln(Ti/Ca) e ln(Fe/Ca) em um HS para a margem continental do SEAS.…”