Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin

Everton Bongiolo,Simone S Mantovanelli,Colombo C G Tassinari,Luigi Jovane,Michel M De Mahiques

doi:10.3389/feart.2018.00074

Everton Bongiolo, Simone S Mantovanelli + Show 3 more

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https://doi.org/10.3389/feart.2018.00074

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Abstract

Based on radiogenic isotope systems of neodymium (Epsilon Neodymium-ɛNd(0), 143Nd/144Nd, 147Sm/144Nd and Sm-Nd Depleted Mantle Model ages-TDM) from current and previous data from current and previous data of continental rocks and associated sediments, this work provides the provenance isotope signatures of Holocene sediments from the Southwestern Atlantic Margininof Core 7616 and Core 7620. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. , this work provides provenance distribution of bulk sediment deposited those proxies inin southeastern South American upper margin, from ~7000 to 900 cal. yr BP. Here The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luis Alves craton and Parana basin rocks. Differences in we present a A Nd isotope isotopic signatures allowed the distinction between the sediment sources of the cores.a conspicuous large range of The variabilitydifference between them. Core 7616 exhibits ɛNd(0) average value of -10.5, which is similar to, TDM =1.4 Ga and 143Nd/144Nd =0.512103, while the Core 7620 shows ɛNd(0) average value of -17.5, TDM =1.8 Ga and 143Nd/144Nd =0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Parana basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2000 and 1800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraiba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic Data from Core metasediments from the Paraiba do Sul geotectonic domain to the Core 7620.

Highlights

An efficient way to reconstruct sediment provenance is the use of radiogenic isotope systems (e.g., Allégre et al, 1996; Wealdeab et al, 2002; Cruces et al, 2004; Fagel et al, 2014) because most of them are not affected by significant fractionation, when submitted by environmental processes (Dickin, 1995; Banner, 2004)
We have considered Paraíba do Sul (PS), Paraná-la Plata (PP), and Ribeira de Iguape (RI) as river systems with potential weathering flux, draining rocks from the Paraná basin and the Ribeira belt, which is inserted in the Precambrian terrains (Figure 1)
The diagram of εNd(0) values and the model age Sm-Nd Depleted Mantle (TDM) displays a comparison among samples of the Core 7616, rocks from the southernmost part of the Ribeira belt, the Luís Alves craton and sedimentary rocks of the Paraná basin (Figure 3)

Summary

Introduction

An efficient way to reconstruct sediment provenance is the use of radiogenic isotope systems (e.g., Allégre et al, 1996; Wealdeab et al, 2002; Cruces et al, 2004; Fagel et al, 2014) because most of them are not affected by significant fractionation, when submitted by environmental processes (Dickin, 1995; Banner, 2004). Brazilian shelf has been reported since the seventies (e.g., Carraro et al, 1974; Miliman, 1975; Rocha et al, 1975), and related to the sediment transport by the Rio de La Plata plume (e.g., de Mahiques et al, 2008; Nagai et al, 2014). The strengthened of the SASM (Cruz et al, 2005) provides an efficient sediment transport from the hydrographic systems to the shelf. This terrigenous input has been associated with the relative high proportion of detrital material deposited in the estuary of Rio de la Plata (Chiessi et al, 2010)

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