Characterization of nd radiogenic isotope signatures in sediments from the southwestern Atlantic margin

Abstract

Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-εNd(0)143 Nd/144 Nd,147 Sm/144 Nd, and Sm-Nd Depleted Mantle Model ages-TDM ] fromcurrent and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments fromthe Southwestern Atlantic Margin. 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. The map is the result of the principal component and clustering analyses of data compiled fromthe Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits εNd(0) average value of −10.5, TDM =1.4 Ga and143 Nd/144 Nd = 0.512103, while the Core 7620 shows εNd(0) average value of −17.5, TDM =1.8 Ga and143 Nd/144 Nd =0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ∼2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence fromthe 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 Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.