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

Abstract

Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε Nd(0), 143 Nd/ 144 Nd, 147 Sm/ 144 Nd, and Sm-Nd Depleted Mantle Model ages-T DM ] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the 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 from the 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 ε Nd(0) average value of −10.5, T DM = 1.4 Ga and 143 Nd/ 144 Nd = 0.512103, while the Core 7620 shows ε Nd(0) average value of −17.5, T DM = 1.8 Ga and 143 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 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 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.

Sediment Export Dynamics Reflecting the Holocene Hydrodynamic Variability of a High-Energy Continental Shelf System (Southeastern South America)

“…8). Following the fundamental studies by Mahiques et al (2008) and Mantovanelli et al (2018), which have defined the εNd signatures for the major rock source areas along the SESA continental margin, these values illustrate a singular and constant supply of sediment to T0 throughout the Holocene from the southern Argentine/Patagonian source province (εNd -4 to 0; Fig. 8).…”

“…Moreover, the BC has experienced periodical changes (ca. 730 yr) in strength throughout the Late Holocene Mantovanelli et al, 2018). This strengthened (weakened) BC intensity would lead to a southward (northward) shift of the position of the STSF placing it farther from (closer to) our core sites, and the sedimentary succession would reflect the long-term high-energy-end of these conditions.…”

“…Neodymium isotopic (εNd) data in the range of -4 to 0 showed that the siliciclastic sands south of 35°S originate from a continental province in Patagonia (younger Andean volcanic rocks), in contrast to the more negative εNd signature of -8 to -11 found in the terrigenous deposits further north (sourced from tholeitic basalts and Paleozoic rocks in the Río de la Plata drainage basin; Mahiques et al, 2008;Mantovanelli et al, 2018).…”

New insights of the influence of ocean circulation on the sedimentary distribution in the Southwestern Atlantic margin (23° S to 55° S) based on Nd and Pb isotopic fingerprinting

“…The Southwestern Atlantic margin is characterized by complex hydrography (Matano et al, 2010). It presents two main oceanographic boundaries, the Subtropical Shelf Front (STSF), as the shelf extension of the Brazil -Malvinas Convergence (BMC) (Piola et al, 2000;Severov et al, 2012), and the less-studied Santos Bifurcation (SB) (Boebel et al, 1997;Boebel et al, 1999a).…”

What feeds shelf‐edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil

“…The growth of this margin has been driven by alternations of major progradational periods with intervals of sedimentary quiescence, in which large margin portions backstepped (Contreras, Zühlke, Bowman, & Bechstädt, 2010). However, most of its Cenozoic growth story has been determined by a suppression of the fluvial supply by the blocking effect of coastal mountains (Cobbold, Meisling, & Mount, 2001;Mantovanelli, Tassinari, Mahiques, Jovane, & Bongiolo, 2018), and by the widespread effect of powerful oceanic currents (Biló, Silveira, Rocha, & Ceccopieri, 2014). Therefore, it appears as an ideal location to study the potential effect of bottom current patterns on distal clinoform generation.…”