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Environmental magnetism evidence for longshore drift distribution of Fe-bearing phases: An example from the Brazilian southeastern coastal region
Journal of Sedimentary Research ( IF 2 ) Pub Date : 2021-11-30 , DOI: 10.2110/jsr.2020.089
Vitor E.P. Silveira 1 , Natália B. dos Santos 1 , Daniel R. Franco 1 , Emanuele F. la Terra 1 , Joshua M. Feinberg 2 , R.B. Scorzelli 3 , Magda B. Fontes 3 , Luiz C. Bertolino 4 , Joice Cagliari 5 , Marcelo K. de Souza 5 , Gelvam A. Hartmann 6
Affiliation  

The accumulation of heavy minerals along a part of the southeastern Brazilian coast (northern coast of Rio de Janeiro State, Brazil) provides insight into sedimentary provenance and transport by longshore drift. In particular, recent work has focused on heavy minerals as tracers to determine sedimentary sources and transport pathways, indicating a mineral distribution according to the northward and southward coastal transport cells. There is also evidence of heavy-mineral transport by the Paraíba do Sul River. However, research has not been done in this area on the opaque fraction (iron oxides and oxyhydroxides), which are good tracers for provenance and distribution processes. Here we intend to: 1) characterize the spatial variation of the magnetic properties of heavy-mineral contents throughout a coastal area of the Itabapoana and Paraíba do Sul River mouths (state of Rio de Janeiro), 2) evaluate the contribution of coastal dynamics on the mineral distribution along this coastal area, 3) provide contributions on the provenance of iron-bearing minerals. Results indicate that a bimodal pattern was observed for the magnetic remanence of magnetite and hematite near the Paraíba do Sul River. For the northernmost section, goethite exhibits a gradual increase in concentration towards the central part of the study area. Additionally, higher heavy-mineral content is observed at the northern coastal section, which may be related to coastal morphology, which is exposed to high-energy beach processes. It is possible to verify three sampling groups in accordance with their magnetic properties: 1) the “southernmost” and 2) the “northernmost” groups, suggesting a mineral provenance related to the Paraíba do Sul and Itabapoana rivers, respectively, as possible major sources, and 3) another at the intermediate section of the area, possibly linked to the erosion of the Barreiras Formation bluffs. Results also show a correspondence between the variability of magnetic parameters and the main directions of the coastal transport cells.

中文翻译:

含铁相沿岸漂移分布的环境磁性证据:以巴西东南沿海地区为例

沿着巴西东南部海岸(巴西里约热内卢州北部海岸)的一部分重矿物的积累提供了对沉积物来源和沿海漂移运输的深入了解。特别是,最近的工作重点是重矿物作为示踪剂,以确定沉积来源和运输途径,根据向北和向南的沿海运输单元指示矿物分布。南帕拉伊巴河也有重矿物运输的证据。然而,该领域尚未对不透明部分(氧化铁和羟基氧化物)进行研究,它们是来源和分配过程的良好示踪剂。在这里,我们打算:1) 表征整个伊塔巴波阿纳河口和南帕拉伊巴河口(里约热内卢州)沿海地区重矿物含量的磁特性的空间变化,2) 评估沿海动态对沿线矿物分布的贡献沿海地区,3) 对含铁矿物的来源做出贡献。结果表明,在南帕拉伊巴河附近观察到磁铁矿和赤铁矿剩磁的双峰模式。对于最北端的部分,针铁矿的浓度向研究区域的中心部分逐渐增加。此外,在北部沿海部分观察到较高的重矿物含量,这可能与暴露于高能量海滩过程的沿海形态有关。可以根据其磁特性验证三个采样组:1)“最南端”和 2)“最北端”组,表明分别与 Paraíba do Sul 和 Itabapoana 河相关的矿物来源可能是主要来源, 和 3) 另一个位于该地区的中间部分,可能与 Barreiras Formation 断崖的侵蚀有关。结果还显示了磁参数的可变性与沿海运输单元的主要方向之间的对应关系。可能与 Barreiras Formation 断崖的侵蚀有关。结果还显示了磁参数的可变性与沿海运输单元的主要方向之间的对应关系。可能与 Barreiras Formation 断崖的侵蚀有关。结果还显示了磁参数的可变性与沿海运输单元的主要方向之间的对应关系。
更新日期:2021-11-07
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