Discovery of enigmatic toroidal carbonate concretions on the Rio Grande Rise (Southwestern Atlantic Ocean)

We present enigmatic toroidal carbonate concretions retrieved from 700 m water depth from two sites in the upper plateau of the Rio Grande Rise. The concretions have a diameter of ~15 cm and a central hole of ~5 cm, and were observed on top of loose bioclastic sand over an area of ~30 m2 at 0.5–1.5 ...

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Bibliographic Details
Published in:Marine geology 2022-01, Vol.443, p.106665, Article 106665
Main Authors: Millo, Christian, Vieira do Nascimento e Silva, Matheus H., de Mello, Renata Moura, Leckie, R. Mark, Benites, Mariana, Fonseca Giannini, Paulo C., Boggiani, Paulo C., Bosence, Dan, Lusty, Paul A.J., Murton, Bramley J., Jovane, Luigi
Format: Article
Language:English
Subjects:
Diagenesis
Foraminifera
Grainstone
Remotely operated vehicles
Rio Grande Rise
Stable isotopes
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Summary:We present enigmatic toroidal carbonate concretions retrieved from 700 m water depth from two sites in the upper plateau of the Rio Grande Rise. The concretions have a diameter of ~15 cm and a central hole of ~5 cm, and were observed on top of loose bioclastic sand over an area of ~30 m2 at 0.5–1.5 m from one another. They consist of brown, porous, bioclastic grainstone, lacking internal structures. Grains consist of sand (< 3% coarse, 30% medium, 35% fine, 25% very fine), composed mainly by planktonic foraminiferal tests, and 
ISSN:0025-3227
1872-6151
DOI:10.1016/j.margeo.2021.106665