Magnetic Mineralogy of Speleothems From Tropical-Subtropical Sites of South America

Plinio Jaqueto, Ricardo I.F. Trindade, Joshua M. Feinberg, Janine Carmo, Valdir F. Novello, Nicolás M. Stríkis, Francisco W. Cruz, Marília H. Shimizu, Ivo Karmann

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Abstract

Fe-bearing minerals are a tiny fraction of the composition of speleothems. They have their origin in the karst system or are transported from the drainage basin into the cave. Recent studies on the magnetism of speleothems focused on the variations of their magnetic mineralogy in specific time intervals and are usually limited to a single sample. In this study, we describe a database of environmental magnetism parameters built from 22 stalagmites from different caves located in Brazil (South America) at different latitudes, comprising different climates and biomes. The magnetic signal observed in these stalagmites is dominated by low-coercivity minerals (∼20 mT) whose magnetic properties resemble those of the magnetite formed in pedogenic environments. Also, a comparison with few samples from soils and the carbonate from cave’s walls shows a good agreement of the magnetic properties of speleothems with those of soil samples, reinforcing previous suggestions that in (sub-)tropical regimes, the dominant magnetic phase in speleothems is associated with the soil above the cave. Spearman’s rank correlation points to a positive strong correlation between magnetic concentration parameters (mass-normalized magnetic susceptibility, natural remanent magnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization). This implies that ultrafine ferrimagnetic minerals are the dominant phase in these (sub-)tropical karst systems, which extend across a diverse range of biomes. Although the samples are concentrated in the savannah biome (Cerrado) (∼70%), comparison with other biomes shows a higher concentration of magnetic minerals in speleothem underlying savannahs and lower concentration in those underlying moist broadleaf forests (Atlantic and Amazon biome) and dry forests (Caatinga). Thus, rainfall, biome, and epikarst dynamics play an important role in the concentration of magnetic minerals in speleothems in (sub-)tropical sites and indicate they can be an important target for paleoenvironmental research in cave systems.

Original languageEnglish (US)
Article number634482
JournalFrontiers in Earth Science
Volume9
DOIs
StatePublished - Apr 30 2021

Bibliographical note

Funding Information:
This work was supported by the São Paulo Research Foundation (grant numbers: 2016/24870-2, 2016/15807-5, 2017/50085-3, 2018/15774-5, and 2019/06709-8) and the National Council for Scientific and Technological Development (CNPq) (grant numbers: 423573/2018-7 and 308769/2018-0 to NS). This work was also supported by the Serrapilheira Institute (grant number: Serra-1812-27990). This work was funded by National Science Foundation grant EAR-2044535 and US-Israel Binational Science Foundation grant #2016402 to JMF. IRM was supported by the US National Science Foundation.

Funding Information:
We are grateful to Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renov?veis for providing permission to collect stalagmite samples. We are also very thankful for the constructive comments of the reviewers and editor. Funding. This work was supported by the S?o Paulo Research Foundation (grant numbers: 2016/24870-2, 2016/15807-5, 2017/50085-3, 2018/15774-5, and 2019/06709-8) and the National Council for Scientific and Technological Development (CNPq) (grant numbers: 423573/2018-7 and 308769/2018-0 to NS). This work was also supported by the Serrapilheira Institute (grant number: Serra-1812-27990). This work was funded by National Science Foundation grant EAR-2044535 and US-Israel Binational Science Foundation grant #2016402 to JMF. IRM was supported by the US National Science Foundation.

Publisher Copyright:
© Copyright © 2021 Jaqueto, Trindade, Feinberg, Carmo, Novello, Stríkis, Cruz, Shimizu and Karmann.

Keywords

  • South America
  • environmental magnetism
  • karst system
  • rock magnetism
  • speleothem magnetism
  • stalagmites

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