agnetic Mineralogy of Speleothems From Tropical-Subtropical Sites of South Americ

Author(s)

Jaqueto, Plinio ^[1] ; Trindade, Ricardo I. F. ^[1] ; Feinberg, Joshua M. ^[2] ; Carmo, Janine ^[1] ; Novello, Valdir F. ^[3] ; Strikis, Nicolas M. ^[4] ; Cruz, Francisco W. ^[3] ; Shimizu, Marilia H. ^[5] ; Karmann, Ivo ^[3]

Affiliation

^[1] Univ Sao Paulo USPmag, Inst Astron Geofis & Ciencias Atmosfer, Dept Geofis, Sao Paulo - Brazil

^[2] Univ Minnesota, Inst Rock Magnetism, Dept Earth & Environm Sci, Minneapolis, MN - USA

^[3] Univ Sao Paulo, Inst Geociencias, Sao Paulo - Brazil

^[4] Univ Fed Fluminense, Dept Geoquim, Niteroi, RJ - Brazil

^[5] Natl Inst Space Res INPE, Ctr Weather Forecasting & Climate Studies CPTEC, Cachoeira Paulista - Brazil

• Document type: Journal article
• Source: Frontiers in Earth Science; v. 9, APR 30 2021.
• Web of Science Citations: 0

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 (similar to 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) (similar to 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. (AU)

• FAPESP's process: 16/24870-2 - Environmental significance of speleothem magnetism
• Grantee: Plinio Francisco Jaqueto
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 18/15774-5 - Geochronoloy of sedimentary deposits in caves from São Desiderio region: implications for speleogenesis and geomorphological evolution of West Bahia State
• Grantee: Ivo Karmann
• Support Opportunities: Regular Research Grants
• FAPESP's process: 17/50085-3 - PIRE: climate research education in the Americas using tree-ring speleothem examples (PIRE-CREATE)
• Grantee: Francisco William da Cruz Junior
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 16/15807-5 - Paleoclimate and paleoenvironmental reconstructions over the last glacial period in the mid-west Brazil
• Grantee: Valdir Felipe Novello
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 19/06709-8 - Speleothem magnetism from the Last Glacial Maximum to the Holocene in South America
• Grantee: Plinio Francisco Jaqueto
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate