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Towards an understanding of magnetic mineralogy in speleothems from South America
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  • Plinio Jaqueto,
  • Joshua Feinberg,
  • Ricardo Trindade,
  • Janine Carmo,
  • Valdir Novello,
  • Nicolas Strikis,
  • Francisco Cruz,
  • Ivo Karmann
Plinio Jaqueto
USP University of Sao Paulo

Corresponding Author:[email protected]

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Joshua Feinberg
University of Minnesota
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Ricardo Trindade
Universidade de São Paulo
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Janine Carmo
Universidade de São Paulo
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Valdir Novello
USP University of Sao Paulo
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Nicolas Strikis
USP University of Sao Paulo
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Francisco Cruz
Universidade de São Paulo
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Ivo Karmann
USP University of Sao Paulo
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Abstract

Paleoclimate studies on speleothems commonly use oxygen isotopes as a record of precipitation variability and carbon isotopes to document soil, vegetation, and atmospheric processes. Magnetic minerals in speleothems record complementary paleoclimate information but need to be interpreted within the context of the particular geographic and geologic setting in which a karst environment occurs. This study surveys 23 caves in South America (7°N to 25°S latitude). The present-day climate is dominated by a monsoon regime, with variable precipitation between 50 to 800 mm/month covering different biomes, therefore making South America a good candidate to explore the properties of magnetic minerals at the tropical/subtropical climate. We share a database of magnetic properties from 23 stalagmites samples (90 specimens), 4 soil samples (34 specimens) and 2 limestone samples (15 specimens). Measured rock magnetic parameters include magnetic susceptibility, natural, anhysteretic, and isothermal remanent magnetization (NRM, ARM, IRM), as well as low-temperature magnetometry and first-order reversal curves. These data help constrain the types and granulometry of the magnetic mineralogy that commonly occur in South American speleothems, their host carbonates, and their overlying soils. We show that concentration-dependent parameters in soils overlying the caves are two to three orders of magnitude higher than those in stalagmite and limestones. Despite these differences, unmixed coercivities between soil (median value of 19 mT) and stalagmites (median value 20 mT) and substantially different from those of host limestones (median 39 mT). Our results suggest that much of the magnetite in South American speleothems is pedogenic in origin, and may allow magnetic measurements to capture changing soil and vegetation dynamics in the epikarst through time.