Linking speleothem and soil magnetism in the Pau d'Alho cave (central South America)

Author(s)

Jaqueto, Plinio ; Trindade, Ricardo I. F. ; Hartmann, Gelvam A. ; Novello, Valdir F. ; Cruz, Francisco W. ; Karmann, Ivo ; Strauss, Becky E. ; Feinberg, Joshua M.

• Document type: Journal article
• Source: JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH; v. 121, n. 10, p. 7024-7039, OCT 2016.
• Web of Science Citations: 8

Abstract

Mineral magnetism of Pau d'Alho cave sediments, soils outside the cave, and in the stalagmite \#6 (ALHO6) in Midwest Brazil is presented. This high growth-rate speleothem (similar to 168 mm/ka) encompasses the past 1355 years. Oxygen and carbon isotope data from the same stalagmite allow for a direct comparison of the magnetic signal with changes in paleoprecipitation and soil dynamics at the surface. Magnetic experiments include isothermal remanent magnetization, anhysteretic remanent magnetization, hysteresis loops, first-order reversal curves, and low-temperature superconducting quantum interference device magnetometry. The main magnetic remanence carriers in ALHO6 are magnetite and goethite, with a nearly constant relative proportion. Remanent coercivities of magnetite in all our samples are within 14-17mT for an average grain-size of similar to 1-2 mu m, in the range of pedogenic magnetite, thus suggesting the detrital grains deposited in the stalagmite were produced in the soil above the cave. Magnetic remanence variations follow delta C-13 and delta O-18 data, suggesting a climatic control on the input of magnetic minerals into the Pau d'Alho cave system. The concentration of magnetic minerals in the stalagmite is governed by soil erosion above the cave, which by its turn is controlled by soil erosion and vegetation cover. Dry periods are associated with less stable soils and result in higher mineral fluxes carried into karst systems. Conversely, wetter periods are associated with soils topped by denser vegetation that retains micrometer-scale pedogenic minerals and thus reduces detrital fluxes into the cave. (AU)

• FAPESP's process: 12/01187-4 - A calibration study in Central Brazil caves: implications for the paleoclimate inferences from speleothem records
• Grantee: Ivo Karmann
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/50260-6 - Structure and evolution of the Amazonian biota and its environment: an integrative approach
• Grantee: Lúcia Garcez Lohmann
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants
• FAPESP's process: 12/03942-4 - South America Monsoon System activity in certer-west of Brazil based in spelothem records associated with other paleoclimate records from South America
• Grantee: Valdir Felipe Novello
• Support Opportunities: Scholarships in Brazil - Doctorate