Late Paleozoic Depositional Environments and Sediment Transport Directions of the Itararé Group Rocks From the State of São Paulo, Brazil, Determined From Rock Magnetism and Magnetic Anisotropy

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Abstract

Sedimentary rocks of the Itararé Group, deposited during the Late Paleozoic Ice Age in the Paraná Basin of South America, were collected throughout the state of São Paulo, Brazil, for an anisotropy of magnetic susceptibility (AMS) and rock-magnetic study. A recent paleomagnetic study conducted on the same samples had determined that these rocks were largely remagnetized during the Cretaceous; however, rock-magnetic experiments demonstrate that the AMS is dominantly carried by paramagnetic minerals and therefore is unaffected by the secondary magnetic overprints. AMS data are analyzed in terms of their shape and orientation, and according to the relationship between the q-value (magnetic lineation/foliation) and the imbrication angle (β) of the minimum susceptibility axes with respect to bedding (q–β diagram). Using multiple lines of evidence, we demonstrate that AMS records primary sedimentary fabrics that reflect the depositional environments and paleocurrent conditions in which these rocks were deposited. The magnetic fabrics consistently record a SE-NW paleocurrent orientation, with dominant direction of transport to the NW throughout the entire state of São Paulo, in agreement with ice flow and sediment transport directions reported from limited numbers of sites possessing sedimentary structures and ice-kinematic indicators.

Original languageEnglish (US)
Article numbere2021EA001703
JournalEarth and Space Science
Volume8
Issue number7
DOIs
StatePublished - Jul 1 2021

Bibliographical note

Funding Information:
Irene Raposo is thanked for all aspects of the field component of this work and use of the lab at the University of São Paulo, Brazil, for the anisotropy of magnetic susceptibility measurements for the sites labeled IT, with funding by the São Paulo Research Foundation (FAPESP) grant 2011/51204‐0. I am indebted to William Callebert for performing the majority of the magnetic anisotropy measurements at the Institute for Rock Magnetism (IRM), University of Minnesota, with funding by the National Science Foundation grants NSF/EAR 1028690 and 1339505, and additional support by the University of Minnesota’s Undergraduate Research Opportunity Program. The IRM is a US National multiuser facility supported through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. This is IRM publication #2102.

Funding Information:
Irene Raposo is thanked for all aspects of the field component of this work and use of the lab at the University of S?o Paulo, Brazil, for the anisotropy of magnetic susceptibility measurements for the sites labeled IT, with funding by the S?o Paulo Research Foundation (FAPESP) grant 2011/51204-0. I am indebted to William Callebert for performing the majority of the magnetic anisotropy measurements at the Institute for Rock Magnetism (IRM), University of Minnesota, with funding by the National Science Foundation grants NSF/EAR 1028690 and 1339505, and additional support by the University of Minnesota?s Undergraduate Research Opportunity Program. The IRM is a US National multiuser facility supported through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. This is IRM publication #2102.

Publisher Copyright:
© 2021. The Authors.

Keywords

  • environmental magnetism
  • glacial transport
  • magnetic anisotropy
  • magnetic fabrics
  • rock magnetism
  • sedimentary transport

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