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A paleomagnetic investigation of the Minturn Formation, Colorado: A study in establishing the timing of remanence acquisition

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DOI: 10.1016/0040-1951(91)90418-r
  • Earth Science


Abstract One hundred sixty-five oriented hand samples were collected from 55 sites in the Minturn Formation located between Wellsville and Howard, Colorado, in an attempt to locate the base of the Permo-Carboniferous Reversed Superchron (PCRS) in western North America. After the samples were demagnetized using thermal and alternating field cleaning techniques, the normal polarity magnetizations (which marks the base of the Permo-Carboniferous Reversed Superchron (PCRS)) were not found in the Minturn Formation. Reversed polarities were consistent throughout the section studied. A conglomerate test was conducted on syndepositional rip-up clasts taken from the formation. The test indicates that a post-depositional, secondary component of magnetization has been acquired by the clasts and remains stable up to temperatures of 610–640°C. However, the high temperature components for three of the four test sites show random directions indicating that a primary remanent magnetization was acquired shortly after deposition. The conglomerate test demonstrates that a secondary Permian direction can be successfully isolated from a primary Pennsylvanian one revealed at blocking temperatures above 650°C. In this study, the two components were isolated using step-wise thermal demagnetization. The results of the study indicate that the base of the PCR superchron lies stratigraphically below the Minturn Formation, probably in Early Atokan or Morrowan age sediments.

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