Red beds are well-known for recording stable natural remanent magnetization (NRM). However, discriminating primary NRM from secondary remanence in red beds is difficult. The Paleogene Nangqian red beds in eastern Tibetan Plateau variably record an overprint related to nearby magmatism and thus provide a great opportunity to characterize remagnetization in red beds. Through comprehensive rock magnetic, Mössbauer spectroscopic, and petrographic analyses, we find that remagnetization was controlled by temperature. Remagnetized red beds contain abundant authigenic hematite and goethite, with some larger grains unblocking at the Néel temperatures and the remainder (nanoparticles) unblocking at lower temperatures. In contrast, red beds retaining primary NRM are characterized by dominance of detrital hematite and magnetite, presence of fine-grained authigenic hematite, and absence of authigenic goethite and magnetite. High temperature behaviors of NRM/susceptibility are indicative of remagnetization, but the presence of goethite appears to be a more sensitive criterion for diagnosing remagnetization in red beds.
Bibliographical noteFunding Information:
supporting information S1 S6 Data to support this article are available in Tables – , which are also deposited in Zenodo (34e50cc1f9cbe4dd35c2a62c35ee91e6). W.H. was supported by three visiting research fellowships from the Institute for Rock Magnetism (IRM) at the University of Minnesota, which is funded by the Instruments and Facilities program of NSF. We thank Dr. Dario Bilardello at the IRM, and Dr. Peter C. Lippert at Utah Pmag Center for laboratory assistance. Dr. Pierrick Roperch and Dr. Guillaume Dupont‐Nivet are especially appreciated for sharing the thermal demagnetization data and discussing. We are also grateful to Dr. Swanson‐Hysell and two anonymous reviewers for their constructive comments, which have greatly helped improve the original manuscript.
- red beds