Application of Cosmogenic Nuclides and Argon Geochronology to Paleoclimate, Paleomagnetism, and Paleohydrology

• Main Author: Balbas, Andrea M.
• Other Authors: Clark, Peter U., Brook, Edward, Koppers, Anthony A. P., Bailey, Mike, Stoner, Joseph, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University. Graduate School
• Format: Doctoral or Postdoctoral Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Geological time; Floods > Missoula; Lake; Cosmogenic nuclides; Geomagnetic reversals; Paleomagnetism; Radioactive dating; Geomagnetic Pole
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6h440w865

This dissertation uses argon geochronology and cosmogenic nuclide surface exposure dating methods to address three research questions. The first question concerns a geomagnetic instability recorded in lava flows on the island of Floreana in the Galapagos Archipelago. Changes in the Earth’s magnetic field (intensity and orientation) occur frequently throughout geologic time for reasons not yet fully understood. Accurately dating these changes is important because these events provide critical stratigraphic markers in many natural archives, and constraints on the timing of geomagnetic change help better our understanding of the geodynamo. The lava flow on Floreana records an 86% reduction in field strength and intermediate virtual geomagnetic pole (VGP) orientations. Our age determination of 925.7 ± 4.6 ka (2σ; n = 6; MSWD = 1.23) indicates that this flow and the flows associated with it that record nearly identical VGP’s, record the Santa Rosa Excursion. We confirm that this site records the second reported terrestrial evidence of this geomagnetic excursion. Our age is in agreement with sediment records, which indicate this event spanned 3 kyrs. The Santa Rosa Excursion can now be characterized as a global short-lived geomagnetic anomaly associated with an 86% reduction in field strength in equatorial regions (as compared to modern day field strength). Similarities between the Santa Rosa and Laschamp excursions illustrate that such events can occur when the geomagnetic field is either in its reversed or normal polarity state. The second research question addresses the timing of the most recent polarity transition of Earth's magnetic field. The Matuyama-Brunhes (M-B) polarity transition is the most well-studied of all polarity transitions however it's timing remains in debate. A ~10 kyrs mismatch between volcanic and sedimentary archives that record the reversal have been reported. Important geodynamic insights can be gained by examining the structure of a reversing field through time, and the reliability of such ...