A Geomagnetic Instability Timescale for the Pleistocene

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Sediments and lava flows have begun to reveal that the Earth's magnetic field becomes unstable, exhibiting large excursions in direction and intensity away from what is presently observed, with a frequency greater than previously imagined. To the extent that these numerous short-lived geomagnetic events can be temporally quantified, they are useful in at least two major endeavors. First, the marine sediment record of paleointensity holds great potential for global stratigraphic correlation of climate changes during the past several hundred thousand years. Second, recent theoretical and numerical models of the geodynamo in the molten outer core make explicit predictions as to the timing, frequency, and geometry of reversals and excursions in attempting to explain the role of the solid inner core or deep mantle in controlling the field. These models are only meaningful insofar as they can explain the observed paleofield behavior. A principal goal of this project is to develop a Geomagnetic Instability Time Scale (GITS) based on extensive 40Ar/39Ar dating of well-known lava flows which record transitional directions or low paleointensity. Through collaborations with paleomagnetists from several countries, it is planned to determine the ages of as many as seven geomagnetic events that occurred during the Brunhes Chron between ca. 700 and 25 thousand years ago and which are recorded in basaltic lava flows at 10 different localities around the globe. Corollaries include linking this record of geomagnetic events to that already developed for the late Matuyama Chron (790 thousand to 2.3 million years ago), and providing an unprecedented number of radioisotopic tie points with which to calibrate and test orbital chronologies for the next generation of paleomagnetic records acquired from marine sediment around the world. Some of the broader impacts include nurturing established international collaborations and fostering new ones that will disseminate technology and ideas far beyond the Rare Gas Geochronology Laboratory at Wisconsin. Graduate students will be exposed to multi-disciplinary (geophysics-geochemistry) field and laboratory-based research, and the international scientific community. Moreover, it is also planned to create an interactive exhibit on geologic time that integrates modern radioisotopic dating with more traditional aspects of the geologic record for the new expansion of the UW-Madison Geology museum.--