Geomagnetic Paleointensity During Anomolous Field Behavior (Mid-Jurassic)

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EAR-0126561Maureen B. SteinerAn exciting discovery of geomagnetic field behavior was made in Jurassic oceanic basalts of the Pacific Ocean. Continuous change of geomagnetic polarity was observed in a four hundred meter basalt sequence. Six polarity "intervals" were observed, corresponding to geomagnetic field reversals roughly once every 50,000 years. Such fast, continuously reversing behavior has never before been observed. The ~170 Ma oceanic crust is remarkably unaltered (similar to 0-20 Ma age oceanic basalt). Magnetic intensities of the basalt are normal to slightly high for unaltered oceanic crust, and microprobe work shows that this is not the result of an unusual chemistry of the titanomagnetite remanence carriers. An abundance of glass, which commonly preserves pristine titanomagnetite is present throughout the 400 m. The glass abundance provides the opportunity to examine geomagnetic field intensity during this unusual field behavior. In the record of constantly changing polarity, numerous intervals of intermediate directions also are present, including intervals of zero inclination at which geomagnetic field intensity would be expected to be lowest. The glass abundance in a record of continuously changing field behavior and the intermediate and zero-inclination directions allow interrogation of the intensity of the geomagnetic field during this unusual directional behavior. Paleointensities will be measured for each "polarity" state and for all intermediate-direction intervals for which glass is present. The result is expected to provide information about the geomagnetic field's ability to change on such a fast time scale. The results should provide data to help constrain geomagnetic dynamo theory.