Cretaceous Intensity of Earth's Magnetic Field from Thellier Analyses of Single Plagioclase Crystals

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Tarduno EAR-0003393 Theoretical considerations and modeling results suggest a relationship between geomagnetic field intensity and polarity reversal rate. No clear relationship, however, is apparent in available paleointensity data. The investigators address this issue using a new paleointensity measurement approach that uses analyses of single plagioclase crystals. These crystals, which contain magnetic inclusions that retain paleofield values, are less susceptible to alteration during paleointensity experiments than some whole rock samples. Results from Thellier-Thellier experiments on plagioclase crystals separated from basalts that formed during the Cretaceous Normal Polarity Superchron (Rajmahal Traps) suggest a time-averaged paleomagnetic dipole moment three times that thought to have typified times of frequent geomagnetic reversals in the Cenozoic and early Cretaceous/late Jurassic. This result leads to their hypothesis that there is a correlation between times of low reversal frequency and high geomagnetic field strength. They propose to test this hypothesis through a study of high- and low-latitude mid-Cretaceous flood basalt sites. These rocks will allow the investigators to examine the spatial (latitudinal) and temporal variation of geomagnetic field intensity during the Cretaceous Normal Polarity Superchron.