A View Into the Cretaceous Geomagnetic Field From Analysis of Gabbros and Submarine Glasses of the Troodos Ophiolite

The nature of the geomagnetic field during the Cretaceous normal polarity superchron (CNS) has been a matter of debate for the last several decades. Numerical geodynamo simulations predict higher intensities, but comparable variability, during times of few reversals than times with frequent reversals. Here we present new paleointensity data from 221 gabbroic samples obtained from 35 sites in the lower oceanic crust of the Troodos ophiolite, many of which can be located with respect to the ancient spreading center hence form a time-series. Together with recently published data from the Troodos upper crust we obtain three independent time series. Our paleointensity sequences reveal quasi-cyclic variations of intensities about a mean value of 54±20×ZAm2, providing insight into the fluctuating nature of the Cretaceous magnetic field. The large amplitudes of these variations explains the wide range of dipole moments previously published, and shows that the CNS field was both weaker and more variable than predicted by the geodynamo simulations