A review of marine magnetic constraints on the behavior of the geomagnetic field during the Cretaceous normal superchron (Invited)

We review recent marine magnetic observations (Granot et al., 2012) that provide important constraints on the evolution of the geomagnetic field during the Cretaceous normal superchron (CNS, 120.6 to 83.5 Ma). By comparing a deep-tow profile from the Central Atlantic Ocean and globally distributed sea-surface magnetic profiles the superchron is divided into three stages: 1) between 120.6 and ~110 Ma the variability of the dipolar field increased gradually both in its amplitude and range of frequencies, 2) between ~110 and ~100 Ma the fluctuation reached a maximum, and 3) between ~100 and the end of the CNS both the frequency content and amplitude decreased to what seems to have been a very stable field. These observations can be explained by two end-member scenarios (or any combination of them): either the fluctuations of the geomagnetic field were increasing and decreasing about a rather steady long-term averaged moment, or the field fluctuated steadily about a long-term increasing, then decreasing dipole moment. We compare our results against published absolute paleointensities and conclude that the average strength of the field was most likely higher during the middle part of the CNS than during its beginning and ending parts. Further absolute and relative paleointensity records are required before a well constrained history of the geomagnetic field during the CNS is obtained.