| Both theory and numerical models speculate that the state of the geodynamo during superchrons (long periods without polarity reversals) is different from its state during (even longer) periods of mixed polarity. Robust observational data, however, are still conspicuously lacking. A recently acquired high-quality red bed record showed non-reduced secular variation during the Permo-Carboniferous Reversed Superchron (PCRS, ~50 Myr). The secular variation is comparable to recent times, a result that contrasts with model predictions. A recent analysis of paleointensities during the Cretaceous Normal Superchron (CNS, ~35 Myr), however, provided tentative support that secular variation indeed may have been reduced during this Superchron. This discrepancy may indicate that the geodynamo was fundamentally different during these two Superchrons. The observational database, however, is still too small and its quality often inadequate, thus prohibiting firm conclusions. Therefore, this proposal aims to provide high-quality secular variation records during the PCRS, a period for which observations are most critical. We intend to analyse red bed sediments because they contain a high-quality magnetic signal. Our recent advance in understanding the natural remanent magnetisation (NRM) in red beds permits to distinguish the various modes of NRM acquisition in these rocks. The primary nature of the NRM will be assessed by an array of paleomagnetic and rock magnetic tests, including recently developed and promising new laboratory techniques. In addition, we aim to develop a suitable method to obtain - for the first time - relative paleointensity records for hematite bearing rocks. The required precise time constraints will be obtained through cyclostratigraphic (Milankovitch) chronology. Finally, we aim to compare our observations to both (new) results from the CNS and to predictions from theory and models. |
