Cruise Magofond 4 aims to investigate the Earth magnetic field during a peculiar, almost 40-million-years long period during which this field did not revert. This period, known as the Cretaceous Normal Superchron (CNS), extends from 83 to 120 million years. We try to constrain the important variation of the field intensity observed during this period, in order to better understand the field and provide constraints to geodynamo models within the Earth core.
To this end, we use the paleomagnetic field recorded by the rocks of the oceanic crust during their cooling at the mid-ocean ridge axis. Towing a magnetometer at slow speed a few hundred meters above the seafloor allow obtaining a high resolution signal. The few deep tow magnetic profiles acquired during the first leg on R/V Pourquoi pas? are complemented by sea-surface magnetic profiles from both the first leg and the ongoing second leg onboard R/V Marion Dufresne to dispose of a consequent dataset.
Moreover, we try to use the most remarkable variations to date the seafloor and achieve plate tectonic reconstructions for this period, pointing out the need to study the southern flank in the Rijser-Larsen Sea on the Antarctic Plate.
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