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Magnetostratigraphy


At the beginning of the sixties it has been definitely proved the existence of the reversals of the Earth’s magnetic field and since then the data concerning the magnetic polarity of the rocks have being used as global and synchronous indicators in stratigraphic studies (fig. 1).

Figure 1 Geomagnetic field flux lines in normal (a) and inverse (b) polarities.

The global character of the Earth’s magnetic field reversals highlights the magnetostratigraphy (the study of the magnetic polarity succession in rock sequences) as the essential tool for the dating and for the correlation between distinct stratigraphic sequences. The magnetostratigraphy involves paleomagnetists, stratigraphists and paleontologists in a joint work about a large variety of geocronological problems. Studies of magnetostratigraphy in Italy have been mainly addressed to fix a time reference for the most important tectonic, paleontological, and paleoenvironmental events in Mediterranean Sea and for the calibration of the Magnetic Polarity Time Scale to the variations in Earth’s orbital parameters for the last 5 million of years (fig. 2).

Figure 2 Magnetic Polarity Time Scale for the last 30 millions of years (modified by Berggren et al., 1995); black indicates normal magnetic polarity; white indicates inverse magnetic polarity.

In opportune stratigraphic sections, with good paleomagnetic properties and high sedimentation rates, the magnetostratigraphy is also used to study some characters of the Earth’s magnetic field during a polarity reversal and, in case of very young sediments, to extend back in geological time the historical instrumental observations of the secular variation of the Earth’s magnetic field.
Within the Cape Roberts project in Antarctica magnetostratigraphy and environmental magnetism data from the Cenozoic sedimentary succession at the bottom of the Ross Sea have been integrated in a narrow interconnection of multidisciplinary data, with the ambitious target of dating and understanding the beginning of the Antarctica glaciation, with its consequences on climate and environment at global scale. INGV substantially contributes at this project, in collaboration with the University of California, Davis with the temporary set up of the first laboratory of paleomagnetism in Antarctica, at the US base in McMurdo (fig. 3).

Figure 3 Group of Paleomagnetism in Crary’s laboratories, Mc Murdo (Antarctica); Cape Roberts Project, October-November 1997.

The ANDRILL project is a new international project focused in understanding the role of Antarctica in global environmental changes during Cenozoic.


Bibliography

Berggren et al., in Soc. Econ. Paleontol. Mineral., Spec. Pubbl. 54, 129-212, 1995


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