During the past 50 years, field measurements of sea-floor magnetic anomalies combined with paleomagnetic studies of volcanic and sedimentary sequences have yielded the construction of the geomagnetic polarity time scale. Excursions represent periods during which the magnetic pole deviates by more than 40° away from the geographic pole.
It is interesting that reversals and excursions occur during periods of very weak dipole field intensity. It is believed that the two geomagnetic events could thus well be associated with similar magnetic processes within the Earth’s core leading to either successful or aborted reversals depending on the conditions that could be related to the influence of the inner core.
Scarcity of sedimentary and volcanic records of excursions indicates that they are indeed very short events. Consequently, very few sedimentary records meet the appropriate resolution as their magnetization processes can smear out the signal and remove the transitional and reversed directions recorded with low magnetization intensity in presence of a weak magnetic field. It is important to note that the paleomagnetic evidence of a magnetic reversal or excursion cannot result in the absence of a significant interval of opposite polarity.
Valet, J., Plenier, G., Herrero-Bervera, E. (2008). Geomagnetic excursions reflect an aborted polarity state. Earth and Planetary Science Letters, 274(2008), 472-478.