On the relationship between paleomagnetic secular variation and excursions – Records from MIS 9 and 10 - ODP Leg 172

Abstract

This paper summarizes paleomagnetic secular variation (PSV) and excursions recorded from MIS 9–10 (300–374 ka) shipboard measurements of sediments from the western North Atlantic Ocean at ODP Sites 1060, 1061, 1062, and 1063. We have identified 33 inclination features, 31 declination features, and 12 paleointensity features that are reproducible among the four ODP Sites. We have dated these records based on estimates of Milankovich carbonate cyclicity in Grutzner et al. (2002). We also dated these records by comparison with the PISO-1500 global paleointensity record (Channel et al., 2009). The two methods give comparable age estimates for this time interval.. We have also recovered a 9-m PSV record from u-channel studies of Hole 1062H. This record is almost identical to the shipboard paleomagnetic results from Site 1062. All records show evidence for the Calabrian Ridge Excursion (329 ± 3 ka); Sites 1062 and 1063 contain the most consistent and high-resolution paleomagnetic records of the excursion. The Calabrian Ridge excursion is associated with a narrow (~12 ky) interval of high angular dispersion and low paleointensity. We have also carried out a statistical study of the PSV records after removing all true excursional directions (Lund, 2018). There is significant PSV directional variability over 104 yr time scales that is common to all four sites. The pattern of angular dispersion variability is bimodal with most time spent with low (~10°) dispersion, with two shorter intervals of high (~25°) dispersion. The high-dispersion intervals are associated with low intensity intervals and excursions.