Geomagnetic excursions: Knowns and unknowns

Abstract

[1] Geomagnetic excursions are short-lived episodes when Earth's magnetic field deviates into an intermediate polarity state. Understanding the origin, frequency, amplitude, duration, and field behavior associated with excursions is a forefront research area within solid earth geophysics. Recent advances in excursion research are summarized here, and key further research is suggested to resolve major unanswered questions. Improving the global distribution of excursion records, particularly from the southern hemisphere, obtaining high-resolution sedimentary excursion records with good age control from sites with sedimentation rates >10 cm/kyr, obtaining volcanic excursion records coupled with high-precision geochronology, and estimating excursion duration with high chronological precision will all facilitate hypothesis testing concerning the deep earth dynamics that generate geomagnetic excursions.

The Blake geomagnetic excursion recorded in a radiometrically dated speleothem

“…Understanding the origin, duration and the field behaviour associated with excursions is a forefront research area within solid earth geophysics (Roberts, 2008). Precise evaluation of the duration of geomagnetic excursions has become a point of interest since Gubbins (1999) proposed that excursions occurred when the field in the Earth's liquid core reverses polarity without accompanying field reversal in the solid inner core.…”

New dating of the Homo erectus cranium from Lantian (Gongwangling), China

“…It has not only been isotopically dated to 1.57 ± 0.05e1.68 ± 0.12 Ma from volcanic rocks (Watkins et al, 1975;Udagawa et al, 1999) but also magnetostratigraphically dated to 1.675 Ma from marine sediments (Valet and Meynadier, 1993), and 1.567e1.575 Ma from astronomically tuned isotopic ages (Channell et al, 2002;Laj and Channell, 2007;Roberts, 2008). The latest age estimate of the Gilsa Event by the Subcommission on Quaternary Stratigraphy is a synthetic age of 1.68 Ma (Gibbard and Cohen, 2008;Cohen and Gibbard, 2013).…”

How does Chinese loess become magnetized?

“…Well-established excursions have the potential to serve as stratigraphic tie points. The Mono Lake and Laschamp excursions are the two excursions that have been confirmed to have a world-wide expression during the past 100 ka (Roberts, 2008); they have also been identified in Chinese loess profiles (for more information see Chapter 1).…”

“…In Figure 5.9, the three normalized remanence records from the studied Yuanbao section are plotted along with the SINT-800 global stack (Guyodo and Valet, 1999), a Portuguese margin stack (Thouveny et al, 2004), a North Pacific stack from ODP sites 883/884 (Roberts et al, 1997) using the revised age model from Roberts (2008) and the high-resolution paleointensity record from ODP sites 983/984 (Channell, 1999 …”

“…Comparisons of normalized remanence records from the Yuanbao section with different relative paleointensity records. (a) Part of the SINT-800 data set (Guyodo and Valet, 1999); (b-d) NRM/IRM, NRM/ARM and NRM/ARM2 for the Yuanbao section; (e) Portuguese margin marine stack (Thouveny et al, 2004), (f) North Pacific ODP 883 and 884 stack (Roberts et al, 1997) using the age model of Roberts (2008), and (g) the high-resolution paleointensity record from ODP sites 983/984 (Channell, 1999). All data are plotted on the same age scale.…”