Paleomagnetic Records from the Chilean Margin


Sites drilled on the Chilean Margin during ODP Leg 202: Site 1233 (41°0. S, 74°26W, water depth 838 m), Site 1234 (36°13 S, 73°40W, water depth 1015 m) and Site 1235 (36°9 S, 73°33 W, water depth 489 m) are providing the highest resolution, well-dated complete vector time series of geomagnetic field variability that is continuous for at least the last 50,000.

Several intervals of high amplitude PSV behavior including at least one reversal excursion are preserved, including one that is chronologically consistent with the Laschamp Excursion observed in the North Atlantic. U-channel results show that the excursion extends over more than 2 meters and displays a remarkable full-polarity reversal. The duration of the reversed polarity interval is only ~ 600 yrs within a relative paleointensity low that lasted  ~ 1500 yrs in duration. The complete transition from normal to reversed directions occurs in less than 200 years!

The timing and sequence of events associated with the Laschamp excursion at Site 1233 are similar to that observed at other locations. Though unlike previous observations that show the Laschamp excursion as only as transitional feature with little time in a southern Hemisphere polar location, at Site 1233 a full-polarity reversal that makes a complete world tour is observed.

Figure 1. Blowup of deconvolved u-channel magnetic data through the Laschamp interval at ODP Site 1233. From top to bottom: VGP latitude based on deconvolved and regular u-channel data. ChRM declination and deconvolved declination. ChRM inclination and deconvolved inclination. Mean NRM/ARM as an RPI proxy.