10:45 AM - 11:00 AM
[SEM15-06] Latest Pleistocene short-lived geomagnetic excursions from Lake Suigetsu varved sediments
Keywords:dipole field, Lake Suigetsu varved sediments, VGP cluster, Tianchi Excursion, IntCal20
Geomagnetic excursions represent fast, dynamic natures of the earth’s magnetic field. It is recently revealed from Lake Suigetsu varved sediments that the main Laschamp Excursion comprises multiple subcentennial directional-swings. The virtual geomagnetic poles (VGPs) during the swing phases make four clusters centred in hemispherically-symmetric regions, three of which encompass the VGPs associated with the Laschamp Excursion recorded in lavas at various locations. Thus, the subcentennial scale excursions are dominated by dipolar fields. Geomagnetic excursions have the potential to reveal decadal scale features of dipole fields.
We conducted magnetic analyses of well dated varved sediments of Lake Suigetsu. Two paleomagnetic data sets by thermal demagnetizations of discrete samples and alternating field demagnetizations of long samples consistently show three short-lived excursions. One that spans about 150 years at about 17.3 IntCal20 cal kyr BP contains near-reversal fields. The virtual geomagnetic pole (VGP) quickly migrated from a Siberian high-latitude to around New Zealand to the coast of Antarctica to stay there for about 100 years, followed by a quick return via West Asia. The VGP just passes on the two excursional VGPs from the Changbaishan Tianchi lavas, whose chronology is in dispute, at the earliest and the final stages, respectively. Thus, the excursion correlates with the Tianchi Excursion. The fast VGP movement is similar to the Laschamp Excursion from the same varved sediment core. Other two excursions, 2700 years predating and 2000 years postdating the Tianchi Excursion, span about 80 and 260 years, respectively. The former has VGPs constrained on the two longitudinal bands through the eastern Africa and the Pacific, like the Laschamp Excursion, while the latter has different VGPs, with a large clockwise open loop through Africa, the South Atlantic, and the Central America, which may be originated from different sources. The three excursions from Lake Suigetsu possibly correlate with the multiple excursional field events from nonmarine sediments of the Jeju Island, Korea during the last melting ice age.
We conducted magnetic analyses of well dated varved sediments of Lake Suigetsu. Two paleomagnetic data sets by thermal demagnetizations of discrete samples and alternating field demagnetizations of long samples consistently show three short-lived excursions. One that spans about 150 years at about 17.3 IntCal20 cal kyr BP contains near-reversal fields. The virtual geomagnetic pole (VGP) quickly migrated from a Siberian high-latitude to around New Zealand to the coast of Antarctica to stay there for about 100 years, followed by a quick return via West Asia. The VGP just passes on the two excursional VGPs from the Changbaishan Tianchi lavas, whose chronology is in dispute, at the earliest and the final stages, respectively. Thus, the excursion correlates with the Tianchi Excursion. The fast VGP movement is similar to the Laschamp Excursion from the same varved sediment core. Other two excursions, 2700 years predating and 2000 years postdating the Tianchi Excursion, span about 80 and 260 years, respectively. The former has VGPs constrained on the two longitudinal bands through the eastern Africa and the Pacific, like the Laschamp Excursion, while the latter has different VGPs, with a large clockwise open loop through Africa, the South Atlantic, and the Central America, which may be originated from different sources. The three excursions from Lake Suigetsu possibly correlate with the multiple excursional field events from nonmarine sediments of the Jeju Island, Korea during the last melting ice age.