Publication Date:
2017-04-04
Description:
We report high-resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of theWilkes
Land Basin (WLB), East Antarctica, in the frame of the Italian/Australian Wilkes Land Glacial History (WEGA) project. The
studied cores, with a length of ca. 4m each, were collected from the gentle and steep sides of sedimentary ridges present in
the lower part of the continental rise, and consist of very fine-grained sediments. Paleomagnetic measurements were carried
out on u-channel samples. Apart from a low-coercivity magnetic overprint, removed after the first steps of alternating field
demagnetization, each core is characterized by a well defined characteristic remanent magnetization. Paleomagnetic inclinations
fluctuate around the expected value (of ca. −77◦) for such high latitude sites and always indicate normal magnetic polarity.
Short period oscillations to anomalously shallow paleomagnetic inclinations (up to −20◦) were identified at different levels of
the sampled sequences; positive (reverse) inclination values were however not observed. Specific rock magnetic measurements
indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences. For each core we reconstructed curves
of relative paleointensity (RPI, as computed by NRM20mT/κ and NRM20mT/ARM20mT) variation of the geomagnetic field. An
original age modelwas established by tuning the individual RPI curves with the available global and regional reference RPI stacks.
Paleomagnetic results, supported by other limited bio- and chronostratigraphic constraints, establish that all the cores are Late
Pleistocene in age: two provide an expanded record of the last ca. 30 ka (PC18 and PC19), three span the last ca. 100, 200 and
300 ka (respectively, PC25, PC27 and PC26), and one reaches back to ca. 780 ka (PC20), approaching the Brunhes–Matuyama
transition. Thus, the WEGA paleomagnetic record provides the first experimental data documenting the dynamics and amplitude
of the geomagnetic field variations at high southern latitudes during the Brunhes Chron. The individual normalized RPI records
were merged in aWEGARPI stacking curve spanning the last 300 kyr. The comparison of theWEGARPI individual and stacked
curves with the global references RPI stacks shows that geomagnetic paleointensity variations, with periods longer than a few to
tens kyr depending on the sedimentation rate, can be safely recognized in this sector of the peri-Antarctic margins. Furthermore,
the stacking of the individual ChRM inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations
may be correlated to the main known geomagnetic excursions of the Brunhes Chron, supporting the validity of the age models.
The reconstructed average sediment accumulation rates for the individual cores range from 0.6 to 19 cm/ka and are compatible
with their position within the WLB, with the lowest rates found close to the ridge of the sedimentary drifts. Moreover, the
high-resolution age models obtained in this study provide original constraints to assess chronology, rates and amplitudes of the
climatic and environmental processes affecting this key area of the peri-Antarctic margins during the Late Pleistocene.
Description:
Published
Description:
223-242
Description:
2.2. Laboratorio di paleomagnetismo
Description:
JCR Journal
Description:
reserved
Keywords:
Paleomagnetism; Relative paleointensity; Geomagnetic excursions; Antarctica; Brunhes Chron
;
04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
;
04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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