Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmgp43b0854e&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #GP43B-0854
Other
1520 Magnetostratigraphy
Scientific paper
ODP Leg 198 to Shatsky Rise recovered a total of ~768 meters of Late Miocene to Recent sediments from 6 Sites. Neogene sediments at the sites consisted mostly of light gray to pale orange nannofossil oozes with varying amounts of clay, radiolarians and diatoms. Site 1208 was drilled on the Central High and provided a Late Miocene to Recent sequence with sedimentation rates ~4-5 cm/kyr. Sites 1209, 1210, 1211 and 1212 were drilled on the Southern High and yielded shorter sequences of Late Miocene to Recent sediments with sedimentation rates ~1-2 cm/kyr. Clearly interpretable magnetic stratigraphies have been obtained from all six sites based on shipboard data. These results have been augmented using discrete sample cubes (7cc) collected shipboard and measured post-cruise. Astrochronologies for Sites 1207 to 1211 were based on cycles seen in reflectance data from shipboard measurements. The reflectance data for these cores were measured using a digital imaging track system equipped with a line-scan camera. ODP Leg 198 was the first cruise after installation of the track, and these measurements provided a high-resolution stratigraphic record of color variations for visible wavelengths. These data were placed on an initial age model by pattern fit of the polarity zones to the geomagnetic polarity timescale (GPTS) of Cande and Kent (1995). Power spectra calculated using this initial age model often show concentration of power at orbital frequencies, particularly around the 41 kyr obliquity cycle, although the orbital power is more pronounced in some parts of the section than in others. The reflectance record was tuned to the astronomical solution for obliquity from Laskar et al. (1993). Astronomically tuned ages were estimated for polarity reversals in the 1-9 Ma interval at Site 1207. At Sites 1208 and 1209 tuning was performed in the 1-7 Ma interval and at Sites 1210 and 1211 in the 1-5 Ma interval. Cross spectral analysis on the tuned age model indicated significant coherence between the astronomic solution and the reflectance data. The tuned timescales are compared with other published ages for this part of the GPTS and indicate that the Shackleton et al., (1995) ages from ODP Leg 138 in the 8-9 Ma interval are too young by ~100 kyrs. The astronomical timescales are in better agreement with the timescale of Hilgen et al., (1995) in this interval.
Channell J. E.
Evans Helen F.
Sager William W.
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