Astronomical Ages for Polarity Chrons C4Ar-C5r (9.3-11.2 Ma, Middle to Late Miocene), and for Three Excursion Chrons Within C5n.2n

Details Astronomical Ages for Polarity Chrons C4Ar-C5r (9.3-11.2 Ma, Middle to Late Miocene), and for Three Excursion Chrons Within C5n.2n Astronomical Ages for Polarity Chrons C4Ar-C5r (9.3-11.2 Ma, Middle to Late Miocene), and for Three Excursion Chrons Within C5n.2n

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmgp42a..02e&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #GP42A-02

Astronomy and Astrophysics

Astronomy

1500 Geomagnetism And Paleomagnetism, 1513 Geomagnetic Excursions, 1520 Magnetostratigraphy

Scientific paper

Ocean Drilling Program (ODP) Site 1092 from the sub-Antarctic South Atlantic produced a clear magnetic stratigraphy for the Late Miocene. Three short intervals of reverse polarity were identified within the long (~ 1 Myr) normal polarity subchron C5n.2n. These were tentatively correlated to the three "cryptochrons" (Cande and Kent, 1992) identified within subchron C5n.2n from marine magnetic anomaly data. New oxygen isotope data from ODP Site 1092 have allowed astronomical calibration of eight polarity chron boundaries in the interval between C4Ar.1n and C5r.1n (9.3-11.2 Ma) as well as calibration of the three excursion chrons identified within C5n.2n. Oxygen isotope data for the Middle to Late Miocene (7-15 Ma) were generated from three different species of foraminifers (one benthic and two planktic) and these records were stacked to produce a composite record. The record was placed on an initial age model based on the magnetic stratigraphy and the ATNTS2004 timescale. For the stacked oxygen isotope record, a power spectrum using the Blackman-Tuckey method with a Bartlett window identified a dominant cycle as the 41 kyr obliquity cycle. The oxygen isotope stack was tuned to the ETP curve from Laskar et al. (2004), and the extracted 41 kyr cycle was then matched to the orbital solution for obliquity. Tuning of the isotope record was only possible in the 9.3-11.2 Ma interval due to lower sedimentation rates and condensed horizons outside this interval. The resulting durations of the three excursion chrons within C5n.2n lie in the 2-5 kyr range, comparable to the magnetic diffusion time of the inner core and therefore consistent with the genetic model for excursions of Gubbins (1999). The new polarity chron ages in the C4Ar.1n-C5r.1n interval differ from previous timescales by up to 82 kyrs, and by up to 44 kyrs when compared with the ATNTS2004 timescale.

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