Calibration of the Cenozoic Polarity Time Scale Based on Intervals of Constant Sea Floor Spreading Rates

Details Calibration of the Cenozoic Polarity Time Scale Based on Intervals of Constant Sea Floor Spreading Rates Calibration of the Cenozoic Polarity Time Scale Based on Intervals of Constant Sea Floor Spreading Rates

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmgp11b0830w&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #GP11B-0830

Other

1535 Reversals (Process, Timescale, Magnetostratigraphy)

Scientific paper

Astronomical calibration of the polarity time scale is now nearly complete for 0-12 Ma and recent work is making rapid progress on calibrating 12-40 Ma. Integration of radiometric dating and sea floor spreading histories allows calibration of the Middle and Early Miocene to an accuracy arguably 0.1 Myr, supporting an Oligocene-Miocene boundary near 23.0 Ma. Spreading rate histories for the Neogene show that all plate pairs have sudden rate changes, that sudden (<0.5 Myr) rate changes are more common than gradual (>2 Myr) rate changes, and that rate changes usually correlate with recognizable changes in fracture zone trends and location of the pole of relative motion. These relations suggest a calibration strategy of identifying intervals of stable relative plate motion and assuming constant, rather than smoothly changing, spreading rates in these intervals. For Oligocene and Late Eocene (C6C-C17), Australia-Antarctica and Pacific-Nazca (Farallon) spreading distances provide excellent constraints when calibrated against Southwest U.S. ignimbrite polarity stratigraphy [McIntosh et al, 1992] with revisions for the FC 40/39 monitor at 28.21 Ma [Kuiper et al 2004]. Calibration of this interval differs subtly from published alternatives, with the Late-Early Oligocene boundary in C10N at about 28.2 Ma, the Eocene-Oligocene boundary in C13R at about 33.7 Ma, and the Middle-Late Eocene boundary in C17N at about 36.9 Ma, all with accuracy arguably 0.2 Myr or better. Calibration of Paleocene through Middle Eocene is much more speculative due to lack of ideal spreading records, lack of consensus calibration points, and apparently global plate-motion reorganization at or near C21. A strategy assuming constant rate for Pacific-Juan de Fuca (Vancouver) for C13-C21 and minimizing rate changes for Pacific-Farallon for C21-C32 appears to be at least as viable as other, published time scales. This alternative strategy brings ages for much of the Middle Eocene younger than on all commonly used time scales, with C21N spanning about 44-45 Ma and the Early-Middle Eocene boundary at about 47-48 Ma. Large differences between this work and the calibrations of Cande and Kent result from this work allowing an interval of slow South Atlantic spreading about C21-C31 to start and end suddenly whereas their cubic-spline technique forces spreading rates to change gradually.

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