Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.v32b..06r&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #V32B-06
Mathematics
Logic
1100 Geochronology, 1165 Sedimentary Geochronology
Scientific paper
Recent refinements of models for the motions of the planets, including the Earth-Moon system, have led to the realization that the calculated cyclical changes in Earth's orbital eccentricity may be approximately correct for the whole of the Cenozoic. This raises the possibility of an astronomically-tuned geological timescale that extends to, and perhaps beyond, the Cretaceous-Tertiary (K-T) boundary. In order to test the validity of these long numerical integrations, we compare calculations of Earth's orbital eccentricity 62-67 million years (Ma) ago with a well-documented succession of basinal limestones and marlstones at Zumaia in the Basque region of Spain. Previous work has shown that each limestone-marlstone couplet records one axial precession cycle (~21 ka). An obvious bundling of couplets defines 36 "short" (~100-ka) eccentricity cycles between a carbonate-rich interval, used previously to tie the Zumaia section to our calculations, and the K-T boundary. If we assume an uninterrupted succession of couplets, each 20.8 ka in duration, and step the amplitudes of the time series according to the color (white, pink, or red) of the carbonates, we retrieve a strong 102-ka eccentricity signal with spectral analysis. This permits other ties to be made between prominent features of the calculated time series and the observed rock record. On this basis, the K-T boundary is >65.83 or >65.84 Ma using the ~100 ka cycles, >65.88 Ma using the 20.8-ka precessional cycles, and ≥65.95 Ma using the metronomic 406-ka eccentricity cycle line frequency, all significantly older than the current consensus age of 65.5 Ma.
Ghil Michael
Jögi Per
Runnegar Bruce
Varadi Ferenc
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