HR: 0800h
AN: PP11A-0555    [Abstracts]
TI: An orbital origin for large oxygen isotopic shifts and sea-level changes during the Oligocene
AU: * Pekar, S F
EM: spekar@qc1.qc.edu
AF: Queens College (CUNY), 65-30 Kissena Blvd., Flushing, NY 11367 United States
AU: * Pekar, S F
EM: spekar@qc1.qc.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, Route 9W, Palisades, NY 10964 United States
AU: Christie-Blick, N
EM: ncb@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Route 9W, Palisades, NY 10964 United States
AB: Recently, it was shown that a relatively rare orbital congruence involving low-amplitude variance in obliquity and a minimum in eccentricity coincides at the Miocene/Oligocene boundary with a large increase in oxygen isotopes (Mi1 event) and ice volume, suggesting a possible causal mechanism for such events at the million-year timescale. We tested this idea against the Oligocene oxygen isotopic and sea-level records and the astronomical timescale of Shackleton et al. (1999). As in the Miocene, large isotopic shifts (Oi events; $\delta$$^{18}$O $>$0.5\permil, with maximum values $>$2.7\permil) and sea-level changes (30-70 m) occurred in the Oligocene at the million-year timescale. Smaller variations in sea level (and corresponding isotopic values) characterize obliquity (10$^{4}$ years) and eccentricity (10$^{5}$ years) timescales: 15-20 m and 20-30 m, respectively. Our analysis shows that, as with the Mi1 event, Oi events relate to the anticipated orbital congruence - resolving one of the outstanding conundrums of the late Paleogene paleoclimate. It also provides support for the robustness of the astronomical time scale of Shackleton et al. (1999) for the Oligocene Epoch.
DE: 9310 Antarctica
DE: 9604 Cenozoic
DE: 4267 Paleoceanography
DE: 4556 Sea level variations
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting