• journal_title：Geology
• Contributor：Gary S. Wilson ; Mark Lavelle ; William C. McIntosh ; Andrew P. Roberts ; David M. Harwood ; David K. Watkins ; Giuliana Villa ; Steven M. Bohaty ; Chris R. Fielding ; Fabio Florindo ; Leonardo Sagnotti ; Timothy R. Naish ; Reed P. Scherer ; Kenneth L. Verosub
• Publisher：Geological Society of America
• Date：2002-
• Format：text/html
• Language：en
• Identifier：10.1130/0091-7613(2002)030<1043:ICCOTO>2.0.CO;2
• journal_abbrev：Geology
• issn：0091-7613
• volume：30
• issue：11
• firstpage：1043

An expanded Oligocene-Miocene boundary interval recovered in the Cape Roberts Project CRP-2A core from beneath the Ross Sea, Antarctica, has yielded a high-resolution integrated chrono stratigraphy that has, in turn, enabled a new, more direct, calibra tion of magnetic polarity and biostratigraphic events. The Oligocene-Miocene boundary interval in the CRP-2A core comprises three ∼60-m-thick, rapidly deposited (>0.5 m/k.y.) sedimentary sequences (sequences 9, 10, and 11). In sequences 10 and 11, single-crystal, laser-fusion ⁴⁰Ar/³⁹Ar analyses of anorthoclase phenocrysts from two tephra horizons independently calibrate the CRP-2A magnetic-polarity stratigraphy and age model. Sequences 10 and 11 encompass subchron C6Cn.3n, which is dated as 24.3 ± 0.1 to 24.16 ± 0.1 Ma. Sequence 9 is interpreted to encompass subchron C6Cn.2n and the Oligocene-Miocene boundary, which is dated as 24.0 ± 0.1 Ma. These ages are ∼0.2 m.y. older than those of the geomagnetic polarity time scale calibrated from seafloor-spreading ridges and ∼0.9–1.3 m.y. older than the newly proposed astronomically calibrated ages. We contend that the discrepancy with the astronomically calibrated ages arises from a mismatch of three 406 k.y. eccentricity cycles or a 1.2 m.y. modulation of obliquity amplitude in the astronomical calibration of the Oligocene–Miocene time scale.