Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 ± 0.1 Ma from the CRP-2A drill core, Ross Sea, Antarctica
- Gary S. Wilson1,
- Mark Lavelle2,
- William C. McIntosh3,
- Andrew P. Roberts4,
- David M. Harwood5,
- David K. Watkins5,
- Giuliana Villa6,
- Steven M. Bohaty7,
- Chris R. Fielding8,
- Fabio Florindo9,
- Leonardo Sagnotti9,
- Timothy R. Naish10,
- Reed P. Scherer11 and
- Kenneth L. Verosub12
- 1Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand
- 2British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK, and Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
- 3New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
- 4School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, UK
- 5Department of Geosciences, University of Nebraska, Lincoln, Nebraska 68588-0340, USA
- 6Dipartimento di Scienze della Terra, Università di Parma, Parco Area delle Scienze 157A, 43100 Parma, Italy
- 7Earth Sciences Department, University of California, 1156 High Street, Santa Cruz, California 95064, USA
- 8Department of Earth Sciences, University of Queensland, Brisbane, QLD 4072, Australia
- 9Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, I-00143 Rome, Italy
- 10Institute of Geological and Nuclear Sciences Ltd, P.O. Box 30-368, Lower Hutt, New Zealand
- 11 Department of Geology and Environmental Geosciences, Northern Illinois University, De Kalb, Illinois 60115, USA
- 12Department of Geology, University of California, Davis, California 95616, USA
Abstract
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.
Footnotes
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- Accepted July 18, 2002.
- Received February 5, 2002.
- Revision received July 16, 2002.
- Geological Society of America
