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Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 ± 0.1 Ma from the CRP-2A drill core, Ross Sea, Antarctica

Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 ± 0.1 Ma from the CRP-2A drill core, Ross Sea, Antarctica
Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 ± 0.1 Ma from the CRP-2A drill core, Ross Sea, Antarctica
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, calibration 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.
chronostratigraphy, isotope dating, Antarctica, biostratigraphy, Cape Roberts Project
0091-7613
1043-1046
Wilson, G.S.
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Roberts, A.P.
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Harwood, D.M.
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Fielding, C.R.
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Watkins, D.K.
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Naish, T.R.
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Florindo, F.
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Sagnotti, L.
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Scherer, R.P.
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Villa, G.
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Lavelle, M.
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McIntosh, W.C.
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Bohaty, S.M.
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Verosub, K.L.
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Wilson, G.S.
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Roberts, A.P.
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Harwood, D.M.
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Fielding, C.R.
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Watkins, D.K.
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Naish, T.R.
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Florindo, F.
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Sagnotti, L.
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Scherer, R.P.
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Villa, G.
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Lavelle, M.
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McIntosh, W.C.
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Bohaty, S.M.
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Verosub, K.L.
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Wilson, G.S., Roberts, A.P., Harwood, D.M., Fielding, C.R., Watkins, D.K., Naish, T.R., Florindo, F., Sagnotti, L., Scherer, R.P., Villa, G., Lavelle, M., McIntosh, W.C., Bohaty, S.M. and Verosub, K.L. (2002) Integrated chronostratigraphic calibration of the Oligocene-Miocene boundary at 24.0 ± 0.1 Ma from the CRP-2A drill core, Ross Sea, Antarctica. Geology, 30 (11), 1043-1046. (doi:10.1130/0091-7613(2002)030<1043:ICCOTO>2.0.CO;2).

Record type: Article

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, calibration 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.

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Published date: 2002
Keywords: chronostratigraphy, isotope dating, Antarctica, biostratigraphy, Cape Roberts Project

Identifiers

Local EPrints ID: 45395
URI: http://eprints.soton.ac.uk/id/eprint/45395
ISSN: 0091-7613
PURE UUID: 23069212-97db-4924-ba28-076dc07946af

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Date deposited: 27 Mar 2007
Last modified: 19 Nov 2021 20:31

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Contributors

Author: G.S. Wilson
Author: A.P. Roberts
Author: D.M. Harwood
Author: C.R. Fielding
Author: D.K. Watkins
Author: T.R. Naish
Author: F. Florindo
Author: L. Sagnotti
Author: R.P. Scherer
Author: G. Villa
Author: M. Lavelle
Author: W.C. McIntosh
Author: S.M. Bohaty
Author: K.L. Verosub

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