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Eocene to Miocene magnetostratigraphy, biostratigraphy, and chemostratigraphy at ODP Site 1090 (sub-Antarctic South Atlantic)

J.E.T. Channell^,1, S. Galeotti^,2, E.E. Martin^,3, K. Billups^,4, H.D. Scher^,5 and J.S. Stoner^,6

¹ Department of Geological Sciences, University of Florida, Post Office Box 112120, Gainesville, Florida 32611, USA
² Istituto di Geologia, Università degli Studi di Urbino, Campus Scientifico, Località Crocicchia, 61029 Urbino, Italy
³ Department of Geological Sciences, University of Florida, Post Office Box 112120, Gainesville, Florida 32611, USA
⁴ College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, Delaware 19958, USA
⁵ Department of Geological Sciences, University of Florida, Post Office Box 112120, Gainesville, Florida 32611, USA
⁶ Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, Colorado 80309, USA

At Ocean Drilling Program (ODP) Site 1090 (lat 42°54.8'S, long 8°54.0'E) located in a water depth of 3702 m on the Agulhas Ridge in the sub-Antarctic South Atlantic, 300 m of middle Eocene to middle Miocene sediments were recovered with the advanced piston corer (APC) and the extended core barrel (XCB). U-channel samples from the 70–230 meters composite depth (mcd) interval provide a magnetic polarity stratigraphy that is extended to 380 mcd by shipboard whole-core and discrete sample data. The magnetostratigraphy can be interpreted by the fit of the polarity-zone pattern to the geomagnetic polarity time scale (GPTS) augmented by isotope data and bioevents with documented correlation to the GPTS. Three normal-polarity subchrons (C5Dr.1n, C7Ar.1n, and C13r.1n), not included in the standard GPTS, are recorded at Site 1090. The base of the sampled section is correlated to C19n (middle Eocene), although the interpretation is unclear beyond C17r. The top of the sampled section is correlated to C5Cn (late early Miocene), although, in the uppermost 10 m of the sampled section, a foraminifer (Globorotalia sphericomiozea) usually associated with the Messinian and early Pliocene has been identified. ⁸⁷Sr/⁸⁶Sr, ¹³C, and ¹⁸O values measured on foraminifera, including the ¹⁸O and ¹³C shifts close to the Eocene/Oligocene boundary, support the correlation to the GPTS. For the interval spanning the Oligocene/Miocene boundary, benthic ¹³C, ¹⁸O, and ⁸⁷Sr/⁸⁶Sr records from Site 1090 can be correlated to isotope records from ODP Site 929 (Ceara Rise), providing support for the recently-published Oligocene/Miocene boundary age (22.92 Ma) of Shackleton et al.

Key Words: Cenozoic • magnetostratigraphy • stable isotopes • strontium isotopes • biostratigraphy • South Atlantic

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