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PALEOCEANOGRAPHY, VOL. 20, PA2017, doi:10.1029/2004PA001067, 2005

A high-resolution record of early Miocene Antarctic glacial history from ODP Site 1165, Prydz Bay

Trevor Williams

Borehole Research Group, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA


David Handwerger

Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, USA


Abstract

ODP Site 1165, located 400 km northwest of Prydz Bay, contains a high-resolution early Miocene record of pulses of ice-rafted debris (IRD) originating from the ancestral Lambert Glacier system and the Antarctic coast to the east. The 520 m of early Miocene sediments consist of dark gray claystone with silt laminae (contourites) alternating with decimeter-scale layers of greenish-gray bioturbated claystone that commonly contain ice-rafted debris. Downhole logs also record the alternations between the two facies: the IRD-bearing greenish-grey claystone corresponds to high resistivity and density values because of increased cementation by silica, and corresponds to lower natural gamma radiation values because of diluted clay content. The downhole logs thus allow a continuous and detailed stratigraphic record of the IRD-bearing layers to be obtained. The IRD-bearing layers represent deglaciations and interglacials, when a high flux of icebergs with incorporated material were melting out over the site; the contourite-rich layers represent glacials, when the Polar Current over the site was relatively strong. The sequence is dated by magnetostratigraphy, and the timing of the major IRD pulses is paced by orbital eccentricity, indicating that the volume of the East Antarctic ice sheet also fluctuates on this timescale. After 19.7 Ma, minor precessional and subprecessional IRD layers appear in the record, indicating that the ice sheet becomes more prone to deglaciation through this interval, perhaps associated with the gradual warming trend through the early Miocene.

Received 2 July 2004; accepted 25 January 2005; published 28 June 2005.

Keywords: Miocene; East Antarctic ice sheet; Prydz Bay; ice-rafted debris; ODP Site 1165; Ocean Drilling Program.

Index Terms: 4207 Oceanography: General: Arctic and Antarctic oceanography (9310, 9315); 3022 Marine Geology and Geophysics: Marine sediments: processes and transport; 0915 Exploration Geophysics: Downhole methods; 9604 Information Related to Geologic Time: Cenozoic; 9310 Geographic Location: Antarctica (4207).

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Citation: Williams, T., and D. Handwerger (2005), A high-resolution record of early Miocene Antarctic glacial history from ODP Site 1165, Prydz Bay, Paleoceanography, 20, PA2017, doi:10.1029/2004PA001067.