Introduction

The paucity of Cenozoic outcrop on the Antarctic craton has led to the reliance on proxy records (isotopic signatures in microfossils, deep-sea erosion events and former sea levels on distal continental margins) to help unravel the history of climate and ice sheets on Antarctica (Kennett and Shackleton, 1976; Kennett, 1977; Wright and Miller, 1993; Miller and Mountain, 1996; Zachos et al., 2001a; Miller et al., 2005). Much attention has been focused on the search for Antarctic data sets to 'ground truth' significant climate trends, events and thresholds observed in these proxy records. Drilling around the Antarctic margin by seven legs of the Deep Sea Drilling Project (DSDP; Kennett et al., 1974; Hayes and Frakes, 1975) and Ocean Drilling Programme (ODP; Barker et al., 1988a, b; Ciesielski et al., 1988; Barron et al., 1989; Barker et al., 1999; O'Brien et al., 2001), and several sea-ice-based drilling projects (Barrett, 1986, 1989; Cape Roberts Science Team, 1998, 1999, 2000; Fig. 9.1) has recovered Cenozoic sequences, which have allowed the testing of interpretations of Antarctic Glacial history from proxy records and climate models. While the DSDP and ODP core recovery has been between 14 and 40%, riser drilling from sea ice in the South Western Ross Sea has enabled recovered of some high-quality intervals of the Cenozoic (95-98%) recovering prima facie documentation of climate and cryospheric changes in Antarctica. One interval that is particularly well-sampled and well-dated in several drill cores is the Oligocene-Miocene boundary, permitting an accurate comparison to deep-sea high-resolution isotopic records from lower latitudes (Naish et al., 2001, 2008; Wilson et al., 2002; Roberts et al., 2003).

This chapter reviews recent evidence for a glacial expansion in Antarctica coincident with the Oligocene-Miocene boundary and the Mi1 deep-sea oxygen isotope excursion. The climatic significance of the boundary has only recently become apparent from recalibration of the Oligocene-Miocene time scale using astrochronology (Zachos et al., 2001b). Consequently, age data and chron-stratigraphy of the Oligocene-Miocene boundary and the Antarctic strata that contain the boundary are also reviewed. Data sets considered to indicate climate and ice-sheet variability across the boundary include benthic and planktic oxygen isotope (818O) records (Kennett and Shackleton, 1976; Miller et al., 1991; Wright and Miller, 1992; Paul et al., 2000; Zachos et al., 2001b; Billups et al., 2002) and microfossil geochemistry (Billups and Schrag, 2002; Lear et al., 2004), sequence stratigraphic analyses of Antarctic (Fielding et al., 1997; Naish et al., 2001, 2008) and mid-latitude (Kominz and Pekar, 2001; Pekar et al., 2002; Miller et al., 2005; Pekar and DeConto, 2006; Pekar and Christie-Blick, 2008) continental margin strata, Antarctic palaeobotany and palynology (Askin and Raine, 2000; Barrett, 2007) and physical properties of Antarctic drill core strata including lithology, clay mineralogy, mudrock geochemistry and magnetic mineralogy (Verosub et al., 2000; Ehrmann et al., 2005; Passchier and Krissek, 2008). Finally, the cause of the Mi1 glaciation is considered.

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