Introduction

The Antarctic continental margin is a tectonic collage of former rifts and subduction zones that are covered by sediments deposited when the adjacent continent was free of regional glaciers (i.e. 'pre-ice-sheet' times) and when glaciers extended onto the margin (i.e. glacial times). Since the 1960s, many seismic surveys and sea-floor cores and a few drill cores have been acquired on the continental margin to decipher the Cenozoic and earlier history of Antarctica's paleoenvironments and paleoclimates - a history hidden onshore in sediments now unreachable beneath the Antarctic Ice Sheet. This chapter summarizes principally key results of seismic and drilling studies for proximal parts of the continental margin done from 1989 to 2004 by the multinational Antarctic Offshore Statigraphy project (ANTOSTRAT) to decipher Antarctic Ice Sheet history. We include some findings of the successor Antarctic Climate Evolution project (ACE) that includes the Cenozoic Antarctic Stratigraphy and Paleobathymetry project (CASP), to create a unified circum-Antarctic stratigraphy from all existing seismic and rock-core data (Davey and Cooper,

2007). Our summary complements istotopic and ice-rafting studies for distal parts of the margin and abyssal areas (e.g. Warnke et al., 1996; Zachos et al., 2001). We first describe work in five geographic sectors of the margin, and then summarize key results for the entire margin.

Multichannel seismic (MCS) reflection data, the principal tool for deep stratigraphic studies of the continental margin, have been recorded by more than 15 nations (Fig. I-1). Many topical MCS studies with maps of select regional data exist (see citations in regional sections below), but few comprehensive data compilations are either published or openly accessible. Notable exceptions are drilling results (e.g. Deep Sea Drilling Project, Ocean Drilling Program, Cape Roberts Project, ANDRILL and other drilling projects), MCS data compilations in the Antarctic Seismic Data Library System (e.g. www.scar-sdls.org; Wardell et al., 2007), a few Antarctic and regional geosciences atlases (e.g. Hayes, 1991; Cooper et al., 1995), online

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Figure I-1: Map showing locations of tracklines for multichannel seismic-reflection data on the Antarctic continental margin as of late 2006 (from Wardell et al., 2007). Regions are RS, Ross Sea; WL, Wilkes Land; PB, Prydz Bay; WS, Weddell Sea; AP, Antarctic Peninsula.

data centres (e.g. World Data Center) and select discussions of Antarctic margin databases (e.g. Anderson, 1999).

In general, Antarctica had a relatively warm climate and normal-water-depth continental shelf (i.e. like low-latitude continental shelves today) in earliest Cenozoic and Late Cretaceous times - conditions that differ from the polar climate of the latest Cenozoic, with its thick ice sheet and an abnormally deep-water-depth and landward sloping shelf (e.g. Cooper et al., 1991b; Anderson, 1999). Ice has played an important role in continental margin evolution by eroding onshore areas (formerly with vegetation) and discharging the debris into the sea, where ocean currents distribute it to the continental shelf, slope and rise. At times the ice has strongly eroded parts of the shelf. Tectonic processes, principally variable thermal and flexural subsidence and uplift, have also modified the margin morphology and hence stratigraphy (e.g. ten Brink et al., 1995).

Offshore Antarctic stratigraphic studies have thus focused on mapping geomorphology and seismic facies of characteristic features (e.g. shelf-edge fans/deltas, mound deposits, unconformities, etc.), and using the limited core and downhole data to decipher their depositional paleoenvironments and relation to nearby ice, if any. Such features help to infer and establish where and when non-glacial and glacial processes acted (e.g. Cooper et al., 1991b). Drilling is the only way to 'ground truth' the regional seismic surveys (i.e. via a direct tie of lithologic facies to seismic facies), and to provide the age and biostratigraphic control needed to decipher depositional and climatic paleoenvironments (e.g. Barker and Camerlenghi, 2002; Cooper and O'Brien, 2004). The following regional subchapters have been written by the regional experts listed. Their bibliographic citations are augmented in a 'selected reference' section that provides additional background on the prior studies done by the Antarctic geoscience community.

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