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doi:10.2204/iodp.pr.317.2010

Introduction

Defining the relative importance of global sea level (eustasy) versus local tectonic, sedimentary, and oceanographic processes in controlling continental margin depositional cyclicity is a fundamental problem in sedimentary geology. A better understanding of how these processes interact to form preserved stratigraphy would greatly enhance our ability to read the record, covering many tens of millions of years, of Earth history contained within the thick sedimentary deposits beneath the world's continental shelves. Integrated Ocean Drilling Program (IODP) Expedition 317 addressed this problem by drilling the Canterbury Basin on the eastern margin of the South Island of New Zealand (Figs. F1, F2, F3).

The geologic record provides an opportunity to quantify the timing, rate, amplitude, mechanisms/controls, and effects (stratigraphic response) of eustatic change, which in turn provides a baseline for predicting future relative sea level changes and assessing anthropogenic influences. However, eustatic effects are complexly intertwined with processes of basin subsidence and sediment supply (e.g., Cloetingh et al., 1985; Karner, 1986; Posamentier et al., 1988; Christie-Blick et al., 1990; Reynolds et al., 1991; Christie-Blick and Driscoll, 1995; Kominz et al., 1998; Kominz and Pekar, 2001). Controversy arises from the application of the sequence stratigraphic model (Mitchum et al., 1977; Van Wagoner et al., 1988; Posamentier et al., 1988; Posamentier and Vail, 1988; Vail et al., 1991) to sea level studies. Sequence stratigraphy highlights the cyclic nature of the continental margin stratigraphic record and led to the theory of eustatic control of sequences and the resultant eustatic cycle chart (Haq et al., 1987). This global sea level model remains contentious (e.g., Cloetingh et al., 1985; Carter, 1985; Karner, 1986; Christie-Blick et al. 1990; Christie-Blick, 1991; Carter et al., 1991; Karner et al., 1993; Christie-Blick and Driscoll, 1995; Dewey and Pitman, 1998; Miall and Miall, 2001).

High rates of Neogene sediment supply preserved a high-frequency (0.1–0.5 m.y.) seismically resolvable record of depositional cyclicity in the offshore Canterbury Basin (Fulthorpe and Carter, 1989; Browne and Naish, 2003; Lu and Fulthorpe, 2004). Exploration wells indicate the presence of middle Miocene to recent sedimentary sequences that are generally correlative with those drilled on the New Jersey margin by the Ocean Drilling Program (ODP). However, the Canterbury Basin differs in ways that allow expanded study of the complex processes of sequence formation in line with the global approach to sea level change advocated by previous planning groups:

1. The stratigraphy records the early development of the Antarctic circumpolar circulation and related southern oceanographic fronts. Currents have strongly influenced deposition, modifying sequence architecture and locally leading to the deposition of large sediment drifts that aggraded to near shelf depths within the prograding Neogene section.

2. Rifting is younger (Cretaceous) than the New Jersey margin (Jurassic), and from the earliest Miocene copious terrigenous sediment was supplied from a rapidly uplifting nearby mountain range (the Southern Alps). Regional tectonic and geological histories have been intensively studied, allowing evaluation of the influence of sediment supply on sequence formation and of the tectonic evolution of the Alpine Fault plate boundary.

The Canterbury Basin is part of the Eastern New Zealand Oceanic Sedimentary System (ENZOSS) (Carter et al., 1996). The distal (up to 4460 m water depth) component of ENZOSS was targeted by ODP Leg 181, which focused on drift development in the southwest Pacific gateway, principally under the influence of the evolving Antarctic Circumpolar Current and the Deep Western Boundary Current (Shipboard Scientific Party, 1999a). Expedition 317 complements Leg 181 drilling by focusing on the landward part of ENZOSS.

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