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doi:10.2204/iodp.sp.317.2009

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. Understanding 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. Proposal 600 addresses this question by drilling the Canterbury Basin on the eastern margin of the South Island of New Zealand (Figs. F1, F2, F3).

High rates of Neogene sediment supply preserved a high-frequency (0.5–1 m.y. periods) seismically resolvable record of depositional cyclicity in the offshore basin (Fulthorpe and Carter, 1989; Browne and Naish, 2003; Lu and Fulthorpe, 2004). Exploration wells indicate the presence of middle Miocene–Holocene sedimentary sequences, generally correlative with those drilled on the New Jersey margin during 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 development of the Antarctic Circumpolar Current and oceanographic fronts. Currents have strongly influenced deposition by locally modifying sequence architecture and leading to the deposition of large sediment drifts, which aggraded to near shelf depths, within the prograding Neogene section.
2. Rifting is younger (Cretaceous) than the New Jersey margin (Jurassic), and sediment is supplied from a rapidly uplifting 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 (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). Proposal 600 complements Leg 181 drilling by focusing on the landward part of ENZOSS.

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