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doi:10.14379/iodp.sp.356.2014

Introduction

During the past 5 m.y., Earth’s climate has experienced a major transition from the mid-Pliocene warmth to the Late Pleistocene ice ages (Rohling et al., 2014). Although we now have increasing numbers of high-resolution records of climate variability from ocean basins in both high-latitude and equatorial regions (McClymont et al., 2013), high-resolution information for the northwestern region of Australia and from other shelfal areas worldwide is rare. The wedge of sediment that has accumulated over the last 5 m.y. on the northwest shelf (NWS) of Australia epitomizes the geological history of Australia’s northern margin (Fig. F1). The section is made up of a variety of sediment types including subtropical to tropical shelf calcarenite, calcilutite, marl, and deepwater mudstone and siltstone eroded by submarine canyons (Wallace et al., 2003). In combination, these sediments make up a prograding shelf-type system typical of much of the Australian continental margin (Wallace et al., 2002).

The foci of Expedition 356 fall under three main headings.

Indonesian Throughflow, Leeuwin Current, and reef development

During the late Neogene, the NWS has acted as a subsiding platform upon which most contemporary environmental changes are recorded. Located at the fringes of the Indo-Pacific Warm Pool, this margin is therefore an ideal region in which to study tropical oceanography (Rosleff-Soerensen et al., 2012) and the history of the Indonesian Throughflow (ITF). The ITF also helps drive the Leeuwin Current, which is the only southward flowing eastern boundary current in the Southern Hemisphere (Cresswell, 1991; Pearce, 2009). This current extended tropical reef development to 29°S during the Late Pleistocene (Collins et al., 2006). The orbital-scale variability of the Leeuwin Current can be estimated using tropical sedimentary (coral reefs and ooids) and fossil biogeographic indexes, so we can determine by proxy the underlying controls that triggered Pliocene–Pleistocene reef development. Coring a latitudinal transect from 18°S to 27°S will provide essential information as to whether the switch to tropical sedimentation was synchronous or diachronous in this region as well as a long-term perspective on how coral reefs in the east Indian Ocean developed through variable climatic conditions.

Australian monsoon and continental aridity

The continental shelf in this region lies directly offshore the semi-arid Australian continent climatically dominated by the Australian monsoon (Suppiah, 1992). Shelf/slope sediments therefore host a vast but barely explored archive of late Neogene climate variability (van der Kaars and De Deckker, 2002). Recovering cores from the NWS will increase our understanding of the long-term geographic controls on Australian monsoonal variability and its relationship to the onset of aridity in Australia (McLaren et al., 2014).

Subsidence and geodynamics of Australian plate

Obtaining high-resolution stratigraphic data from the NWS will lead to improved burial and subsidence estimates for this region. These data will enable us to decipher the contribution of large-scale geodynamic processes, such as dynamic topography, on the vertical motions of the Earth’s surface and associated effects on the NWS sedimentary system (Czarnota et al., 2013).

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