Carbonate sediments and sedimentary rocks contain a particularly sensitive record of paleoceanographic and biostratigraphic evolution. The focus of the Ocean Drilling Program (ODP) carbonate drilling on continental margins has largely been in warm-water environments. There is a complete sedimentary realm whose nature and history have not yet been investigated— that of continental margin cool-water carbonates. These biogenic sediments, formed where seawater temperatures rarely rise above 20°C, commonly mantle continental margins in middle and high latitudes. They are untapped storehouses of information regarding the evolution of global climates, eustacy, and marine biology.

The southern Australian continental margin is the ideal location to study cool-water carbonate facies and evolution. The shelf has been the site of cool-water carbonate sedimentation since Eocene time, resulting in an almost 1-km-thick succession. It is now the largest area on the globe composed of such sediments. In addition, slight tectonic tilting during the late Miocene has led to subaerial exposure of Eocene–middle Miocene strata in extensive, shallow basins. These sediments form a more compressed and less continuous section than the section offshore, yet they have allowed the development of actualistic models for the formation and development of cool water carbonates. These models can be tested and greatly expanded by drilling.

A critically important benefit of drilling in the Great Australian Bight is that, because the shelf is latitudinally parallel to the southern margin of the Australian plate, the sediments contain a record of the development of the Southern Ocean. In particular, the region offers the potential to collect high-resolution stable isotopic and biostratigraphic profiles to clarify several important stages in the evolution of the Southern Ocean.

Drilling in the Great Australian Bight provided essential and original information on the contrast between the sedimentologic, paleontologic, paleoceanographic, and climatic records from warm- and cool-water realms. It will also allow the development of well-constrained and greatly needed models that can be used in the interpretation of older Mesozoic and Paleozoic continental margin carbonate systems.


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