The area discussed in this Bulletin covers the Capricorn and Curtis Channels, Hervey Bay, and the continental shelf and slope off the northern part of Fraser Island; it also includes the reefs of the Capricorn and Bunker Groups, and the southern edge of the Swain Reefs. This study has concentrated on the morphology, sediments, and shallow stratigraphy and structure of the region. The area is bounded by the Queensland mainland to the west and the Tasman Basin to the east. The floor of the Capricorn Channel slopes down to the southeast and eventually merges with the Tasman abyssal plain. There is no well defined shelf break in this area, and although there is an increase in gradient between the 600 and 1000-m isobaths, no true continental slope exists. East of the Swain Reefs the sea floor slopes down to the Marion Plateau, a wide marginal plateau between depths of 200 and 600 m. This in turn slopes down into the Cato Trough. Fraser Island has been built out across the continental shelf and its northward extension, the Breaksea Spit, extends almost to the edge of the shelf. A submarine canyon system dissects the continental slope to the north and east of Breaksea Spit. The Capricorn Channel forms a large embayment between the Swain Reefs and the Capricorn and Bunker Groups. The floor of the channel shows very little topographic expression except for some reefal banks, a zone of high-amplitude sand waves, and a shallow trough near the 200-m isobath. All these features are considered to be relict, although the reefal banks immediately north of the Capricorn Group support an abundant living fauna. They also provide evidence of low sea levels during the time of their formation. Features on the shelf south of the Capricorn and Bunker Groups and in Hervey Bay include symmetric and asymmetric sand waves, and an ancient subaerial drainage system that extends across the shelf to the continental slope. The sediments have been divided into nine lithofacies primarily on the basis of texture and carbonate content. Most of the shelf is covered by sands while the Capricorn Channel is floored by predominantly fine-grained sediments. The main structural elements of the area are the Bunker High, Swains High, and the intervening Capricorn Basin. Seismic results show a draping of sediments over the Bunker High and the presence of shallow basement in the area. The Capricorn Basin is considered to have begun subsiding towards the end of the Cretaceous, possibly as a result of the opening of the northern Tasman Basin. The thick sequence of sediments in the basin consists of a predominantly non-marine Palaeogene succession and a marine Neogene succession.
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