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Abstract
The submarine Kenn Plateau, with an area of about 140 000 km2, lies some 400 km east of central Queensland beyond the Marion Plateau. It is one of several thinned continental fragments east of Australia that were once part of Australia, and it originally fitted south of the Marion Plateau and as far south as Brisbane. It is cut into smaller blocks by east- and northeast-trending faults, with thinly sedimented basement highs separated by basins containing several kilometres of sediment. In the Cretaceous precursor of the Kenn Plateau, Late Triassic to Late Cretaceous basins probably rested unconformably on Palaeozoic to Triassic rocks of the New England Fold Belt. Rift volcanism was common on the northern plateau and was probably of Early Cretaceous age. Late Cretaceous extension and breakup were followed by Paleocene drifting, and the Kenn Plateau moved to the northeast, rotated 30° anticlockwise and left space that was filled by Tasman Basin oceanic basalts. During these events, siliciclastic sediments poured into the basins from the continental mainland and from locally eroding highs. After a regional Late Paleocene to Early Eocene unconformity, siliciclastic sedimentation resumed in proximal areas. In deep water, radiolarian chalks were widely deposited until biosiliceous sediment accumulation ended at the regional Late Eocene to Early Oligocene unconformity, and warming surface waters led to accumulation of pure biogenic carbonates. Calcarenite formed in shallow water on the margins of the subsiding plateau from the Middle Eocene onward. Some seismic profiles show Middle to Late Eocene compression related to New Caledonian obduction to the east. Hotspots formed parts of two volcanic chains on or near the plateau as it moved northward: Late Eocene and younger volcanics of the Tasmantid chain in the west, and Late Oligocene and younger volcanics of the Lord Howe chain in the east. As the volcanoes subsided, they were fringed by reefs, some of which have persisted until the present day. Other reefs have not kept up with subsidence, so guyots formed. The plateau has subsided 2000 m or more since breakup and is now subject solely to pelagic carbonate sedimentation.
Acknowledgements
We are grateful to the National Facility Science Advisory Committee and Steering Committee for making Southern Surveyor ship time available for two expeditions (SS5/2004 and SS2/2005). Dietmar Müller and Carmen Gaina (University of Sydney) helped formulate the scientific hypotheses that were tested on these cruises. We are very grateful to the ship's Masters, Ian Taylor and Les Morrow, the mates, and all the maritime crew for their support throughout the expeditions. The CSIRO Marine Division staff and the Geoscience Australia technical group, plus the scientists from various organisations, all did an excellent job aboard ship. Special thanks are due to those who helped describe the dredged rocks aboard ship, in particular Kinta Hoffmann (Geological Survey of Queensland) and Julie Brown (Australian National University). After Survey SS5/2004, Patrick Quilty (University of Tasmania, foraminifers) and Richard Howe (Geoscience Australia, nannofossils) provided biostratigraphic information. During and after Survey SS2/2005, Claire Findlay (Geoscience Australia) worked on the nannofossils, and after the survey, Patrick Quilty worked on the foraminifers. We thank them and draw from all their work in this paper. We thank Jim Colwell and Tony Stephenson of Geoscience Australia for thoughtful reviews of an early version of the paper. Journal reviewers, Patrick Quilty and Carmen Gaina, provided valuable input. Angie Jaensch, Shannon Muir and Brian Pashley of Geoscience Australia got the figures into final shape. NFE, PJH and GB publish with the permission of the Chief Executive Officer of Geoscience Australia.