Insights on seabed physical features and habitats in a sediment starved setting, Rottnest Shelf, southwestern Australia  

Authors / CoAuthors

Nicholas, W.A. | Borissova, I. | Carroll, A.G. | Howard, F.J.F. | Tran, M. | Bernardel, G. | Nichol, S.L. | Brooke, B.P.

Abstract

Lithified, drowned coastal dunes preserved below sea-level on continental shelves are rarely observed. Here we present new insights into the evolution of the Rottnest Shelf, southwestern Australia, where drowned parabolic dunes have been identified in high-resolution multibeam bathymetry (Figure 1). In 2012 Geoscience Australia undertook a marine survey of the warm temperate, carbonate-dominated, sediment-starved Rottnest Shelf, overlying the Vlaming Sub-basin, southwest Australia. This work supports an assessment of the CO2 storage potential of the basin, part of the Australian Government's National CO2 Infrastructure Plan. The survey acquired a range of data for sedimentological, geochemical and biological characterisation of the seabed, including multibeam sonar bathymetry and backscatter, side-scan sonar, acoustic sub-bottom profiles, towed underwater video and grab samples. Two areas were surveyed, one each north and south of Rottnest Island. The seabed surface comprised plains, ridges, and nested parabolic dunes, as well as high-relief mounds, shallow depressions, sediment waves, rhodolith beds and fault scarps. The seabed is dominantly a hard carbonate surface thinly veneered with biogenic carbonate sediment. Parabolic and crescent shaped ridges, with steep landward-facing slopes, form the most conspicuous features, with up to 10 m of relief above the seabed (water depths of 29-54 m). The ridges are interpreted to be the remnants of Late Quaternary coastal barriers and dunefields. Annular ridges are present within fields of parabolic ridges, the latter supporting high densities of sessile biota including hard corals, macroalgae, red algae, massive sponges and bryozoans. Here we propose a model to account for the geomorphic development of the Rottnest Shelf that relates the formation of the relict barrier dune system to eustatic changes in sea-level, prevailing winds and sediment supply. Additional factors considered include local variability in hydrodynamic regime and its interaction with geomorphic features.

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nonGeographicDataset

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83196

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• External PublicationAbstract

( Theme )

• marine

• Western Australia

Australian and New Zealand Standard Research Classification (ANZSRC)

• Quaternary Environments

• Published_Internal

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2015-01-01T00:00:00

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Abstract written 23 April 2015

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