Authors / CoAuthors
Ryan, D.A. | Bostock, H. | Brooke, B.P. | Skene, D.
Abstract
Keppel Bay is a large, semi-enclosed and relatively shallow coastal embayment adjacent to the Fitzroy River, in the southern section of the Great Barrier Reef Marine Park. The geomorphology and distribution of sediment in Keppel Bay is complex due to the influence of sea-level change, relict topography, a geologically diverse catchment, macrotidal hydrodynamic processes and flood events. As part of the Cooperative Research Centre for Estuarine, Coastal and Waterway Management (Coastal CRC) Fitzroy Agricultural Contaminants (AC) project, a major objective was to determine the spatial distribution and accumulation history of sediments in Keppel Bay that are derived from the Fitzroy River catchment. This was achieved through the analysis of sediment grab samples, vibracores, and `chirp' sub-bottom profiler information. Seabed morphology, sub-bottom profiles and sediment cores reveal the former path of the Fitzroy River across Keppel Bay and the continental shelf. The palaeo-Fitzroy River flowed west across the shelf to the north of Northwest Reef, to a position on the shelf that is now in approximately 60 m of water. With the rise in sea level during the early Holocene, the mouth of the Fitzroy River retreated across the continental shelf and by the middle Holocene it was landwards of its present location, towards Rockhampton. During the last few thousand years under a relatively stable sea level, much of the shallow inner region of Keppel Bay has been infilled and the coast has prograded up to a few kilometres. Palaeochannels in the inner section of Keppel Bay have mostly been infilled with sediment, which comprises muddy sand from the Fitzroy River and marine bioclastic sand and gravel. In the outer bay and on the shelf further west many relict channels have not been infilled with marine sediment, indicating the outer bay and shelf is relatively starved of sediment. Sediments in outer Keppel Bay are dominantly relict fluvial deposits of terrigenous sediment that are well sorted with only a minor mud component. Subaqueous dunes in the outer southeastern section of Keppel Bay and Centre Bank indicate that tidal currents and the predominant southeasterly winds, and associated currents, appear to be transporting marine biogenic sediments and coarse terrigenous sediments into Keppel Bay. Fine sediment is presently accumulating in the mouth of the estuary where muddy sand bars have recently formed, and have been stabilised by mangroves. Accumulation of fine sediment currently occurs within the estuary, in the deep relict channels of southern Keppel Bay, and adjacent to Long Beach in central Keppel Bay. Some accumulation of fines also occurs within palaeochannels. The thickest accumulations of sediment occurs in the south of the inner bay, with the sediment wedge thinning to the north away from the mouth of the estuary. Sediment accumulation rates cannot be determined at present as dates are not yet available for the vibracores. The distribution of modern sediments in Keppel Bay indicates that fine sediment deposited by the Fitzroy River is largely transported out of Keppel Bay in suspension, while coarser material is deposited in the mouth of the estuary and in the southern section of the bay. The coarser sediment is rapidly reworked by advection to the north and onshore where it accumulates in dunes and beach ridge deposits.
Product Type
nonGeographicDataset
eCat Id
65323
Contact for the resource
Custodian
Point of contact
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
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- GA PublicationRecord
- ( Theme )
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- marine survey
- ( Theme )
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- sedimentology
- ( Theme )
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- seabed
- ( Theme )
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- marine
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- AU-QLD
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2007-01-01T00:00:00
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unknown
Topic Category
geoscientificInformation
Series Information
Record 2007/020
Lineage
Unknown
Parent Information
Extents
[-23.75, -22.95, 150.35, 151.3]
Reference System
Spatial Resolution
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