Bathymetric Expression of the Fitzroy River Palaeochannel: Implications for Sediment Transport on the Semi-rimmed Southern Great Barrier Reef, Australia

Brief description

We report the presence of a prominent bathymetric expression of the Fitzroy River palaeochannel on the continental shelf of the southern Great Barrier Reef (GBR), Australia. The Fitzroy River, and the Burdekin River are the two largest point sources of terrigenous sediment to the GBR, which represents the worlds largest tropical mixed siliciclastic-carbonate sedimentary province. The Fitzroy River palaeochannel differs from that of the previously discovered Burdekin palaeochannel in that it has not yet been buried by sediments. Evidently, the dominance of platform reef rather than barrier reef geomorphology, coupled with macrotidal oceanographic conditions has limited aggradation behind the shelf edge, as postulated for the Burdekin region. Contrary to current models for the central GBR which suggest that slope sedimentation is limited to periods of transgression, the palaeo-Fitzroy probably contributed sediment directly to the continental slope of the southern GBR throughout the lowstand. Additionally, it appears that during the highstand, accumulation of terrigenous sediment on the middle and outer shelf has been minimal. The southern GBR represents a transition between the mainly terrigenous wave and ocean current dominated shelf of southeastern Australia, and the mixed siliciclastic-carbonate storm-influenced shelf of the GBR. The discovery of the Fitzroy River palaeochannel in the southern GBR physiographic setting provides new data by which the response of major rivers to sea level change can be characterised.

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